Author Topic: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'  (Read 101778 times)

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Offline ve7xen

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1350 on: January 08, 2021, 09:56:52 pm »
Well, the difference is that in all 737's up through the NG, the AOA sensor is for information ONLY, it does not control ANY flight control surface.
It may be used to provide a correction factor to the air data computer.  On the 737MAX, however, through MCAS, it DOES control the trimmable horizontal stabilizer, which moves it into a totally DIFFERENT class of sensor.  In this case, much greater attention to failure modes SHOULD have been given.

It also controls the stick shaker/stall horn, and several other computed indications like the 'eyebrows', but yes it doesn't touch any flight controls. The addition of such functionality without properly considering the risks of bad AoA data was the problem, not the AoA sensor itself. I think we are in agreement here, I just don't see the AoA sensor component failure itself as anything significant in this story, but you seem to be pushing it as a major part of the issue. The fundamental problem was the failure of the aircraft to appropriately react to that failure.

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The AOA sensors on the MAX are NOT redundant!  Only one is used at a time, although through the ARINC bus both flight computers can read both sensors.

Yeah, I misspoke here, redundant is incorrect terminology, since it can't recover from failure, only (potentially) detect it. They are (intended to be) fault tolerant, in that bad sensors will be detected, indicated, and data discarded, regardless of the fact that the ADIRU only uses one source of data at any one time. In any case, the point was that the AoA data isn't necessary for safe flight, so they could 'get away with' this methodology - as long as they correctly discard bad data - not that their detection of bad data was sufficient. MCAS is also not required for safe flight, and depends on the AOA data. As much as I think MCAS is a gigantic kludge and this sort of thing should never be acceptable in the design of an aircraft, the logic does make sense.

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  That's why there was an ($80K) optional AOA disagree light that could be purchased.  Most airlines did NOT purchase this option, as then you had to TRAIN for what the light meant.  So, the MAX has two flight computers.  Only one is actively controlling flight control surfaces at any time.  The active computer is switched every takeoff.  The output of each computer drives the instruments on one side (captain / first officer), using the sensors (AOA, air data computer, etc.) on that side.  So, while there is a "standby" redudant system of sensors, instruments and computers, it is NOT a dual redundant system.  Most of the larger and newer commercial aircraft use triple-redundant systems with voting logic, so that any component that fails can be cut out of the control loops.  Even the flight surface actuators have three separate actuators in series, so that any failure can simply be overridden by the other two.

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but then made this programming an expensive "add on" price option, with no explanation as to what the system does, as far as the information buying clients were given.

AOA DISAGREE was not an optional feature. An AOA (value) indicator was the expensive option. The problem here is that AOA DISAGREE was broken for years due to a software bug/misunderstanding that Boeing instructed Collins not to fix once it was discovered, and neglected to inform its customers or pilots about. The 737MAX was certificated with this indicator available, so for regulatory compliance, it MUST be present, but wasn't due to the unfixed bug.

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But, not the 737.

This is because these modern aircraft are fly-by-wire and depend on AoA data for safety of flight. I absolutely agree that 737MAX should never have been certificated without a modern FBW system and cohesive envelope protection. But, again, that has nothing to do with the AoA sensor itself.

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As for the "several legs safely" comment, not quite true.  (I'm getting the two 737 crashes confused, now.)  So, first, every other flight, if the plane is left powered up, it switches which computer and sensors are being used.  (If powered off, then it starts with computer #1 again.)

So, half the flights would APPEAR fine, but they had no backup computer/sensor set to fall back on.  Then, at least one of the flights had the stick shaker and alarms going off for the ENTIRE flight!  This, of course, is totally amazing, imagine the management pressure causing a pilot to complete an entire flight leg with this level of malfunction of the aircraft!  That is clear mis-management, of course!

What I'm talking about is that the Lion Air aircraft flew several legs with a faulty AoA sensor. This was detected, logged by the crews, and looked into by maintenance. None of these flights had any safety issue because the failure was a hard one - the resolver failed open as temperature fell, the flight computers detected this and knew the data was bad, so it didn't lead to any safety (or otherwise) issues. Eventually maintenance got around to replacing the sensor with the accident one that had a calibration bias. It was after this replacement that the flight you're mentioning occurred, where the crew experienced the same conditions as the accident flight, and just managed to deal with it better. This just shows that AoA *failure* is not a problem for this aircraft, the problem was that the sensor appeared to be functional as far as the flight computers could tell, but was producing biased indications, which wasn't something the Boeing design handled properly.

