Author Topic: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'  (Read 13030 times)

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Offline Homer J Simpson

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Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« on: October 30, 2018, 06:54:41 am »
Will be interesting to see where this goes.

"A technical log obtained by the BBC from the plane's previous flight suggests that the airspeed reading on the captain's instrument was unreliable, and the altitude readings differed on the captain's and first officer's instruments."

"Identified that CAPT [captain's] instrument was unreliable and handover control to FO [first officer]," the log reads. "Continue NNC of Airspeed Unreliable and ALT disagree."


https://www.bbc.com/news/world-asia-46022390
« Last Edit: October 30, 2018, 06:56:19 am by Homer J Simpson »
 

Offline rx8pilot

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1 on: October 30, 2018, 07:06:21 am »
The level of redundancy and fault handling automation in a brand new 737 is pretty amazing -, especially on airspeed and altitude.

Patiently waiting to see what happened. I could have been similar to the Air France crash where a relatively minor malfunction led to auto-pilot disconnect and the pilot reacted inappropriately to the situation. Failing gauges in real life are really challenging to understand and react properly.

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Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #2 on: October 30, 2018, 07:23:48 am »
I see 737's have issues with their five(!) pitot tubes as well, going back a few years.
http://aviationweek.com/awin/boeing-addresses-pitot-tube-anomaly-its-737s

I don't understand why heating a pipe is so difficult to engineer, redundancy doesn't help and there are still crashes happening from a corrupted sensor.

Pic "thermal imaging of a partially shorted pitot probe {heater?} shows that heat (red) does not reach the tip, where ice can form and corrupt airspeed measurements". (Credit: Irish Air Accident Investigation Unit)
 

Offline SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #3 on: October 30, 2018, 07:34:11 am »
Have not yet enough info on this to get an idea of what would have happened, but I don't agree with the general claim that crashes "happen from a corrupted sensor."

That's sometimes the starting point, but almost never the real cause. Unless the plane is already at a very low altitude (on approach for instance) with low visibility, a bad airspeed indication doesn't itself cause a crash. An experienced pilot knows 1/ how to spot a defective pitot when it happens and 2/ that the best way of dealing with it is usually not to do anything until the measurement gets back to normal. Unfortunately, a lot of airline pilots are not as experienced as they used to be or as they should be, and sometimes they will act irrationally on commands until the plane stalls. That's pretty much what happened with the (in)famous Rio-Paris flight, for instance. The reports are all publicly available.

 
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Offline rx8pilot

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #4 on: October 30, 2018, 07:58:11 am »
Unconfirmed information suggests this crew was rather experienced.

I had a pitot tube clog on an IFR flight in a single-engine airplane about 10 years ago. The hard part of identifying the problem is that it came on rather slowly. The aircraft only had a single tube, but the pitch, power, altitude, and temp of the aircraft did not agree with the number I was seeing. My reaction was to keep the wings level, the pitch level, and the power constant while I tried to understand what was happening. Once I was pretty sure there was no fixing it - I called ATC to help get me out of the clouds with a very slow decent. All ended well, but much more confusing and intense than my training ever suggested.

The systems in a 737 are massively more complex and I believe they have an automatic reversion when a single system is out of agreement. Even if it does not, the identification and response to a pitot/static error or total failure is among the most rehearsed emergency in my experience. Perhaps less so in the heavy iron aircraft with all the redundancy.

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Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #5 on: October 30, 2018, 08:09:57 am »
Air France 447 was a night flight in heavy rain.

Lion 610 was a morning flight in what appears to have been VFR conditions. Yes, there were clouds, but weather was reported good enough (2000-and-5) that student pilots could have been out soloing airplanes in it. You can't comfortably fly a transport jet solely by visual references, but you ought to be able to keep it out of the water, IMO.
 
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Offline boffin

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #6 on: October 30, 2018, 08:26:03 am »

I had a pitot tube clog on an IFR flight in a single-engine airplane about 10 years ago. The hard part of identifying the problem is that it came on rather slowly. The aircraft only had a single tube, but the pitch, power, altitude, and temp of the aircraft did not agree with the number I was seeing. My reaction was to keep the wings level, the pitch level, and the power constant while I tried to understand what was happening. Once I was pretty sure there was no fixing it - I called ATC to help get me out of the clouds with a very slow decent. All ended well, but much more confusing and intense than my training ever suggested.

Keep flying the plane in a configuration you know works.  That was the experience I was given by two very high time old timers that were my instructors.  AFR447 was an example of doing the opposite.

I'm sure we'll find out why this plane went down, but all of the people  immediate jumping to conclusions is just silly
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Offline nctnico

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #7 on: October 30, 2018, 08:29:52 am »
Have not yet enough info on this to get an idea of what would have happened, but I don't agree with the general claim that crashes "happen from a corrupted sensor."

That's sometimes the starting point, but almost never the real cause. Unless the plane is already at a very low altitude (on approach for instance) with low visibility, a bad airspeed indication doesn't itself cause a crash. An experienced pilot knows 1/ how to spot a defective pitot when it happens and 2/ that the best way of dealing with it is usually not to do anything until the measurement gets back to normal. Unfortunately, a lot of airline pilots are not as experienced as they used to be or as they should be, and sometimes they will act irrationally on commands until the plane stalls. That's pretty much what happened with the (in)famous Rio-Paris flight, for instance. The reports are all publicly available.
Same here: https://en.wikipedia.org/wiki/Turkish_Airlines_Flight_1951 and also a Boeing 737 with faulty sensor readings.
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Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #8 on: October 30, 2018, 08:39:50 am »
There's so many pitot tube incidents. I question the airplane's software algorithms, a pitot tube reading wrong seems to generate alarms that confuses the crew and causes a lethal panic. The software should be able to estimate from the other sensors or roll back to GPS for speed, or just stop issuing a fake airspeed if you know the sensors have failed and can't make a concensus.
 
737
"Three of the probes are on the nose for airspeed measurements—for the pilot, the co-pilot, and as a backup—and two are on the vertical stabilizer for the elevator feel-and-centering unit. If the airspeed difference between the pilot and co-pilot probes is greater than 5 kt. for 5 sec. consecutively, the pilots receive an “IAS (indicated airspeed) Disagree” alert. "

"A man with a watch knows what time it is. A man with two watches is never sure."
You can't take a concensus with two sensors.
So captain and co-pilot are lost as to the airplane's true speed but the backup sensor does nothing?
« Last Edit: October 30, 2018, 08:56:57 am by floobydust »
 
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Offline jpanhalt

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #9 on: October 30, 2018, 09:15:18 am »
Unconfirmed information suggests this crew was rather experienced.

I had a pitot tube clog on an IFR flight in a single-engine airplane about 10 years ago. The hard part of identifying the problem is that it came on rather slowly. The aircraft only had a single tube, but the pitch, power, altitude, and temp of the aircraft did not agree with the number I was seeing. My reaction was to keep the wings level, the pitch level, and the power constant while I tried to understand what was happening. Once I was pretty sure there was no fixing it - I called ATC to help get me out of the clouds with a very slow decent. All ended well, but much more confusing and intense than my training ever suggested.

The systems in a 737 are massively more complex and I believe they have an automatic reversion when a single system is out of agreement. Even if it does not, the identification and response to a pitot/static error or total failure is among the most rehearsed emergency in my experience. Perhaps less so in the heavy iron aircraft with all the redundancy.

Almost same thing happened to me in 1975 or so.   Piper Arrow.   Moral is that airspeed, while very important, is not the only indicator of the aircraft's airspeed.
 

Offline Macbeth

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #10 on: October 30, 2018, 09:32:13 am »
This plane was brand new, just entered service in August.

Apparently Lion are considered shit - possibly even worse than Ryanair if that is even possible, like they actually charge budding pilots money to fly their planes instead of paying them!!  :palm:

But the pilot of this plane was a pro and had at least 6000 hours flying experience.

Terrible incident for all involved. Damn. We need answers.
 
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Offline jpanhalt

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #11 on: October 30, 2018, 09:40:27 am »
This plane was brand new, just entered service in August.

Apparently Lion are considered shit - possibly even worse than Ryanair if that is even possible, like they actually charge budding pilots money to fly their planes instead of paying them!!  :palm:

But the pilot of this plane was a pro and had at least 6000 hours flying experience.

Terrible incident for all involved. Damn. We need answers.

Sure, just like we got for MH370!   Complete disinformation from the authorities who are more interested in their jobs than saving lives.
 

Offline rx8pilot

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #12 on: October 30, 2018, 09:52:50 am »
Boeing may be the best source of answers on this one. Since the plane is so new - ALL of Boeings customers and the NTSB are going to be asking a pile of questions.
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #13 on: October 30, 2018, 09:56:00 am »
For those interested in this stuff I highly recommend the book QF32
The captain takes you blow by blow through what it's like to get multiple conflicting warnings and whatnot

https://www.amazon.com.au/QF32-author-Life-Lessons-Cockpit-ebook/dp/B007KTLQ5W
 
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Offline Mr. Scram

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #14 on: October 30, 2018, 09:56:28 am »
Sure, just like we got for MH370!   Complete disinformation from the authorities who are more interested in their jobs than saving lives.
They found the aircraft, so that seems unlikely. The stakes are much too much for it to be brushed under the carpet.
 

Online Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #15 on: October 30, 2018, 10:29:41 am »
... or roll back to GPS for speed, or just stop issuing a fake airspeed if you know the sensors have failed and can't make a concensus.
GPS shows ground speed, not air speed. Not entirely useless, but they're usually not the same number.

The IAS alert will tell the pilots the left and right numbers don't agree. Odds are one of them is correct, so letting the pilots know the readings is still useful. They have airspeed unreliable procedure, which involves turning off the autopilots and putting the plane in a particular power and pitch setting to maintain airspeed, at least until they evaluate the problem.

Quote

737
"Three of the probes are on the nose for airspeed measurements—for the pilot, the co-pilot, and as a backup—and two are on the vertical stabilizer for the elevator feel-and-centering unit. If the airspeed difference between the pilot and co-pilot probes is greater than 5 kt. for 5 sec. consecutively, the pilots receive an “IAS (indicated airspeed) Disagree” alert. "

"A man with a watch knows what time it is. A man with two watches is never sure."
You can't take a concensus with two sensors.
So captain and co-pilot are lost as to the airplane's true speed but the backup sensor does nothing?
The aux pilot tube is for the ISFD, the backup flight instrument that's self-contained, including internal backup-power in the event the cockpit goes dark. So that's a third airspeed report available to the pilots.

I suspect we'll find the cause of the crash is something else entirely. They will find the black boxes, so we will know eventually.
 

Offline boffin

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #16 on: October 30, 2018, 03:42:11 pm »
For those interested in this stuff I highly recommend the book QF32
The captain takes you blow by blow through what it's like to get multiple conflicting warnings and whatnot

https://www.amazon.com.au/QF32-author-Life-Lessons-Cockpit-ebook/dp/B007KTLQ5W

Worth watching the episode of "Mayday" about QFA32 too.
 


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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #17 on: October 30, 2018, 03:59:03 pm »
There's so many pitot tube incidents.
Yep, especially when the pilots and ground crew on their pre-flight walk arounds can't/don't/won't see the socks placed on them to keep the various mason wasps from building nests in them.
Not all parts of the world have this problem but it's bad enough in some locations that covering the pitot tubes is mandatory but easily overlooked in pre-flight checks.  ::)
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Online Brumby

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #18 on: October 30, 2018, 04:08:02 pm »
... or roll back to GPS for speed, or just stop issuing a fake airspeed if you know the sensors have failed and can't make a concensus.
GPS shows ground speed, not air speed. Not entirely useless, but they're usually not the same number.

I'm no pilot, but I would suggest GPS speed determination would be pretty much useless unless you know the direction and speed of the winds in your location at your flight level.
 

Offline NiHaoMike

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #19 on: October 30, 2018, 04:09:13 pm »
Yep, especially when the pilots and ground crew on their pre-flight walk arounds can't/don't/won't see the socks placed on them to keep the various mason wasps from building nests in them.
Not all parts of the world have this problem but it's bad enough in some locations that covering the pitot tubes is mandatory but easily overlooked in pre-flight checks.  ::)
They should make the covers striped fluorescent pink/orange/glow in the dark green balls that are hard to miss, and designed to tear away at typical flight speeds should one be forgotten.
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #20 on: October 30, 2018, 05:07:45 pm »
Yep, especially when the pilots and ground crew on their pre-flight walk arounds can't/don't/won't see the socks placed on them to keep the various mason wasps from building nests in them.
Not all parts of the world have this problem but it's bad enough in some locations that covering the pitot tubes is mandatory but easily overlooked in pre-flight checks.  ::)
They should make the covers striped fluorescent pink/orange/glow in the dark green balls that are hard to miss, and designed to tear away at typical flight speeds should one be forgotten.
Well they do have ribbons on them but apparently that isn't always enough.



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Offline Berni

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #21 on: October 30, 2018, 05:17:32 pm »
Yep anything that must be removed before flight is tagged bright red. This includes inside the cockpit (Small lanes often physically lock the controls so prevent the wind banging the directly connected control surfaces around)

And there have been cases where a pressure sensing port on the side of a plane was covered up with tape to protect it while the plane was washed. But then someone forgot to remove it and nobody noticed it so it caused all sorts of strange readings on the instruments once the plane has taken off.
 

Online Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #22 on: October 30, 2018, 06:19:03 pm »
... or roll back to GPS for speed, or just stop issuing a fake airspeed if you know the sensors have failed and can't make a concensus.
GPS shows ground speed, not air speed. Not entirely useless, but they're usually not the same number.

I'm no pilot, but I would suggest GPS speed determination would be pretty much useless unless you know the direction and speed of the winds in your location at your flight level.

That was my point. On the other hand, often one does have at least a ballpark idea of that information, especially when it comes time to land the plane. And ground speed remains useful for navigation purposes.
 

Online station240

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #23 on: October 31, 2018, 03:51:30 am »
Something really has gone wrong with this flight soon after take off.

Data from https://www.flightradar24.com/blog/flightradar24-data-regarding-lion-air-flight-jt610/

Graph of entire flight altitude/rate of climb


Graph of takeoff altitude/rate of climb

Flight is not a smooth climb to flight level, altitude and rate of climb are all over the place.
Indicates flight being flown manually.

Graph of last minute of flight altitude/rate of climb

This is at what appears on radar maps (and radio comms) to be at the point where the plane was to turn around to return to the airport.
-33,000 ft/minute, no chance of survival.
I think the altitude values don't show the true horror of what occurred
My guess is the plane in fact attempted the turn while descending rapidly, this caused it to roll over and become impossible to recover from.

Various theories about causes, we can rule out engine problems, as planes with no working engines can still fly to some extent.
That just leaves:
A) pilot actions (combined with faulty instrumentation).
B) flight control malfunction or mechanical failure.
A is looking very likely, but B could also be involved or the main cause.

The crash people should be looking at is Air France Flight 447, where inconsistencies between the airspeed measurements were involved.
« Last Edit: October 31, 2018, 04:16:40 am by station240 »
 
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Offline edy

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #24 on: October 31, 2018, 04:20:41 am »
I'm not a pilot and have only rudimentary knowledge about this. Hopefully not too much of a noob question.... but if a Pitot tube or aircraft speed sensor was blocked or malfunctioning, it would tell the pilot the aircraft is going too slow? So wouldn't they speed up the airplane? Wouldn't speeding up help keep it flying in the air? I would imagine the reverse would be worse, where the sensor is telling you that you are going fast and you slow down and stall.
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Online station240

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #25 on: October 31, 2018, 04:56:05 am »
I'm not a pilot and have only rudimentary knowledge about this. Hopefully not too much of a noob question.... but if a Pitot tube or aircraft speed sensor was blocked or malfunctioning, it would tell the pilot the aircraft is going too slow? So wouldn't they speed up the airplane? Wouldn't speeding up help keep it flying in the air? I would imagine the reverse would be worse, where the sensor is telling you that you are going fast and you slow down and stall.

The sensors give erratic readings, if one is bad you have to figure out which one it is. They work on air pressure within the sensor tube, the tube could be partially blocked, slow to respond etc.
Lets say there is an unwanted item (dead bug) inside the pitot tube, and it's rolling around inside. Changes in angle/altitude of the plane will give all sorts of crazy readings.
If you have more than one sensor malfunction, it becomes a very tricky task.

Planes fly within an envelope where too fast or too slow results in it falling out of the sky, or at least trying to.
Faster = more lift, climbing too fast results in reduced airspeed, which then results in almost no lift (a stall)
Slower = less lift, descending too slow results in increased airspeed, decreased lift, which then results in inability to climb back up.

If you don't trust the instruments, there are procedures to fly just with particular throttle and stick positions. There is a whole table to look at.

In other words, fly the plane carefully, ask the tower for altitude information on your plane, don't use instruments if you don't believe them.
 

Offline janoc

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #26 on: October 31, 2018, 05:02:03 am »
If you are interested how it works when there is an unreliable airspeed situation, here is an explanation from an actual 737 captain:

https://youtu.be/xiB1eejdgdQ?t=489

Basically annoying but, if correctly handled, a non-event. He explains that they even have tables that allow him to fly the plane without any airspeed indicator at all, only using known combination of pitch and power to achieve certain airspeeds (e.g. for landing). Furthermore, most of the procedures for this are memory items (i.e. something the pilot needs to know from memory, without having to rely on a checklist).

So should this happen the pilot flying is supposed to fly pitch and power, wings level. The crew cross-checks the instruments, see that two sets (e.g. backup + first officer's) agree and the third set (captain's) is wrong, the captain hands control over to the first officer and problem solved - exactly what happened on the flight the day before the crash.

And even if all three sets go out there is no reason for the plane to go down unless there is some other problem. Of course, that requires some hand-flying skills because autopilot is of no use in such situation. E.g. there has been an Airbus A330 in Brisbane that took off with the pitot covers still in place. The crew declared emergency and safely returned back to the airport.

I'm not a pilot and have only rudimentary knowledge about this. Hopefully not too much of a noob question.... but if a Pitot tube or aircraft speed sensor was blocked or malfunctioning, it would tell the pilot the aircraft is going too slow? So wouldn't they speed up the airplane? Wouldn't speeding up help keep it flying in the air? I would imagine the reverse would be worse, where the sensor is telling you that you are going fast and you slow down and stall.

When a pitot malfunctions, it could indicate basically anything. Pitot works by comparing the pressure of the oncoming air with pressure from a static port (usually at the bottom of the plane, not facing the airstream) and the airspeed indication is derived from that.

So if e.g. the pitot tube gets clogged you may not get any airspeed data at all (e.g. because someone forgot to remove the covers!), the data between the different tubes could be different (airliners have usually at least 3 pitots - one for captain and one for the first officer + one for the backup instruments), you may get lower than usual speeds if the tube is clogged partially.

Then you can have problems with the static port too. That is much more insidious because that causes a cascade of failures in the cockpit and it is not always immediately apparent what the problem is - you will lose airspeed indication, altimeters will go haywire, also vertical speed indication. Basically anything that depends on atmospheric pressure. There have been several accidents caused by clogged/covered static ports too.

That was my point. On the other hand, often one does have at least a ballpark idea of that information, especially when it comes time to land the plane. And ground speed remains useful for navigation purposes.

You have the ground speed available. However, ground speed is of little use for actually flying the plane - your lift (and thus the ability to stay aloft and not make a smoking crater on the ground) depends on the airspeed (the speed of the plane relative to the air) and not on ground speed.

Worse, the difference between indicated airspeed and ground speed grows the higher you are (and the lower the air pressure is) and also with any wind - if you have ever seen a plane land into a strong headwind by dropping down almost vertically on the runway with little forward movement that is why. The ground speed was low but the airspeed was still sufficient to maintain lift and to not stall (and crash) thanks to the headwind. Also the opposite has happened - e.g. if a plane encounters a strong windshear it could lose enough airspeed that it would stall and crash despite moving fast relative to the ground.

« Last Edit: October 31, 2018, 05:06:06 am by janoc »
 

Offline Jr460

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #27 on: October 31, 2018, 05:08:02 am »
I'm not a pilot and have only rudimentary knowledge about this. Hopefully not too much of a noob question.... but if a Pitot tube or aircraft speed sensor was blocked or malfunctioning, it would tell the pilot the aircraft is going too slow? So wouldn't they speed up the airplane? Wouldn't speeding up help keep it flying in the air? I would imagine the reverse would be worse, where the sensor is telling you that you are going fast and you slow down and stall.

Simple.  You need two things for Indicated Air Speed, IAS, the ram air dynamic pressure and the static air pressure.   Block one or the other and changes in altitude will change your IAS.

Depending on the plane the Pitot tube might have the static port as part of the same structure, in other cases it is a flat hole on the side of the plane.


Had my static port freeze over once in the clouds when I picked up a tad of ice.   The Pitot heat had been one for the past hour or more.   I pulled a tad of power and started down as I called ATC and told them what I was doing.   I only needed about 1000 feet to get into above freezing air.  The ice broke loose and the airspeed and altimeter quickly snapped into place.  Done a bit more and broke out o the clouds into snow.  I knew what MEA and the ceiling so I knew I could breaking to VMC safely.  2 hours after getting the ice, landing in 50F weather and still had ice stuck to wingtip nav lights.   It comes on quick and stays put.

One other time, and we had a cover on the Pitot tube while parked, took the plane out, run up, takeoff, altimeter is not right, slow moving, doing odd things.   Nice VFR day, just came right around the pattern and landed based on eyes and feel of the plane.  Long story short, a spider had partly blocked way up into the static port with eggs.
 

Offline edy

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #28 on: October 31, 2018, 06:55:53 am »
Thanks for the explanations. I assumed like most smaller/simpler airplanes of the past you would just fly based on feel and feedback and what you saw, but that could be difficult at night or bad weather conditions (when you need to rely more on instruments). I guess it is very hard to tell how fast you are going or whether you are going up or dropping when you are far up from the ground. With enough experience in a particular aircraft you would have an intuitive sense of what kind of pitch and engine throttle is needed and when you are low to the ground you may be able to see if it is doing what you want the airplane to do.

With this particular new airplane, with fly-by-wire systems and computers automating a lot of the conditions (and perhaps, if I am to assume correctly, over-riding perhaps pilots in certain situations?) then could this be a case of AI or "smart algorithms" gone wrong? Or are pilots pretty much in control. I know it is too early to assume anything, we still don't know.
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Offline boffin

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #29 on: October 31, 2018, 07:13:13 am »
On a slight side note, it takes next to nothing to receive ADS-B transmissions.  I have a Raspberry Pi + $12 USB Software Defined Radio in my garage uploading data to Flightradar24 (and by being a source node, you get full business level access to fr24)


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Offline Kleinstein

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #30 on: October 31, 2018, 07:52:48 am »
As the a not working pitot tube seems to be a rather common problem, the pilots should have regularly seen such a scenario in the simulator during training.

If the standard procedure is as simple as flying by setting power and other settings to a standard value depending on altitude, weight and whatever, I would even expect the auto-pilot to be able to do such a simple calculation / look in the table. At least for the first few seconds to minutes I would prefer this over a sudden turn over to manual control.


Still a lot of speculations to what causes the accident - just wait a few more days to get more info.
 

