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Old 17th Nov 2018, 22:44
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CurtainTwitcher
 
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Originally Posted by MickG0105
If the trim system senses that the AoA is already at or aboveabove stickshaker AoA will it recognise nose up trim commands using the main electric trim? (ie will it allow the aircraft to be trimmed further into the 'perceived' stall?)
Good insights MickG0105, good addition to the knowledge base.

My understanding is that manual electric trim overrides the Speed Trim System (STS) for 5 seconds, ie if a manual electric trim input is added every 4.9 seconds, STS will not apply nose down trip at high AoA. However as you correctly note, the Elevator forces to hold this high AoA will increase dramatically due to the EFS operation. Pushing forward will feel easy, any back pressure will be significantly more difficult. This protection is another subtle way the system is saying "do you really want to keep pitching nose up", together with the other clues stick shaker and the "stall stall stall" callouts added after the Turkish accident IIRC.

The MCAS however, appears operate at high AoA unless the stab trim switches are in the cutout position. These switch are never touched in normal operation.

Here is a recent stall training video, I believe it may be the MAX. Unfortunately, the trim wheel is difficult to see, and it's not clear if the PF or STS/MCAS is trimming.

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