Don't get me wrong here. The level of incompetence, malfeasance on Boeing's part, and the extent of regulatory capture of the FAA is staggering, and the people who were documented to have mislead customers and pushed to cover this up absolutely deserve jail time. I just don't want people to think that AoA sensors failing is something we should really care about - because it is going to happen and the systems must be designed to tolerate any sort of failure, including a bias like this.
« Last Edit: January 08, 2021, 10:06:38 pm by ve7xen »
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Offline floobydust

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1351 on: January 08, 2021, 11:17:59 pm »
Don't forget the old adage from Segal's law- "with two clocks one can never know the correct time". The probability proof shows redundant watches (sensors) are useless.
You need a majority vote, one reason Airbus uses three pitot tubes and even then, having identical physical configuration means they like to fail the same way, bad heater design and ice included.
AF447 crash shows automation is lost without accurate sensor input. Try writing S/W that deals with sensor failures, it is a lot of math and at some point the machine needs the pilot to decide what action to take.
 

Offline ve7xen

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1352 on: January 08, 2021, 11:59:29 pm »
Don't forget the old adage from Segal's law- "with two clocks one can never know the correct time". The probability proof shows redundant watches (sensors) are useless.
You need a majority vote, one reason Airbus uses three pitot tubes and even then, having identical physical configuration means they like to fail the same way, bad heater design and ice included.
AF447 crash shows automation is lost without accurate sensor input. Try writing S/W that deals with sensor failures, it is a lot of math and at some point the machine needs the pilot to decide what action to take.

You need a majority vote if you need valid data for safe flight, as in an FBW aircraft, and especially for IAS which is quite critical both for manual and automatic flight in a normal regime. The concept of 737MAX design was (and still is) that AoA data (and by extension, MCAS) is not essential to the safety of flight, which I think is a fair assessment. Losing it changes effectively nothing except during approach to stall, which a transport aircraft should never encounter. If you accept that premise, two sensors is sufficient to detect a disagree and disable any (automated, at least) uses of the data. This is the basis under which the aircraft will be returned to service.

AF447 is almost the opposite case as 737MAX - the aircraft detected the problem, and degraded the automation as necessary to make safe recovery possible - this is exactly what should have happened with MAX (minus the inappropriate pilot response and ensuing crash, of course - but in the MAX case this wouldn't have changed the flight characteristics or indications in any meaningful way).
« Last Edit: January 09, 2021, 12:02:19 am by ve7xen »
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Online madires

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1353 on: January 09, 2021, 12:55:50 pm »
Yes and no! ;) The 737MAX can be operated without MCAS. But if you tell pilots that the 737MAX behaves the same like the 737NG MCAS becomes a critical system. WIthout MCAS the pilots would experience a non expected behavior in specific critical situations.
 

Offline langwadt

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1354 on: January 09, 2021, 01:10:39 pm »
Yes and no! ;) The 737MAX can be operated without MCAS. But if you tell pilots that the 737MAX behaves the same like the 737NG MCAS becomes a critical system. WIthout MCAS the pilots would experience a non expected behavior in specific critical situations.

but I'd think in a critical situation a plane behaving different is much preferred to a plane that behaves unpredictable
 

Offline langwadt

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1355 on: January 09, 2021, 01:20:39 pm »
Don't forget the old adage from Segal's law- "with two clocks one can never know the correct time". The probability proof shows redundant watches (sensors) are useless.
You need a majority vote, one reason Airbus uses three pitot tubes and even then, having identical physical configuration means they like to fail the same way, bad heater design and ice included.
AF447 crash shows automation is lost without accurate sensor input. Try writing S/W that deals with sensor failures, it is a lot of math and at some point the machine needs the pilot to decide what action to take.

yep, there have been cases where the one functional sensor was ignored because the two other sensors failed with the same wrong value


 

Offline Nusa

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Re: ++ another Boeing 737 down ++
« Reply #1356 on: January 09, 2021, 02:21:59 pm »
another one down (09 Jan 2021)

Boeing 737-524
https://www.nytimes.com/2021/01/09/world/asia/indonesia-plane.html

"another one" is misleading, since this thread is about the MAX.