Offline Jr460

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #31 on: October 31, 2018, 07:58:30 am »
Thanks for the explanations. I assumed like most smaller/simpler airplanes of the past you would just fly based on feel and feedback and what you saw, but that could be difficult at night or bad weather conditions (when you need to rely more on instruments). I guess it is very hard to tell how fast you are going or whether you are going up or dropping when you are far up from the ground. With enough experience in a particular aircraft you would have an intuitive sense of what kind of pitch and engine throttle is needed and when you are low to the ground you may be able to see if it is doing what you want the airplane to do.

Even low to the ground your sense of airspeed is way off.   The problem is we see ground speed.   Other factors to into play, for example at night for some reason venting on the ground seems to be going by much faster.   But the biggest is that the plane and the wings perform based on IAS, Indicated airspeed, you then have TAS, true airspeed which corrects for air density, and then from that winds give you ground speed.  Now estimate IAS to better that +/- 5 knots based on all of that.   And even 5 knots fast or slow is not good.

That said, yes once you get good in a model and have been in and out of the same airport a lot, you know I need X power to hold altitude right at the top of the white arc with one notch of flaps.  Drop the gear abeam the numbers and touch nothing else, add flaps as you come base and then final.  In a PA28-200R that put me setup great for final.

I got a chance to try it by "feel" with a complete electrical failure at night, couldn't see any instruments, no time to reach and grab my flashlight.  I was already entering the pattern, just did what I always did hundreds of times.  Ended up down with no problems, I suspect maybe was  a tad slow.  I will say the pucker factor was very high.
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #32 on: October 31, 2018, 08:03:20 am »
Looking at Air France flight 447:
"The loss of airspeed indications caused the autopilot, flight director, and autothrust to disconnect, as they require airspeed information to operate. The airplane’s handling characteristics also changed, as the airplane’s fly-by-wire flight controls degraded from its Normal to Alternate law. This led to the loss of many automatic protection mechanisms built into Normal law, including stall protection."
https://risk-engineering.org/concept/AF447-Rio-Paris

 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #33 on: October 31, 2018, 08:11:21 am »
Looking at Air France flight 447:
"The loss of airspeed indications caused the autopilot, flight director, and autothrust to disconnect, as they require airspeed information to operate. The airplane’s handling characteristics also changed, as the airplane’s fly-by-wire flight controls degraded from its Normal to Alternate law. This led to the loss of many automatic protection mechanisms built into Normal law, including stall protection."
https://risk-engineering.org/concept/AF447-Rio-Paris
Yep.
Adding to this, if you then only have ground speed (GPS) to work with and a 100kt tailwind things won't end well.
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Offline rx8pilot

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #34 on: October 31, 2018, 08:32:41 am »
Yep.
Adding to this, if you then only have ground speed (GPS) to work with and a 100kt tailwind things won't end well.

Pitch + Power = Performance.
Any pilot can get rather close to a target airspeed with a known pitch+power (adjusted for altitude and temp).

The real trick is to understand that the system is in a state of failure and stop flying the airplane based on the potentially erroneous information. Identifying that a problem exists can easily be more challenging than dealing with it.
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #35 on: October 31, 2018, 08:59:47 am »
I hope the black boxes survived.
I know they are tough, but it's not unlimited tough, and this was about as fast an impact as you can get. And the water is only approx 30m deep, so it might as well have just hit the ground.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #36 on: October 31, 2018, 09:02:41 am »
I hope the black boxes survived.
I know they are tough, but it's not unlimited tough, and this was about as fast an impact as you can get. And the water is only approx 30m deep, so it might as well have just hit the ground.
At the relevant impact speed, water is pretty damned hard. I doubt that the aircraft impacted the bottom with any kind of significant speed (meaning 30m, 100m, and 500m would be essentially "the same" wrt impact forces).

From another aviation forum that I waste spend a lot of time, aircraft might have impacted ~475 knots TAS and 40° nose down.
« Last Edit: October 31, 2018, 09:04:47 am by sokoloff »
 

Offline alsetalokin4017

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #37 on: October 31, 2018, 09:15:15 am »
This thread reminds me of when pilots start discussing electrical engineering on PPRuNe. 

This tragic loss of life MAY have been caused by faulty instrument indications which in turn caused the pilots to act inappropriately in some way. Maybe. They clearly struggled with the aircraft for many minutes before finally losing control and diving into the sea at very high speed.

"Unreliable airspeed" is something that airline pilots are supposed to be practicing in simulators regularly. Pitch and power settings to establish a gentle climb at a reasonable airspeed despite faulty indications are supposed to be embedded in the pilot's memory and trained regularly in sim. This flight was in daylight, good visibility and good weather, so nothing at all like AF447. The 737 MAX has mechanical primary flight controls, it is not totally "fly by wire" like Airbus.

Faulty instrument indications could be caused by many things, all of which would have the same outcome, supposedly manageable safely by the crew if they had time, and it appears this crew did have time but didn't manage safely. The case of the B2 at Guam that had the blocked pitot system on takeoff did not allow the pilots enough time to do anything but eject; it was out of control from the moment of liftoff.


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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #38 on: October 31, 2018, 09:31:24 am »
I hope the black boxes survived.
I know they are tough, but it's not unlimited tough, and this was about as fast an impact as you can get. And the water is only approx 30m deep, so it might as well have just hit the ground.
At the relevant impact speed, water is pretty damned hard.

Yep, I have experience drop testing stuff onto water, it can be as hard as a rock. But it has a lot to do with how surface areas impact etc.

Quote
I doubt that the aircraft impacted the bottom with any kind of significant speed (meaning 30m, 100m, and 500m would be essentially "the same" wrt impact forces).
From another aviation forum that I waste spend a lot of time, aircraft might have impacted ~475 knots TAS and 40° nose down.

Possibly. If it was very nose down, then the bottom would have impacted in some way I suspect. But at 40deg that kinda flat-ish in the scheme of thing, so may not have hit bottom in that case.
In any case, it they haven't located the black box by now (which have transponders), then it's likely they are damaged. Although it's also possible the transponder could have sheered off the recorder housing, so they may not be together.
They are located in the tail, so hopefully are just sitting on the bottom somehow instead of buried in the sand.
« Last Edit: October 31, 2018, 09:33:53 am by EEVblog »
 

Offline MT

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #39 on: October 31, 2018, 09:59:53 am »
For those interested in this stuff I highly recommend the book QF32
The captain takes you blow by blow through what it's like to get multiple conflicting warnings and whatnot

https://www.amazon.com.au/QF32-author-Life-Lessons-Cockpit-ebook/dp/B007KTLQ5W

Better up the ATSB report is like a Agatha Christie multiplied by the Lord of the rings! Hairy, quite close to total death!
Many detailed pictures.
http://www.atsb.gov.au/publications/investigation_reports/2010/aair/ao-2010-089.aspx
« Last Edit: October 31, 2018, 10:02:28 am by MT »
 

Offline Lord of nothing

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #40 on: October 31, 2018, 10:03:23 am »
Quote
I have a Raspberry Pi + $12 USB Software Defined Radio in my garage
o you share? I use a proper Equipment for.
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Online EEVblog

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #41 on: October 31, 2018, 10:04:53 am »
Quote
I have a Raspberry Pi + $12 USB Software Defined Radio in my garage
o you share? I use a proper Equipment for.

I wouldn't mind setting up a receiver, but i can't find a map of existing installations?
 

Offline edy

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #42 on: October 31, 2018, 04:37:14 pm »
Not to derail the main thread, but I just noticed this article on CNN and thought :wtf::

https://www.cnn.com/travel/article/electric-easyjet-planes-intl/index.html

I think it is mostly a marketing strategy the company concocted to get more media coverage, but I am concerned about the 10-15 years timeline they expect these to be viable, tested and practical. I know they have small airplanes on short routes already in operation but is it something that paying passengers are willing to risk? If an electric car fails vs. electric plane, your chances of surviving may vary quite a bit.

We are just on the heels of this 737 tragedy which is a brand new plane, but I don't know the history of electric planes well enough to say if they are as reliable and safe at this point. From a small Cessna-style 2 seater to 9 seater electric with maybe 500km range (short flights) seem to be already on the near horizon, but I can't imagine yet seeing anything like the picture below without a major breakthrough:

« Last Edit: October 31, 2018, 04:39:17 pm by edy »
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Offline Lord of nothing

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #43 on: October 31, 2018, 08:41:22 pm »
Quote
I wouldn't mind setting up a receiver, but i can't find a map of existing installations?
depend on the national law you could end in Jail for but on the other end there are so many People go get them all is impossible.
There arent any Maps because you must/ can/ have to share from IP to IP.
Its like a Black Marked Business you need to know someone to get he Data.
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Offline nfmax

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #44 on: October 31, 2018, 08:55:44 pm »
Of course, the previous day's problems may have had nothing at all to do with the cause of the accident. It is also possible that knowledge of the previous failure may have misled the aircrew into inappropriate response to the actual failure, whatever that may turn out to be. There is a term for this, I can't remember - getting locked into a wrong interpretation of the situation causing you to disregard evidence (that you are interpreting wrongly).
 

Offline janoc

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #45 on: October 31, 2018, 09:38:17 pm »
With this particular new airplane, with fly-by-wire systems and computers automating a lot of the conditions (and perhaps, if I am to assume correctly, over-riding perhaps pilots in certain situations?) then could this be a case of AI or "smart algorithms" gone wrong? Or are pilots pretty much in control. I know it is too early to assume anything, we still don't know.

737 is not a fly-by-wire, it has classic flight controls (hydraulics for the most part).

There is also no "AI" or "smart algorithms" overriding the pilots, not even on the Airbuses. The electronics is designed in a way that whenever something seems out of whack, the automation will warn the crew and disconnect, handing the entire mess to the human sitting there to sort out.

What some planes (Airbus, not the crashed 737) have are things like the "alpha floor" protections (it prevents stalling under certain conditions) but these are typically the first ones lost/disabled when the computers detect some kind of anomaly - that's what Airbus refers to as "laws" (normal vs alternate when something is wrong for ex).

And when the pilot feels the automation is doing something it shouldn't for whatever reason, there is a disconnect button on the yoke/sidestick and for the worst case there is always a circuit breaker that can be pulled. Even on the Airbus you can fly the plane without the computers - it is going to be difficult but it is still possible.

Looking at Air France flight 447:
"The loss of airspeed indications caused the autopilot, flight director, and autothrust to disconnect, as they require airspeed information to operate. The airplane’s handling characteristics also changed, as the airplane’s fly-by-wire flight controls degraded from its Normal to Alternate law. This led to the loss of many automatic protection mechanisms built into Normal law, including stall protection."
https://risk-engineering.org/concept/AF447-Rio-Paris


Guys, AF447 is not a comparable situation. AF447 was first and foremost caused by relatively inexperienced crew mishandling the controls in a major way - newer attempting the "pitch and power" stable configuration and causing the plane to stall by keeping pulling at the side stick almost all the way down. The crew has never recognized the stall and never attempted to correct it, despite the warnings and buffet they were feeling. It was also not clear who (if anyone) was actually flying - both crewmen were trying to make control inputs at the same time.

The plane was perfectly flyable the entire time, though. At the time of crash it was flown by two rather inexperienced first officers (captain went to sleep after the departure from Rio, I believe, as it was supposed to be a rather uneventful part of the trip). The failure has also occurred at night, at high altitude and in turbulence. None of that was the case for the Lion Air flight (experienced crew, daytime, low altitude, good weather).

Also, since then a lot of training since the AF447 has been focused on both manual flying and recovery from similar failures (the AF447 pilots except of the captain apparently didn't have any training of dealing with unreliable airspeed in a "manual" plane, both having been trained directly on the Airbus).

Here is the AF447 report:
https://www.bea.aero/docspa/2009/f-cp090601.en/pdf/f-cp090601.en.pdf

Given the (few) data we have about the Lion Air flight, it would surprise me if there was any similarity at all to the AF447 flight. The Lion Air crew was obviously not in a stall, they were trying to maintain level flight but ultimately failed.

This entire pitot discussion is very likely a red herring caused by the maintenance log from the day before and there had to be some other major mechanical problem on board  (uncontained engine failure, explosion, decompression, whatever) to cause a crash like this. This kind of speculation is pretty pointless until there is more data available, e.g. from the black boxes.

« Last Edit: October 31, 2018, 09:45:55 pm by janoc »
 

Offline amyk

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #46 on: October 31, 2018, 10:54:50 pm »
This entire pitot discussion is very likely a red herring caused by the maintenance log from the day before and there had to be some other major mechanical problem on board  (uncontained engine failure, explosion, decompression, whatever) to cause a crash like this. This kind of speculation is pretty pointless until there is more data available, e.g. from the black boxes.
Something like https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261 ?
 

Offline janoc

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #47 on: November 01, 2018, 02:47:38 am »
This entire pitot discussion is very likely a red herring caused by the maintenance log from the day before and there had to be some other major mechanical problem on board  (uncontained engine failure, explosion, decompression, whatever) to cause a crash like this. This kind of speculation is pretty pointless until there is more data available, e.g. from the black boxes.
Something like https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261 ?

Flight 261 was an MD83, not a 737, the rudder is driven in a different way. And given that this was a brand new plane, the chance that something has worn out already (in the 261 crash the rudder jackscrew threads were worn off due to poor maintenance) is minimal.

It could be literally anything at this point. Even something like losing the rudder fin or even an entire vertical stabilizer (happened in Japan before bcs of poorly repaired tailstrike - the plane flew for a while before hitting a mountain, also old models of 737,  not NG or MAX, had a history of rudder problems). Or an engine blowing up and taking out the hydraulics lines (Sioux City crash landing - landed using differential engine thrust and manual trim because main flight controls were inop). Or a bomb going off. Or even a fight in the cockpit for all we know. I am not saying that any of these are likely but until we know more it is a speculation equally good as any other.

Could it be that the crash was related to a poorly repaired failure from the day before and the crew stuffing it up? Sure. But it could have also been a completely different problem.

So far the only information are rather inaccurate Flightradar data, crew requesting a return to Jakarta (suggesting a mechanical problem on board) and the information that there has been an avionics failure the day before. Nothing else. Trying to conclude anything from only that is a fool's errand.

« Last Edit: November 01, 2018, 02:53:34 am by janoc »
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #48 on: November 01, 2018, 03:54:07 am »
Something like https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261 ?
Flight 261 was an MD83, not a 737, the rudder is driven in a different way. And given that this was a brand new plane, the chance that something has worn out already (in the 261 crash the rudder jackscrew threads were worn off due to poor maintenance) is minimal.
Alaska 261 was a horizontal stabilizer (controls pitch trim) jackscrew issue, not a rudder (controls yaw) defect.

That it is almost surely unrelated is 100% true (other than both flights ending in water with loss of all aboard).
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #49 on: November 01, 2018, 04:29:05 am »
There's so many pitot tube incidents.
Yep, especially when the pilots and ground crew on their pre-flight walk arounds can't/don't/won't see the socks placed on them to keep the various mason wasps from building nests in them.
Not all parts of the world have this problem but it's bad enough in some locations that covering the pitot tubes is mandatory but easily overlooked in pre-flight checks.  ::)

Worked Avionics Instruments in the USAF late 70's early 80's and we had a couple occasions where we needed to replace a pitot tube because the cover wasn't removed and burned up in-flight.  I don't know how that could be missed during takeoff roll as the IAS for that circuit would be AFU.  I kind of doubt this crash was due to a covered pitot tube as it should have been obvious pretty early.  OTH, the crash did happen shortly after takeoff.  The FDR and CVR should clear things up.


Brian
 

Offline janoc

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #50 on: November 01, 2018, 04:29:41 am »
Alaska 261 was a horizontal stabilizer (controls pitch trim) jackscrew issue, not a rudder (controls yaw) defect.

That it is almost surely unrelated is 100% true (other than both flights ending in water with loss of all aboard).

Ah right, not sure why I wrote "rudder". D'oh. Thanks for the correction.
 

Online BravoV

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #51 on: November 01, 2018, 03:01:07 pm »
Latest update from local news by the reporter that on the SAR ship, black box recovered today at 10 am local time, and apparently undamaged, and it was buried under the mud at about 30m from the surface.

The signals were detected at these coordinates S 05 48 48.051 - E 107 07 37.622 and S 05 48 46.545 - E 107 07 38.393.






Transferred into proper & safe container.

« Last Edit: November 01, 2018, 03:30:20 pm by BravoV »
 

Online EEVblog

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #52 on: November 01, 2018, 04:30:06 pm »
Latest update from local news by the reporter that on the SAR ship, black box recovered today at 10 am local time, and apparently undamaged, and it was buried under the mud at about 30m from the surface.

I'm surprised the pinger worked under the mud, but then again, 30m of water makes it vastly easier
 

Offline amyk

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #53 on: November 01, 2018, 11:15:35 pm »
Something like https://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261 ?
Flight 261 was an MD83, not a 737, the rudder is driven in a different way. And given that this was a brand new plane, the chance that something has worn out already (in the 261 crash the rudder jackscrew threads were worn off due to poor maintenance) is minimal.
Alaska 261 was a horizontal stabilizer (controls pitch trim) jackscrew issue, not a rudder (controls yaw) defect.

That it is almost surely unrelated is 100% true (other than both flights ending in water with loss of all aboard).
I meant related as in "sudden failure of control surface". The fact that the plane was so new means it could be a manufacturing defect.

Good they recovered the recorders, we should get the answer soon.
 

Offline Homer J Simpson

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #54 on: November 01, 2018, 11:36:15 pm »

Scanning the Wikipedia article on the 737 Max...........

https://en.wikipedia.org/wiki/Boeing_737_MAX

Seems to have been / is a lot of pressure to produce as many planes as possible.



"On August 13, 2015, the first 737 MAX fuselage completed assembly at Spirit Aerosystems in Wichita, Kansas, for a test aircraft that would eventually be delivered to launch customer Southwest Airlines.[26] On December 8, 2015, the first 737 MAX—a MAX 8 named "Spirit of Renton"—was rolled out at the Boeing Renton Factory.[27][28]

Because GKN could not produce the titanium honeycomb inner walls for the thrust reversers quickly enough, Boeing switched to a composite part produced by Spirit to deliver 47 MAXs per month in 2017. Spirit supplies 70 percent of the 737 airframe, including the fuselage, thrust reverser, engine pylons, nacelles, and wing leading edges.[29]

A new spar-assembly line with robotic drilling machines should increase throughput by 33 percent. The Electroimpact automated panel assembly line sped up the wing lower-skin assembly by 35 percent.[30] Boeing plans to increase its 737 MAX monthly production rate from 42 planes in 2017 to 57 planes by 2019.[31]

The rate increase strains the production and by August 2018, over 40 unfinished jets were parked in Renton, awaiting parts or engine installation, as CFM engines and Spirit fuselages were delivered late.[32] After parked airplanes peaked at 53 at the beginning of September, Boeing reduced this by nine the following month, as deliveries rose to 61 from 29 in July and 48 in August.[33] "



Interesting if it turns out to be related to manufacturing.

 

Offline boffin

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #55 on: November 02, 2018, 04:55:36 am »
The rate increase strains the production and by August 2018, over 40 unfinished jets were parked in Renton, awaiting parts or engine installation, as CFM engines and Spirit fuselages were delivered late.[32] After parked airplanes peaked at 53 at the beginning of September, Boeing reduced this by nine the following month, as deliveries rose to 61 from 29 in July and 48 in August.[33] "

Hard to imagine there's room for 40 unfinished jets at Renton, it's a pretty small airport.  There's 27 parked there (all over the airfield) in the Google Sat image; and they're spread out all over the place, not sure where you'd find the room to double that.

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Offline boffin

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #56 on: November 02, 2018, 04:59:20 am »
I'm reading that it's the Flight Data Recorder (there are two 'black boxes' the FDR and the Cockpit Voice Recorder)..

In the past there have been issues with 737 rudders (https://en.wikipedia.org/wiki/Boeing_737_rudder_issues) , but that was completely redesigned  with the previous generation of the 73.  Until they start looking at what's on that recording, we really wont know.
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Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #57 on: November 02, 2018, 05:20:25 am »
As a Avionics Instruments tech while working in the USAF back in the day the reports from a previous flight that also had a problem shortly after takeoff that cleared and they continued on there flight it's looking to me that rather than a cover on a pitot tube it looks like a fitting in the system maybe lose giving erratic readings but then stabilize later.  The pitot static system consists of two lines: the static line that monitor atmospheric pressure used for altitude and vertical velocity, and a ram pressure that's used for indicated airspeed and used in combination with the static pressure and temperature for TAS.  I suspect that the static line had a lose fitting and if that's true it's also possible a ram pressure line may also have been lose.

During maintenance of the pitot static system lines are opened to hook up test equipment to provide calibrated pressures to check the altimeters and airspeed indicators for correct readings.  Of course, when the tests are done the equipment is disconnected AND the lines must then be reconnected.  I've seen it happen where this is done but the fittings are not tightened -- they are snugged up but not immediately tightened so at some point down the road the back off a bit and...

The FDR should reveal this even of the pilots didn't properly identify it.


Brian
 

Offline Wolfgang

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #58 on: November 03, 2018, 12:20:37 am »
one of the more trivial reasons for a Pitot failure is an insect stuck in the inlet.
The incoming air then never reaches the heater, icing could occur and the readings are nonsense.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #59 on: November 03, 2018, 05:20:09 am »
one of the more trivial reasons for a Pitot failure is an insect stuck in the inlet.
The incoming air then never reaches the heater, icing could occur and the readings are nonsense.


Yes, that's true, however the previous flight reported similar issues so you would THINK they would do an inspection of the pitot tubes before the next flight.

But, erratic readings could be explained by an inspect or other FOD in the pitot tube.

Again, this should be plainly obvious in the FDR data.


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Offline IanMacdonald

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #60 on: November 03, 2018, 06:11:10 am »
I'm not a pilot and have only rudimentary knowledge about this. Hopefully not too much of a noob question.... but if a Pitot tube or aircraft speed sensor was blocked or malfunctioning, it would tell the pilot the aircraft is going too slow? So wouldn't they speed up the airplane? Wouldn't speeding up help keep it flying in the air? I would imagine the reverse would be worse, where the sensor is telling you that you are going fast and you slow down and stall.

No. The ASI measures the difference in pressure between the pitot and static vents. The pitot pressure would remain as it was before it was blocked, so the instrument would likely read the same regardless of a speed increase or decrease in level flight. Although as you gained altitude the indicated speed would increase due to the reducing pressure on the static side. That's maybe what happened, and lead to a stall.

In fact, for VMC flying anyway, most of the stuff on the instrument panel is eye candy. The one thing you really need is to know your airspeed, as it's hard to judge visually.  The rest you can tell with the Mk1 eyeball.

 

Offline Gyro

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #61 on: November 03, 2018, 06:23:48 am »
Is there no sanity check built into the system for the airspeed indication (other than the duplicated pitots and instruments)?

