Indonesian aircraft missing off Jakarta
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There is a lot to be learned from this incident, but please stop the drama because it's irrational and unscientific.
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What worries me a bit more is the sentence
I'm not that closely familiar with 737MAX systems, but how can the trim still run away if the switches have been set to "CUTOUT"? Aren't they mechanical circuit breakers?
[...] set stabilizer trim switches to CUTOUT. If runaway continues, hold the stabilizer trim wheel against rotation and trim the airplane manually.
[...] unless the system inputs are counteracted completely by pilot trim inputs and both STAB TRIM CUTOUT switches are moved to CUTOUT
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Yes, that the same defect apparently persisted through four consecutive sectors, and successive crews were in effect testing the outcome of failed rectification attempts, is inexcusable.
That said, an "inherent and unknown programming defect" (in any software environment, not just aerospace) by definition requires a specific, unforeseen combination of factors (possibly including other defects) in order to trigger it. It's entirely possible that the required combination of factors never emerged during the certification process.
If there had been precursors to this issue, while we might not have heard about them prior to the crash, they would undoubtedly have emerged in the last 10 days. AFAIK, none have.
That said, an "inherent and unknown programming defect" (in any software environment, not just aerospace) by definition requires a specific, unforeseen combination of factors (possibly including other defects) in order to trigger it. It's entirely possible that the required combination of factors never emerged during the certification process.
If there had been precursors to this issue, while we might not have heard about them prior to the crash, they would undoubtedly have emerged in the last 10 days. AFAIK, none have.
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Unless I'm mistaken there are two recurring themes being repeated here which are (1) that the technology is fatally flawed and/or (2) most contemporary pilots are incompetent. Neither is true. Incidents like this are rare. It's too easy to call out Lion Air's relatively poor safety record and it's more than somewhat Luddite to be suspicious of automation. Despite the very low frequency of incidents, many of you seem to myopically think we are living in some kind of crisis of aviation, possibly because this forum focusses on incidents. The stats don't tell that story.
There is a lot to be learned from this incident, but please stop the drama because it's irrational and unscientific.
There is a lot to be learned from this incident, but please stop the drama because it's irrational and unscientific.
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The whole "the aircraft design is safe", "the manufacturer did a good job", "well trained pilots would have recovered", "maintenance did a bad job", "third world habits" is arrogant and very biased to say the least. This accident happened in the aviation world of FAA certification processes that cost taxpayers and aircraft buyers millions.
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Two questions I think are still unclear:
Through what pathway did the faulty AoA sensor feed bad data to the trim stabiliser?
People are discussing the STS as a possibility, but AoA is not a direct input to this system. Instead from the AD it seems that a single AoA failure can contaminate the CAS at the ADIRU and generate airspeed disagree even with no faults in the pitot/static system. Under this scenario the STS could continue to operate, trimming the stab down in response to faulty low CAS. However, it seems unlikely that this would present as stabiliser runaway to the stop, as even with faulty AoA data it shouldn't be able to revise CAS that much (CAS is primarily based on the presumably working pitot/static). If this was the case, this would be a known problem with NGs as well as MAX, with single AoA failures in the past would leading to similar problems (which doesn't seem to be the case). Which leads to:
Does the MAX use AoA data in any way differently to the NG?
If the use of AoA sensor data hasn't changed from the NG then this accident must truly be a black swan event, with some other secondary malfunction to the AoA fault interacting to give the trim runaway. This is a pretty terrible combination with the elevator feel system (which is directly acting on AoA data), a faulty high alpha value will trigger stall protection and make it much harder to pull against the faulty automatic down trim, probably with the extra burden of simultaneous stick shaker.
The confusing fact the AoA sensor failure seems to only announce itself by it's flow-on effects on other systems (IAS DISAGREE, FEEL DIFF PRESS) seemed to affect not only the crew but maintenance, who after replacing the AoA sensor and still getting problems (suggesting the AoA failure is not in the outer sensor module), returned to hopefully trying maintenance items on the ports and checking the connectors on the feel computer.
Through what pathway did the faulty AoA sensor feed bad data to the trim stabiliser?
