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Old 27th Nov 2018, 18:00
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Concours77
 
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Originally Posted by birdspeed
Concours77, as the stab seems to trim to full ND at a normal rate, I don’t think there is a mechanical failure of the stab jackscrew.
What perhaps happens is a breakout of the control yokes just before the dive. FDR shows a difference in the applied control force on the yokes. I believe when elevator breakout occurs there is sudden loss of elevator effectiveness. This would cause a sudden bunt over, with a wtf moment and the pilots stopped any sustained opposite trim.

what do you think?

“Switching”..... NOSE UP Trim was Lost, inhibited. There are two small spikes in the downward line, but obviously not significantly effective. Weak, transient or failed switch at the yoke? I noted the steady increase of ND Trim, so yes, the jackscrew was (remained) effective....

NU had lost its effect. Signal loss in that channel to the motor? Heat?

Loss (literally) of elevator? That is consistent with loss of all downward force on the Tailplane. Nothing left to slow TRIM ND? The problem with that is that mightn’t a “release” of Elevator reduce drag on ND (MCAS) TRIM? Showing an increase of rate ND?

(That’s backwards, the loss of Nose Up Elevator would reduce force on Tailplane trailing edge down, slowing the rate of ND TRIM).....

imo
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