I would have though that the system ought to be able to combine engine thrust, altitude, attitude, control surface settings, takeoff weight, fuel used etc. to calculate and generate an airspeed display plausibility warning. Maybe even to provide a emergency backup 'estimated' airspeed indication?
« Last Edit: November 03, 2018, 06:25:35 am by Gyro »
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Offline cdev

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #62 on: November 03, 2018, 06:49:42 am »
One would think that after the accident over the Atlantic several years ago, that the pitot tube icing issue would have been solved by installing multiple redundant pitot tubes, as well as multiple redundant everything else. the same thing with the satellite data link. Every multimillion dollar aircraft that flies should have one tied to a pair of redundant GPS receivers, one at the nose and one near the tail. Using the two it should be possible to get the exact position and heading anywhere in the world of every one of those planes, in seconds. They get a very good quality of data simply from GPS of their airspeed. The pitot tubes might be good to have but they should all be looked at at the same time and if any of the readings is wildly divergent, it should be eliminated as such an outlier its almost certainly wrong.
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #63 on: November 03, 2018, 06:53:59 am »
Is there no sanity check built into the system for the airspeed indication (other than the duplicated pitots and instruments)?

I would have though that the system ought to be able to combine engine thrust, altitude, attitude, control surface settings, takeoff weight, fuel used etc. to calculate and generate an airspeed display plausibility warning. Maybe even to provide a emergency backup 'estimated' airspeed indication?

Of course there is, and it's been well established in this thread already. If two completely independent systems don't agree on airspeed, the pilots are going to be alerted. If they follow their training, they'll go to pitch and power settings to ensure a proper airspeed, then they can reference the backup instrument for a third independent reading. If there's no consensus, they can fly pitch and power settings all the way to a safe landing.

If machines were good enough to be trusted to do the job all the time, there wouldn't be pilots on board at all.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #64 on: November 03, 2018, 06:57:18 am »
One would think that after the accident over the Atlantic several years ago, that the pitot tube icing issue would have been solved by installing multiple redundant pitot tubes, as well as multiple redundant everything else. the same thing with the satellite data link. Every multimillion dollar aircraft that flies should have one tied to a pair of redundant GPS receivers, one at the nose and one near the tail. Using the two it should be possible to get the exact position and heading anywhere in the world of every one of those planes, in seconds. They get a very good quality of data simply from GPS of their airspeed. The pitot tubes might be good to have but they should all be looked at at the same time and if any of the readings is wildly divergent, it should be eliminated as such an outlier its almost certainly wrong.

GPS doesn't give airspeed, it gives ground speed. Great for navigation, but very inaccurate as an airspeed replacement. Could differ by as much as 250mph if the plane is in a jet stream.
« Last Edit: November 03, 2018, 06:59:11 am by Nusa »
 
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #65 on: November 03, 2018, 07:00:02 am »
One would think that after the accident over the Atlantic several years ago, that the pitot tube icing issue would have been solved by installing multiple redundant pitot tubes, as well as multiple redundant everything else. the same thing with the satellite data link. Every multimillion dollar aircraft that flies should have one tied to a pair of redundant GPS receivers, one at the nose and one near the tail. Using the two it should be possible to get the exact position and heading anywhere in the world of every one of those planes, in seconds. They get a very good quality of data simply from GPS of their airspeed. The pitot tubes might be good to have but they should all be looked at at the same time and if any of the readings is wildly divergent, it should be eliminated as such an outlier its almost certainly wrong.
GPS derived ground speed means shit for flying a plane, you need airspeed which can be influenced by prevailing winds that could be all over the place at different altitudes.
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Offline Gyro

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #66 on: November 03, 2018, 07:08:34 am »
Is there no sanity check built into the system for the airspeed indication (other than the duplicated pitots and instruments)?

I would have though that the system ought to be able to combine engine thrust, altitude, attitude, control surface settings, takeoff weight, fuel used etc. to calculate and generate an airspeed display plausibility warning. Maybe even to provide a emergency backup 'estimated' airspeed indication?

Of course there is, and it's been well established in this thread already. If two completely independent systems don't agree on airspeed, the pilots are going to be alerted. If they follow their training, they'll go to pitch and power settings to ensure a proper airspeed, then they can reference the backup instrument for a third independent reading. If there's no consensus, they can fly pitch and power settings all the way to a safe landing.

If machines were good enough to be trusted to do the job all the time, there wouldn't be pilots on board at all.

So there's a nice big indicator saying one or both of your airspeed indications may be implausible, without relying on the pilots constantly visually cross-checking their indicators?

Edit: Sorry, I missed the reference to a third, backup, instrument. Is that Pitot too?... and is it linked into the automatic comparison warning too?
« Last Edit: November 03, 2018, 07:40:06 am by Gyro »
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Offline cdev

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #67 on: November 03, 2018, 08:11:07 am »
I bet!

 the speed of the gulf stream etc, adds a substantial boost/slow down to planes flying in it, you can see that happening when they change their heading in relation to it.
GPS derived ground speed means shit for flying a plane, you need airspeed which can be influenced by prevailing winds that could be all over the place at different altitudes.

Multiple, heated pitot tubes would be good, I wonder what other kinds of air speed sensors exist.

Anything mechanical that I can think of right now at least, besides a pitot pressure indicator would likely fail at a typical jets speed though.
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Offline Mr. Scram

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #68 on: November 03, 2018, 08:23:45 am »
Multiple, heated pitot tubes would be good, I wonder what other kinds of air speed sensors exist.

Anything mechanical that I can think of right now at least, besides a pitot pressure indicator would likely fail at a typical jets speed though.
Mechanical measures aren't completely infeasible. A small propeller device is deployed when all engines and the APU fail to power the bare essentials. This device is obviously capable of dealing with fairly substantial forces, even though a gliding jet liner will be slower than at cruising speeds.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #69 on: November 03, 2018, 08:24:09 am »
I bet!

 the speed of the gulf stream etc, adds a substantial boost/slow down to planes flying in it, you can see that happening when they change their heading in relation to it.
GPS derived ground speed means shit for flying a plane, you need airspeed which can be influenced by prevailing winds that could be all over the place at different altitudes.

Multiple, heated pitot tubes would be good, I wonder what other kinds of air speed sensors exist.

Anything mechanical that I can think of right now at least, besides a pitot pressure indicator would likely fail at a typical jets speed though.

When I took my flying lessons (AS350B3) the procedure for a suspect Pitot was to fly a circle and to look at the difference of TAS and ground speed.
 

Offline khs

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #70 on: November 03, 2018, 09:13:44 am »
here a link to an Austrian website (English) discussing crashes & accidents..

http://avherald.com/h?article=4bf90724&opt=0
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #71 on: November 03, 2018, 09:26:19 am »
When I took my flying lessons (AS350B3) the procedure for a suspect Pitot was to fly a circle and to look at the difference of TAS and ground speed.

Perfectly reasonable for a helicopter, for which low airspeed by itself typically isn't an emergency. Maneuvers that cause low rotor speeds/blade stall are the real killers, as I understand it. Not that I've had any rotor training.
 

Offline Wolfgang

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #72 on: November 03, 2018, 09:37:13 am »
When I took my flying lessons (AS350B3) the procedure for a suspect Pitot was to fly a circle and to look at the difference of TAS and ground speed.

Perfectly reasonable for a helicopter, for which low airspeed by itself typically isn't an emergency. Maneuvers that cause low rotor speeds/blade stall are the real killers, as I understand it. Not that I've had any rotor training.

You would run this maneuvre at a medium power setting (80% MCP) and a level flight, and try a 2 minutes turn. Bank angle should be very moderate then.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #73 on: November 03, 2018, 07:33:20 pm »
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #74 on: November 03, 2018, 07:36:57 pm »
Surprised at how intact the black box is, pinger still attached:

 

Offline Berni

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #75 on: November 03, 2018, 07:52:17 pm »
Then again the black box is a solid metal block. Crashes on land are probably harder for it, especially if the impact is something like straight into a mountain, topped off with the fuel catching fire.

Also why are they called black boxes if they are never actually painted black?
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #76 on: November 04, 2018, 04:33:19 am »
Press is saying the flight data recorder is damaged or needs parts for repair or it was found in deep water. Load of bollocks.

A few professionals speculating the airplane was going around 600MPH at impact, explaining why it basically shattered into pieces. This is using the FlightData numbers and it would have to be nose down with engine power to get that fast.

old Boeing article:
"Beginning in 1965, FDRs (commonly known as "black boxes") were required to be painted bright orange or bright yellow, making them easier to locate at a crash site. "

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Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #77 on: November 04, 2018, 04:53:47 am »
If they were going 600mph at impact something else has to be going on -- they never got that high so unless they did a powered dive at high angle it's hard to see how they could have been going that fast.  At this point I'm beginning to wonder if maybe the CVR won't be more telling.


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Offline amyk

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #78 on: November 04, 2018, 05:27:28 am »
The FDR is still very intact because it would've had the whole length of the plane to decelerate (probably while punching through materials softer than it) as it hit the water, so the G forces it experienced weren't that high.

On the other hand, everything in the nose is probably crushed beyond recognition.
 

Offline Lord of nothing

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #79 on: November 04, 2018, 06:11:38 am »
Quote
600mph
a What?!  :palm:
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Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #80 on: November 04, 2018, 07:37:41 am »
Knots are not SI and not far from MPH as a layman's comparison I guess. American aerospace people were doing the speed numbers.

OK FDR is totally ripped off the base with power supply and I/O, all they pulled is the 'crash survivable memory unit' out of the water?
That seems very strange to have all the metal nicely ripped off, leaving a more or less handheld FDR for press pictures. Those divers must use tin snips  :o
Lion Air possibly chose the L3 tech FDR FA2100.
 

Offline SeanB

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #81 on: November 04, 2018, 08:53:46 am »
It ripped off the base sheet, probably part of the design to reduce the impact on the inner memory stack. That it is all nice and intact with the pinger is not a surprise, it is designed to do that.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #82 on: November 04, 2018, 09:18:36 am »
If they were going 600mph at impact something else has to be going on --

33,000 ft/min = 167 meters/second = 600 kilometers/hour = 375 miles/hour. Someone got their numbers and units mixed up.
 

Offline cdev

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #83 on: November 04, 2018, 09:39:13 am »
Did the accident happen during a storm or unusual weather of any kind?
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Offline Mr. Scram

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #84 on: November 04, 2018, 09:41:57 am »
Did the accident happen during a storm or unusual weather of any kind?
It's on the first page somewhere near the top.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #85 on: November 04, 2018, 09:59:38 am »
If they were going 600mph at impact something else has to be going on --

33,000 ft/min = 167 meters/second = 600 kilometers/hour = 375 miles/hour. Someone got their numbers and units mixed up.
I believe it was 31K fpm vertical velocity and something like 360 knots of ground speed (horizontal velocity).
Solves to something around 475 knots (about 550 mph) 40° below horizontal.
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #86 on: November 04, 2018, 10:21:15 am »
Kill me for starting with Bloomberg numbers supposedly backed up by:
Expert 1: "Scott Dunham, a former National Transportation Safety Board investigator, who combined the distance the plane traveled horizontally and vertically to arrive at a speed estimate." {600mph}
Expert 2: "John Hansman, a Massachusetts Institute of Technology aeronautics and astronautics professor, estimated the plane was flying at 540mph in the final moments..."
Expert 3: Jasenka Rakas, a lecturer in engineering and aviation at the University of California at Berkeley "...the speed could have been between 586 and 633 mph."
added Bloomberg hype? "At the end, it fell 1,025ft in 1.6 seconds."

I thought the ~600mph was vector sum of vertical and horizontal velocities.

Flightradar24 data looking at timestamps, it was at 28,000ft and took minutes to drop, so -33,000ft/min seems wrong too.
2018-10-28 23:31:56Z.030 last two samples do say it fell 1,025ft in 1.6 seconds.

edit: confused flight JT610 with JT43.
« Last Edit: November 04, 2018, 03:49:53 pm by floobydust »
 

Offline SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #87 on: November 04, 2018, 01:50:18 pm »
Quote
600mph
a What?!  :palm:

Almost breaking the sound barrier! :-DD
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #88 on: November 04, 2018, 01:56:13 pm »
Flightradar24 data looking at timestamps, it was at 28,000ft and took minutes to drop, so -33,000ft/min seems wrong too.
You're confusing the data for the prior flight with that of the fatal flight. On it's last flight, it never got much over 6000 ft.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #89 on: November 04, 2018, 03:49:32 pm »
Flightradar24 data looking at timestamps, it was at 28,000ft and took minutes to drop, so -33,000ft/min seems wrong too.
You're confusing the data for the prior flight with that of the fatal flight. On it's last flight, it never got much over 6000 ft.
Fixed, it is 1,025ft in 1.6 seconds at the end.
 

Offline Lord of nothing

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #90 on: November 04, 2018, 05:55:54 pm »
Why not put some SD Cards across the Aircraft when the Crash the have some additional infos when the get found.
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #91 on: November 04, 2018, 06:22:47 pm »
Kill me for starting with Bloomberg numbers supposedly backed up by:
Expert 1: "Scott Dunham, a former National Transportation Safety Board investigator, who combined the distance the plane traveled horizontally and vertically to arrive at a speed estimate." {600mph}
Expert 2: "John Hansman, a Massachusetts Institute of Technology aeronautics and astronautics professor, estimated the plane was flying at 540mph in the final moments..."
Expert 3: Jasenka Rakas, a lecturer in engineering and aviation at the University of California at Berkeley "...the speed could have been between 586 and 633 mph."
added Bloomberg hype? "At the end, it fell 1,025ft in 1.6 seconds."

Ah yes, Bloomberg, the well known purveyor of fake news. I wouldn't trust them to tell me the right time.   :palm:
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #92 on: November 04, 2018, 09:55:46 pm »
480mph
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #93 on: November 06, 2018, 06:44:50 am »
Apparently the plane had airspeed indicator problems on its final FOUR flights! Surely enough opportunities for someone to check the pitot tubes and do some sort of investigation?  :-\

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #94 on: November 06, 2018, 07:11:01 am »
Well they do have ribbons on them but apparently that isn't always enough.
Why not some kind of lockout/tagout system then? Put a code in the box which requires keys from all the tags to open (or a bolt cutter for eventualities) and which needs to be transmitted to the pilot.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #95 on: November 06, 2018, 07:21:54 am »
Well they do have ribbons on them but apparently that isn't always enough.
Why not some kind of lockout/tagout system then? Put a code in the box which requires keys from all the tags to open (or a bolt cutter for eventualities) and which needs to be transmitted to the pilot.
Yes it certainly wouldn't be hard to add some sort of fail-safe system so that pilots had live info on their displays on the status of pitot condoms.
Even near proximity RFID tags linked to the flight systems so the aircraft couldn't taxi under its own power would eliminate all stuff ups.

Ain't hard, only the willingness to do so is.  :palm:
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Offline glarsson

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #96 on: November 06, 2018, 07:31:12 am »
Even near proximity RFID tags linked to the flight systems so the aircraft couldn't taxi under its own power would eliminate all stuff ups.

Ain't hard, only the willingness to do so is.  :palm:
Not so easy. The manufacturer has to certify that this mechanism will not be a hazard, e.g. will never disable the aircraft during normal operation.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #97 on: November 06, 2018, 07:37:51 am »
Even near proximity RFID tags linked to the flight systems so the aircraft couldn't taxi under its own power would eliminate all stuff ups.

Ain't hard, only the willingness to do so is.  :palm:
Not so easy. The manufacturer has to certify that this mechanism will not be a hazard, e.g. will never disable the aircraft during normal operation.
Yer what ? ? ?
No different to any other sensor or system code in the modern aircraft !

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Offline glarsson

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #98 on: November 06, 2018, 08:14:12 am »
They are also not easy, but a device that can disable the aircraft (even designed to do it) is something else. Can you guarantee that these RFID sensors can't fail and disable the aircraft during takeoff, cruise or landing?
What is worse; a failed pitot tube or one sensor that disables the aircraft?
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #99 on: November 06, 2018, 08:37:19 am »
Aircraft manufacturers have probably figured pitot safety out better than random EE enthusiasts brainstorming here.
There's an airspeed alive callout and an 80-knot cross-check to catch gross pitot errors. It's extremely unlikely that this airplane took off with pitot covers installed (if that's the case, RFID tagged covers are a non-solution).

They have the FDR; they can hear roughly where the CVR is and are likely to recover it. That will tell a lot more than all the internet speculation combined.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #100 on: November 06, 2018, 08:38:32 am »
Apparently the plane had airspeed indicator problems on its final FOUR flights! Surely enough opportunities for someone to check the pitot tubes and do some sort of investigation?  :-\

https://www.bbc.co.uk/news/world-asia-46094495

Not looking good for Lion Air, sadly it looks like the techs are going to take the fall even though you can bet it was management saying 'no delays, keep flying'. 

So. the two most likely causes appear to me to be either debris (insect etc) clogging the pitot tube or a leak (lose fittings) in the pitot-static system.  Of the two I suspect the later is more likely given the fact that the problem came and went on previous flights which I'd argue is less likely to happen with a clog than with a lose fitting.


Brian
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #101 on: November 06, 2018, 08:42:30 am »
Aircraft manufacturers have probably figured pitot safety out better than random EE enthusiasts brainstorming here.
There's an airspeed alive callout and an 80-knot cross-check to catch gross pitot errors. It's extremely unlikely that this airplane took off with pitot covers installed (if that's the case, RFID tagged covers are a non-solution).

They have the FDR; they can hear roughly where the CVR is and are likely to recover it. That will tell a lot more than all the internet speculation combined.


I think pitot covers are completely ruled out as that would be glaringly obvious even if it was missed on the first flight with the problem -- how likely is it that they'd miss a pitot cover on four flights in a row?  It is possible a cover may have been on during the first flight and they chose to attempt to clean/repair the pitot tube rather than replace it.  Again, I think that's very unlikely. 


Brian
 

Offline Marco

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #102 on: November 06, 2018, 08:56:36 am »
Not so easy. The manufacturer has to certify that this mechanism will not be a hazard, e.g. will never disable the aircraft during normal operation.
Lockout/tagout would make no functional change to the plane though, you just tie a key to the cap.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #103 on: November 06, 2018, 08:59:41 am »
Apparently the plane had airspeed indicator problems on its final FOUR flights! Surely enough opportunities for someone to check the pitot tubes and do some sort of investigation?  :-\

https://www.bbc.co.uk/news/world-asia-46094495

Not looking good for Lion Air, sadly it looks like the techs are going to take the fall even though you can bet it was management saying 'no delays, keep flying'.
I'm not trying to be flippant here, but the flight crew already took the fall and is likely to take the fall in the official findings as well.
This probably will not get an NTSB report due to where it happened (outside US and non-N carrier), but if it were an NTSB report, it would likely read:

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The pilot's loss of airplane control due to spatial disorientation during the initial climb after takeoff in day visual meteorological conditions.
Contributing factors to the accident were confusing PFD displays due to unreliable airspeed measurements from the pitot-static systems, broken/layered clouds over water, providing a difficult horizon to use as an alternate visual reference for orientation. Additional factors in the accident were flat morning light conditions and inadequately addressed maintenance squawks on prior flights of the pitot-static system.

It's hard to say exactly what they're going to find, but the probable cause is almost certain to start with "The pilot's loss of control..."
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #104 on: November 06, 2018, 09:06:18 am »
Pitch + Power = Performance.
Any pilot can get rather close to a target airspeed with a known pitch+power (adjusted for altitude and temp).

I'm coming to this thread pretty late, but this is the whole ball of wax right here. I don't fly big iron, but the the laws of physics are the same for them as anybody else. The AF447 crew screwed up. If it was a pitot problem, this crew screwed up, too. The plane is flyable without IAS.

In fact, in the AF447 situation where all the plane's automatic systems punted, that was (and probably remains) a design defect IMO, because the computers hand the airplane back to the captain at the worse possible moment. A better approach would be for the computer itself to start flying the aircraft by attitude and notify the pilot accordingly.


 

Offline glarsson

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #105 on: November 06, 2018, 09:38:51 am »
Aircraft manufacturers have probably figured pitot safety out better than random EE enthusiasts brainstorming here.
I'm not random.
 

Offline eugenenine

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #106 on: November 06, 2018, 09:47:48 am »
Not so easy. The manufacturer has to certify that this mechanism will not be a hazard, e.g. will never disable the aircraft during normal operation.
Lockout/tagout would make no functional change to the plane though, you just tie a key to the cap.

I was going to say the ignition key and then post the ignition key from Airplane II but I couldn't find a clip of it.

seems like they could just put a string on the tube cover and have a little suction cup on the other end that sticks to the front window of the airplane.
 

Offline MT

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #107 on: November 06, 2018, 09:56:27 am »
So. the two most likely causes appear to me to be either debris (insect etc) clogging the pitot tube or a leak (lose fittings) in the pitot-static system.  Of the two I suspect the later is more likely given the fact that the problem came and went on previous flights which I'd argue is less likely to happen with a clog than with a lose fitting.
Brian
Yes, insects nesting in pitot tubes have caused crashes before and they cant bee seen by external visual check i heard.
 

Offline eugenenine

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #108 on: November 06, 2018, 01:13:36 pm »
sounds like they need a way to divert the jet engine thrust into the tube for a second to clear it.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #109 on: November 06, 2018, 01:31:16 pm »
sounds like they need a way to divert the jet engine thrust into the tube for a second to clear it.
The pitot tubes are generally up front by the nose on multi-engine aircraft. They need to be in undisturbed air to sense properly.

They're nowhere near the engines and a blast of jet engine thrust would only serve to destroy the tubing and sensors behind. (The system measures the stagnation pressure and relates that back to airspeed. That stagnation sensing loop is closed [or very nearly closed].)
 

Offline amyk

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #110 on: November 06, 2018, 02:21:39 pm »
https://patents.google.com/patent/US3380298

"Device for purging pitot tubes" patented 1968-04-30. Essentially a valve that can disconnect the sensors and then connect the pitot to a compressed air source to blow out any obstructions from behind. Do planes have something similar?
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #111 on: November 06, 2018, 05:24:14 pm »
https://patents.google.com/patent/US3380298

"Device for purging pitot tubes" patented 1968-04-30. Essentially a valve that can disconnect the sensors and then connect the pitot to a compressed air source to blow out any obstructions from behind. Do planes have something similar?


I don't think any such devise has been employed outside of testing.  Here's the concern...  First, it may not work and second, if anything goes wrong you could destroy a lot of expensive avionics.  Also, such a devise would be limited to ground use and could never be trusted in-flight.  A competent service technician or team of such would know what to do to isolate the problem and fix it -- this happens ALL THE TIME!  I suspect the ground crew were told they have 30 minutes before the next flight and if it isn't fixed before then they'd fly just as they did the previous three flights with the problem.  A bit like NASA being pressured to launch the Challenger because they wanted there teacher in space.


Brian
 

Offline eugenenine

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #112 on: November 06, 2018, 11:26:57 pm »
https://patents.google.com/patent/US3380298

"Device for purging pitot tubes" patented 1968-04-30. Essentially a valve that can disconnect the sensors and then connect the pitot to a compressed air source to blow out any obstructions from behind. Do planes have something similar?

someone should patent this for cleaning pilot tubes

« Last Edit: November 06, 2018, 11:28:56 pm by eugenenine »
 

Offline Homer J Simpson

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #113 on: November 07, 2018, 09:36:06 pm »


Boeing and FAA to issue advice to airlines on 737 Max jets AoA sensor.


