Originally Posted by
safetypee
737Driver, Matt48,
‘…
evidence to suggest that the electric motor could stall under the loads …’
This may depend on the direction of applied load. MCAS ‘nose down’ could be easier than a resorting ‘nose up’ crew trim switch input. Similar problems for manual trim wheel, particularly if the elevator is deflected to demand aircraft nose up.
Also see the discussions about deliberate electric trim inhibition -
https://www.satcom.guru/2019/04/what...-on-et302.html diagram of electric trim limit. Was MCAS wired through this restriction or not ?
The basic point was identified in the EASA certification query, which was answered as the alternative trim wheel input would be available
Again, no evidence from either of these accidents or from historical data that the electric stab trim motor could stall under load. The matter of the electric trim inhibition discussed in the link above is a completely separate issue. That inhibition prevents main electric trimming (pilot actuated)
into a certain region of forward trim, but it
does not prevent the use of electric trim to move out of that region.
All this being said, one of the causal factors of these accidents is that the pilots let the aircraft so far out of trim in the first place. It is absolutely clear from the data (both ET302, and both LA610 flights) that the pilot actuated stab trim stopped and reversed the MCAS trim input every time it was used. As powerful as MCAS was, it could not overcome the strength inherent in the Captain's left thumb - if he had chosen to use it.