Ethiopian airliner down in Africa
"The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope. Furthermore, the additional crew procedures and training material will clearly explain to pilots the situations where use of the trim wheel may be needed due to lack of trim authority with the wheel mounted switches."
THUNDERTAILED
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Are the complex systems not the problem? Do you really need an electric trimmer to move a stabilizer in a 15 degree range? Do you really need a electric motor to close your car boot?
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Fully agreed. There could be much more on the list (e.g. same sound for cabin pressure altitude warning and t/o config, which killed 121 people)
Sensors will continue to break in future. Bits will continue to flip. Wires will continue to fail. Connectors will continue to corrode. People will continue to be humans.
It is the damned duty of every OEM lead design and certification engineer and every FAA, EASA and have you representative to think of possible failure modes and ask for solid and sane design.
It is not the duty to think about saving money by keeping a 40 years old certification in place. Which lets the boss, the boss of the boss and the boss of the boss of the boss smile.
It seems basic airmen and engineering knowledge is lost in the industry and substituted by plain software commodity engineering skills, that are typical for games, desktop software and iOS apps. These do not run airplanes.
Not the only thing that is lost in this world.
Sensors will continue to break in future. Bits will continue to flip. Wires will continue to fail. Connectors will continue to corrode. People will continue to be humans.
It is the damned duty of every OEM lead design and certification engineer and every FAA, EASA and have you representative to think of possible failure modes and ask for solid and sane design.
It is not the duty to think about saving money by keeping a 40 years old certification in place. Which lets the boss, the boss of the boss and the boss of the boss of the boss smile.
It seems basic airmen and engineering knowledge is lost in the industry and substituted by plain software commodity engineering skills, that are typical for games, desktop software and iOS apps. These do not run airplanes.
Not the only thing that is lost in this world.
Ttfn
I have read all the comments made on this forum concerning the Lion Air, and now the Ethiopian 737 Max crashes. It seems to me that the majority of comments focus on what could, or should, have been done by the crews involved. The Ethiopian pilots especially, whilst doubtless fully knowledgeable of the previous incident, were faced with the extraordinary and bizarre coincidence of a 2nd failure on the Max of the AOA vane, supplying erroneous data to the MCAS. This happened at the worst possible time where they were at their busiest, and with no height or time to play with. Whilst we all now have the benefit of knowledge, hindsight and time to analyse the situation . . . they didn’t. Of course they did their best, attempting to follow the memory items and new procedures as this crisis developed, but who, hand on heart, can lay any blame on them for not getting it exactly right? They may have been an average crew, with maybe less than average experience, but they were a trained and qualified crew and presumably signed off to fly the Max.
Even Boeing chief executive Dennis Muilenburg has publically stated: “As pilots have told us, erroneous activation of the MCAS function can add to what is already a high workload environment”. The Max, and in fact all commercial aircraft, simply have to be designed, built and certified to be within the flying ability of all pilots deemed qualified by their authorities to fly the Max. Two crews have shown sadly that the Max was outside their ability, particularly the 302 crew even with prior knowledge of the potential failure, and the industry therefore has to assume that this is the norm, not the exception.
Even Boeing chief executive Dennis Muilenburg has publically stated: “As pilots have told us, erroneous activation of the MCAS function can add to what is already a high workload environment”. The Max, and in fact all commercial aircraft, simply have to be designed, built and certified to be within the flying ability of all pilots deemed qualified by their authorities to fly the Max. Two crews have shown sadly that the Max was outside their ability, particularly the 302 crew even with prior knowledge of the potential failure, and the industry therefore has to assume that this is the norm, not the exception.
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The 737 instrumentation is a dual-redundant system, comprising two completely separate systems such that in the event of a single failure one completely operational system is still available. With the aid of appropriate disagreement monitors, standby instruments and checklists, pilots are trained to detect and diagnose such failures and take appropriate action.
This system was state-of-the-art at the time the 737 was launched and is still in use in smaller, non-FBW airliners. It is totally adequate for its stated task, that is to provide information to a well-trained human crew. It should never have been allowed to provide inputs to a system that will automatically drive flight control surfaces.
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trim blips
Seems to me that the final hole in the cheese which dictated the outcome of both flights is, that at higher speeds the trim is jammed (in the direction of nose up) if trimmed nose down. On the Ethopian flight a single nose down command by the MCAS system was enough to seal their fate.
I do not believe that in the time where they clung on the column for nose up, that they did not try to use the trim switches to unload the back pressure. Elevator trimming you learn from day one in your SEP trainer.
On the Lion air you can see that the PF did constant fight the MCAS AND trim with nose up. As soon as he transferred command there are only few blips of nose up trim to see on the FDR. Same here on the Ethopian flight.