"potentially suspect flight-control software that can confuse pilots and lead to a steep descent of the affected aircraft model"



https://www.wsj.com/articles/boeing-faa-to-issue-safety-alerts-following-lion-air-crash-1541562339
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #114 on: November 07, 2018, 11:16:56 pm »
Boeing and FAA to issue advice to airlines on 737 Max jets AoA sensor.
"potentially suspect flight-control software that can confuse pilots and lead to a steep descent of the affected aircraft model"
https://www.wsj.com/articles/boeing-faa-to-issue-safety-alerts-following-lion-air-crash-1541562339

That sounds like it's ultimately going to be pilot error.
 
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Offline PA0PBZ

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #117 on: November 08, 2018, 01:57:18 am »
Keyboard error: Press F1 to continue.
 
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Offline Koen

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #118 on: November 08, 2018, 04:07:21 am »
Googling "Boeing Issues Safety Alert Following Lion Air Crash" did the trick for me.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #119 on: November 08, 2018, 05:32:39 am »
https://www.abc.net.au/news/2018-11-08/lion-air-flight-had-crucial-sensor-replaced-prior-to-fatal-crash/10475468
Quote
A crucial sensor that is the subject of a Boeing safety bulletin was replaced on a Lion Air jet the day before it plunged into the Java Sea and possibly worsened other problems with the plane, Indonesian investigators have revealed.

Indonesia's National Transportation Safety Committee (NTSC) said it had agreed with Boeing on procedures that the airplane manufacturer should distribute globally on how flight crews can deal with "angle of attack" sensor problems following the October 29 crash that killed all 189 people on board.

Experts say the angle of attack is a crucial parameter that helps the aircraft's computers understand whether its nose is too high relative to the current of air.

The sensor keeps track of the angle of the aircraft nose relative to oncoming air to prevent the plane from stalling and diving.

But a Boeing statement said a safety bulletin, sent to airlines this week, directs flight crews to existing guidelines on how they should respond to erroneous "angle of attack" data.

"The point is that after the AOA [sensor] is replaced the problem is not solved, but the problem might even increase. Is this fatal? NTSC wants to explore this," he said.

So in other words, simply replacing the sensor can not only not work, but can make the problem worse.
I assume as you then have an un-calibrated sensor.

Quote
Transport safety committee chairman Soerjanto Tjahjono said airspeed indicator malfunctions on the jet's last four flights, which were revealed by an analysis of the flight data recorder, were intertwined with the sensor issue.

So they have bad readings from both the Angle of Attack and Airspeed sensors, this sounds more like a wiring/electronics issue to me.
 

Offline Homer J Simpson

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #120 on: November 08, 2018, 05:33:42 am »

Boeing jet crashed in Indonesia a day after key sensor replaced

"Lion Air's first two attempts to address the airspeed indicator problem didn't work and for the Boeing 737 MAX 8 plane's second to last flight on Oct. 28, the angle of attack sensors were replaced, Tjahjono said.

On that flight, from Bali to Jakarta, the pilot's and copilot's sensors disagreed. The 2-month-old plane went into a sudden dive minutes after takeoff, which the pilots were able to recover from. They decided to fly on to Jakarta at a lower than normal altitude."



https://komonews.com/news/nation-world/boeing-jet-crashed-in-indonesia-a-day-after-key-sensor-replaced


 

Offline alsetalokin4017

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #121 on: November 08, 2018, 06:42:18 am »
Boeing and FAA to issue advice to airlines on 737 Max jets AoA sensor.
"potentially suspect flight-control software that can confuse pilots and lead to a steep descent of the affected aircraft model"
https://www.wsj.com/articles/boeing-faa-to-issue-safety-alerts-following-lion-air-crash-1541562339

That sounds like it's ultimately going to be pilot error.

Well, sure, but it all depends on how far back you go to "ultimately". Myself, I'd say that the major pilot error was to accept the aircraft for flight in the first place, after maintenance on the sensor system. Let a test pilot crew test such critical systems without pax on board first!

But once off the ground, the situation is something like this: you are driving along, fat dumb and happy, at night on a smoothly paved road. Suddenly the pavement ends and you are bouncing along on ruts and potholes, and suddenly a thunderstorm starts dumping hail on you, and your windshield wipers short out, your headlights fail and your horn inexplicably starts blaring. Right at that moment a kangaroo leaps out onto what's left of the road, your brakes fail and you run into it, destroying your vehicle and killing all on board. Ultimately... it's driver error, for not avoiding the 'roo. Innit?

I am not disagreeing though. The pilots evidently did not perform the correct actions for dealing with unreliable air data, therefore "pilot error", but you really have to consider the environment and the demands of the task at hand. The "roo in the road" above doesn't even come close to the disorientation and distractions that must have been happening in that cockpit.

The easiest person to fool is yourself. -- Richard Feynman
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #122 on: November 08, 2018, 06:58:22 am »
That sounds like it's ultimately going to be pilot error.
Well, sure, but it all depends on how far back you go to "ultimately". Myself, I'd say that the major pilot error was to accept the aircraft for flight in the first place, after maintenance on the sensor system. Let a test pilot crew test such critical systems without pax on board first!
You seriously believe that airliners are commonly flown by test pilots without pax after maintenance items? No way that happens after minor maintenance. It gets a signoff from maintenance and the next flight has pax on board. Ultimately, it's the crew's discretion whether or not to take an aircraft, but not taking an aircraft because maintenance was just performed is a short road to unemployment at an air carrier.
But once off the ground, the situation is something like this: you are driving along, fat dumb and happy, at night on a smoothly paved road. Suddenly the pavement ends and you are bouncing along on ruts and potholes, and suddenly a thunderstorm starts dumping hail on you, and your windshield wipers short out, your headlights fail and your horn inexplicably starts blaring. Right at that moment a kangaroo leaps out onto what's left of the road, your brakes fail and you run into it, destroying your vehicle and killing all on board. Ultimately... it's driver error, for not avoiding the 'roo. Innit?

I am not disagreeing though. The pilots evidently did not perform the correct actions for dealing with unreliable air data, therefore "pilot error", but you really have to consider the environment and the demands of the task at hand. The "roo in the road" above doesn't even come close to the disorientation and distractions that must have been happening in that cockpit.
That is a pretty reasonable description of the hand that the Air France 447 crew was handed (and that they were unable to handle).

Lion Air was a daytime flight, with largely visual conditions prevailing. I'm going to fully withhold judgment until more information (including CVR transcripts) is available, but based on the information available, this seems a lot closer to "speedometer was covered up by a piece of paper fluttering around the cabin and operator couldn't keep the car between 40 and 80 mph without that reference" than the scenario you describe (which I'd argue was still salvageable by fully-qualified crew, on an average day, but not by that crew on that evening).
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #123 on: November 08, 2018, 08:56:24 am »
A new player in this crash is the AOA indicator, or more accurately, the AOA probe.  For some reason the AOA transmitter was replaced and I'm kind of wondering how this relates to the pitot/static system.  The AOA indicator should indicate the angle the aircraft is flying relative to the air they're flying in and if the new transmitter was not installed properly it could give an erroneous AOA indication.

Additionally, since they appear to have been flying with autopilot the flight control outputs would have been determined by the flight computer taking into account the data from the sensors.  It appears that there maybe an issue in the software as it relates to the AOA sensor data and on a previous flight the plane went into a dive that the pilots were able to recover from.  Ultimately, with as many issues as they had in the previous flights it is unacceptable that the plane remained in service until the problem was nailed down. 

So, the lawyers will have a field day with everyone to blame.  The pilots, the ground crew, the airline management, and Boeing.  I can well imagine a bunch of lawyers are at this very moment placing orders for new cars and a second home.


Brian
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #124 on: November 08, 2018, 10:03:45 am »
AOA seems to be a second pressure port on the pitot probe. One for airspeed, another for critical (stall) angle.
There is a cal file specific to the aircraft. I'm not sure if it was a generic pitot part that was swapped out and cal file left alone or corrupted...

How was the autopilot working for the previous flights?
With a pitot discrepancy, Airbus goes to manual mode.
It seems odd previous flights had issues after takeoff and somehow did fine afterwards.

There are billions of dollars at stake here, I doubt the blame will be proper between parties.
 

Offline MT

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #125 on: November 08, 2018, 12:44:47 pm »
Time for a AirFrance thread reminder, so whatever potentially disastrous during flight always:
1:Aviate , 2:Navigate , 3:Communicate. Also for pilots taking off is optional, landing is mandatory.
Just sayin!
« Last Edit: November 08, 2018, 12:48:53 pm by MT »
 
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #126 on: November 08, 2018, 01:00:04 pm »
Lion Air was a daytime flight, with largely visual conditions prevailing. I'm going to fully withhold judgment until more information (including CVR transcripts) is available, but based on the information available, this seems a lot closer to "speedometer was covered up by a piece of paper fluttering around the cabin and operator couldn't keep the car between 40 and 80 mph without that reference" than the scenario you describe (which I'd argue was still salvageable by fully-qualified crew, on an average day, but not by that crew on that evening).

At this stage that's my guess too (with my obvious in-depth knowledge of aviation with one flight and 3hrs flying time under my belt  ::) ).
No bad weather, daytime, maybe some clouds making horizon reference a bit tricky, but with no actual fault in the plane control systems, it should have been work-aroundable and completely flyable.
But of course one small thing can often send you down a path that doesn't end well.
They did report issues and were returning to the airport at the time of the incident, so should have been in super-alert troubleshooting mode fresh into the lfight, and not half way across the atlantic 8 hours in and tired and shit suddenly hits the fan.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #127 on: November 08, 2018, 04:43:16 pm »
Lion Air was a daytime flight, with largely visual conditions prevailing. I'm going to fully withhold judgment until more information (including CVR transcripts) is available, but based on the information available, this seems a lot closer to "speedometer was covered up by a piece of paper fluttering around the cabin and operator couldn't keep the car between 40 and 80 mph without that reference" than the scenario you describe (which I'd argue was still salvageable by fully-qualified crew, on an average day, but not by that crew on that evening).

At this stage that's my guess too (with my obvious in-depth knowledge of aviation with one flight and 3hrs flying time under my belt  ::) ).
No bad weather, daytime, maybe some clouds making horizon reference a bit tricky, but with no actual fault in the plane control systems, it should have been work-aroundable and completely flyable.
But of course one small thing can often send you down a path that doesn't end well.
They did report issues and were returning to the airport at the time of the incident, so should have been in super-alert troubleshooting mode fresh into the lfight, and not half way across the atlantic 8 hours in and tired and shit suddenly hits the fan.

Modern commercial fly by wire AC don't let the pilot have full control even when the autopilot is disengaged.  The AOA factor is critical and I expect Boeing will be releasing updated flight control software sometime in the not too distant future. 

In order for a pilot to override the control decisions of the computer the pilots must deactivate a number of systems and until they do this the computer is still in charge.

Beyond what I've already posted on this I think what Boeing did today was the first step in addressing an actual control problem that can occur when the right, or wrong, set of airspeed, altitude and AOA data is presented to the computer.  The fact that the previous flight had pretty similar problems, issued a Pan-Pan and asked to return, but then the problem went away and they decided to continue with the flight would not be permitted most places in the world but Lion Air appears to operate with the schedule being more important than safety.

There are many at fault here and the consequence is going to be expensive.


Brian
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #128 on: November 08, 2018, 05:57:20 pm »
However, the Boeing 737 is NOT a fly-by-wire aircraft.
 
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Offline IanMacdonald

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #129 on: November 08, 2018, 07:00:27 pm »
1:Aviate , 2:Navigate , 3:Communicate.

4: M....bate.

Though  if you are flying a Dalek mothership you may have more success with:
1:Aviate , 2:Navigate , 3:Exterminate 4: Communicate.
Than with 3 and 4 in conventional order. By which time The Doctor has gotten away.
« Last Edit: November 08, 2018, 07:10:17 pm by IanMacdonald »
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #130 on: November 08, 2018, 07:02:30 pm »
The fact that the previous flight had pretty similar problems, issued a Pan-Pan and asked to return, but then the problem went away and they decided to continue with the flight would not be permitted most places in the world but Lion Air appears to operate with the schedule being more important than safety.
The captain/pilot-in-command has significant discretion as to the conduct of the flight. I can think of several valid reasons a flight may initially decide they need to return only to overcome the problem and elect to continue. A mis-programmed FMS/FD may very well give the crew reason for concern and then the crew may overcome that and safely continue the flight. Weather is another. An abnormal or emergency may crop up that is subsequently remedied by reference to the QRH/checklist procedures. Continuing may very well be the safest (or equally safe and more economical) choice.

BA268 is a classic example of that. They lost an engine (with external flames) 300 feet into the climb off LAX en route to Heathrow. ATC declared an emergency on their behalf (also permitted by their job orders (section 10-1)). Crew shut the engine down, continued the climb, and did an assessment to continue the flight rather than dump fuel and return. Passing the east coast of the US, another assessment by them allowed them to continue for England. Ultimately, crew declared an emergency for fuel and landed in Manchester, short of Heathrow.

The first actual section of Federal law governing aviation in the US is 14 CFR 91.3, which reads:
Quote
§ 91.3 Responsibility and authority of the pilot in command.
(a) The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.

(b) In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule of this part to the extent required to meet that emergency.

(c) Each pilot in command who deviates from a rule under paragraph (b) of this section shall, upon the request of the Administrator, send a written report of that deviation to the Administrator.
Airline Ops are additionally governed by part 121, which includes 14 CFR 121.557, with substantially similar text. Of course there is pressure in the airline world to complete trips as planned. Because the pilots are generally the first ones to arrive at the scene of the crash, there's also a high degree of pressure to complete flights safely.
 

Offline IanMacdonald

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #131 on: November 08, 2018, 07:16:25 pm »
"Ultimately, crew declared an emergency for fuel and landed in Manchester, short of Heathrow."

Which underlines that in aviation, once you are in an unfamiliar situation you may encounter other unfamiliar situations. In this case an increased fuel burn. 
 

Offline khs

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #132 on: November 08, 2018, 07:19:25 pm »
The AOS sensor sounds harmless.

But it is not.

As I've learned, the AOS sensor controls the trim system of the aircraft.

The trim system of the aircraft sounds harmless.

But it is not.

As I've learned (from the comments from avherald.com), trimming is not a little bit nose up or down.
In the worst case, trimming cannot be compensated by the pilot's input, because the range of the trim system is greater(!!) than the range of the stick.

If the AOS sensor is faulty, the STAB TRIM CUTOUT switches must be set to CUTOUT by the pilot.

I do not understand why Boeing does not turn off the trim system by software when the AOS sensor generates bad data.
 
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Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #133 on: November 08, 2018, 07:32:18 pm »
IIRC, the issue was the flight crew's uncertainty that they could access all the fuel onboard during one-engine-INOP operations, not that they didn't have enough overall fuel onboard.
IOW, they were concerned about fuel starvation, not fuel exhaustion.
 

Online Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #134 on: November 08, 2018, 08:42:47 pm »
IIRC, the issue was the flight crew's uncertainty that they could access all the fuel onboard during one-engine-INOP operations, not that they didn't have enough overall fuel onboard.
IOW, they were concerned about fuel starvation, not fuel exhaustion.

Then the FAA tried to fine them for not being airworthy. A UK aircraft in international or UK airspace when the fuel emergency was called. The UK CAA (their equivalent of the FAA) disagreed and said the plane was certified airworthy with only 3 engines. I gather the FAA accepted that in the end.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #135 on: November 09, 2018, 01:02:05 am »
They did. The FAA concern was over the engine out in California, not the later emergency in Manchester. But the FAA backed down as the aircraft was certified to operate on 3. (Uncomplicated loss of engine in a 747 is an "abnormal" procedure, not an "emergency" procedure.)
 

Offline IanMacdonald

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #136 on: November 09, 2018, 02:41:34 am »
Large airliners undergo substantial changes in elevator trim, particularly when landing flaps are deployed. It is often marginal as to whether the pilots could exert enough force on the controls to maintain attitude without the help of the trim tabs. Conversely if a trim tab goes to an extreme position and cannot be reset, this can be a mission critical situation.

Interestingly, in the event of elevator drive failure it is often possible for a skilled pilot to make a safe landing by flying the plane with the trim control.
« Last Edit: November 09, 2018, 02:44:22 am by IanMacdonald »
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #137 on: November 09, 2018, 10:23:32 am »
However, the Boeing 737 is NOT a fly-by-wire aircraft.


It's not a 100% fly by wire AC but it does have fly-by-wire control of spoilers.


Brian
 

Online Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #138 on: November 09, 2018, 11:22:55 am »
However, the Boeing 737 is NOT a fly-by-wire aircraft.


It's not a 100% fly by wire AC but it does have fly-by-wire control of spoilers.


Brian

I learned something new. You're right, but ONLY for the ~200 737-MAX's that have been delivered. Most of the thousands of 737's out there are 0% fly-by-wire. So for the MAX, let's call it 5% to be generous? Spoiler use in normal flight is limited to descents and landings. Most of its advanced features have to be enabled by the pilots, and most features are locked out when the flaps are not extended, even if turned on.
http://www.b737.org.uk/max-spoilers.htm

I'd be pretty surprised if the spoilers were a negative factor in this crash.
 

Online Bratster

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #139 on: November 09, 2018, 02:14:11 pm »
Quote
I have a Raspberry Pi + $12 USB Software Defined Radio in my garage
o you share? I use a proper Equipment for.

I wouldn't mind setting up a receiver, but i can't find a map of existing installations?

https://flightaware.com/adsb/coverage#feeder-sites

I just got the stuff to set up a receiver and came across this page that shows the existing feeder sites and coverage.
 

Offline alsetalokin4017

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #140 on: November 09, 2018, 02:31:11 pm »
Lion Air was a daytime flight, with largely visual conditions prevailing. I'm going to fully withhold judgment until more information (including CVR transcripts) is available, but based on the information available, this seems a lot closer to "speedometer was covered up by a piece of paper fluttering around the cabin and operator couldn't keep the car between 40 and 80 mph without that reference" than the scenario you describe (which I'd argue was still salvageable by fully-qualified crew, on an average day, but not by that crew on that evening).

At this stage that's my guess too (with my obvious in-depth knowledge of aviation with one flight and 3hrs flying time under my belt  ::) ).
No bad weather, daytime, maybe some clouds making horizon reference a bit tricky, but with no actual fault in the plane control systems, it should have been work-aroundable and completely flyable.
But of course one small thing can often send you down a path that doesn't end well.
They did report issues and were returning to the airport at the time of the incident, so should have been in super-alert troubleshooting mode fresh into the lfight, and not half way across the atlantic 8 hours in and tired and shit suddenly hits the fan.

Actually the weather was very hazy so, over the water, the horizon would have been very indistinct and maybe even invisible. And the aircraft was undergoing radical pitch excursions resulting in wildly varying g-forces, and several different audible alarms were going off in the cockpit. Cabin crew, unsecured in seats, may have been injured or having to deal with passenger injuries due to the aircraft's attitude changes during the struggle to maintain control. This is why I described the "roo" situation as I did. In many ways this event was _worse_ than AF447, which was in a stable "mushing stall" all the way to the water and could have been flown out to normal flight had the pilots actually flown it out by simply lowering the nose and adding power. This aircraft was broken, and even if the pilots could have recovered it, it would still be broken and causing problems all the way until landed -- or crashed.

So yes -- pilot error, but in an environment where it was incredibly easy to make errors and be distracted, and at an altitude that did not allow time for evaluation -- or mistakes.
The easiest person to fool is yourself. -- Richard Feynman
 

Online Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #141 on: November 09, 2018, 07:16:17 pm »
When the cabin crew is seated in their jumpseats, they are typically secured by shoulder straps. This plane was in trouble so soon after takeoff, I doubt the cabin crew was ever given clearance to move around, nor are they likely to do so on their own when things are clearly going wrong. Not that it mattered in the end, dead is dead.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #142 on: November 10, 2018, 10:02:39 am »
However, the Boeing 737 is NOT a fly-by-wire aircraft.


It's not a 100% fly by wire AC but it does have fly-by-wire control of spoilers.


Brian

I learned something new. You're right, but ONLY for the ~200 737-MAX's that have been delivered. Most of the thousands of 737's out there are 0% fly-by-wire. So for the MAX, let's call it 5% to be generous? Spoiler use in normal flight is limited to descents and landings. Most of its advanced features have to be enabled by the pilots, and most features are locked out when the flaps are not extended, even if turned on.
http://www.b737.org.uk/max-spoilers.htm

I'd be pretty surprised if the spoilers were a negative factor in this crash.


All aircraft have autopilot and this is true for more than 50 years -- these system permit the computer to control the aircraft even in AC that are not fly-by-wire.  So, the fact remains that modern aircraft place a computer between the pilot and the control surfaces even when the plane is not fly-by-wire in the technical sense.  In operation the computer fly's the plane most of the time including climb-out and descent.  If the pilots are not well versed in the methods to arrest control from the computer they are in trouble -- and again, this also applies to non fly-by-wire AC though to a lessor extent. 

It will be interesting to find out which system, the pilots or the computer, were responsible for the dive that doomed them!


Brian
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #143 on: November 12, 2018, 04:35:01 am »
But of course one small thing can often send you down a path that doesn't end well.

Just a nit here, but few aviation accidents are caused by one thing going wrong. There is usually a rather long accident chain. In this case, we already know that there is a) potentially a design error b) definitely a flight manual documentation error (this is what the AD that Boeing put out modifies) c) a known sensor issue that was sent for repair d) a plane that was not test-flown after a sensor repair and then e,f,... whatever happened in the cockpit that we do not know about yet, but I'm willing to bet that more than one mistake was made.

I'm not an airline pilot, but I am an instrument-rated private pilot with about 500 hours and I'm also a voracious consumer of accident reports.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #144 on: November 12, 2018, 04:45:06 am »
Just for reference, this is the actual emergency Airworthiness Directive that Boeing has sent out:


https://c-3sux78kvnkay76x24znkgox78iax78x78ktzx2eius.g00.flyingmag.com/g00/3_c-3ccc.lreotmsgm.ius_/c-3SUXKVNKAY76x24nzzvyx3ax2fx2fznkgox78iax78x78ktz.iusx2fcv-iutzktzx2favrugjyx2f8674x2f77x2fH393-SGD-GJ-7763.vjl_$/$/$/$/$/$?i10c.ua=1&i10c.dv=14

It is, in its entirety, an update to the flight manual.

I see three basic elements to it:

 1. x, y, and z are signs of a AOA sensor failure, with certain confusing instrument indications, including a potentially erroneous and changing minimum speed bar on the ASI
 2. pilots should respond to such failures by disconnecting the auto stabilizer trim system
 3. pilots should expect to need to use extra control force to overcome the auto stab system until it has been disconnected

Based on this, it would seem that Boeing suspects that the airplane was flyable, but that the crew did not react as they should, perhaps due to poor training or lack of awareness of this particular failure mode. Of course, that's what Boeing would say. OTOH, crashes are really bad PR and they'd ground the planes if they suspected there was areal system problem.