People are discussing the STS as a possibility, but AoA is not a direct input to this system. Instead from the AD it seems that a single AoA failure can contaminate the CAS at the ADIRU and generate airspeed disagree even with no faults in the pitot/static system. Under this scenario the STS could continue to operate, trimming the stab down in response to faulty low CAS. However, it seems unlikely that this would present as stabiliser runaway to the stop, as even with faulty AoA data it shouldn't be able to revise CAS that much (CAS is primarily based on the presumably working pitot/static). If this was the case, this would be a known problem with NGs as well as MAX, with single AoA failures in the past would leading to similar problems (which doesn't seem to be the case). Which leads to:
Does the MAX use AoA data in any way differently to the NG?
If the use of AoA sensor data hasn't changed from the NG then this accident must truly be a black swan event, with some other secondary malfunction to the AoA fault interacting to give the trim runaway. This is a pretty terrible combination with the elevator feel system (which is directly acting on AoA data), a faulty high alpha value will trigger stall protection and make it much harder to pull against the faulty automatic down trim, probably with the extra burden of simultaneous stick shaker.
The confusing fact the AoA sensor failure seems to only announce itself by it's flow-on effects on other systems (IAS DISAGREE, FEEL DIFF PRESS) seemed to affect not only the crew but maintenance, who after replacing the AoA sensor and still getting problems (suggesting the AoA failure is not in the outer sensor module), returned to hopefully trying maintenance items on the ports and checking the connectors on the feel computer.
To the best of my admitted limited knowledge this is the 1st incident I can recall where a single plane had significant issues across multiple consecutive flights and remained in service and suffered a catastrophic event. So it's really an economic and cultural issue, possibly specific to Lion Air or potentially more wide spread. I realize that planes are routinely dispatched with degraded capabilities but from what I have read here it would seem that many of those who work in the pointy end have expressed dismay (or am I wrong) that the plane was cleared given the nature of the ongoing issues. Once the problem persisted in spite of the swap out how could you "sign off" for a revenue flight?
I became a big hero to a particular operator many years ago when, after looking at some DFDR data, I figured out that their recurrent FADEC problem they'd be trying to solve for a month was occurring when the leading edge devices were retracted. I told them to go look at the wire bundles in the vicinity of the leading edge actuators and they found the chaffed bundle problem the next day.
I wouldn't be too quick to condemn maintenance because they struggled to correct an intermittent fault.
Ian W #926, you may have overlooked the stage that actions only follow understanding (with a few startling exceptions).
My concern with the AD, and your view, is that these assume that the crew have an adequate understanding for ‘the case’.
The dominant cue, or initially the more likely one for this failure appears to be stick force. This is only available to the PF. There is no annunciation.
In order to confirm the specific failure there are a series of ‘ands’ to add to the ‘if then’ sequence, any one of which could divert thoughts to alternative situations and actions.
The better design principle is that all failures should be annunciated, and also provide adequate guidance towards understanding, i.e. AoA Comparator in isolation directs attention to the AoA, but in this instance the problem is trim. Similarly for Alt, Speed, Feel, disagreement, none helps to identify trim except in combination, which is a effortful mental task in a situation where time is critical.
My concern with the AD, and your view, is that these assume that the crew have an adequate understanding for ‘the case’.
The dominant cue, or initially the more likely one for this failure appears to be stick force. This is only available to the PF. There is no annunciation.
In order to confirm the specific failure there are a series of ‘ands’ to add to the ‘if then’ sequence, any one of which could divert thoughts to alternative situations and actions.
The better design principle is that all failures should be annunciated, and also provide adequate guidance towards understanding, i.e. AoA Comparator in isolation directs attention to the AoA, but in this instance the problem is trim. Similarly for Alt, Speed, Feel, disagreement, none helps to identify trim except in combination, which is a effortful mental task in a situation where time is critical.
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Bob then one-ups himself by POURING a glass of tea while performing a barrel roll. Even though the aircraft is inverted, the stream of tea always flows toward the floor of the aircraft.
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Pilots May have thought STS was automatically disabled due to their increased speed. If what has been posted here is correct, prior versions had various activation triggers amongst which was low speed. Not higher speed, which they had invoked.
The MAX (it seems) is now adding AoA Disagree as a trigger. Did pilots know this ?
Is it Possible the pilots thought, given their increased speed, HAL would not mess w their stabilizer?
