Originally Posted by
JohnBurke
You understand neither the report, nor the aircraft, nor the system.
The control wheel nose-up trim attempt at 5:43:11 occurred as pilot-action. This is very significant, because at 5:40:35, nearly three minutes prior, the crew had already used the stab trim cutoff switches. Once the stab trim cutoff switches have been moved to the cutoff position, stab trim may not e re-engaged.
The recording of pilot electric trim input at 5:43:11, with subsequent increase from 2.1 to 2.3 units, is evidence that the crew re-engaged the pitch trim motors.
The pitch trim then moved nose down from 2.3 units to 1.0 unit. THIS WOULD NOT HAVE OCCURRED IF THE CREW HAD NOT RE-ESTABLISHED PITCH TRIM MOTOR CAPABILITY BY RESTORING THE POSITION OF THE STAB TRIM SWITCHES.
Read that again in case you didn't get it.
Once the stab trim motors have been cut off, the stab trim motor cutoff switches must NOT be restored. The crew restored them, thus enabling the trim to run away again.
At the same time, they continued to make the trim force problem WORSE by accelerating.
I am not exactly sure why you are arguing as I essentially said the same thing in my first post. They re-engaged the trim motors. I am assuming they kept accelerating and probably realized they could not maintain level flight in that configuration due to the control column pressure, and they could not move the trim wheel manually, again presumably because of the aerodynamic forces involved at that speed.
I am not sure where the disconnect is.
If we put aside whether they should or should not deviate from a procedure, whether they should or should not exceed Vmo, and everything else they may or may not have done right - at some point they found themselves with electric stab trim restored. Right or wrong, they did it. We can analyze and debate what they did right and wrong prior to that point, but lets put that aside, as it detracts from my main point - which is that after the electric trim was restored, at that point one would assume they would aggressively trim with the thumb switches (and in the process override MCAS), instead they barely did anything - two clicks at around 5:43:11 and 5:43:15. That in my mind is incredible. Then the MCAS commands nose down trim at what looks like 5:43:20 for about six seconds and shortly after they lose control.
Originally Posted by
JohnBurke
The captain made several requests of the F/O. Trim with me. Pitch with me. Pitch with me.
The crew didn't trim in the wrong direction. The issue of a "feedback loop" is irrelevant. The controls were heavy nose down, due to an out of trim condition. They made an attempt to restore it, with minor success, but the let the trim run nose down again. They attempted to retrim, cut it off, and would have been required to maintain back pressure based on an out of trim condition, but it was manageable and flyable at that point. Only two things could have made it worse: re-engage the stab trim motors, and increase airspeed.
I agree they did not trim in the wrong direction, but they did not trim much at all to relieve the pressure. This is before they cut off the trim. This is exactly where the feedback loop is relevant.
By the way, when they cut off the stab trim motors, they were so out of trim that it is not a given, based on what we know, that the plane was flyable, no matter the speed. You can hold the pressure for so long until your muscles give out.