Ethiopian airliner down in Africa
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Well, it was cut out by the pilots. They had the option to re-trim the aircraft using electric trim before hitting the cutout. I believe this "option" occurred to the crew close to the end when they re-enabled the electric trim but their attempts to re-trim with the column switches was unsuccessful (either through pilot error or malfunction). Had they done this earlier, right before they activated the STAB TRIM CUTOUT, they would have been in a very similar situation to the pre-accident LionAir flight -- a trimmed, stable aircraft, with AP disconnected, and stick shaker going off on PF side.
A couple of points, one made a few posts back.
Firstly, it seems the lessons from the pre-accident LionAir flight and the subsequent accident flight were not learned well enough. As far as we know, the MCAS issue that occurs as a result of PF-side erroneous AoA signal is completely survivable by the crew taking the correct course of action. It seems that the correct course of action wasn't spelled out clearly enough for the ET302 crew, or it was not drummed into them methodically enough. That's a further failing of the airline industry following the initial accident.
Secondly, it has been remarked here on numerous occasions that it is extremely rare for a transport crew to encounter a stick shaker alert. Had the pre-accident LionAir B737 been grounded following that flight, and had the ET302 crew leveled the aircraft before disabling the electric trim and subsequently managed to land, that would have been two flights with PF-side stick shaker active for the duration of those flights. That would suggest a systemic issue, but it does not appear to have received the same attention as the MCAS response.
A couple of points, one made a few posts back.
Firstly, it seems the lessons from the pre-accident LionAir flight and the subsequent accident flight were not learned well enough. As far as we know, the MCAS issue that occurs as a result of PF-side erroneous AoA signal is completely survivable by the crew taking the correct course of action. It seems that the correct course of action wasn't spelled out clearly enough for the ET302 crew, or it was not drummed into them methodically enough. That's a further failing of the airline industry following the initial accident.
Secondly, it has been remarked here on numerous occasions that it is extremely rare for a transport crew to encounter a stick shaker alert. Had the pre-accident LionAir B737 been grounded following that flight, and had the ET302 crew leveled the aircraft before disabling the electric trim and subsequently managed to land, that would have been two flights with PF-side stick shaker active for the duration of those flights. That would suggest a systemic issue, but it does not appear to have received the same attention as the MCAS response.
With regard to lessons learnt from Lionair: an Emergency AD is a quite ultimate document. If that is not well thought through and written by lawyers there is not much room left.
But they elected to start a 30 degrees bank manual flown turn at 340 kIAS without the ability to pull or trim ANU.
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Is that sure ? Can the electric trim work despite aerodynamic forces in all situations (overspeed, trim full nose down) ? Does it even work in more situations than manual trim ?
At ultra high speed the stab can only be trimmed after releasing up-elevator. This is because of loading to the stab mechanism.
This is the reason for elevator release during upset training.
But if you are at tree top height you can’t do that.
So trim, Manual or Electric is, as the man said, not possible under certain conditions - and those were the conditions encountered here.
Is it primarily speed dependent, stabilizer positon-dependent, yoke dependent, or a combination of all 3?
Dave and others,
At ultra high speed the stab can only be trimmed after releasing up-elevator. This is because of loading to the stab mechanism.
This is the reason for elevator release during upset training.
But if you are at tree top height you can’t do that.
So trim, Manual or Electric is, as the man said, not possible under certain conditions - and those were the conditions encountered here.
This is the reason for elevator release during upset training.
But if you are at tree top height you can’t do that.
So trim, Manual or Electric is, as the man said, not possible under certain conditions - and those were the conditions encountered here.
With respect, we don't have any evidence of that being a factor here - there are no points in the FDR trace that show trim input without corresponding stab movement. Even the last two very brief ANU inputs appear to have had an effect, although the stab only moved by a fraction of a degree before the the inputs ceased.
Last edited by DaveReidUK; 9th Apr 2019 at 06:45. Reason: Edited to answer Bill's point too
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Well, [electrical trim] was cut out by the pilots. They had the option to re-trim the aircraft using electric trim before hitting the cutout..