 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #145 on: November 13, 2018, 04:20:56 am »
Just for reference, this is the actual emergency Airworthiness Directive that Boeing has sent out:


https://c-3sux78kvnkay76x24znkgox78iax78x78ktzx2eius.g00.flyingmag.com/g00/3_c-3ccc.lreotmsgm.ius_/c-3SUXKVNKAY76x24nzzvyx3ax2fx2fznkgox78iax78x78ktz.iusx2fcv-iutzktzx2favrugjyx2f8674x2f77x2fH393-SGD-GJ-7763.vjl_$/$/$/$/$/$?i10c.ua=1&i10c.dv=14

It is, in its entirety, an update to the flight manual.

I see three basic elements to it:

 1. x, y, and z are signs of a AOA sensor failure, with certain confusing instrument indications, including a potentially erroneous and changing minimum speed bar on the ASI
 2. pilots should respond to such failures by disconnecting the auto stabilizer trim system
 3. pilots should expect to need to use extra control force to overcome the auto stab system until it has been disconnected

Based on this, it would seem that Boeing suspects that the airplane was flyable, but that the crew did not react as they should, perhaps due to poor training or lack of awareness of this particular failure mode. Of course, that's what Boeing would say. OTOH, crashes are really bad PR and they'd ground the planes if they suspected there was areal system problem.

Boeing seems to have acted quickly and responsibly here though time will tell.  And, as I pointed out before and in spite of the fact that this plane is not technically fly-by-wire, the computer interposes itself between the pilot and control surfaces in a myriad of ways so taking 100% manual control is rather more complicated than pressing a single button. 

Best guess is that the pilots were too 'heads down' trying to make sense of things and didn't notice the plane was in descent until it was too late.  Again, there is going to be blame enough for everyone and the lawyers will profit...


Brian
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #146 on: November 13, 2018, 06:58:17 am »
And, as I pointed out before and in spite of the fact that this plane is not technically fly-by-wire, the computer interposes itself between the pilot and control surfaces in a myriad of ways so taking 100% manual control is rather more complicated than pressing a single button. 

You have said this, and I'm pretty sure it's not correct in any operational sense in any Boeing airliner. Disconnecting the AP is indeed a single button push -- and that button is on the yoke, too, right where it can be pressed in an instant. The plane can also adjust the trim automatically, and as the AD makes clear, that can also be turned off. But even if not turned off, it can be overridden by the pilot's controls without any special action other than pushing or pulling harder than usual. Similarly, there's an  trim and automatic yaw damper on the rudder which the pilot can disengage, but he can also kick the rudder however he wants and the machine will obey.

Boeing has aircraft such as the 777 that have FBW, but their philosophy is quite a bit different than Airbus's. The machine will essentially inform the pilot that he is about to exceed the aircraft's envelope by making it increasingly difficult for him to assert his control input (by pushing back against his inputs), but it will not override him. Check out section 11.3 of this document: http://www.davi.ws/avionics/TheAvionicsHandbook_Cap_11.pdf

So, though there are systems (electric, hydraulic) between the pilot an the control surfaces, the pilots commands ARE obeyed unless something has actually broken.

This is totally different from an Airbus aircraft, where the computer under "normal law" enforces the flight envelope no matter the control inputs. There are several other modes the aircraft can be in, such as "alternate law 1" where the plane continues to enforce most of the envelope except AOA and overspeed, and "alternate law 2" where only load factor is enforced, and of course "direct law" which is basically "you're on your own kid."



In this case, it looks like the computer might have pushed the nose down, but the pilot could have counterracted that with the normal controls, albeit, with extra force.


« Last Edit: November 13, 2018, 10:19:44 am by djacobow »
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #147 on: November 13, 2018, 07:40:24 am »
And, as I pointed out before and in spite of the fact that this plane is not technically fly-by-wire, the computer interposes itself between the pilot and control surfaces in a myriad of ways so taking 100% manual control is rather more complicated than pressing a single button. 
You have said this, and I'm pretty sure it's not correct in any operational sense in any Boeing airliner. Disconnecting the AP is indeed a single button push -- and that button is on the yolk, too, right where it can be pressed in an instant. The plane can also adjust the trim automatically, and as the AD makes clear, that can also be turned off. But even if not turned off, it can be overridden by the pilots controls without any special action other than pushing or pulling harder than usual.
The problem with applying continued force to overcome the airplane's trim is that the auto-trim will continue to trim against you (essentially by design). Airplane is on autopilot and trying to fly a course consistently lower than the aircraft is heading? The airplane will add nose-down trim. If the pilot continues to pull against that, they can, but the airplane will sense that the autopilot is not following the programmed pitch and will continue to trim nose down. On every aircraft I've flown, which is mostly piston singles and twins, but includes a few jets, pressing and holding the AP Disconnect switch will kill power to the auto-trim system and pitch trim motors.

Minor nit: it's "yoke" not "yolk"
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #148 on: November 13, 2018, 10:18:46 am »
Minor nit: it's "yoke" not "yolk"

Hah, I promised myself I would never do that again. Oh well.

I think we're in agreement. Yes, the AP/trim will work against you more and more but at the same time, that feeling of working against trim is going to be very familiar to any pilot who has ever flown with an AP. Particularly when you're having a "what is Otto doing now" moment, I can't think of anything more natural than disconnecting the AP and putting the plane into the state I want, while I figure out why the AP has different plans.

Admittedly, this is coming from someone whose time is mostly in older light singles with reliably unreliable autopilots.

 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #149 on: November 14, 2018, 01:54:18 am »
I suspect we agree on almost everything about this crash, at least based on what is known now.

One difference in larger aircraft than in the light singles that you have experience in is that many larger aircraft trim systems work by changing the angle of incidence of the horizontal stabilizer with respect to the fuselage. (It literally cranks the tail "nose up" or "nose down" usually with a jackscrew.) Systems like this have the capability to overpower the pilot's inputs to a much greater extent than the "flying trim tabs" on most light singles. (Among light singles, as far as I know the only common types to use this system are most Mooneys, Piper's TriPacer, and the Cessna 185.)
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #150 on: November 14, 2018, 06:17:50 am »
I don't know how long it will take for the formal report but I would expect an overview of the FDR and CVR within 4-6 weeks.  It may not answer all questions, but it should provide more details on the technical problems and, hopefully, address the factual situation with respect to which system, pilots or computer, produced the nose down attitude that resulted in the crash.  We can quibble over just how much automation this AC had but the fact remains this wasn't a purely manual AC and the pilots would need to do certain things to take the computer out of the loop. 

The facts about that particular truth should be clear as day in the FDR and the CDR should help elucidate the pilots actions during the 13 minutes of the flight. 


Brian
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #151 on: November 14, 2018, 06:39:27 am »
Boeing screwed up putting an extra (undocumented) "Maneuvering Characteristics Augmentation System" to compensate for "some unique aircraft handling characteristics."

It relies on the AOA sensor and automatically lowers the plane's nose into a dive if it figures a stall condition exists.

No way for pilots to know about it- Boeing has nothing mentioned in training, difference, manuals etc.
APA to American's pilots "This is the first description you, as 737 pilots, have seen"  :palm:

https://www.chicagotribune.com/business/ct-biz-boeing-indonesia-737-crash-20181113-story,amp.html
 
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Online tautech

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #152 on: November 14, 2018, 07:19:12 am »
Boeing screwed up putting an extra (undocumented) "Maneuvering Characteristics Augmentation System" to compensate for "some unique aircraft handling characteristics."

It relies on the AOA sensor and automatically lowers the plane's nose into a dive if it figures a stall condition exists.

No way for pilots to know about it- Boeing has nothing mentioned in training, difference, manuals etc.
APA to American's pilots "This is the first description you, as 737 pilots, have seen"  :palm:

https://www.chicagotribune.com/business/ct-biz-boeing-indonesia-737-crash-20181113-story,amp.html
How can it determine that ?

Airspeed ?
Are we back to suspecting blocked pitot tubes for this to happen ?
Avid Rabid Hobbyist
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #153 on: November 14, 2018, 09:29:24 am »
I'm not sure who makes the 737 max sensor pitot or AOA sensor, it's kind of hush. Thales or UTC etc.

My understanding is the AOA sensor measures pressure at the wing leading edge and together with the pitot you get differential (wing) pressure indicating lift. Some sensors combine both (mechanically) with a second pressure port in the pitot sensor. AOA is not an absolute angle sensor.

If either pressure sensor is malfunctioning, software may act thinking there is a stall condition, there is no lift.

 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #154 on: November 14, 2018, 09:42:38 am »
Yes thanks, some further understanding here:
http://www.dynonavionics.com/aoa-pitot-probes.php
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Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #155 on: November 14, 2018, 10:11:07 am »
Well, we'll all guessing here, but I still would be very surprised if pilots were not mentally equipped for a "runaway" trim problem where the trim/AP does something unexpected. Even if the cause of this runaway is novel, the idea that it can happen, and what you would do in that case would hardly be.

Yes, I'm pulling this from my rear, but at the same time, it's such a basic airmanship thing: you are flying an airplane that has (not so) little motors that can adjust control surface trims and those motors are connected to a sophisticated box that, though pretty great, is fallible. You need to be ready to disconnect those motors in a hurry, and the "why is the control system doing this" question can be handled later.

Which is not to say that there isn't be a problem with the aircraft design -- it sounds like there very well may be. I just think that some of the fault is going to remain on the pilots.

Accidents can have more than one contributing cause.

by the way, here's a relevant page from a 737 QRH (not a -MAX, I'm sure) (http://jira.icesoft.org/secure/attachment/21680/qrh%20rev36%20-800%2027k.pdf) for runaway stab trim


It does not get more straightforward than that.
« Last Edit: November 14, 2018, 11:04:27 am by djacobow »
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #156 on: November 14, 2018, 11:12:37 am »
Yes, I'm pulling this from my rear, but at the same time, it's such a basic airmanship thing: you are flying an airplane that has (not so) little motors that can adjust control surface trims and those motors are connected to a sophisticated box that, though pretty great, is fallible. You need to be ready to disconnect those motors in a hurry, and the "why is the control system doing this" question can be handled later.

Which is not to say that there isn't be a problem with the aircraft design -- it sounds like there very well may be. I just think that some of the fault is going to remain on the pilots.

Accidents can have more than one contributing cause.
Given that the emergency AD is a slightly wordier version of "in case of runaway trim, follow the existing runaway trim procedure", it's a pretty safe bet that a lot of the blame is going to land on the dead guys up front.

No specific differences training, blah, blah, blah, don't care. You're right; it is a basic airmanship thing and there are several ways to kill the trim, 3 of which I believe are memory items.

The trim wheels are also not small (intentionally so) and make a clicking racket when in motion (also intentional):
 

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Offline SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #158 on: November 14, 2018, 12:43:30 pm »
Pilots says Boeing didn't disclose 737's new control feature
https://komonews.com/news/nation-world/were-p-sed-pilots-says-boeing-didnt-disclose-737s-new-control-feature

Hmm, now that's interesting.

"But if that nose-down command is triggered by faulty sensor readings — as suspected in the Lion Air crash — pilots can struggle to control the plane, which can go into a dive and perhaps crash, according to a Boeing safety bulletin and safety regulators."

This sounds fishy. Faulty sensor readings, as those sensors are redundant, should be caught (if they aren't caught, then it's a very serious design problem).

Any decent flight helper such as this anti-stall mechanism SHOULD be automatically disconnected (of course with a clear warning) in case of faulty sensor readings. This would be way too dangerous otherwise. Interested in knowing more about all this...
 

Offline Marco

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #159 on: November 14, 2018, 01:05:10 pm »
So how fast can that trim throw the plane into a completely vertical dive?
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #160 on: November 14, 2018, 01:19:54 pm »
"But if that nose-down command is triggered by faulty sensor readings — as suspected in the Lion Air crash — pilots can struggle to control the plane, which can go into a dive and perhaps crash, according to a Boeing safety bulletin and safety regulators."

This sounds fishy. Faulty sensor readings, as those sensors are redundant, should be caught (if they aren't caught, then it's a very serious design problem).
Suppose you have two independent pitot systems and they don't agree; which one is faulty? Suppose you have N independent pitot systems and they all agree but are all wrong (because of a common-mode maintenance failure, most likely); how do you automatically catch the fault?

Any decent flight helper such as this anti-stall mechanism SHOULD be automatically disconnected (of course with a clear warning) in case of faulty sensor readings. This would be way too dangerous otherwise. Interested in knowing more about all this...
IMO, we haven't established that the airplane can automatically "know" that a sensor reading is faulty. That's part (to a lot) of what the crew is there for. Unfortunately for this flight, that crew doesn't seem to have been up to the challenge of the hand they were dealt on that day.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #161 on: November 14, 2018, 01:43:59 pm »
Suppose you have two independent pitot systems and they don't agree; which one is faulty? Suppose you have N independent pitot systems and they all agree but are all wrong (because of a common-mode maintenance failure, most likely); how do you automatically catch the fault?

This. Furthermore, strange or divergent readings do not necessarily mean that any sensor is malfunctioning. You can have sensors on each wing and one wing might be stalled while the other is still flying. You can fly through a wind shear event that only effects one side of the airplane, or through another aircraft's wake turbulence, or get too slow while turning, or a combination of those factors -- all of which are the kinds of scenarios that have led to accidents and that one would imagine such a system is designed to detect.

It's a tricky business.
 

Offline SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #162 on: November 14, 2018, 02:57:25 pm »
"But if that nose-down command is triggered by faulty sensor readings — as suspected in the Lion Air crash — pilots can struggle to control the plane, which can go into a dive and perhaps crash, according to a Boeing safety bulletin and safety regulators."

This sounds fishy. Faulty sensor readings, as those sensors are redundant, should be caught (if they aren't caught, then it's a very serious design problem).
Suppose you have two independent pitot systems and they don't agree; which one is faulty? Suppose you have N independent pitot systems and they all agree but are all wrong (because of a common-mode maintenance failure, most likely); how do you automatically catch the fault?

If there is disagreement, it obviously doesn't matter which one is wrong to detect there is a malfunction. This case would warrant the disconnection of any automatic system that could rely on or even be influenced by those sensors, and issue a warning. First thing that happens is usually the disconnection of the autopilot, and I'm pretty sure that happens when there is a faulty pitot, at least on Airbus planes. This is the first thing that happened on the AF447 for instance, AFAIK. Of course, this could be different in this case. Maybe.

Any redundant sensor system that would give the same figures but all wrong, and that those wrong figures could still pass as valid would be severely badly designed IMO, or this would be a case of extreme bad luck. Usually the different sensors should be located at different spots, ideally from different vendors, etc, so this should be rather unlikely. If it still happened, it can usually be figured out by the calculators since they would likely give figures that make no sense physically. The case were the measurements would all still seem valid to the calculators is not impossible but not very likely.
This is the whole point of redundant systems.

Any decent flight helper such as this anti-stall mechanism SHOULD be automatically disconnected (of course with a clear warning) in case of faulty sensor readings. This would be way too dangerous otherwise. Interested in knowing more about all this...
IMO, we haven't established that the airplane can automatically "know" that a sensor reading is faulty.

See above. If it can't, then there's a serious design flaw, or extreme bad luck IMO. When it comes to faulty sensors, the most common case is the crew either not able to fly the plane without the corresponding readings, or normally able but troubled under high stress and starting to not trust ANY of the plane readings and warnings, leading to sometimes deadly maneuvers.

We'll see.
« Last Edit: November 14, 2018, 03:01:45 pm by SiliconWizard »
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #163 on: November 14, 2018, 03:36:43 pm »
If there is disagreement, it obviously doesn't matter which one is wrong to detect there is a malfunction. This case would warrant the disconnection of any automatic system that could rely on or even be influenced by those sensors, and issue a warning. First thing that happens is usually the disconnection of the autopilot, and I'm pretty sure that happens when there is a faulty pitot, at least on Airbus planes. This is the first thing that happened on the AF447 for instance, AFAIK. Of course, this could be different in this case. Maybe.

In the AF447 scenario, the computer decided it did not have reliable air data, so it not only disconnected the autopilot, it dropped into alternate law. Basically, the computer just punted and said "your airplane!" This might seem like reasonable behavior, but one might imagine that handing a degraded airplane to a pilot at the very worst moment is not a satisfactory failure mode, and in the AF447 scenario the outcome was obviously bad.

What else could the computer have been programmed to do? It could have perhaps dropped into an attitude-based straight-and-level flight mode, and made an annunciation inviting the pilots to take over, but not insisting that they do so that very instant.

But it's easy to second-guess these sorts of systems. It's not nearly as easy to design them so that they always do the thing that seems smartest in retrospect.

Any redundant sensor system that would give the same figures but all wrong, and that those wrong figures could still pass as valid would be severely badly designed IMO, or this would be a case of extreme bad luck.

I think you are underestimating the difficulty of this problem, because unusual attitudes and airspeeds are going to generate odd readings, and these are the exact situations -- not totally predictable -- where an AOA system is interesting.

Yes, one solution would be to have an array of AOA sensors from different vendors using different technologies, but you have to draw the line somewhere and you still need to integrate the data, and you still have to deal with the possibility that sensor #n, giving a strange reading is giving a correct strange reading. Maybe one sensor is at the wing root and another is at the tip, and the root is stalled and the tip is not. Or one wing is stalled and the other is not. Or both roots and one tip, but not the other, etc. Maybe the wing is physically damaged in some way that affects airflow and the sensor is correctly reporting that. All of those are aerodynamic situations that can happen.

Usually the different sensors should be located at different spots, ideally from different vendors, etc, so this should be rather unlikely.

But if they are in different spots, they're measuring different things. And "unlikely" is the exact problem. These aircraft are going to be flown 10's of thousands of hours and most of them are never going to ever get near a stall condition in their entire operational lives. Everything interesting an AOA system does is in well into the regime of "unlikely."



 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #164 on: November 14, 2018, 10:22:22 pm »
"But if that nose-down command is triggered by faulty sensor readings — as suspected in the Lion Air crash — pilots can struggle to control the plane, which can go into a dive and perhaps crash, according to a Boeing safety bulletin and safety regulators."

This sounds fishy. Faulty sensor readings, as those sensors are redundant, should be caught (if they aren't caught, then it's a very serious design problem).
Suppose you have two independent pitot systems and they don't agree; which one is faulty? Suppose you have N independent pitot systems and they all agree but are all wrong (because of a common-mode maintenance failure, most likely); how do you automatically catch the fault?
If there is disagreement, it obviously doesn't matter which one is wrong to detect there is a malfunction. This case would warrant the disconnection of any automatic system that could rely on or even be influenced by those sensors, and issue a warning. First thing that happens is usually the disconnection of the autopilot, and I'm pretty sure that happens when there is a faulty pitot, at least on Airbus planes. This is the first thing that happened on the AF447 for instance, AFAIK. Of course, this could be different in this case. Maybe.

Any redundant sensor system that would give the same figures but all wrong, and that those wrong figures could still pass as valid would be severely badly designed IMO, or this would be a case of extreme bad luck. Usually the different sensors should be located at different spots, ideally from different vendors, etc, so this should be rather unlikely. If it still happened, it can usually be figured out by the calculators since they would likely give figures that make no sense physically. The case were the measurements would all still seem valid to the calculators is not impossible but not very likely.
This is the whole point of redundant systems.
It turns out the airplane has to house and lift all these redundant systems into the air and carry them around the world. There's a real cost (in $$ and in safety) to excess weight in an airplane and a genuine engineering challenge to make the planes as safe as feasible, but when you add weight to an airplane, all else being equal, almost nothing good happens to safety. Runway performance is degraded, climb performance is degraded, range/fuel efficiency is degraded, stress on the tires and brakes is increased (longer, heavier, faster takeoff roll, more energy to dissipate in an RTO, etc), all of which have negative safety implications. (About the only thing that gets better is one specific input into the calculation of turbulent air penetration speed.)

When you start taking multiple different sensors of different types or from different vendors, now you have more complexity overall and wider tolerances to determine whether these two sensors agree or not. If you start adding a third or more to help break the tie, you have even more. At some point, you paid more in reduced safety than the safety you bought with the more redundant design. (Very quickly you paid more in $$, of course.)

I suspect that you're quite good in whatever your specific field is. I also suspect that there's something counterintuitive about your field where something is done a certain way, for good reason, but that reason isn't obvious to an outsider. When that situation has a light shone on it, outsiders might assume that they know more and that the practitioners in the field are obviously wrong, or they can wonder why something is done that way and start from an assumption that the skilled practitioners have a reason for it.

cf. Chesterton's Fence
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #165 on: November 15, 2018, 12:03:08 am »
I don't know how long it will take for the formal report but I would expect an overview of the FDR and CVR within 4-6 weeks.

Did they find the CVR? I haven't been keeping up to date.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #166 on: November 15, 2018, 12:07:45 am »
Not yet. (and the batteries on the locator beacon have now run out)

They found the AF447 black boxes though, long after they stopped pinging, so I'd expect there's a better than even chance that Lion Air's will be recovered eventually. It's mostly a question of how much money they are able to spend looking. I suspect it's properly "a lot".
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #167 on: November 15, 2018, 12:44:42 am »
The black box batteries are designed to operate the pinger for 30 days, and the crash was only 16 days ago. While it's correct to say we aren't hearing pings anymore, assuming the battery is the root cause of that is probably not correct.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #168 on: November 15, 2018, 02:37:13 am »
Fair point taken.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #169 on: November 15, 2018, 05:54:20 am »
I'm not sure who makes the 737 max sensor pitot or AOA sensor, it's kind of hush. Thales or UTC etc.

My understanding is the AOA sensor measures pressure at the wing leading edge and together with the pitot you get differential (wing) pressure indicating lift. Some sensors combine both (mechanically) with a second pressure port in the pitot sensor. AOA is not an absolute angle sensor.

If either pressure sensor is malfunctioning, software may act thinking there is a stall condition, there is no lift.


AOA sensors typically have a vane that turns as the relative wind angle changes.  The vane will tend to rotate to the trailing edge of the wind-stream and as it does it reports that angle.  Think of it as kind of like a small windmill that has a vane to keep the prop pointed into the wind.

As I mentioned before even AC that are not full on fly-by-wire AC have systems controlled by the computer that interpose themselves between the flight control surfaces and the pilot and if the story now being painted about an automated system installed by Boeing is correct then it makes it out to be perhaps more of a concern than a full fly-by-wire AC as the pilots may not be fully aware of the computer being in control.

Not looking good for Boeing if true...


Brian
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #170 on: November 15, 2018, 05:58:17 am »
I don't know anything about plane nor piloting one, its just watching this commentary from a former Inspector General US Dept of Transportation makes me worry me as an avg Joe.

-> https://edition.cnn.com/videos/tv/2018/11/14/ns-nov-14-intvw-boeing-witholds-info-mary-schiavo.cnn

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #171 on: November 15, 2018, 06:07:42 am »
I don't know how long it will take for the formal report but I would expect an overview of the FDR and CVR within 4-6 weeks.

Did they find the CVR? I haven't been keeping up to date.


I haven't heard, but given the relatively shallow water and proximity near shore it is just a matter of time before they do find it.  I think the CVR may wind up being just as important as the FDR given the fact that the pilots have to do certain things to arrest control and at relatively low altitude if the computer commands a fairly steep dive they may only have a few seconds before its too late.

Hard to believe that 4.5 years later and we still haven't found MH370 -- if the Lion Air crash is something of a mystery the loss of MH370 is the mystery of the century.


