Originally Posted by
737 Driver
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.
What do you make of this from ET:
05:40:27 - the Captain advised the First-Officer to trim up with him
Bearing in mind preceding it is an ineffective (in timing and duration compared to 1st MCAS input) period of manual ANU trim, and following it is a period of manual trim that both interrupts the 2nd MCAS input, is constant/continuous and reverses it (but doesn't reverse the first MCAS input).
It sounds (to this non-pilot engineering type) awfully like the Captain's left thumb (or it's switch) does not have the Captain's confidence, and not at all like he has just not "chosen to use it".
Or, put another way, under what circumstances as a 737 driver would you ask your co-driver to "trim up (or down) with you"? If the answer is "don't know any circumstances " or "would never do that", then WTF was going on in the ET cockpit to trigger that request?