Yes, it is sure. We know this because MCAS drives the stabilizer using the electric motor, and MCAS dialed in another batch of nose-down trim AFTER the pilots re-enabled electric trim and blipped the column switches (which had negligible affect on stabilizer position). Therefore, the electric trim motor was able to drive the stabilizer with the stabilizer in its final position prior to stab trim cutout activation. As such, I think it is fair to conclude that the pilots decided against trimming back to neutral before activating the cutout (or were cognitively overwhelmed at the time and did not think to do so).
Yes, it is sure. We know this because MCAS drives the stabilizer using the electric motor, and MCAS dialed in another batch of nose-down trim AFTER the pilots re-enabled electric trim and blipped the column switches (which had negligible affect on stabilizer position). Therefore, the electric trim motor was able to drive the stabilizer with the stabilizer in its final position prior to stab trim cutout activation. As such, I think it is fair to conclude that the pilots decided against trimming back to neutral before activating the cutout (or were cognitively overwhelmed at the time and did not think to do so).
Last edited by gmx; 9th Apr 2019 at 06:49. Reason: provide additional context
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Therefore, the electric trim motor was able to drive the stabilizer with the stabilizer in its final position
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It was able to move trim nose up, although ever so slightly. The movement is there is you zoom into FDR trace. I suppose it trimmed slower against the load than along with the load, but some nose-up capability was there. I presume the motor has some overheat/overload protection. Does anyone know the reset criteria, if any, of the motor going back to operation after whatever protection is tripped?
Well, [electrical trim] was cut out by the pilots. They had the option to re-trim the aircraft using electric trim before hitting the cutout..
Yes, it is sure. We know this because MCAS drives the stabilizer using the electric motor, and MCAS dialed in another batch of nose-down trim AFTER the pilots re-enabled electric trim and blipped the column switches (which had negligible affect on stabilizer position).
Yes, it is sure. We know this because MCAS drives the stabilizer using the electric motor, and MCAS dialed in another batch of nose-down trim AFTER the pilots re-enabled electric trim and blipped the column switches (which had negligible affect on stabilizer position).
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Oh, just one question:
People claim that the manual trim may not be operable in certain flight conditions while the electric trim motor is more powerful.
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?
People claim that the manual trim may not be operable in certain flight conditions while the electric trim motor is more powerful.
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?
I think all the check lists that say something about manually trimming with the wheel and/or hold/grasp the wheels will need to be rewritten.
And then, what will the new procedure for trimming with cut out switches set to cut out be? How to stop trim runaway when wheels supposedly cant be stopped by grabbing them?
I think there hides a lot of problems for Boeing in the manual trim wheel system.
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Probably not. What would be the point? It is a vital pitch control surface. Why would you intentionally make it unavailable because it might fail at some later time? It is better to have it available, and damage it, rather than to make it unavailable and potentially lose the entire aircraft.
I don't think there will be more than an overcurrent circuit breaker, but that is mostly to protect the wiring.
Bernd
I don't think there will be more than an overcurrent circuit breaker, but that is mostly to protect the wiring.
Bernd
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We can't see the wood for the trees.
This one was just a faulty sensor(not even UAS)..
If MCAS would activate alone,any crew would simply
counter-trim and cut off its electrical supply without much thought.
But combine it with a "confusing" UAS scenario and shakers and
warnings and bingo..you get a smoking hole in the ground...
Pilots have to be trained more on these UAS scenarios before they kill again.
Aeroperu,birgenAF447 and the 2 MAXs,and others.....
This one was just a faulty sensor(not even UAS)..
If MCAS would activate alone,any crew would simply
counter-trim and cut off its electrical supply without much thought.
But combine it with a "confusing" UAS scenario and shakers and
warnings and bingo..you get a smoking hole in the ground...
Pilots have to be trained more on these UAS scenarios before they kill again.