I can’t believe that you only try with two short blips if the landscape becomes larger fast.
I do not believe that in the time where they clung on the column for nose up, that they did not try to use the trim switches to unload the back pressure. Elevator trimming you learn from day one in your SEP trainer.
On the Lion air you can see that the PF did constant fight the MCAS AND trim with nose up. As soon as he transferred command there are only few blips of nose up trim to see on the FDR. Same here on the Ethopian flight.
I can’t believe that you only try with two short blips if the landscape becomes larger fast.
I am curious as to where the FDR data for the stabilizer trim is read from - yoke trim switches or the motor drive electronics? Most high power motor drives have feedback that detects if the power demand is exceeded. If this happens, power to the motor is disabled, in order to protect it. Therefore a situation could arise where even though the pilot is activating ANU trim, it results in just a short ANU motor movement, before the motor power limit is exceeded. So if the FDR records from the drive electronics, the trim ANU 'request' by the pilot, will be seen as just a 'blip' although the trim switch is still activated,
This would account for AND trim running the full period as motor power demand is not exceeded (low aerodynamic load), but ANU trim is fighting against high aerodynamic load, which activates the motor protection. Thoughts?
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Disagree. May address the issues that caused the latest accident, but contradicts the entire concept of the 737's instrumentation system, and will invalidate the safety calculations on which certification is based, as well as possibly opening the doors to other failure modes.
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Disregarding AOA for speed calculation (for example) will contradict which concept? Which safety calculation will it invalidate? Which other failure mode can you imagine if we do that? (note that the difference is about 5knt at takeoff speed between correct and bat**** crazy AOA, so the error between fixed assumed AOA value and real AOA may be as low as 2knts).
Advicing the crew of inability to trim at high speed will harm how? We think it is worthy to throw them an alarm about the AOA heater not heating, and keep the stick shaker all along, but we believe it would be too distracting to remind them that he will loose trim ability due to high speeds?
Those are the official excuses. I don't buy them. It was honestly a very reasonable system when safety was important but not as important as today, data buses did not exist and pilots came from the military.
Not any more.We have better tools now and even if we break concepts and need to recertify things, it is simply too easy today to fool a 737 computer.
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https://leehamnews.com/2019/04/05/bj...is/#more-29839
Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls
Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls
The full range (from the AMM) of the stab is 17°. This range is not available to all controls, (electric, manual, wheel), as noted in this thread, but let us assume the available range is -1 AND to 16 ANU using the big wheel.
Now we can calculate turns and degrees of trim, (remembering the comments on the difficulty of turning the wheel under some circumstances).
250 turns / 17 degrees = 14.7 turns per degree, or,
17 degrees / 250 turns = 0.07° per turn.
If the thinking and the math is correct, we can see that there is a lot of work and time to manually modify the stab trim using the wheel. In fact, those who fly/flew the B727/B737 will recall just how fast the wheel goes around when electrically-trimming in normal flight, flaps-up; the white mark on the wheel is almost a blur...
PJ2
https://leehamnews.com/2019/04/05/bj...is/#more-29839
Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls
Thinks that the force when electric tirm/ MCAS was switched back on probably bounced the crew out of their seats, causing them to lose/ weaken grip on the controls
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In the prelim. report is a clear statement by the FO that the manual trim attempt did not work as advertised in the AD.
There is also a subtle hint that probably shows why the pilots in a last desperate attempt did reengage the trim motors, and how the pilots were desperately trying to follow the AD and manually resetting the trim, which was most likely aerodynamically blocked:
After the cutout, there is a very slow, long, subtle nose-down movement of the fin according to the report. What do you do when the crank is blocked, instinctively? You're rattling it! And then in this phase it moves only a few hairs nose-down, but not a bit Nose-Up.
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.
This last attempt to implement the AD has now reset MCAS. And then comes design-wise (but is not in the FCOM or the AD, was never mentioned in training), while they still think about what to do next, after 5 s the final death blow of MCAS ...
The plane systems (MCAS and Trim) and the AD procedure just did not give them a fair chance IMHO.
An excellent overview over these 60 year old speed issues with the 737 trim system can be found in many old manuals and here: https://www.satcom.guru/2019/04/stab...and-range.html
There is also a subtle hint that probably shows why the pilots in a last desperate attempt did reengage the trim motors, and how the pilots were desperately trying to follow the AD and manually resetting the trim, which was most likely aerodynamically blocked:
After the cutout, there is a very slow, long, subtle nose-down movement of the fin according to the report. What do you do when the crank is blocked, instinctively? You're rattling it! And then in this phase it moves only a few hairs nose-down, but not a bit Nose-Up.