Yet another reason why what was actually happening was not something they imagined?
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Assuming the problem was "intermittent", troubleshooting becomes very, very difficult and the Maintenance Manual/Fault Isolation Manual are not always a lot of help. Anyone who's a backyard mechanic can appreciate how frustrating it can be to find a problem that only occurs when you're driving 60 miles per hour - but not every time you drive 60 miles per hour. [snip]
I wouldn't be too quick to condemn maintenance because they struggled to correct an intermittent fault.
I wouldn't be too quick to condemn maintenance because they struggled to correct an intermittent fault.
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Assuming the problem was "intermittent", troubleshooting becomes very, very difficult and the Maintenance Manual/Fault Isolation Manual are not always a lot of help. Anyone who's a backyard mechanic can appreciate how frustrating it can be to find a problem that only occurs when you're driving 60 miles per hour - but not every time you drive 60 miles per hour.
I became a big hero to a particular operator many years ago when, after looking at some DFDR data, I figured out that their recurrent FADEC problem they'd be trying to solve for a month was occurring when the leading edge devices were retracted. I told them to go look at the wire bundles in the vicinity of the leading edge actuators and they found the chaffed bundle problem the next day.
I wouldn't be too quick to condemn maintenance because they struggled to correct an intermittent fault.
I became a big hero to a particular operator many years ago when, after looking at some DFDR data, I figured out that their recurrent FADEC problem they'd be trying to solve for a month was occurring when the leading edge devices were retracted. I told them to go look at the wire bundles in the vicinity of the leading edge actuators and they found the chaffed bundle problem the next day.
I wouldn't be too quick to condemn maintenance because they struggled to correct an intermittent fault.
Seems the NG is different
“Does the MAX use AoA data in any way differently to the NG?
If the use of AoA sensor data hasn't changed from the NG then this accident must truly be a black swan event”
Based on the Boeing and subsequent FAA Emergency AD, which very specifically identifies the 737-8 and -9, I think we can assume the MAX is different.
- GY
If the use of AoA sensor data hasn't changed from the NG then this accident must truly be a black swan event”
Based on the Boeing and subsequent FAA Emergency AD, which very specifically identifies the 737-8 and -9, I think we can assume the MAX is different.
- GY
“Does the MAX use AoA data in any way differently to the NG?
...although a version of this automated system has been on the 737 since the first ones were built in 1967, only on the MAX is this particular sensor able to trigger uncommanded movements of the jet’s horizontal tail.
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If the use of AoA sensor data hasn't changed from the NG then this accident must truly be a black swan event”
Based on the Boeing and subsequent FAA Emergency AD, which very specifically identifies the 737-8 and -9, I think we can assume the MAX is different.
Based on the Boeing and subsequent FAA Emergency AD, which very specifically identifies the 737-8 and -9, I think we can assume the MAX is different.
Thanks for your insight, but if you have a recurring (so not intermittent) issue with a critical flight control system/component would you "troubleshoot" on a revenue flight. The only clearly different variable across the 4 flight segments (that I'm aware of) is the presence of the engineer (in the cockpit?)...
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Lots of emotive responses and "opines"........
The Boeing 737,on balance,is a remarkably safe design.
Manufacturers cant be praised one day for a stick shaker helping a pilot identify a stall and the next day be blamed for that same stick
shaker causing confusion and masking if its input is false..One accepts the good with the bad.Its an imperfect world.
Anti-stall and speed stability devices are desirable and mandatory for certification.They require inputs.These inputs are dependent on the
reliability of the pitot static system.That system is not invulnerable.Checklists,procedures and a pilots airmanship will overcome a UAS event.
The level of airmanship in pilots,like training and experience,is very variable.Nothing is guaranteed though.Highly competent crews can and do make mistakes.The human species is entirely fallible.
Manual raw data flying skills are at an all time low in the industry.Many pilots are highly automation dependent.This is a worrying trend and needs
addressing.
Many airlines prescribe more automation dependence via SOPs and mistakenly see more automation as a panacea for incidents/accidents.