Brian
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #172 on: November 15, 2018, 06:28:27 am »
I don't know anything about plane nor piloting one, its just watching this commentary from a former Inspector General US Dept of Transportation makes me worry me as an avg Joe.

-> https://edition.cnn.com/videos/tv/2018/11/14/ns-nov-14-intvw-boeing-witholds-info-mary-schiavo.cnn
IMO, as a pilot (albeit one with under 20 hours of jet time, though around 1500 hours in high performance singles and twins, and having attended type and recurrent trainings in simulators a handful of times), this is being overblown by the breathless media anxious for a story.

Yes, it seems like Boeing downplayed the differences in this airplane vs others on the same type certificate. Do I think that it rises to level of "not looking good for Boeing"? Sure. Do I think it rises to the level of "not being good for Boeing"? No, at least not yet. There's a lot of pressure to keep new airplanes on the same TC as existing designs. It seems very much expected that Boeing would pursue that course of action, including making design decisions with the constraint of "let's keep this airplane an A16WE".

From what I've read and viewed, I don't think that Boeing "withheld information" so much as "didn't highlight this particular system" and the same checklists and emergency procedures still applied as were applicable to the prior jets.
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #173 on: November 15, 2018, 06:46:52 am »
Making the new airplane fuel efficient at the expense of handling, then quietly adding an undocumented MCAS system to make up for it to supposedly keep the plane backwards-compatible with previous generations of 737's... Right now, Boeing's mistake is rightly causing a shitstorm.
https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610

But the root cause of the airspeed or AOA malfunction is still unknown. Even after Lion Air maintenance worked three times to fix the problem.

The plane's previous pilot encountered the same unintentional dive and then switched off the trim system, even though "it's not in the manual".
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #174 on: November 15, 2018, 07:07:32 am »
Making the new airplane fuel efficient at the expense of handling, then quietly adding an undocumented MCAS system to make up for it to supposedly keep the plane backwards-compatible with previous generations of 737's... Right now, Boeing's mistake is rightly causing a shitstorm.
https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610

But the root cause of the airspeed or AOA malfunction is still unknown. Even after Lion Air maintenance worked three times to fix the problem.

The plane's previous pilot encountered the same unintentional dive and then switched off the trim system, even though "it's not in the manual".
It is in the manual.

Previously posted by djacobow in this post:
http://www.eevblog.com/forum/chat/lion-air-crash-jakarta-boeing-737-had-prior-instrument-error/msg1963691/#msg1963691
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #175 on: November 15, 2018, 09:25:09 am »
Making the new airplane fuel efficient at the expense of handling, then quietly adding an undocumented MCAS system to make up for it to supposedly keep the plane backwards-compatible with previous generations of 737's... Right now, Boeing's mistake is rightly causing a shitstorm.
https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610

But the root cause of the airspeed or AOA malfunction is still unknown. Even after Lion Air maintenance worked three times to fix the problem.

The plane's previous pilot encountered the same unintentional dive and then switched off the trim system, even though "it's not in the manual".
It is in the manual.

Previously posted by djacobow in this post:
http://www.eevblog.com/forum/chat/lion-air-crash-jakarta-boeing-737-had-prior-instrument-error/msg1963691/#msg1963691

They omitted the total nightmare portion:

"The nose down stabilizer trim movement can be stopped and reversed with the use of the electric stabilizer trim switches but may restart 5 seconds after the electric stabilizer trim switches are released.
Repetitive cycles of uncommanded nose down stabilizer continue to occur unless the stabilizer trim system is deactivated through use of both STAB TRIM CUTOUT switches in accordance with the existing procedures in the Runaway Stabilizer NNC."

The bulletin was just issued by Boeing Nov. 6
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #176 on: November 15, 2018, 09:35:20 am »
Making the new airplane fuel efficient at the expense of handling, then quietly adding an undocumented MCAS system to make up for it to supposedly keep the plane backwards-compatible with previous generations of 737's... Right now, Boeing's mistake is rightly causing a shitstorm.
https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610

But the root cause of the airspeed or AOA malfunction is still unknown. Even after Lion Air maintenance worked three times to fix the problem.

The plane's previous pilot encountered the same unintentional dive and then switched off the trim system, even though "it's not in the manual".
It is in the manual.

Previously posted by djacobow in this post:
http://www.eevblog.com/forum/chat/lion-air-crash-jakarta-boeing-737-had-prior-instrument-error/msg1963691/#msg1963691

They omitted the total nightmare portion:

"The nose down stabilizer trim movement can be stopped and reversed with the use of the electric stabilizer trim switches but may restart 5 seconds after the electric stabilizer trim switches are released.
Repetitive cycles of uncommanded nose down stabilizer continue to occur unless the stabilizer trim system is deactivated through use of both STAB TRIM CUTOUT switches in accordance with the existing procedures in the Runaway Stabilizer NNC."

The bulletin was just issued by Boeing Nov. 6

Yes, that's what can happen if you don't put the trim in cutout. If you follow the QRH and don't re-engage the trim, you're fine.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #177 on: November 15, 2018, 10:06:22 am »
The bulletin was just issued by Boeing Nov. 6
That bulletin contains the following quote: (emphasis Boeing's)
Quote
Subject: Uncommanded Nose Down Stabilizer Trim Due to Erroneous Angle of Attack (AOA) During Manual Flight Only
Reason: To Emphasize the Procedures Provided in the Runaway Stabilizer Non Normal Checklist (NNC).

In other words, "follow the existing procedures as previously published".
 

Online Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #178 on: November 15, 2018, 10:19:37 am »
... systems controlled by the computer that interpose themselves between the flight control surfaces and the pilot ...
You keep saying BETWEEN, trying to impose the definition of fly-by-wire on systems that aren't. The reality is ALONGSIDE; manual controls still work, and in most cases can overpower the automatics even if they are not switched off. The pilots are NOT disconnected from the control surfaces. Even with all the updates over decades, the 737 remains a very successful 1960's era design at the core.

The data recorder is going to have all we need to know about automatic vs manual inputs to the system, as well as what the instruments were saying at the time. It should also shoot down 95% of the speculation in this thread, once a decent analysis is released. But we really need that cockpit recorder to know what was going on in the heads of the pilots for those last 10 minutes.

However they got there, I'm guessing they ended up in an actual aerodynamic stall. Which, even when in full control, is likely not recoverable in the <5000 feet they had available. It fits the information we have so far. (For the benefit of the non-pilots, the way to regain control from a full stall is to enter a dive to regain airspeed, and then you have to recover from the dive. You lose a LOT of altitude in the process, very quickly.)
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #179 on: November 15, 2018, 10:33:20 am »
It's too easy to blame the pilots for "not flipping the off switch" in the stabilizer trim circus. Assuming that is the fatal error here.

The finest engineering and latest technology, and the system to prevent pilot error (stall) malfunctions with bad sensor data and ends up causing pilot error. An automatic control system fighting the pilot to his death.

Cryptic annunciators from the 1960's are still in the cockpit and yet the LCD displays are just mimicking old analog gauges and cannot offer any assistance to help a panicked crew. A lot of people have died due to these aircraft sensor malfunctions causing control system and pilot errors. I would come up with something to stop this shit instead of attributing it to human error and repeating the tragedies.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #180 on: November 15, 2018, 10:35:23 am »
However they got there, I'm guessing they ended up in an actual aerodynamic stall. Which, even when in full control, is likely not recoverable in the <5000 feet they had available. It fits the information we have so far. (For the benefit of the non-pilots, the way to regain control from a full stall is to enter a dive to regain airspeed, and then you have to recover from the dive. You lose a LOT of altitude in the process, very quickly.)
I don't think that theory fits the flightradar24 data, nor does it fit the data of Boeing/FAA releasing an emergency AD about preventing stab trim runaway in the face of the stability augmentation system malfunction due to possibly erroneous AoA inputs. Neither of those is ironclad of course, but the high sink rate began to develop at a ground speed well in excess of the typical unaccelerated stall speed even fully clean.

It looks like the sink rate begins to develop with the ground speed in excess of 310 knots and the ground speed increases as the sink rate increases. That seems more consistent with a[n aerodynamically] controlled flight scenario rather than a departure [from controlled flight].
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #181 on: November 15, 2018, 10:36:20 am »
It's too easy to blame the pilots for "not flipping the off switch" in the stabilizer trim circus. Assuming that is the fatal error here.
Is it too much to ask a trained flight crew to follow checklists? IMO, it's not.
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #182 on: November 15, 2018, 11:14:37 am »
It's too easy to blame the pilots for "not flipping the off switch" in the stabilizer trim circus. Assuming that is the fatal error here.
Is it too much to ask a trained flight crew to follow checklists? IMO, it's not.
3 out of 4 flight crews seemed to handle this airplane's issues. Human error is well known to exist. Especially with a mystery control system that we also assume is flawless, containing no software errors from its human software engineers.

We don't know what happened in the cockpit that prevented the flight crew to follow a checklist. The alarms, stick shaking and sharp dive causing near zero G, wonky airspeed may have been part of it.

At some point it's like engineering has given up on humans, their reliability is poor and they are error-prone, so embedded systems are trying to take over.

Cars are heading full force towards self driving. I have already seen "driver assist" technology with automobiles malfunction.
The radar malfunctions in rain/snow and thinks you are going to hit an obstacle on a good puddle splash. Next gen is full brakes/steering/accelerator capability  :o
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #183 on: November 15, 2018, 11:40:13 am »
... systems controlled by the computer that interpose themselves between the flight control surfaces and the pilot ...
You keep saying BETWEEN, trying to impose the definition of fly-by-wire on systems that aren't. The reality is ALONGSIDE; manual controls still work, and in most cases can overpower the automatics even if they are not switched off. The pilots are NOT disconnected from the control surfaces. Even with all the updates over decades, the 737 remains a very successful 1960's era design at the core.

The data recorder is going to have all we need to know about automatic vs manual inputs to the system, as well as what the instruments were saying at the time. It should also shoot down 95% of the speculation in this thread, once a decent analysis is released. But we really need that cockpit recorder to know what was going on in the heads of the pilots for those last 10 minutes.

However they got there, I'm guessing they ended up in an actual aerodynamic stall. Which, even when in full control, is likely not recoverable in the <5000 feet they had available. It fits the information we have so far. (For the benefit of the non-pilots, the way to regain control from a full stall is to enter a dive to regain airspeed, and then you have to recover from the dive. You lose a LOT of altitude in the process, very quickly.)


The pilot in a non-fly-by-wire AC is the controlling element and the control surfaces are the elements being controlled.  When a pilot commends an action but the computer commands something else the pilot in command is not in command the way they may wish.  The computer has its say and while you could play semantics and say its ALONGSIDE versus in between the consequence is the same is it not.  The fact remains that even in a non-fly-by-wire AC the computer can take control and circumvent the intentions of the pilots. 

I'm not sure what's driving your semantic dispute but as far as I'm concerned this is what it is.  At low altitude if the computer puts the plane into a dive the pilots may not have enough time to turn off the system and recover.  Let's say the plane is at 5000 feet at 400 knots and the computer issues a trim command that puts the plane into a 30 degree dive -- without intervention they would be less than 17 seconds before impact.  They would have much less than that to react, turn off the system, and pull out of the 30 degree dive.  In fact, if the plane got to a 30 degree dive at 5000 feet it may already be too late and there would be nothing to prevent disaster even if they turned off the system, correctly, the instant that happened.


Brian
 

Offline amyk

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #184 on: November 15, 2018, 01:31:03 pm »
The trim wheels are also not small (intentionally so) and make a clicking racket when in motion (also intentional):

Quote
do NOT attempt to stop it by putting your palm over a running wheel as this leads to a burn
:o I'm not a pilot but trying to grab hold of a rapidly and forcefully spinning object sounds rather dangerous and reminds me of lathe safety lessons... there's no disconnect mechanism?
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #185 on: November 15, 2018, 01:50:46 pm »
The first means to stop runaway trim is auto-pilot disconnect (generally the biggest red switch on the outside yoke arm, easily accessible by your thumb).
The second means is by turning the switch off to the system.
The third means is to grab the metal wheel and force against the clutch that's driving it.

It's not especially dangerous and certainly is less dangerous than allowing a runaway trim condition to continue!
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #186 on: November 15, 2018, 04:01:28 pm »

I'm not sure what's driving your semantic dispute but as far as I'm concerned this is what it is.  At low altitude if the computer puts the plane into a dive the pilots may not have enough time to turn off the system and recover.  Let's say the plane is at 5000 feet at 400 knots and the computer issues a trim command that puts the plane into a 30 degree dive -- without intervention they would be less than 17 seconds before impact.

The dispute, I think, comes from you not quite getting how flying feels. If the plane is flying on AP and your attention is elsewhere, yes, the computer can put the plane into a dive. (Though honestly, 17 seconds is a long time to grab the control right in front of you and arrest that dive -- though not too fast, you don't want an accelerated stall.)

But if your hands are on the controls, the computer cannot "put the plane into a dive." What it can do is trim the plane to dive, which you will immediately (as in before the attitude actually changes) perceive as a very unpleasant sudden nose heaviness. Every pilot knows what an uncommanded trim change feels like while flying. It doesn't feel good, it's a lizard brain muscle memory, and I think the vast majority of pilots would fight it immediately while simultaneously reaching for the trim controls.

The exception to this would be if the pilot was also getting stall warnings; then he might hesitate before pulling back. But in clear weather I think it would only be a few seconds before, looking at the aircraft's attitude and power settings, he could surmise that the aircraft wasn't actually near a stall.
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #187 on: November 15, 2018, 04:15:10 pm »
... systems controlled by the computer that interpose themselves between the flight control surfaces and the pilot ...
You keep saying BETWEEN, trying to impose the definition of fly-by-wire on systems that aren't. The reality is ALONGSIDE; manual controls still work, and in most cases can overpower the automatics even if they are not switched off. The pilots are NOT disconnected from the control surfaces. Even with all the updates over decades, the 737 remains a very successful 1960's era design at the core.

The data recorder is going to have all we need to know about automatic vs manual inputs to the system, as well as what the instruments were saying at the time. It should also shoot down 95% of the speculation in this thread, once a decent analysis is released. But we really need that cockpit recorder to know what was going on in the heads of the pilots for those last 10 minutes.

However they got there, I'm guessing they ended up in an actual aerodynamic stall. Which, even when in full control, is likely not recoverable in the <5000 feet they had available. It fits the information we have so far. (For the benefit of the non-pilots, the way to regain control from a full stall is to enter a dive to regain airspeed, and then you have to recover from the dive. You lose a LOT of altitude in the process, very quickly.)

You're right, I'm not familiar with fly-by-hose where you have two hydraulic systems battling it out.
It's still not making sense from many perspectives.

If a pilot makes an error causing a stall and the MCAS tries to correct it yet still allows the pilot to override that, I'm not sure what the point is. An adamant pilot can still go into and stay in a stall condition, as flight 447 did.
Why are you needing to switch off power to the stab trim system if you can overrule it.

The AOA sensor had been replaced, so the airspeed sensor or something else must have been aggravating all this.

The cockpit voice recorder beacon looks like its rated for 90-day battery life and 1.8-3.6km range. 160dB chirp at 37.5kHz but buried under mud or debris. It would have many answers.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #188 on: November 15, 2018, 05:12:05 pm »
If a pilot makes an error causing a stall and the MCAS tries to correct it yet still allows the pilot to override that, I'm not sure what the point is.

The point is that the system has "told" the pilot something. The pilot can integrate that information in his picture of what is going on. He can let the automation do what it wants, or, if he believes he knows something the computer doesn't, he can fight it. That's the Boeing philosophy. The Airbus philosophy is that the pilot will need to take extraordinary steps (in advance) to override the aircraft.

I really do not think there is enough accident data out there these days to make a good assessment of which approach is safer overall. It's a very complex question because very sophisticated automation tend to de-skill operators, which becomes an acute problem in the few cases where the automation fails.

(such as An adamant pilot can still go into and stay in a stall condition, as flight 447 did.

But the A320 is an FBW aircraft, and so normally, a pilot could not stall it. But in this case, the computer had punted and dropped into "alternate law" where the not all the normal envelope protections were applied.

Why are you needing to switch off power to the stab trim system if you can overrule it.

Because you will tire of overruling it continuously. It takes physical and mental effort to fly an untrimmed aircraft, much less one that keeps trying to make itself  untrimmed.

 

Online Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #189 on: November 15, 2018, 07:11:28 pm »
Because it's not just semantics, especially when your primary argument is about what happens when computers misbehave.

In a fly-by-wire setup, if you lose all the flight control computers, you CANNOT fly the plane. The pilot controls are merely input devices to the computer, like a joystick, keyboard or mouse on a PC. No computer, no control. Turning them off is NOT an option if you want to live.

In the 737, while a lot of electronics are important, none of it is absolutely essential for flight. You can turn them all off and still have operating controls to fly the plane with.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #190 on: November 16, 2018, 12:41:01 pm »

I'm not sure what's driving your semantic dispute but as far as I'm concerned this is what it is.  At low altitude if the computer puts the plane into a dive the pilots may not have enough time to turn off the system and recover.  Let's say the plane is at 5000 feet at 400 knots and the computer issues a trim command that puts the plane into a 30 degree dive -- without intervention they would be less than 17 seconds before impact.

The dispute, I think, comes from you not quite getting how flying feels. If the plane is flying on AP and your attention is elsewhere, yes, the computer can put the plane into a dive. (Though honestly, 17 seconds is a long time to grab the control right in front of you and arrest that dive -- though not too fast, you don't want an accelerated stall.)

But if your hands are on the controls, the computer cannot "put the plane into a dive." What it can do is trim the plane to dive, which you will immediately (as in before the attitude actually changes) perceive as a very unpleasant sudden nose heaviness. Every pilot knows what an uncommanded trim change feels like while flying. It doesn't feel good, it's a lizard brain muscle memory, and I think the vast majority of pilots would fight it immediately while simultaneously reaching for the trim controls.

The exception to this would be if the pilot was also getting stall warnings; then he might hesitate before pulling back. But in clear weather I think it would only be a few seconds before, looking at the aircraft's attitude and power settings, he could surmise that the aircraft wasn't actually near a stall.


If the plane is in a 30 degree dive at 5000 feet you'd have less than 17 seconds if you did nothing.  However, disabling the trim then pulling out of the dive and doing that with 5000 feet to play with means you have less time than 17 seconds.  If you were heads down and didn't notice until the plane was 30 degrees down at 5000 feet its a good bet you would not be able to recover even if you acted with zero delay.  You don't arrest a 30 degree dive at 400+ knots without losing a fair bit of altitude.  Physics is a bitch!


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Offline alsetalokin4017

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #191 on: November 16, 2018, 01:53:42 pm »
However, even the heads-down pilots will notice the bunt from level pitch to 30 degrees nose down. That's a negative g maneuver! Or if they have hands on the yoke (the suspect system allegedly only operates when manually flying) they will notice the sudden trim change as they have to apply considerable back pressure to prevent or recover from the bunt.
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Offline SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #192 on: November 16, 2018, 02:49:52 pm »
In the AF447 scenario, the computer decided it did not have reliable air data, so it not only disconnected the autopilot, it dropped into alternate law. Basically, the computer just punted and said "your airplane!" This might seem like reasonable behavior, but one might imagine that handing a degraded airplane to a pilot at the very worst moment is not a satisfactory failure mode, and in the AF447 scenario the outcome was obviously bad.

This seems reasonable, and I still think it is. I don't think Airbus has changed this behavior after this tragedy (but don't hesitate to tell us if they did, as I may have missed the info), so a lot of people have probably considered it reasonable as well. The moment this happened, the plane was NOT in a critical situation whatsoever as far as I remember, so yes this was stressful and pilots got misled somehow, but they would have had ample time to handle this the right way. Turns out that the training on those airliners with a lot of automation don't always have enough simulation sessions for handling this kind of situations, and that's one of the things they improved after the accident: training sessions. The warning indicators are not always very clear either, and this surely could be improved, but at least in this case, they were certainly not lacking as there was a continuous stream of warnings including stall warnings IIRC. The main point as I remember is the pilots were not trusting ANY indication anymore, so obviously they lost all reference and situational awareness.

Again, if some automated system RELIES on some sensor data and this data is DETECTED as not reliable, the system should obviously be disconnected.
That said, if alternate systems that DONT need those sensor data can still be activated to make it safer, of course this could be a good idea to activate them. But keeping on a system that takes some of the controll OFF the hands of the pilots based on unreliable data is a recipe for disaster. That's all I'm saying here, and this is also what has been pointed out and suspected in this Lion Air case by some.

Very interested in reading the final report.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #193 on: November 16, 2018, 06:37:35 pm »
In the AF447 scenario, the computer decided it did not have reliable air data, so it not only disconnected the autopilot, it dropped into alternate law. Basically, the computer just punted and said "your airplane!"

This seems reasonable, and I still think it is. I don't think Airbus has changed this behavior after this tragedy (but don't hesitate to tell us if they did, as I may have missed the info), so a lot of people have probably considered it reasonable as well.

I'd say it was reasonable, but unfortunate. And yes, I think if you have a crew that was so deficient in basic airmanship, there's ultimately not much you can do to help folks who are going to do stupid things. Assuming all your instruments are wrong because some of your instruments are wrong is not just dumb in an Airbus, it is dumb in any airplane. You can go right back to your basic instrument training in piston single: you can get work out and bad air data from the remaining instruments. In turbulence, I'm sure it's scary and difficult, but if the pilots had simply flown an attitude and power setting, they would have been fine. I think there's not much doubt about that.

This is the final BAE report on AF447, translated in English: https://www.bea.aero/docspa/2009/f-cp090601.en/pdf/f-cp090601.en.pdf

(SiWizard, from your flag, I suspect this version will be more to your liking: https://www.bea.aero/docspa/2009/f-cp090601/pdf/f-cp090601.pdf)


Section 5 lists the changes after the aircraft. Basically, other than improving the pitot heaters, I don't think any changes were made to the aircraft. Several training and flight manual changes were made, such as making sure pilots understand that they are not getting stall protection under alternate law.

Completely revamping the flight control software on an airliner that has been in production for a long time perhaps would be a bridge too far, and add additional risk. Furthermore, improving the pitot system so that you don't get a total loss of air data would certainly be a simpler option. I wonder how many times since AF447 an A320 has lost air data. Maybe none?

« Last Edit: November 16, 2018, 06:41:31 pm by djacobow »
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #194 on: November 17, 2018, 05:36:41 am »
... systems controlled by the computer that interpose themselves between the flight control surfaces and the pilot ...
You keep saying BETWEEN, trying to impose the definition of fly-by-wire on systems that aren't. The reality is ALONGSIDE; manual controls still work, and in most cases can overpower the automatics even if they are not switched off. The pilots are NOT disconnected from the control surfaces. Even with all the updates over decades, the 737 remains a very successful 1960's era design at the core.

Multiple sources are saying the MCAS system cannot be overridden by the pilot, unless power is cut.
This seems counter to what many are saying about fly-by-hose/wire systems or Boeing's philosophy?

"Any pilot’s natural reaction when a plane’s nose begins to tilt down uncommanded is to pull back on the yoke and raise the nose. In normal flight mode, that would work, because pulling back on the yoke triggers breakout switches that stop any automatic tail movement tending to move the nose of the plane down.

