Albino, #3008, further to the post
Ethiopian airliner down in Africa
and EASA text via
Boeing advice on "aerodynamically relieving airloads" using manual stabilizer trim there could be questions about the validity of the AD procedure, at least if it was evaluated in the abnormal conditons or only in theory.
Also see the video (via
SteinerN)
https://www.youtube.com/watch?v=EzgBft-79U8&feature=youtu.be
Whilst it appears easier to set nose down trim, it is less so to recover back to a trimmed condition. The nose down direction might be aided by the aerodynamic forces, whilst nose up the trim wheel has to overcome them.
Also, MCAS could run the trim nose down after flap retraction - lower stab trim loads, but if speed increases due to descending flight, then back trim at a higher speed is less achievable, having to overcome much higher stab trim loads.
This is a dynamic, escalating situation. And for those following the ‘40secs time to react’ theme, consider that recognition might take two MCAS cycles 10sec trim, 5 sec pause / back trim, 15 x 2 = 30 sec, only leaves 10secs for action - select trim inhibit, then apply back trim wheel. See the video, move seat back, pull the handle out, then wind - how much, how long, if able.