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.
This last attempt to implement the AD has now reset MCAS. And then comes design-wise (but is not in the FCOM or the AD, was never mentioned in training), while they still think about what to do next, after 5 s the final death blow of MCAS ...
The plane systems (MCAS and Trim) and the AD procedure just did not give them a fair chance IMHO.
An excellent overview over these 60 year old speed issues with the 737 trim system can be found in many old manuals and here: https://www.satcom.guru/2019/04/stab...and-range.html
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(From an ex hardware/software tech writer) - a comment about software rather than aeronautics. If the timeline story (CVR derived) in comparison to the FDR traces is accurate, here is something weird from the preliminary report's data nobody has commented on.
The third MCAS activation lasting 9 or so seconds starting at 05:40:41 did not alter stab pitch trim because the FO had just cut power to the stabilizer jackscrew motor. The report glibly notes that fact. But why did MCAS even try to activate, as if sitting there fat, dumb and stupid? Exactly what type of coding allows the FCC to attempt to command AND trim when both STAB TRIM switches are already set to CUTOUT? Seems the designed use case never anticipated this sequence.
So it appears that this bolted on chunk of MAX-only software was not monitoring real-time trim motor electrics. Hell no, you cannot do that - a loom change might be required and that would disturb the production line and possibly delay certification! Or better yet, a few lines of more rigorous code were required.
Way up in the thread at least 2 incredulous posters suggested, sarcastically I think, that an intern might have programmed MCAS_1? Makes you wonder.
The third MCAS activation lasting 9 or so seconds starting at 05:40:41 did not alter stab pitch trim because the FO had just cut power to the stabilizer jackscrew motor. The report glibly notes that fact. But why did MCAS even try to activate, as if sitting there fat, dumb and stupid? Exactly what type of coding allows the FCC to attempt to command AND trim when both STAB TRIM switches are already set to CUTOUT? Seems the designed use case never anticipated this sequence.
So it appears that this bolted on chunk of MAX-only software was not monitoring real-time trim motor electrics. Hell no, you cannot do that - a loom change might be required and that would disturb the production line and possibly delay certification! Or better yet, a few lines of more rigorous code were required.
Way up in the thread at least 2 incredulous posters suggested, sarcastically I think, that an intern might have programmed MCAS_1? Makes you wonder.
It is fairly obvious that the automated system should have disabled MCAS authority as soon as there was significant disagreement with the two AoA sensors. Blaming the pilots is not sufficient, the more fundamental defect is plainly a Boeing issue and seemingly inexcusable. I feel that the pilots needed to act within the first 15 or 20 seconds of stick shaker but failed to recognize the issue quickly enough. The question is how many crews would have acted quickly enough and why should they have to react at all? It is all so unnecessary.
It is suggested that Boeing provided the MCAS system to overcome approval considerations. However, it does not make sense to leave it to the pilots to disable MCAS when it could be handled automatically. Neither does it make any sense to disable electric trim completely in order to disable MCAS.
...Just touching the surface of the negligent design and certification issues...
DaveReidUK
I assume from your post that you understand what this gobbledygook means? Can you explain it in English?
"The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."
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What you're proposing is a hybrid system (disabling an input to a good system in case of a single failure on the other system) which will have its own consequences.
There is a solution, as has been implemented in FBW aircraft - if you are going to patch FBW onto a dinosaur, then its sensor suite must also be upgraded to meet those requirements and not rely on more patching to a grandfathered certification.
From what I`ve read ,the MCAS operates when flaps are `UP`...What is the flap limiting speed,and does the system(MCAS) depend on the flap lever position only...?
I used to fly C-130,which had power controls,but power to the rudderboost was limited when the flaps were UP,but full hydraulic power beyond 20 deg,primarily to prevent overstressing the fin at `high speed`,but cover the lower speed asymmetric case requiring more rudder...
However,if one was doing `tactical/fighter affiliation/more aggressive flying,one could `cheat` by pulling a c/b for the FLAP hydraulics,and then select the flap lever to 20 deg.This then gave the rudder full hyd.,but the flaps were still `UP`..
I would have thought that the immediate actions drill would have also stated to have reduced speed to perhaps below 300 kts..
I used to fly C-130,which had power controls,but power to the rudderboost was limited when the flaps were UP,but full hydraulic power beyond 20 deg,primarily to prevent overstressing the fin at `high speed`,but cover the lower speed asymmetric case requiring more rudder...
However,if one was doing `tactical/fighter affiliation/more aggressive flying,one could `cheat` by pulling a c/b for the FLAP hydraulics,and then select the flap lever to 20 deg.This then gave the rudder full hyd.,but the flaps were still `UP`..