The 737-500's were produced from 1990-1999. This particular one is a 27-year-old former United Airlines plane (no major operators still use them in the US). Way too early to say what went wrong.

https://aviation-safety.net/database/record.php?id=20210109-0
https://avherald.com/h?article=4e18553c
 
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Offline jmelson

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1357 on: January 09, 2021, 07:37:56 pm »
I think we are in agreement here, I just don't see the AoA sensor component failure itself as anything significant in this story, but you seem to be pushing it as a major part of the issue.
I think that may have been some other commenter.  As a delicate vane sticking out the side of the aircraft, the AOA vane is quite susceptibel to damage, they get broken all the time during ground handling and jetway movement.  And, the aircraft systems should be able to deal with crazy readings.  If the vane is banged, it can easily give a jammed or just incorrect reading.
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AOA DISAGREE was not an optional feature. An AOA (value) indicator was the expensive option. The problem here is that AOA DISAGREE was broken for years due to a software bug/misunderstanding that Boeing instructed Collins not to fix once it was discovered, and neglected to inform its customers or pilots about. The 737MAX was certificated with this indicator available, so for regulatory compliance, it MUST be present, but wasn't due to the unfixed bug.
Thanks for this clarification, I think my incorrect understanding of this has been coming from multiple sources, so I'm not the only one who got it wrong.
OK, so what, exactly, is the Collins bug on AOA disagree?  Does it NEVER light up?  Or, only in certain cases, but not this one?
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This is because these modern aircraft are fly-by-wire and depend on AoA data for safety of flight. I absolutely agree that 737MAX should never have been certificated without a modern FBW system and cohesive envelope protection.
Well, I partially agree.  It would have been a BETTER, and safer, plane with a triple-redundant fly by wire control system, 3 AOA sensors, etc.  But that would have increased costs quite a bit.  If the existing flight control system had a working AOA disagree and MCAS would not allow the stabilizer trim to automatically go into extreme positions, I don't really see a problem with the 737MAX.  Sure, it IS old-school, but there are a TON of them flying pretty safely all over the world (since they got that nasty rudder actualtor issue solved about 30 years ago.)

Jon
 

Offline ve7xen

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1358 on: January 10, 2021, 12:00:56 am »
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I think that may have been some other commenter.  As a delicate vane sticking out the side of the aircraft, the AOA vane is quite susceptibel to damage, they get broken all the time during ground handling and jetway movement.  And, the aircraft systems should be able to deal with crazy readings.  If the vane is banged, it can easily give a jammed or just incorrect reading.
Apologies then!

Thanks for this clarification, I think my incorrect understanding of this has been coming from multiple sources, so I'm not the only one who got it wrong.
OK, so what, exactly, is the Collins bug on AOA disagree?  Does it NEVER light up?  Or, only in certain cases, but not this one?

Basically it incorrectly got tied to the paid AOA indicator, which is where the confusion comes from, I think. This wasn't what the design intended, but due to a misunderstanding/miscommunication between Boeing and Collins on a related trouble report, it is what ended up being implemented. Collins actually found this bug some years ago, and informed Boeing, but it was requested that Collins hold off on a fix until a future anticipated firmware update or some such weak reasoning, and Boeing never informed its customers. This is documented in the Congressional report, I haven't really seen it discussed much elsewhere.

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Well, I partially agree.  It would have been a BETTER, and safer, plane with a triple-redundant fly by wire control system, 3 AOA sensors, etc.  But that would have increased costs quite a bit.  If the existing flight control system had a working AOA disagree and MCAS would not allow the stabilizer trim to automatically go into extreme positions, I don't really see a problem with the 737MAX.  Sure, it IS old-school, but there are a TON of them flying pretty safely all over the world (since they got that nasty rudder actualtor issue solved about 30 years ago.)

Fair enough, I think 737MAX will be safe once the required changes are done, notwithstanding some other failures due to Boeing's just massive bungling of this project.

However, I strongly believe that this concept of 'update the 50 year old airframe on the same type certificate under relaxed rules and with minimal pilot training' is fundamentally flawed. It seems to create perverse incentives, discouraging safety improvements while simultaneously encouraging nasty (and fundamentally useless, other than to satisfy the similarity requirement) hacks like MCAS that are far more likely to lead to design flaws, as they aren't considered as part of a cohesive design process, but as a tacked on standalone project. As the industry matures and these old designs get older and older, we need to do something to push the industry forward without bandaid fix on top of bandaid fix. The 737NG already has some...weird...design choices due to this, and MAX just takes it too far. What next? Wasn't such a big deal 30 years ago, but now this design is over 50 years old and a lot has been learned since that should be integrated into every new plane coming off an assembly line. There was a lot else going on at Boeing that was problematic, but this is where I think the regulators really need to step up and redesign their type certification scheme.
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Offline Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1359 on: January 10, 2021, 01:30:11 am »
Fair enough, I think 737MAX will be safe once the required changes are done, notwithstanding some other failures due to Boeing's just massive bungling of this project.

