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Old 14th Nov 2018, 05:12
  #1142 (permalink)  
hans brinker
Join Date: Nov 2010
Location: Denver
Age: 52
Posts: 38
Originally Posted by silverstrata View Post

Ok, I did not know the Max has a new stall assistance system. As mentioned before, the STS normally trims down after take off, so it would be operating in the same manner as the new stall system. So again the tech log entry about STS appears incorrect.

And why did Boeing incorportate a stall assistance system that trims, instead of using a stick pusher? This seems to go against the normal rules for flying. You fly the aircraft with the control column, not the trimmer.

A stick-pusher acts on the control columm, to increase speed, and withdraws its influence instantaneously to allow you to recover from the dive. A stall trimmer will trim you down, but leave that nose-down pressure on and impede your recovery from the dive.

A stick pusher is flying the control column, in the normal manner; while a stall trimmer is flying the trimmer. Is this how the new stall system works? I cannot find details on-line.


The way I understand it from reading here:
On a normal flight you would expect the STS to trim ANU during acceleration as it is trying to keep the aircraft at the previous speed. The previous captain said the STS was trimming incorrectly, so different from normal, so AND. The MAX has a new MCAS system, that will trim AND if it senses a low speed situation. There were reports the AOA on the captain side was giving erroneous high AOA values, leading to stick shaker as well, if the MCAS used these faulty values it could have kept on trying to trim AND every time the pilots stopped using elevator trim (if the even tried to override the airplane trim inputs manually). This could have resulted in the stabilizer being full AND, and the elevators not having enough authority to keep the nose up. The aircraft trim input could be stopped by using the elevator trim or, more permanentely, by the cutout switches (apparently is has been confirmed this would stop the MCAS from trimming.

TLDR: I think the STS trim being wrong write up was "correct", because the STS will during acceleration trim ANU not AND.
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