But with the MCAS activated, said Fehrm, those breakout switches wouldn’t work. MCAS assumes the yoke is already aggressively pulled back and won’t allow further pullback to counter its action, which is to hold the nose down."

FAA evaluates a potential design flaw on Boeing’s 737 MAX after Lion Air crash
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #195 on: November 17, 2018, 06:29:47 am »

Multiple sources are saying the MCAS system cannot be overridden by the pilot, unless power is cut.
This seems counter to what many are saying about fly-by-hose/wire systems or Boeing's philosophy?


Yes, it does certainly seem so based on this reporting. I think that's why former avionics engineers and a bunch of pilots are alarmed, especially if the behavior of the airplane has changed but the AFM doesn't reflect that change. It's subtle, I think. If you follow the procedure in the AFM to disable the trim system, it sounds like you're OK, but if you are relying on expectations that you can just pull back (as you have on all previous 737s), you'll get different behavior. Just speculating, but I'd bet the flight manual probably never said "just pull back until you can get the trim sorted," but perhaps pilots do exactly that, since in normal flight that works. I have no jet time, but in the much simpler aircraft I've flown, it's just what I would do. If the AP was doing something unusual, I would simultaneously disable the AP and use the primary controls first and then adjust trim to relieve control forces second.

But with the MCAS activated, said Fehrm, those breakout switches wouldn’t work. MCAS assumes the yoke is already aggressively pulled back and won’t allow further pullback to counter its action, which is to hold the nose down."

I'm a bit surprised the computer assumes anything about the position of the yoke. I'd have hoped it would know the position of the yoke. So, if the AOA sensor is saying one thing, but the position of the yoke and trim are not consistent with a stall, it might "think twice" about assuming a stall and forcing the nose down. But that might be a bit too much fuzzy reasoning to expect from a system like that.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #196 on: November 17, 2018, 02:17:07 pm »

Multiple sources are saying the MCAS system cannot be overridden by the pilot, unless power is cut.
This seems counter to what many are saying about fly-by-hose/wire systems or Boeing's philosophy?


Yes, it does certainly seem so based on this reporting. I think that's why former avionics engineers and a bunch of pilots are alarmed, especially if the behavior of the airplane has changed but the AFM doesn't reflect that change. It's subtle, I think. If you follow the procedure in the AFM to disable the trim system, it sounds like you're OK, but if you are relying on expectations that you can just pull back (as you have on all previous 737s), you'll get different behavior. Just speculating, but I'd bet the flight manual probably never said "just pull back until you can get the trim sorted," but perhaps pilots do exactly that, since in normal flight that works. I have no jet time, but in the much simpler aircraft I've flown, it's just what I would do. If the AP was doing something unusual, I would simultaneously disable the AP and use the primary controls first and then adjust trim to relieve control forces second.

But with the MCAS activated, said Fehrm, those breakout switches wouldn’t work. MCAS assumes the yoke is already aggressively pulled back and won’t allow further pullback to counter its action, which is to hold the nose down."

I'm a bit surprised the computer assumes anything about the position of the yoke. I'd have hoped it would know the position of the yoke. So, if the AOA sensor is saying one thing, but the position of the yoke and trim are not consistent with a stall, it might "think twice" about assuming a stall and forcing the nose down. But that might be a bit too much fuzzy reasoning to expect from a system like that.


And, if the pilots went with the 'pull back the stick option' as there first attempt at the altitude and airspeed they were at they would not have had time for option two -- this software system will have to be removed until a better thought out system can be implemented.  Boeing is going to eat this one and it will cost there insurer hundreds of millions I'd wager. 

The law of unintended consequences sometimes makes fools of your best plans.


Brian
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #197 on: November 19, 2018, 12:12:50 pm »
 

Offline maginnovision

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #198 on: November 19, 2018, 12:47:46 pm »


The way he explains it makes it seem even worse than I thought. Potentially single failure combined with lack of training.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #199 on: November 20, 2018, 12:32:35 pm »


I don't think there's much in this video that is different from what has been discussed on this thread so far. For now, I'm sticking with my "prediction" that the pilots and Boeing will end up with some of the responsibility. There's nothing here to imply that the aircraft could not be flown. It's definitely not okay that Boeing put in a new flight control system and made no mention of it in the  true-up training for the MAX. On the other hand, if that system started moving trim according to rules unknown to them, that would seem like the very definition of runaway trim to pilots who didn't know about MCAS, and if they followed the procedure for that, they would have been fine.
 

Offline Marco

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #200 on: November 20, 2018, 10:35:35 pm »
Lets say they used the thumb sticks to pull trim back and then took out the checklist because they assume they have corrected the problem for now and have some breathing room, so now they are distracted and then the system hits trim again after the time out. It's just such a fucking mess.

IMO they need a big red button to turn off autopilot, but really, actually, completely, not partially.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #201 on: November 21, 2018, 12:16:20 am »
It's a two-crew airplane for a reason. Pilot Flying (PF) does the memory items and calls for the checklist. Pilot Not Flying (PNF) pulls out the Quick Reference Handbook (QRH) and reads the checklist items in challenge form. PF responds with the response. The whole time PF keeps flying the airplane and monitoring its performance, including attitude and airspeed.

You don't have two people going heads-down into the books. (It happens, most notably, tragically, and avoidable in something in Eastern 401, where 101 people died because a cockpit crew of three mismanaged a burned out landing gear position indicator bulb. Since then, CRM classes have taught the division of duties to avoid future "two researchers, zero pilots" situations.)
 

Offline daddylonglegs

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #202 on: November 21, 2018, 05:07:50 am »
If there is disagreement, it obviously doesn't matter which one is wrong to detect there is a malfunction. This case would warrant the disconnection of any automatic system that could rely on or even be influenced by those sensors, and issue a warning. First thing that happens is usually the disconnection of the autopilot, and I'm pretty sure that happens when there is a faulty pitot, at least on Airbus planes. This is the first thing that happened on the AF447 for instance, AFAIK. Of course, this could be different in this case. Maybe.

In the AF447 scenario, the computer decided it did not have reliable air data, so it not only disconnected the autopilot, it dropped into alternate law. Basically, the computer just punted and said "your airplane!" This might seem like reasonable behavior, but one might imagine that handing a degraded airplane to a pilot at the very worst moment is not a satisfactory failure mode, and in the AF447 scenario the outcome was obviously bad.


  ISTM that Airbus have made fairly clear and consistent design choices. The flight envelope protection will not allow the pilots to stall or overspeed the aircraft unless the sensors start playing up (in a detectable way) or the pilots deliberately disable this system (which takes a single action). Not everyone likes the choices but they are reasonable. I agree with you that it is difficult to make changes that are unambiguously better.

  Judging by the AD, the accretion of changes to the 737 has produced a system that is:
A - Badly documented (supposedly a deliberate choice to save time and money during training).
B - Does not completely handover control when the sensors disagree (even warning the pilots that the sensors are playing up is an optional extra! [1]).
C - Requires two actions, both disabling the autopilot and cutting out the trimming system.

  I think Boeing have been caught out by the compromises involve in updating a very old design[2], marketing pressures[3] and - possibly - by their own propaganda regarding how traditional the flight controls on a Boeing are. My predictions are that:
A - Training will now heavily cover the auto trim systems.
B - The sensor disagreement warning will not be optional in practice (everyone will buy it)
C - Boeing may have to change the MCAS system by adding a cut-out when the sensors disagree (should have done that from the start IMHO).

  I'm surprised at what is hidden from pilots both in the manuals and by making the sensor warnings optional. If pilots get a stall warning without an explicit indication that the sensors disagree[4] they may well believe it. Particularly if they have already been surprised by changes in the aircraft's motion (driven by the automated system's intervention) and so lost their 'feel' for whether the aircraft might plausibly be close to stalling. A curious and sad inversion of the AF447 crash if so.

  All of this is my ill-informed opinion. Both Airbii and Boeings are flown very safely by sensible airlines. The Lion Air crash may well be something completely different, etc.

[1] Maybe Boeing could consider in-appflight purchases in this case? "We've noticed that your subscription does not include information helpful to your continued survival. Would you like to upgrade? (T&C apply. Always make sure you have the permission of the credit card holder. Offer not valid if you're going to sue us.)"

[2] First flight in 1967, 51 years ago and 64 years after the Wright brothers. Dates from wonkypedia, maths from my sligtly tired brain.

[3] Honestly, I get infuriated by manufacturers making an oscilloscope's actual capabilities an optional (i.e. expensive) upgrade and now Boeing's marketing department gets in on the game? And then nobbles the flight manual/ conversion course to boot?

[4] Do any of the checklists (memory or written) call for comparing the instruments?
 
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Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #203 on: November 21, 2018, 05:22:32 am »
C - Requires two actions, both disabling the autopilot and cutting out the trimming system.
This is standard. My 3600-pound airplane has the same basic response for an AP or electric trim malfunction. My previous 2800-pound airplane didn't have electric trim installed, but if it did, it would have been the same.
[4] Do any of the checklists (memory or written) call for comparing the instruments?
This is the fundamental skill of all instrument-rated pilots and a primary focus of instrument flight instruction.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #204 on: November 21, 2018, 05:55:55 am »


I don't think there's much in this video that is different from what has been discussed on this thread so far. For now, I'm sticking with my "prediction" that the pilots and Boeing will end up with some of the responsibility. There's nothing here to imply that the aircraft could not be flown. It's definitely not okay that Boeing put in a new flight control system and made no mention of it in the  true-up training for the MAX. On the other hand, if that system started moving trim according to rules unknown to them, that would seem like the very definition of runaway trim to pilots who didn't know about MCAS, and if they followed the procedure for that, they would have been fine.


Umm, no...

If this runaway trim happened at 5000 feet and they spent even a few seconds fighting the stick by the time they did turn things off the plane would be at 3000 feet and 30 degrees down -- you won't recover from that even with the trim system turned off.

The idea that pilots will automatically and with zero delay jump to a seldom used (or never used) emergency procedure is delusional -- that's not how humans respond.  They will attempt to pull back on the stick and then, maybe, realize they need to turn the trim off but by then...


Brian
« Last Edit: November 22, 2018, 06:52:13 am by raptor1956 »
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #205 on: November 21, 2018, 06:04:20 am »
You have to manually crank the stabilizers back to center, after shutting off power to the motors.
Can you imagine how hard that is, it's two BLDC with screw-jack and you don't have much time.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #206 on: November 21, 2018, 06:24:46 am »

If this runaway trim happened at 5000 feet and they spent even a few seconds fighting the stick by the time they did turn things off the plane would be at 300 feet and 30 degrees down -- you won't recover from that even with the trim system turned off.

The idea that pilots will automatically and with zero delay jump to a seldom used (or never used) emergency procedure is delusional -- that's not how humans respond.  They will attempt to pull back on the stick and then, maybe, realize they need to turn the trim off but by then...

I think neither of us are airline pilots, so we'll just have to disagree about this and find out what's in the reports when they come out. My sense as a pilot (not an airline pilot) is that this is EXACTLY the kind of thing that is -- or should be -- on a pilot's mind, particularly when climbing out at low altitude. As I've said before, these trim changes, though fast, are not instantaneous. They can be felt. Furthermore, a sudden trim change doesn't result in an instantaneous attitude change. (The plane has a moment of inertia and it takes time for the nose to rotate down). And an instantaneous attitude change does not result in an instantaneous altitude change. Some of these delays work against you as you try to arrest a descent just as they work for you at the start of the descent, but I'm nearly certain that proficient, attentive pilots can recovery from a runaway trim situation that starts at 5000 feet.

Yes, if you get into a 6000 fpm minute descent then you are probably screwed, but you'd really have to let the plane get into a seriously unusual attitude to get that kind of descent.

It may seem as if a few armchair pilots are being perhaps a bit too harsh on the pilots in this scenario -- and I'm willing to concede that maybe we are. But you have to understand that pilots are always supposed to be thinking of what can go wrong in each phase of flight and what they'd do about it. It's the essence of piloting. Flying a working airplane is not particularly hard. Managing a "normal" flight takes up a surprisingly small fraction of overall flight training. Most flight training is about handling abnormal situations, and dealing with those is the crux of a pilot's job. Cross checking instruments (including checking them against the huge non-artificial horizon available in VMC) and avoid and recovering from unusual attitudes are definitely in this category.


 

Offline rx8pilot

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #207 on: November 21, 2018, 06:47:58 am »
You have to manually crank the stabilizers back to center, after shutting off power to the motors.
Can you imagine how hard that is, it's two BLDC with screw-jack and you don't have much time.

Pretty sure it is somewhere between 'very hard' and 'impossible' once the system has gone full nose heavy. In a manual operation, it is a LOT of turns and needs considerable effort to move. All of that has to be accomplished in the middle of a very confusing and scary emergency event that is very rapidly getting worse. There is little doubt that both pilots knew it was a deadly situation early on which would make rational decision making that much harder.

The speculation will slowly give way to actual facts.....but it is looking like the pilots would need to be superhuman to have avoided the outcome.
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Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #208 on: November 21, 2018, 07:32:51 am »
Pretty sure it is somewhere between 'very hard' and 'impossible' once the system has gone full nose heavy. In a manual operation, it is a LOT of turns and needs considerable effort to move
This is true, but they struggled with the airplane for quite some number of minutes. It's during this time, before the stab trim runs full nose-down, that was the time to interrupt the power to the trim system.

They were dealt a crap hand to be sure. I'm much less sure that a majority of 737 pilots would fall victim to that crap hand. I think the CVR will be enlightening to understand what was going on in their heads as they fought the airplane. The FDR and wreckage can tell us a lot of the WHAT; the CVR will help with the WHY.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #209 on: November 22, 2018, 07:01:14 am »
As is common in major tragedies the end result stems from more than one problem.  If the stab ran-away as a singular event I'd guess they would have responded as they should and they would still be alive.  However, going back over time to the 3 previous flights, which the pilots must have been aware of, the thing of concern appears to have been BOTH a pitot/static problem and an AOA problem.  So, on the day of the crash there first indications may well have been in line with what the previous pilots reported and they were very likely working that problem when the stab trim system threw them for a loop -- a stab trim system they did not fully understand because Boeing neglected to provide that information.

When you're working one or two known problems and a third rears its head you can bet there was a period of seconds at least where they tried to correlate the new problem with the existing ones.  At 5000 feet they don't have that time.  And, as other suggest, once the system threw the plane into a nose down attitude with, potentially, substantial down trim, they would have to manually rotate the trim wheels which, again, at 5000 feet they would have very little time.

This has the makings of a horror story!


Brian
 
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Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #210 on: November 23, 2018, 08:01:08 am »
The video from the Mentor pilot about the MCAS system provides some interesting info about what may have necessitated the MCAS system.  The 737MAX uses larger more fuel efficient engines but do to the low ground clearance of the basic 737 design they need to mount the engine further forward and up to gain some clearance.  Doing that would have changed the balance of the AC meaning that all things being equal it would need the stabilizer to be trimmed up more than previous 737 AC for a given flight condition.  It's not clear to me if there were any other changes to compensate for the changed balance or if the stabilizer was changed in some way, but his mention of the larger engine and the need to alter the mounting location certainly raises some questions in my mind.  In a perfect world such an alteration would necessitate other changes to return the balance -- perhaps moving some gear further aft, perhaps moving some of the fuel tanks further aft, perhaps altering the stabilizer to account for what would otherwise be a nose heavy tendency. 

We are likely to see an interim report within a couple weeks but the FAA and Boeing probably know already exactly what happened.  Hopefully the interim report provides some closure on this.  OTH, if the engine change started a chain of other changes that lead to this Boeing could have bigger problems than the legal one they are no doubt going to face.


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Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #211 on: November 24, 2018, 12:10:51 am »
I think folks here are ignoring some key facts. First, that the emergency bulletin from Boeing does nothing but explain MCAS behavior and amplify existing procedures. Second, that the -MAX aircraft are still in service.

This strongly suggests that the aircraft are believed safe by Boeing and the FAA and that at least for the interim, the only extra training pilots need is a reminder not to let the plane get way out of trim.

I find the points that the pilots were screwed once the plane was way out of trim to be mostly irrelevant. Yes, there may not be time to recover by manually re-trimming a plane that is totally nose heavy at low altitude. That's why you don't let the aircraft into that condition. There are many conditions that you can get into that are not recoverable. You just don't let the aircraft get there.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #212 on: November 24, 2018, 06:42:51 am »
I think folks here are ignoring some key facts. First, that the emergency bulletin from Boeing does nothing but explain MCAS behavior and amplify existing procedures. Second, that the -MAX aircraft are still in service.

This strongly suggests that the aircraft are believed safe by Boeing and the FAA and that at least for the interim, the only extra training pilots need is a reminder not to let the plane get way out of trim.

I find the points that the pilots were screwed once the plane was way out of trim to be mostly irrelevant. Yes, there may not be time to recover by manually re-trimming a plane that is totally nose heavy at low altitude. That's why you don't let the aircraft into that condition. There are many conditions that you can get into that are not recoverable. You just don't let the aircraft get there.


You are presupposing that the pilots chose to remain at low altitude when in a normal climb-out they would have been much higher at 13 minutes.  The flight profile shows a lot of erratic up and down which I should point out is not typical of a normal climb-out. 

So, it looks to me that the plane was at a dangerously low altitude and when the final push happened, or whatever the final event was, they were too low to recover even if they had the control authority to do so which is highly suspect at this point.  The emergency bulletin from the FAA and the technical bulletin from Boeing would hardly be considered business as usual.


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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #213 on: November 24, 2018, 08:17:39 am »
Actually, such alerts probably are business as usual when pilots point out a safety/training deficiency.

Until we get more info, it's just speculation that it had anything to do with the crash.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #214 on: November 27, 2018, 10:05:49 am »
Actually, such alerts probably are business as usual when pilots point out a safety/training deficiency.

Until we get more info, it's just speculation that it had anything to do with the crash.


The FAA seldom uses the word "Emergency" to issue nothing out of the ordinary messages. 

We should see the interim report in a few days and have a better idea of what is fact and what has been speculation.


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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #215 on: November 27, 2018, 02:07:31 pm »
Actually, such alerts probably are business as usual when pilots point out a safety/training deficiency.

Until we get more info, it's just speculation that it had anything to do with the crash.


The FAA seldom uses the word "Emergency" to issue nothing out of the ordinary messages. 

We should see the interim report in a few days and have a better idea of what is fact and what has been speculation.


Brian
You missed my point. Issuing Airworthiness Directives is simply one of the things the FAA does. That includes emergency ones, of which you'll find at least a handful every year, sometimes more. They're just doing their job. It's not unusual when deciding what qualifies as an emergency is normal procedure, so it's business as usual.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #216 on: November 27, 2018, 03:53:22 pm »
I think folks here are ignoring some key facts. First, that the emergency bulletin from Boeing does nothing but explain MCAS behavior and amplify existing procedures. Second, that the -MAX aircraft are still in service.

This strongly suggests that the aircraft are believed safe by Boeing and the FAA and that at least for the interim, the only extra training pilots need is a reminder not to let the plane get way out of trim.

I find the points that the pilots were screwed once the plane was way out of trim to be mostly irrelevant. Yes, there may not be time to recover by manually re-trimming a plane that is totally nose heavy at low altitude. That's why you don't let the aircraft into that condition. There are many conditions that you can get into that are not recoverable. You just don't let the aircraft get there.

You are presupposing that the pilots chose to remain at low altitude when in a normal climb-out they would have been much higher at 13 minutes.  The flight profile shows a lot of erratic up and down which I should point out is not typical of a normal climb-out. 

So, it looks to me that the plane was at a dangerously low altitude and when the final push happened, or whatever the final event was, they were too low to recover even if they had the control authority to do so which is highly suspect at this point.  The emergency bulletin from the FAA and the technical bulletin from Boeing would hardly be considered business as usual.


Brian

I'm trying to reason based on clearly stated suppositions -- none of which require that the pilots "chose to remain at low altitude."

- It is a fact that the aircraft are still in service.
- It is arguably a fact that Boeing and the FAA are extremely risk-averse. Certainly, the repercussions for another crash due to the same or a related problem would be severe.

This strongly suggests that the model is safely flyable, including under all but the most improbably failure circumstances. It also suggests that a "design fault" is not the proximate cause of this accident.

If that is true, then either:

 - the accident aircraft was "broke" in some very unlikely way
 OR
 - the operator of the accident aircraft conducted maintenance malpractice and sent an unairworthy aircraft into service
 OR
 - the pilots screwed up
 OR
 - some combination of the above


As for why the pilots maneuvered at low altitude, we simply do not know.

As others have stated before, accidents do have multiple causes, and I expect this one will, too.
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #217 on: November 27, 2018, 04:26:34 pm »
The root cause, the AOA or air speed sensor issue I don't think has been figured out. Another airline, Southwest had replaced a couple of AOA sensors on their 737 MAX 8's.

The problem looks like it was intermittent, on and off. Previous flights had the same problem, sensor was replaced etc.
Air Asia Crash Report : Cracked Solder Joint on Rudder Limit Circuit Board http://www.eevblog.com/forum/chat/air-asia-crash-report-cracked-solder-joint-on-rudder-limit-circuit-board/

How MCAS resolves a discrepancy when you only have two sensors that can (normally) read different, it's like the redundancy engineering is shit (=not there) and the pilot is expected to cover for it.

Boeing has a backlog of 4,783 orders for 737 MAX. for multi-billions $. I hope they don't put all this on the flight crew.
 

Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #218 on: November 27, 2018, 05:03:56 pm »
I hope they don't put all this on the flight crew.
I hope they put the blame on wherever the right place for the blame to go is.
If that's on the crew, so be it...
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #219 on: November 27, 2018, 05:55:00 pm »
Actually, such alerts probably are business as usual when pilots point out a safety/training deficiency.

Until we get more info, it's just speculation that it had anything to do with the crash.


The FAA seldom uses the word "Emergency" to issue nothing out of the ordinary messages. 

We should see the interim report in a few days and have a better idea of what is fact and what has been speculation.


Brian
You missed my point. Issuing Airworthiness Directives is simply one of the things the FAA does. That includes emergency ones, of which you'll find at least a handful every year, sometimes more. They're just doing their job. It's not unusual when deciding what qualifies as an emergency is normal procedure, so it's business as usual.

Well of course the FAA issues emergency reports with some frequency, there are hundreds of different AC each with issues that rare there head from time to time.  FDR, like all US presidents, addresses Congress and on December 8th 1941 he did so again -- I would not describe his speech on that day as 'business as usual' even though numerous other presidents have made similar speeches.  The circumstances that preceded his speech made it something of an emergency.

When the FAA issues an emergency directive its because something time critical makes it an emergency so postponing the directive isn't acceptable.  When FDR declared war on Japan it wasn't business as usual even though doing so was the job of the president.

The terms 'business as usual' and 'emergency' or not synonymous -- they are in fact incongruous.


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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #220 on: November 28, 2018, 01:51:26 am »
Actually, such alerts probably are business as usual when pilots point out a safety/training deficiency.

Until we get more info, it's just speculation that it had anything to do with the crash.


The FAA seldom uses the word "Emergency" to issue nothing out of the ordinary messages. 

We should see the interim report in a few days and have a better idea of what is fact and what has been speculation.