Note that all Lionair B737s are fitted with Honeywells RAAS.An automated system to remind pilots of how to fly an airplane.....does it make sense to you??When they invent something like that,you know somethings wrong in the system.Some pilots perhaps who have logged 5000 hours on type on line may have manipulated the flight controls manually for 50 of those 5000 hours.No wonder then they need RAAS and FDs and AT and AP.This oversight can cause problems during non-normals when proficiency in manual flight will become the difference between life and death."If I hear I will forget,If I see I will remember,if I do I will understand"(Confucius)
Lionair maintenance failed to rectify a very high priority glitch in 4 consecutive attempts.After the 1st failed attempt to repair the glitch,the plane should have been grounded and subject to a test flight before further revenue flight.Lionair maintenance will be looked at very closely to be sure.If you think you can save money/time in maintenance,try having an accident....you may find that soon you dont have a fleet to maintain.
STS is poorly understood and seen as a nuisance by some pilots.Its not.Its required by certification and serves a valid purpose
FCC A controls both STS and AP stab trim on 1st flight of the day.FCC A gets data from Left ADIRU.If that data is corrupt,you will get unwanted incorrect trim.
STS trimming using bad data will trim to the stops if the pilot does not intervene.
Startle factor can occur if crews are insufficiently trained/experienced...this will lead to mental capacity overload and panic....repeated attempts to engage the AP are a sign of panic in UAS.
The STS trims using the quieter slower AP stab trim motor.Its not a runaway technically as its intermittent.If aural/tactile warnings,like stick shaker,are operating the crews ability to focus and THINK(never mind intuit) will be effected.They will pull on the stick and use main electrical trim to trim up,both of which will override but not disable the STS.They will think they are in control but as soon as they stop,the STS trim down returns.
The Boeing AD addresses this by an emergency order to KILL ALL TRIM by putting both stab trim cutout switches to cutout(RUNAWAY STABILIZER NNC).If they make it a recall item,then the pilots no longer have to think do they.......thats about where we are in aviation these days....Pay to fly,tick the boxes instructors,no pilots at board level,automation dependance gone awry,B777 pilots that cant land on a clear day in SFO without a glideslope signal.....yep,that just about sums up where we are......Rananim sends or opines....whatever the hell that means
The Boeing 737,on balance,is a remarkably safe design.
Manufacturers cant be praised one day for a stick shaker helping a pilot identify a stall and the next day be blamed for that same stick
shaker causing confusion and masking if its input is false..One accepts the good with the bad.Its an imperfect world.
Anti-stall and speed stability devices are desirable and mandatory for certification.They require inputs.These inputs are dependent on the
reliability of the pitot static system.That system is not invulnerable.Checklists,procedures and a pilots airmanship will overcome a UAS event.
The level of airmanship in pilots,like training and experience,is very variable.Nothing is guaranteed though.Highly competent crews can and do make mistakes.The human species is entirely fallible.
Manual raw data flying skills are at an all time low in the industry.Many pilots are highly automation dependent.This is a worrying trend and needs
addressing.
Many airlines prescribe more automation dependence via SOPs and mistakenly see more automation as a panacea for incidents/accidents.
Note that all Lionair B737s are fitted with Honeywells RAAS.An automated system to remind pilots of how to fly an airplane.....does it make sense to you??When they invent something like that,you know somethings wrong in the system.Some pilots perhaps who have logged 5000 hours on type on line may have manipulated the flight controls manually for 50 of those 5000 hours.No wonder then they need RAAS and FDs and AT and AP.This oversight can cause problems during non-normals when proficiency in manual flight will become the difference between life and death."If I hear I will forget,If I see I will remember,if I do I will understand"(Confucius)
Lionair maintenance failed to rectify a very high priority glitch in 4 consecutive attempts.After the 1st failed attempt to repair the glitch,the plane should have been grounded and subject to a test flight before further revenue flight.Lionair maintenance will be looked at very closely to be sure.If you think you can save money/time in maintenance,try having an accident....you may find that soon you dont have a fleet to maintain.
STS is poorly understood and seen as a nuisance by some pilots.Its not.Its required by certification and serves a valid purpose
FCC A controls both STS and AP stab trim on 1st flight of the day.FCC A gets data from Left ADIRU.If that data is corrupt,you will get unwanted incorrect trim.
STS trimming using bad data will trim to the stops if the pilot does not intervene.