I would have thought that the immediate actions drill would have also stated to have reduced speed to perhaps below 300 kts..
Gender Faculty Specialist
Chesty, we discussed this earlier, and you said you have flown the 737 with manual trim and it was no problem.
I’ve only tried this a few times, but found the manual trim to be pretty hard. A friend of mine got «Stab out of trim» enroute and diverted because he thought he had a jammed stab. This after he tried manual trim and found it so hard he concluded he had a jammed stab.
It now looks like manual trim is nearly impossible at higher speeds.
It puzzels me a bit that the stab can be trimmed so far it will bring the aircraft out of the pilot’s control. And then you can’t manually bring it back under control because the trim forces are too high.
How Boeing will solve this is beyond me. MCAS is a killer and if they restrict it it will affect the certification. In order to get rid of MCAS they have to redesign the aircraft.
IMHO the MAX will stay on ground for a long time.
My point was that anyone can turn a wheel regardless of hours (obviously if it's not prevented by aerodynamic load) so to suggest that the FO couldn't turn it because he had only 200 hours was and is total nonsense (and I know you didn't make that point).
DaveReidUK
I assume from your post that you understand what this gobbledygook means? Can you explain it in English?
"The increased safety provided by the Boeing design limits on the thumb switches (for out-of-trim dive characteristics) provides a compensating factor for the inability to use the thumb switches throughout the entire flight envelope."
I think that a rough translation is "when electric trim runs out, pray you have enough time, strength and altitude left to start winding ..."
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Is that what it is?...250 turns of the trim wheel from stop to stop? That info wasn't available anywhere in the AMM, the FCOM or even the FCTM. Like some, I wondered how many turns it was, so thanks.
The full range (from the AMM) of the stab is 17°. This range is not available to all controls, (electric, manual, wheel), as noted in this thread, but let us assume the available range is -1 AND to 16 ANU using the big wheel.
Now we can calculate turns and degrees of trim, (remembering the comments on the difficulty of turning the wheel under some circumstances).
250 turns / 17 degrees = 14.7 turns per degree, or,
17 degrees / 250 turns = 0.07° per turn.
If the thinking and the math is correct, we can see that there is a lot of work and time to manually modify the stab trim using the wheel. In fact, those who fly/flew the B727/B737 will recall just how fast the wheel goes around when electrically-trimming in normal flight, flaps-up; the white mark on the wheel is almost a blur...
PJ2
The full range (from the AMM) of the stab is 17°. This range is not available to all controls, (electric, manual, wheel), as noted in this thread, but let us assume the available range is -1 AND to 16 ANU using the big wheel.
Now we can calculate turns and degrees of trim, (remembering the comments on the difficulty of turning the wheel under some circumstances).
250 turns / 17 degrees = 14.7 turns per degree, or,
17 degrees / 250 turns = 0.07° per turn.
If the thinking and the math is correct, we can see that there is a lot of work and time to manually modify the stab trim using the wheel. In fact, those who fly/flew the B727/B737 will recall just how fast the wheel goes around when electrically-trimming in normal flight, flaps-up; the white mark on the wheel is almost a blur...
PJ2
1 stop wheel turning before you get way out of trim is the drill. But you have to notice. I note in the video posted here it took 10 seconds to disable STAB. Lion air struggled for 10 ?? minutes. In other words STAB is off so quickly that all these situations we speak of here don’t occur. And if they do, go to next step >>
2 old trick as mentioned earlier- off load stab by releasing back pressure for a few seconds allows you to trim ANU in any load situation . Both pilots both wheels with handles extended. Very quick. It’s the elevator loads against the STAB jackscrew that causes the high loads . But you have to know this and I think it’s not taught any more.
3 Stab is three times more powerful than elevators - they don’t ‘blow back’- just not designed to overcome STAB.
4 if you’ve turned off STAB ELECTRICS you can turn them on to enable ANU trim. Thumb switches. Then when back in green range - safe range- STAB OFF and trim manually.
5 But- and this all gets back to training- you have to know all this. Not look in manuals. It has to be in the core of your airplane skill base. Trained by the trainers. And if the trainers don’t have it ........
Summary. Are pilots new to 737 aware of the dangers posed by the stabiliser?
They do runaway stab, jammed stab and manual reversion during type rating training- at least did until recently! So they know how tough an animal the STAN can be but manageable.
MCAS
So. MCAS being sorted. Good thing. Does that leave us still with a much bigger problem? The elephant in the room! What’s going to happen next time an automated function badly misbehaves- and it will.
Y
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Having been on the jumpiest of a classic or NG (never been in a MAX), those trim wheels seemed to turn quite a lot even for very short bursts of trim input, so 250 is quite credible.