Aeroperu,birgenAF447 and the 2 MAXs,and others.....
Today, the artificial manual feedback stuff is degrading the primary flight control ergonomics, and distracting and stressing the crew. Instead of providing clues, it may even make pilots loose the trim switch with their thumb as a result of a hydraulically shaken column with massive artificial pull on top.
MCAS could then be seen as the ultimate perversion of that concept. Abuse a secondary flight control to create artificial stick force, give it a delay of 5 s so the pilot will not intuitively get the message, and give it so much authority, that it effectively overrides the primary control.
2 ct
Last edited by spornrad; 9th Apr 2019 at 12:52.
Oh, just one question:
People claim that the manual trim may not be operable in certain flight conditions while the electric trim motor is more powerful.
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?
People claim that the manual trim may not be operable in certain flight conditions while the electric trim motor is more powerful.
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?
Once the wheel is held, you are not fighting against the electric trim motor, which is disabled if resistance is detected at the cable drum.
I never tried ( in the sim! ) grabbing and trying to hold the trim wheel during a runaway stab. Not sure it was possible without burning my hand or losing some fingers !
Was it possible?
Sorry, DR s post was being written as I was typing !
However, anyone actually have any first hand ( no pun intended ) experience of doing it ?
Was it possible?
Sorry, DR s post was being written as I was typing !
However, anyone actually have any first hand ( no pun intended ) experience of doing it ?
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People claim that the manual trim may not be operable in certain flight conditions while the electric trim motor is more powerful.
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?
On the other hand the manual states that in case CUTOUT does not work, one should grasp and hold the wheel (?against the motor?). Did I miss something?
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Also DaveReid's post above about motors stopping if they meet resistance.
I can't see any reason for the 'blips' in nose up trim other than pilot trying it and it not working/ not appearing to work. Why else would you release the switch when it's the one thing you're focussing on, the one thing you know you need?
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The 737 manuals says that incase of extreme nose-down out-of-trim, one should INCREASE speed to relieve elevator load and permit manual trimming.
That's insane !
(see https://www.satcom.guru/2019/04/what...-on-et302.html)
That's insane !
(see https://www.satcom.guru/2019/04/what...-on-et302.html)
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so why not have a separate cutout switch just for MCAS, keep the other two to cutout electric trim. But the new MCAS cutout switch would leave electric trim available.
I'm also unclear since the certification requirement was for force feedback on the stick during certain stall regimes why Boeing didn't just use some kind of motor/pneumatic on the stick to give this force, rather than connecting MCAS to control surfaces! Seems overkill, no pun intended. I mean the stick shaker no doubt uses a motor to shake the stick, it doesn't shake the ailerons in order to make the stick shake!
G
I'm also unclear since the certification requirement was for force feedback on the stick during certain stall regimes why Boeing didn't just use some kind of motor/pneumatic on the stick to give this force, rather than connecting MCAS to control surfaces! Seems overkill, no pun intended. I mean the stick shaker no doubt uses a motor to shake the stick, it doesn't shake the ailerons in order to make the stick shake!
G
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What I can't see is why they did not continue as many times as needed to trim back
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so why not have a separate cutout switch just for MCAS, keep the other two to cutout electric trim. But the new MCAS cutout switch would leave electric trim available.
I'm also unclear since the certification requirement was for force feedback on the stick during certain stall regimes why Boeing didn't just use some kind of motor/pneumatic on the stick to give this force, rather than connecting MCAS to control surfaces! Seems overkill, no pun intended. I mean the stick shaker no doubt uses a motor to shake the stick, it doesn't shake the ailerons in order to make the stick shake!
G
I'm also unclear since the certification requirement was for force feedback on the stick during certain stall regimes why Boeing didn't just use some kind of motor/pneumatic on the stick to give this force, rather than connecting MCAS to control surfaces! Seems overkill, no pun intended. I mean the stick shaker no doubt uses a motor to shake the stick, it doesn't shake the ailerons in order to make the stick shake!
G