You seem to be out of date. The FAA lifted the grounding order in November, subject to a list of fixes for each aircraft and training for pilots. American, with 24 MAX-8's, has been flying revenue flights since December 29th. United took delivery of its 15th MAX-9 in December and is planning to start flying them on Feb 11th. Southwest, with 31 MAX-8's, is planning to resume using them in March.
 

Offline ve7xen

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1360 on: January 10, 2021, 03:00:46 am »
Fair enough, I think 737MAX will be safe once the required changes are done, notwithstanding some other failures due to Boeing's just massive bungling of this project.

You seem to be out of date. The FAA lifted the grounding order in November, subject to a list of fixes for each aircraft and training for pilots. American, with 24 MAX-8's, has been flying revenue flights since December 29th. United took delivery of its 15th MAX-9 in December and is planning to start flying them on Feb 11th. Southwest, with 31 MAX-8's, is planning to resume using them in March.

I'm not sure how my comment is out of date, it doesn't relate to regulatory action at all, but was a comment on the safety of the aircraft itself...which comes from changes done to the aircraft itself, not the regulator requiring them.

The US FAA is the only major regulatory body to have ungrounded the 737MAX (and I am not in America); it remains grounded in Europe, Canada, Australia, China and I think most other countries, though that's expected to change in the next couple of months.
« Last Edit: January 10, 2021, 03:02:19 am by ve7xen »
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Offline Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1361 on: January 10, 2021, 05:49:47 am »
Twas simply your use the future tense of your statement, rather than past tense.

As for Canada, they accepted the changes to the MAX last month, although the airworthiness directive is still "soon". But you just said your comment had nothing to do with regulation part, so that's beside the point.

I'm not sure exactly where EASA is on approval for the EU, but I suspect it's not far in the future.
« Last Edit: January 10, 2021, 05:54:50 am by Nusa »
 

Offline jmelson

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1362 on: January 10, 2021, 05:17:51 pm »
Basically it incorrectly got tied to the paid AOA indicator, which is where the confusion comes from, I think. This wasn't what the design intended, but due to a misunderstanding/miscommunication between Boeing and Collins on a related trouble report, it is what ended up being implemented. Collins actually found this bug some years ago, and informed Boeing, but it was requested that Collins hold off on a fix until a future anticipated firmware update or some such weak reasoning, and Boeing never informed its customers. This is documented in the Congressional report, I haven't really seen it discussed much elsewhere.
So, if you DON'T pay for the extra indicator, the AOA disagree light NEVER goes ON?  YIKES!  How could Collins just SIT on that malfunction??!!??
That seems like something they really NEEDED to report to the FAA pronto!
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However, I strongly believe that this concept of 'update the 50 year old airframe on the same type certificate under relaxed rules and with minimal pilot training' is fundamentally flawed.
Yes, I understand how they got here, between pressure from SouthWest Airlines and just making incremental changes on a really successful product line, and wanting to just deliver a more fuel-efficient machine, quickly, to existing customers who were chomping at the bit for a lower fuel burn.

But, YES, you are right, that keeping adding more hacks to a 50 year-old design eventually needs to end!
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There was a lot else going on at Boeing that was problematic, but this is where I think the regulators really need to step up and redesign their type certification scheme.
Well, they have got the MAX back into the air, with additional fixes on top of the MCAS fixes, and are probably going to crank out a bunch more of the MAX aircraft over the next few years.  But, I suspect that there's going to be a LOT more scrutiny over ANYTHING Boeing comes up with next for certification.  And, then, eventually, they will need to address the narrow body market, and I can't IMAGINE it well be another hack on the 737 carcass.  But, I could be wrong.

