Author Topic: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'  (Read 76661 times)

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Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #150 on: November 13, 2018, 07:17:50 pm »
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 13, 2018, 07:39:27 pm »
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 13, 2018, 08:19:12 pm »
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 ?
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Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #153 on: November 13, 2018, 10:29:24 pm »
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.

 

Online tautech

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #154 on: November 13, 2018, 10:42:38 pm »
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 13, 2018, 11:11:07 pm »
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, 12:04:27 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, 12:12:37 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):
 

Offline Homer J Simpson

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Online SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #158 on: November 14, 2018, 01:43:30 am »
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, 02:05:10 am »
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, 02:19:54 am »
"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, 02:43:59 am »
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.
 

Online SiliconWizard

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #162 on: November 14, 2018, 03:57:25 am »
"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, 04:01:45 am 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, 04:36:43 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.

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, 11:22:22 am »
"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
 

Offline EEVblog

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #165 on: November 14, 2018, 01:03:08 pm »
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 14, 2018, 01:07:45 pm »
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".
 

Offline Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #167 on: November 14, 2018, 01:44:42 pm »
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 14, 2018, 03:37:13 pm »
Fair point taken.
 

Offline raptor1956

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #169 on: November 14, 2018, 06:54:20 pm »
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
 

Online BravoV

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #170 on: November 14, 2018, 06:58:17 pm »
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 14, 2018, 07:07:42 pm »
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 14, 2018, 07:28:27 pm »
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 14, 2018, 07:46:52 pm »
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 14, 2018, 08:07:32 pm »
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:
https://www.eevblog.com/forum/chat/lion-air-crash-jakarta-boeing-737-had-prior-instrument-error/msg1963691/#msg1963691
 


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