Brian
You missed my point. Issuing Airworthiness Directives is simply one of the things the FAA does. That includes emergency ones, of which you'll find at least a handful every year, sometimes more. They're just doing their job. It's not unusual when deciding what qualifies as an emergency is normal procedure, so it's business as usual.

Well of course the FAA issues emergency reports with some frequency, there are hundreds of different AC each with issues that rare there head from time to time.  FDR, like all US presidents, addresses Congress and on December 8th 1941 he did so again -- I would not describe his speech on that day as 'business as usual' even though numerous other presidents have made similar speeches.  The circumstances that preceded his speech made it something of an emergency.

When the FAA issues an emergency directive its because something time critical makes it an emergency so postponing the directive isn't acceptable.  When FDR declared war on Japan it wasn't business as usual even though doing so was the job of the president.

The terms 'business as usual' and 'emergency' or not synonymous -- they are in fact incongruous.


Brian

Tell that to a 911 dispatch service, where every call is an emergency, by definition, until determined otherwise. They decide which calls are real emergencys many times an hour, and also the type of emergency....and it's still business as usual FOR THEM.

This FAA directive does not compare to an FDR declaration of war at all, which I do agree was a fairly unique event. It doesn't even describe anything wrong with an aircraft. All it demands are a few updates to training manuals in reaction to information put out by Boeing. I still call that business as usual FOR THE FAA. They determined the information was sufficiently urgent and reacted like they're supposed to.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #221 on: November 28, 2018, 12:25:23 pm »
From https://www.nytimes.com/2018/11/27/world/asia/indonesia-lion-air-crash-.html

Quote
"""
The information from the flight data recorder, contained in a preliminary report prepared by Indonesian crash investigators and scheduled to be released Wednesday, documents a fatal tug-of-war between man and machine, with the plane’s nose forced dangerously downward over two dozen times during the 11-minute flight. The pilots managed to pull the nose back up over and over until finally losing control, leaving the plane, Lion Air Flight 610, to plummet into the ocean at 450 miles per hour, killing all 189 people on board.
"""

Eleven Minutes.

Two dozen attempts.

Sorry, there's no way these pilots did not screw up. Again, that's not to say that the undocumented MCAS system and potentially erratic behavior from potentially bad air data are not factors. But these pilots most definitely screwed up.

Also:

Quote
"""
Despite Boeing’s insistence that the proper procedures were in the handbook, also called the emergency checklist, pilots have said since the accident that Boeing had not been clear about one potentially vital difference between the system on the new 737s and the older models. In the older versions, pilots could help address the problem of the nose being forced down improperly — a situation known as “runaway stabilizer trim” — by pulling back on the control column in front of them, the pilots say.

Family members grieving after police handed over the remains of their relatives who had been aboard Lion Air Flight 610.CreditEd Wray/Getty Images
In the latest 737 generation, called the Max, that measure does not work, they said, citing information they have received since the crash. The pilots on Lion Air Flight 610 appear to have forcefully pulled back on their control columns to no avail, before the final dive, according to the information from the flight data recorder.

Capt. Dennis Tajer, spokesman for the American Airlines pilot union and a 737 pilot, said he could not comment on any aspect of the investigation. But, he said, “in the previous model of the 737, pulling back on the control column, Boeing says will stop a stabilizer runaway.”

Information provided to American Airlines from Boeing since the crash, Captain Tajer said, “specifically says that pulling back on the control column in the Max will not stop the runaway if M.C.A.S. is triggered. That is an important difference to know.”

Boeing said in its statement on Tuesday that the existing procedures covered the latest 737 model.
"""


This strongly hints at something I suggested earlier, that the written procedures, when followed, work, but that 737 pilots may have been accustomed to another procedure (pulling back on the control column) that was never the official book procedure, but which also worked on all 737's until the -MAX.

« Last Edit: November 28, 2018, 12:29:34 pm by djacobow »
 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #222 on: November 28, 2018, 07:05:20 pm »
Two dozen attempts -
It's an automatic system switching in and out, doing retries on its own, and possibly operating with bad noisy sensor data.

You have at least four oscillators. The MCAS software, the sensor(s), the pilot, the co-pilot.
The airplane or the pilot as the ultimate authority is yet another conflict.

Investigators are saying the plane was not airworthy. It should have been grounded as soon as problems surfaced on the previous flight.
One AOA sensor had been replaced, but still a 20 degree discrepancy.

Really need the CVR to figure out all that happened.
 

Offline Berni

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #223 on: November 28, 2018, 07:23:00 pm »
Yeah it seams to me like the pilots could have easily prevented the crash if they knew what to do, even if they spent a while to diagnose the problem.

But that's not to say they are completely at fault. The finger pointing should instead be focused more towards the training the pilots ware given. Clearly they should have known about such a significant system on the aircraft.

And this doesn't just mean hammering a bunch of step by step procedures into there head on what to do if something goes wrong. They should understand why each step of the procedure is on the list and how it interacts with the problem. Yes there need to be defined procedures for dealing with faults, but in the event that the procedure does not work (Such as a fault they did not foresee) or there are multiple interacting faults that render the procedure useless they shouldn't just be repeating the procedure over and over because that's all they know to do. They should instead start thinking about why the procedure did not help and try other things.

Tho in this case the pilots surely should have noticed the big noisy trim wheels spinning all the time. If the aircraft is pitching down and trim wheels are moving that should have been an instant association of it being a trim problem. You don't need to look trough a manual for a troubleshooting procedure if you can see where the problem is. Fix it quickly and then try to figure out why it happened so that you can make a decision if its safe to continue flying to the destination.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #224 on: November 28, 2018, 07:27:14 pm »
Well it looks as if there is some progress in not making the poor pilots the scapegoats....

Quote
Indonesian investigators have said the Lion Air plane that crashed last month killing 189 people was not airworthy and should have been grounded.


https://www.bbc.co.uk/news/world-asia-46121127
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Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #225 on: November 28, 2018, 07:53:23 pm »
It looks like there were similar problems on previous flights and the PIC of the previous flight eventually turned off the trim system after, I think, the third round of AND (automatic nose down) commands from the computer.  So, the PIC on the previous flight appears to have done what needed to be done but the crew on the doomed flight did not.

It's also clear that there were more than one problem with airspeed and altitude as well as AOA readings being wrong. 

One truly scary thing is that even the previous flight that landed safely the PIC's stick shaker was on almost the entire flight -- that had to be unnerving.  Page 14 of the preliminary report shows some graphs of a few of the relevant data items during the 13 minute flight and you can see the near constant sequencing of the AND commands and the near constant manual nose up commands from the pilots and this continues all the way till the end.  I'd like to know if the AND commands would still show up even of the system were turned off, I suspect they would not and that would tend to confirm they never turned it off.

By my estimate reading the charts it took less than 20 seconds for the plane to depart the flight altitude and impact the ground.  Also interesting is the fact than during the final approximately 45 seconds the pitch trim position, which was a battle between the computer issued AND commands and the pilots manual pitch up commands, shows the computer continuing to issue the AND commands and the pilots continuing to issue manual nose up commands but in that final 45 seconds it doesn't look like the pilots commands had any effect.  So, for about 25 seconds of that final battle the AC pitched down a bit and lost a little altitude, but in the final 20 seconds the AC pitched down more noticeably, the altitude dropped more quickly, and the airspeed increased.

The graph from the previous flight is more compressed in time owing to the much longer flight but it appears the crew fought with the computer for about 20 minutes and then there doesn't seem to be any AND commands for over an hour which kind of suggests that with the trim system turned off there are no AND commands.

So, at this point we have:

1.   Numerous instrument issues covering several flights involving altitude, airspeed and AOA indications on the PIC (left) side -- this should have been fixed and confirmed fixed before passengers were allowed to fly on it
2.   The previous flight reported much the same problems and issued a PAN-PAN but continued the flight after turning off the trim system -- this should have been a PAN-PAN without the option to cancel
3.   The pilots of the doomed flight did not turn off the trim system and lost the fight at the end -- the pilots will get significant blame and that appears warranted
4.   The maintenance activities appear to suggest the techs relied on computer self tests which seemed to indicate no problems and its not clear what level of physical inspections were done -- did they do a leak test of the pitot static lines or not
5.   How was the AOA transmitter installed and does it have a registration pin or other mechanism to make sure it's installed at the right angle -- it not how did the techs set the angle on installation


Brian


 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #226 on: November 28, 2018, 08:00:30 pm »
3.   The pilots of the doomed flight did not turn off the trim system and lost the fight at the end -- the pilots will get significant blame and that appears warranted
Unless:
The airline is shown not to have provided sufficient documentation or training on how to fully manage this new MCAS flight system.
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Offline Gyro

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #227 on: November 28, 2018, 08:12:52 pm »
Well it looks as if there is some progress in not making the poor pilots the scapegoats....

Quote
Indonesian investigators have said the Lion Air plane that crashed last month killing 189 people was not airworthy and should have been grounded.


https://www.bbc.co.uk/news/world-asia-46121127


Therefore, the pilots should never have been placed in that position in the first place!

It seems to me that this thread has taken an distasteful turn towards establishing the guilt of the pilots, prior to the issuing of the full report.
« Last Edit: November 28, 2018, 08:52:57 pm by Gyro »
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Offline sokoloff

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #228 on: November 28, 2018, 11:30:41 pm »
2.   The previous flight reported much the same problems and issued a PAN-PAN but continued the flight after turning off the trim system -- this should have been a PAN-PAN without the option to cancel
From a systems design standpoint, it is undesirable to create one-way doors IMO. If you make it impossible to cancel an urgency or emergency declaration, you increase the cognitive decision-making hurdle for a human to make that declaration. Aircraft and passengers have been lost from crews not declaring emergencies or otherwise clearly communicating the danger the flight was in. (Avianca 52 is the first one that comes to most people's mind, but there are others.)

There is already some resistance in non-commercial pilot community to declaring an emergency when it seems warranted. (There's another fairly vocal sub-group who argues against this position; I find myself in that group at times.) Pilots fear repercussions, paperwork, an investigation that might turn up something unrelated, etc. It's why the Aviation Safety Reporting System is not run by the FAA and provides immunity to crews, mechanics, and other license-holders, etc. I don't fly professionally, but I can only imagine that the pressure to not lose your job makes rule-following even more high stakes.

IMO, there's good reason for the pilot in command to be the final authority as to the conduct of the flight and would argue against taking that authority and responsibility away in normal ops, abnormal ops, or emergencies.
http://www.eevblog.com/forum/chat/lion-air-crash-jakarta-boeing-737-had-prior-instrument-error/msg1949761/#msg1949761

I want my pilots to be thinking "Aviate, Navigate, Communicate" (in that order of priority). I don't want "Litigate" to be on their minds at all; that can all be done at 0' AGL and 0 knots airspeed.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #229 on: November 29, 2018, 06:01:30 am »
2.   The previous flight reported much the same problems and issued a PAN-PAN but continued the flight after turning off the trim system -- this should have been a PAN-PAN without the option to cancel
From a systems design standpoint, it is undesirable to create one-way doors IMO. If you make it impossible to cancel an urgency or emergency declaration, you increase the cognitive decision-making hurdle for a human to make that declaration. Aircraft and passengers have been lost from crews not declaring emergencies or otherwise clearly communicating the danger the flight was in. (Avianca 52 is the first one that comes to most people's mind, but there are others.)

There is already some resistance in non-commercial pilot community to declaring an emergency when it seems warranted. (There's another fairly vocal sub-group who argues against this position; I find myself in that group at times.) Pilots fear repercussions, paperwork, an investigation that might turn up something unrelated, etc. It's why the Aviation Safety Reporting System is not run by the FAA and provides immunity to crews, mechanics, and other license-holders, etc. I don't fly professionally, but I can only imagine that the pressure to not lose your job makes rule-following even more high stakes.

IMO, there's good reason for the pilot in command to be the final authority as to the conduct of the flight and would argue against taking that authority and responsibility away in normal ops, abnormal ops, or emergencies.
http://www.eevblog.com/forum/chat/lion-air-crash-jakarta-boeing-737-had-prior-instrument-error/msg1949761/#msg1949761

I want my pilots to be thinking "Aviate, Navigate, Communicate" (in that order of priority). I don't want "Litigate" to be on their minds at all; that can all be done at 0' AGL and 0 knots airspeed.


Yes, that is the dilemma and I know of no easy solution to it.  Pilots a reticent to delay or cancel a flight for maintenance issues do to pressure from the airline to stay on schedule so they tend to fly even when conditions should dictate they not fly.  You are quite right that having no choice in returning when a PAN-PAN is called might make it less likely they will call in one when deserved -- a kind of catch 22.  If this were an isolated event that would be one thing, but given the previous flights with similar issues I think this escalates the problem.  We are now seeing people in the aviation community stating publicly that this plane was not air worthy and I would agree with that.

As to the comment that we are being too quick to lay blame on the pilots, well, they should have known to turn of the stab trim system which suggests to me the pilots had an inadequate understanding of the flight controls and that's not acceptable for a commercial pilot, even a junior one.   To be sure, the failure to clarify the difference between the 737MAX and previous versions with respect to MCAS has to be seen as a contributing factor here.


Brian
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #230 on: November 29, 2018, 06:46:09 am »
Two dozen attempts -
It's an automatic system switching in and out, doing retries on its own, and possibly operating with bad noisy sensor data.

You have at least four oscillators. The MCAS software, the sensor(s), the pilot, the co-pilot.
The airplane or the pilot as the ultimate authority is yet another conflict.

You will note from the QRH handbook page I posted earlier that there is nothing there about "turn the system back on and see if it does it again." You don't re-enable a dodgy flight control system. You just don't.
 
Investigators are saying the plane was not airworthy. It should have been grounded as soon as problems surfaced on the previous flight.
One AOA sensor had been replaced, but still a 20 degree discrepancy.

And nobody here is disagreeing with that.

"Airworthy" has a specific, technical legal meaning, and it is not "plane could not be flown." In highly colloquial language it means "the plane should not be flown." It's a huge difference. For example, if an engine fails in flight, the aircraft is obviously not airworthy, but it can still be flown and landed safely.

I have never said that the airplane was airworthy, or that there is nothing wrong with the MCAS by designed or (lack of) training. I have said that the pilots crashed a plane that unless we learn something new and very strange (like the cutout switches didn't work) could have been landed.

Accidents have multiple causes, and one of those causes is the pilots not following procedures.

Really need the CVR to figure out all that happened.

CVRs are very useful, but are only one clue among many that investigators use to determine the cause of accidents. Few GA aircraft have CVRs (or FDRs, for that matter) and yet the US NTSB routinely determines proximate and contributing causes to the vast majority of air crashes in the US. Searchable database is here https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx and always fascinating reading.


 

Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #231 on: November 29, 2018, 08:05:52 am »
We don't know the malfunctions the plane experienced.

An intermittent, something cutting in and out can confuse anyone as to what is working properly or not.
Simply switching off the trim motors leaves the stabilizer actuator where it last was- presumably set at nose down. Maybe it was switched back on to get the motors to move it back, if the sensor data smartened up. Maybe they couldn't manually crank them back in time.

Human psychology is to "blame the victim" and the pilot had 6,000hrs and co-pilot 5,000hrs so they may not have been inept. Boeing certainly is.
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #232 on: November 29, 2018, 09:12:45 am »
An intermittent, something cutting in and out can confuse anyone as to what is working properly or not.

These guys weren't anyone, they were airline pilots. Furthermore, as has been discussed here ad nauseum, you don't need to know what is working properly or not to get out of this situation. You need to follow the book procedures. (Aside: it turns out that the QRH procedures for runaway stab are also memory items.)

Plenty of airliners have been lost from crews trying to debug something that should have been switched off or ignored.

Simply switching off the trim motors leaves the stabilizer actuator where it last was- presumably set at nose down. Maybe it was switched back on to get the motors to move it back, if the sensor data smartened up. Maybe they couldn't manually crank them back in time.

As has already been shown, there was a lot of time, and there was a significant period of more or less level flight. It will be interesting to know if in that period they could have climbed.



Human psychology is to "blame the victim" and the pilot had 6,000hrs and co-pilot 5,000hrs so they may not have been inept.

This is not an argument.

Boeing certainly is.

Wait, what?

Human psychology is a lot of things, like a desire to be contrarian, or to defer to experts, or not to defer to experts, or to blame big companies, or not wanting to admit that airlines pilots might be fallible, or that 6000 hours of experience can go by without much in the way of experiences.

I think portraying the pilots as victims "before we know what happened" is also probably premature.
 

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Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #234 on: November 29, 2018, 05:42:14 pm »
Reading the Preliminary Report, previous flight did OK:
"Airspeed unreliable and alt disagree shown after take off. STS was also running to the wrong direction, suspected because of speed difference. Identified that CAPT instrument was unreliable and handover control to FO. Continue NNC of Airspeed Unreliable and ALT disagree."

"... the airline confirmed one of their maintenance engineers was on board of the aircraft during the accident flight. This was an "anticipatory measure" in the event of technical problems with the new aircraft."

A third opinion who may have added confusion or given wrong instructions or flipped a breaker.


I'm of the view Boeing has blood on their hands for the engineering.
One of the many questions put forth to the FAA by The Aviation Herald:

- Why was the MCAS permitted to operate on the base of a single AoA value showing too high angle of attacks? Why does the MCAS not consider the other AoA value?

This is a failure of the software algorithm and fault tree analysis. Can't think of one reason to keep the robot going. AoA also seems to feed corrections to airspeed and altitude.

The forum poster, about knowing to shut off a system you don't even know about:
"As a captain on Boeing 737, I feel betrayed about Boeing's statements about their documentation. Even as of now, the MCAS has not been incorporated into the FCOM, nor into the FCTM. Their press release is a shameless lie."
 

Online mrpackethead

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #235 on: November 29, 2018, 07:14:03 pm »






On a quest to find increasingly complicated ways to blink things
 

Offline djacobow

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #236 on: November 30, 2018, 03:16:34 am »
Reading the Preliminary Report, previous flight did OK:
"Airspeed unreliable and alt disagree shown after take off. STS was also running to the wrong direction, suspected because of speed difference. Identified that CAPT instrument was unreliable and handover control to FO. Continue NNC of Airspeed Unreliable and ALT disagree."

"... the airline confirmed one of their maintenance engineers was on board of the aircraft during the accident flight. This was an "anticipatory measure" in the event of technical problems with the new aircraft."

A third opinion who may have added confusion or given wrong instructions or flipped a breaker.

This is just the thing. It was poor aeronautical decision making to attempt to figure out what is going, and there was no need to figure out what what going on. None. Zip. Nada. What needed to happen was for the pilots to quickly execute three memory items, then assess the situation further after the airplane is under full control.

I mean, look at the situation you're describing. They had a tech on board to help debug a system they knew was misbehaving that directly affected safety of flight, with revenue passengers in the back. What kind of ADM is that? And that decision was made on the ground. And given that they were anticipating stab problems, you'd think the crew would be spring-loaded to execute the runaway trim procedures at the first sign of trouble. But it is obvious they never did this. Maybe we'll find out from the CVR why. If it is because they thought they could figure it out, it will be a textbook case of poor ADM.

I'm of the view Boeing has blood on their hands for the engineering.
One of the many questions put forth to the FAA by The Aviation Herald:

- Why was the MCAS permitted to operate on the base of a single AoA value showing too high angle of attacks? Why does the MCAS not consider the other AoA value?

I tend to agree that Boeing probably screwed up. That doesn't mean the pilots didn't screw up. This is not unlike AF447 where a bad pitot heater design allowed the pitot system to fail, which caused the computer to stop providing envelope protection -- but that did not force the pilot to execute a zoom climb and then stall the aircraft.

The forum poster, about knowing to shut off a system you don't even know about:
"As a captain on Boeing 737, I feel betrayed about Boeing's statements about their documentation. Even as of now, the MCAS has not been incorporated into the FCOM, nor into the FCTM. Their press release is a shameless lie."

The pilot is being misleading, as you do not have to shut off a system you don't know about. You have to shut off the stab trim system.

I think Boeing's position on this is pretty clear: if you follow the procedure, it doesn't matter. Some pilots are saying it does matter. We'll find out.
 

Online BravoV

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Cockpit voice recorder recovered
« Reply #237 on: January 14, 2019, 03:53:21 pm »
Update today , the CVR is recovered, buried 8 meters underneath the mud in about 30 meters deep.

https://www.reuters.com/article/us-indonesia-crash-recorder/indonesian-officials-say-crashed-lion-air-jets-cockpit-voice-recorder-found-idUSKCN1P808C?il=0

Local news mentioned they used ROV with side scan sonar, magnetometer to find it.

« Last Edit: January 14, 2019, 05:14:30 pm by BravoV »
 

Offline raptor1956

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Re: Cockpit voice recorder recovered
« Reply #238 on: January 14, 2019, 04:59:41 pm »
Update today , the CVR is recovered, buried 8 meters underneath the mud in about 30 meters deep.

https://www.reuters.com/article/us-indonesia-crash-recorder/indonesian-officials-say-crashed-lion-air-jets-cockpit-voice-recorder-found-idUSKCN1P808C?il=0

Local news mentioned they used ROV with side scan sonar, magnetometer to find it.


That is good news and hopefully this will clear up the actions the pilots made and provide an insight into the sequence of actions they took.  The great question is:  why did they not turn of the Stab Trim and did they talk about doing so.

The upside to the crash, if there is an upside, is that there can't be a single 737MAX pilot that does not now know what MCAS is and how and when to power off the Stab Trim.


Brian
 

Online BravoV

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #239 on: January 14, 2019, 05:21:30 pm »
Hopefully the recording data is still ok, as from the look, the outer physical unit looks badly wrecked.

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #240 on: January 14, 2019, 05:24:58 pm »
Hopefully the recording data is still ok, as from the look, the outer physical unit looks badly wrecked.

WOW, had not looked at the pic before, but damn that thing is busted up.  The odd thing is you would expect the damage to be less with an impact with water versus land, but at the speed it must have hit the water it might as well have been land. 


Brian
 

Offline Berni

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #241 on: January 14, 2019, 05:47:31 pm »
Well crash landings on water are not actually any better than on land.

At the sort of speeds an impact with water makes it feel pretty much as hard as rock. But with the extra problem of also being very slippery and easy to dig into at the same time, if something actually does poke down into the water it experiences a massive amount of drag that slows it down very fast. So when something like the end of a wing touches the water surface the whole plane will suddenly be jerked into a sharp turn before the wing can't take it anymore and tears apart. Once the plane stops its not air tight anymore so it will just sink like a rock and if you do make it out alive you are now swimming in the middle of the sea with no land in sight while the top layer of water if full of kerosine.

Then again such a noise first crash straight into land would be impossible to survive too. But a more controlled crash landing is certainly more survivable on a open field of land rather than at sea.
 

Online BravoV

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #242 on: January 14, 2019, 06:00:22 pm »
Hopefully the recording data is still ok, as from the look, the outer physical unit looks badly wrecked.

WOW, had not looked at the pic before, but damn that thing is busted up.  The odd thing is you would expect the damage to be less with an impact with water versus land, but at the speed it must have hit the water it might as well have been land. 


Brian

See for youself for.more.photos ...

https://m.detik.com/news/foto-news/d-4383483/penampakan-cvr-lion-air-pk-lqp-yang-akhirnya-ditemukan

Offline SeanB

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