Startle factor can occur if crews are insufficiently trained/experienced...this will lead to mental capacity overload and panic....repeated attempts to engage the AP are a sign of panic in UAS.
The STS trims using the quieter slower AP stab trim motor.Its not a runaway technically as its intermittent.If aural/tactile warnings,like stick shaker,are operating the crews ability to focus and THINK(never mind intuit) will be effected.They will pull on the stick and use main electrical trim to trim up,both of which will override but not disable the STS.They will think they are in control but as soon as they stop,the STS trim down returns.
The Boeing AD addresses this by an emergency order to KILL ALL TRIM by putting both stab trim cutout switches to cutout(RUNAWAY STABILIZER NNC).If they make it a recall item,then the pilots no longer have to think do they.......thats about where we are in aviation these days....Pay to fly,tick the boxes instructors,no pilots at board level,automation dependance gone awry,B777 pilots that cant land on a clear day in SFO without a glideslope signal.....yep,that just about sums up where we are......Rananim sends or opines....whatever the hell that means
I am SLF. I have read this entire thread. I am a science driven person. I am extremely interested in aviation. Please correct me if I'm wrong.
What I don't understand is that in a UAS event the pilot should fly attitude and N1 per the QRH; this will assure the airplane won't just fall from the sky and gives the pilots time to regroup and analyze the situation. If the pilots are flying attitude they won't be concerned with AoA will they? If the trim system keeps trying to change the attitude every ten seconds why would the pilots not shut if off and then trim manually if necessary? Is trim of the aircraft that important in this situation? Is this a training issue in that it seems the most important part, keeping the plane flying, has become secondary? On a personal note before I get hammered, I used to race single seat formula cars and never panicked even while going off the road after brake failure at high speed, so I do know some things about exposure and brain function, at least my own.
What I don't understand is that in a UAS event the pilot should fly attitude and N1 per the QRH; this will assure the airplane won't just fall from the sky and gives the pilots time to regroup and analyze the situation. If the pilots are flying attitude they won't be concerned with AoA will they? If the trim system keeps trying to change the attitude every ten seconds why would the pilots not shut if off and then trim manually if necessary? Is trim of the aircraft that important in this situation? Is this a training issue in that it seems the most important part, keeping the plane flying, has become secondary? On a personal note before I get hammered, I used to race single seat formula cars and never panicked even while going off the road after brake failure at high speed, so I do know some things about exposure and brain function, at least my own.
@winemaker: it would appear that low cost airlines (or a number of them) do just enough training to get by the regulators' requirements. The difference between currency, and recency, and proficiency is lost on the profit driven philosophy of a low cost airline's management and ownership. So while your point on pitch and power certainly fits how I was trained to fly, how pilots are trained, kept current, and retain proficiency (across their entire area of responsibility) in the year 2018 is not a fixed value. It varies with corporate culture, among other things. There isn't a single standard ... and more's the pity.
c'mon, Rana....... tell us how you really feel or opine or assert or whatever. We can handle it.
As a pilot, my worst fear is when the plane does something I didn't command or ask it to do. And to do it at a critical phase of flight.
This "discovery" that a poor AoA input to one or more subsystems can result in runaway trim is scary beyond belief. Especially when it only occurs when flying without the A/P engaged. You know, the so-called hand flying or manual flying exercise that many of we geriatric folks talk about.
My feeling is all the technical aspects about static stability and Boeing's efforts to help with trim and feel and so forth would be better discussed over on the Tech Log as we did with AF447.
Meanwhile we wait for news and maybe another bulletin from Boeing or the U.S. and other country aviation agencies.
out,
As a pilot, my worst fear is when the plane does something I didn't command or ask it to do. And to do it at a critical phase of flight.
This "discovery" that a poor AoA input to one or more subsystems can result in runaway trim is scary beyond belief. Especially when it only occurs when flying without the A/P engaged. You know, the so-called hand flying or manual flying exercise that many of we geriatric folks talk about.
My feeling is all the technical aspects about static stability and Boeing's efforts to help with trim and feel and so forth would be better discussed over on the Tech Log as we did with AF447.
Meanwhile we wait for news and maybe another bulletin from Boeing or the U.S. and other country aviation agencies.
out,