Jon
 

Offline boffin

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1363 on: January 10, 2021, 06:39:52 pm »
Currently airborne in 737MAX  (2021-01-10 1839Z)
3 American Airlines passenger flights
3 Aeromexico passenger flights
4 GOL (Brazil) passenger flights
1 COPA (Panama) passeger flights
2 SouthWest (USA) repositioning flights
[attachimg=1]
 

Offline ve7xen

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1364 on: January 10, 2021, 11:47:08 pm »
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So, if you DON'T pay for the extra indicator, the AOA disagree light NEVER goes ON?  YIKES!  How could Collins just SIT on that malfunction??!!??
That seems like something they really NEEDED to report to the FAA pronto!

Yup. This is beyond my understanding of the legal situation, but my guess is that Collins isn't directly beholden to the FAA. They work for Boeing from Boeing's design requirements, and it's the entire aircraft that is subject to FAA certification, and honestly they probably don't really have experts on exactly what the regulations require of Boeing to address issues like that. Should someone at Collins have blown the whistle? Maybe, but I'm willing to cut them a bit of slack, it seems like an honest mistake and they reported it to Boeing as soon as it was discovered. How Boeing let that sit when it clearly meant there were planes flying around that didn't meet their certification basis though is beyond comprehension. How serious would it have been to at least notify customers and offer a firmware update FFS, even if it was only recommended. What is that, an hour of engineer time at most, that customers can probably slot in to the rest of their maintenance schedule? I just don't get what Boeing gains from denying this information and fix to customers and pilots, it's really worrisome how they arrived at this decision for such a relatively trivial thing.

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And, then, eventually, they will need to address the narrow body market, and I can't IMAGINE it well be another hack on the 737 carcass.  But, I could be wrong.

Let's hope so. As I understand it, they basically canned their next-gen narrowbody project to focus on 737MAX. Maybe they start a clean-sheet design today and it's flying in 20 years, but I'm not very optimistic about that...
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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1365 on: January 28, 2021, 11:24:54 pm »
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline boffin

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1366 on: January 29, 2021, 11:13:32 pm »
Let's hope so. As I understand it, they basically canned their next-gen narrowbody project to focus on 737MAX. Maybe they start a clean-sheet design today and it's flying in 20 years, but I'm not very optimistic about that...

Boeing have the problem that  they've tried to use the 737NG and 737-MAX series to simultaneously replace the 1500 mi / 125 passenger 737-200 and the 4500mi 190-220 passenger 757-200/767-200 with the same airframe, and you're running into issues that it's hard to do both effectively.

I think if they go 'clean sheet', they may end up having to make two aircraft; or work with another vendor (Embraer?) to fill the smaller side.

Same thing is happening on the prop-side of the world, no one at all competes with ATR and the ATR42 at the 40-50 seat size, with DHC only making 75 seater DHC8-400s.  And at the smaller 20 seat size, the only current production aircraft I can think of are the new Cessna 408 &  DHC6-400s both of which are really special purpose (the former being a cargo hauler and the latter highly optimized for STOL/rugged operations),  which isn't really ideal to replace things like the B1900s of the world.
« Last Edit: January 29, 2021, 11:27:45 pm by boffin »
 

Offline james_s

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1367 on: February 05, 2021, 01:26:02 am »
Same thing is happening on the prop-side of the world, no one at all competes with ATR and the ATR42 at the 40-50 seat size, with DHC only making 75 seater DHC8-400s.  And at the smaller 20 seat size, the only current production aircraft I can think of are the new Cessna 408 &  DHC6-400s both of which are really special purpose (the former being a cargo hauler and the latter highly optimized for STOL/rugged operations),  which isn't really ideal to replace things like the B1900s of the world.

Seems like a DC-3 would be a nice fit there, maybe they should put those back into production. Lots of planes are faster and bigger and more luxurious but nothing I can think of has really quite hit that perfect sweet spot that has kept dozens of DC-3 airframes in revenue service for ~80 years.
 

Offline bw2341

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1368 on: February 05, 2021, 02:14:10 am »
I thought that DC-3s are still flying because there were so many made that they'll never run out of old planes to take parts from. If we're talking about safety, I don't think a unpressurized plane built to safety standards from 80 years ago would be appealing to current operators.

I think there are a few companies that have rebuilt DC-3s and modernized them with turboprop engines. If they made sense for airlines, we would see them everywhere.

I haven't looked up the regulations myself, but I think there is a difference between small planes with up to 19 passengers versus the big airliners. This would explain the hole in the market between 19 and 50 passengers.

If an airline has to meet tougher safety standards and have higher levels of staffing per flight, it might be impossible to make money flying a 20 or 30 passenger plane.
 

Offline james_s

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1369 on: February 05, 2021, 09:31:00 pm »
They're already running out of parts, prices on used DC-3s have gone up sharply in recent years but they keep going because they are still relatively affordable for a plan of that size and capability. It probably wouldn't make sense to start producing them again, given all the regulations I'm guessing it would be impossible to build them the same as the old ones, I can dream though. It's hard to think of an aircraft that is more timeless and classic, it's the grandfather of modern airliners. A great many of the planes meant to replace it went out of revenue service decades ago, many have no airworthy examples remaining at all.
 

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1370 on: February 05, 2021, 11:27:10 pm »
They're already running out of parts, prices on used DC-3s have gone up sharply in recent years but they keep going because they are still relatively affordable for a plan of that size and capability. It probably wouldn't make sense to start producing them again, given all the regulations I'm guessing it would be impossible to build them the same as the old ones, I can dream though. It's hard to think of an aircraft that is more timeless and classic, it's the grandfather of modern airliners. A great many of the planes meant to replace it went out of revenue service decades ago, many have no airworthy examples remaining at all.

The first plane I ever flew on was a DC-3.  I was 5 and it was very exciting, flying alone - taken care of by a stewardess in full, impeccably pressed uniform, with impossibly shiny brass buttons and badges!  I remember being awestruck at the thunder of the engines as they started and revved up, massive amounts of blue and black smoke (I guess fuel and piston oil control rings were "good enough for Australia" back then, and mufflers etc. was not something real men or women had any use for whatsoever)...   I remember the feeling of the small miracle as the plane accelerated down the runway with incredible noise, watching the ground disappearing under the plane...  I still feel that way at every take-off and always sit by the window for that reason alone, even if modern planes are a quite anodyne experience compared to a DC-3!  :D 


 

Offline Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1371 on: February 06, 2021, 12:14:34 am »
I thought that DC-3s are still flying because there were so many made that they'll never run out of old planes to take parts from. If we're talking about safety, I don't think a unpressurized plane built to safety standards from 80 years ago would be appealing to current operators.

I think there are a few companies that have rebuilt DC-3s and modernized them with turboprop engines. If they made sense for airlines, we would see them everywhere.
We're down to a few hundred in active service now, out of the 16000 DC-3/C-47 variants that were built. But they fill a niche. The tail-dragger configuration is simply superior at operating on short rough fields compared to modern aircraft of similar size. Rough fields were common in the era/war they were designed for.

As for turboprop conversions, the Jeopardy clue would be: This aircraft worth $300,000 is now worth $8,000,000.      Answer: What is a DC-3 turbo-prop conversion? 

Why? A lot more than the engine has to be upgraded to be properly certified, and it's nearly all hand labor...but you end up with a like-new aircraft you can fly another 50 years. So your commercial reality has to be pretty strong to invest that much to replace something that is still working.
Here's the longer story on that:
« Last Edit: February 06, 2021, 02:41:19 am by Nusa »
 

Online SilverSolder

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1372 on: February 06, 2021, 12:48:50 am »

Don't the airframes have a limited number of take-offs and landings, like modern planes?  Or are they simply so strong and over-engineered that it isn't an issue?
 

Offline Nusa

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1373 on: February 06, 2021, 02:39:37 am »

Don't the airframes have a limited number of take-offs and landings, like modern planes?  Or are they simply so strong and over-engineered that it isn't an issue?

No, the DC-3 requires regular inspection and maintenance like every other aircraft. However, your implication that airplanes have to be discarded at a certain point is not correct. Barring obvious calamities, aircraft can be kept flying for generations, so long as they are properly maintained. Airlines get rid of old planes and buy new ones for economic/business/pilot training reasons, not because the old ones are suddenly unusable.

Modern or antique, there are all sorts of maintenance requirements triggered by hours of use, cycles, landings, age, or unusual events. All documented in the maintenance manual with updates from airworthiness directives over the years. Some things you just have to inspect, some things you test, some things you overhaul, some things you replace.
 
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Offline Gixy

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Re: Lion Air crash: Jakarta Boeing 737 'had prior instrument error'
« Reply #1374 on: February 06, 2021, 08:19:17 am »
Hum, aircraft structure is designed and certified for a given number of cycles (a cycle is complete flight, with take-off and landing). Once this number is achieved, either the aircraft manufacturer make additional tests and computations to certify more cycles, either the aircraft is grounded for ever.
 
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