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Old 28th Apr 2019, 17:06
  #4509 (permalink)  
MurphyWasRight
 
Join Date: May 2010
Location: Boston
Age: 69
Posts: 440
Originally Posted by 737 Driver View Post
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That being said, except for your initial takeoff setting, you don't operate the trim by reference to the index. You operate by feel. If you are holding in any sustained control pressures around any axis (pitch, roll, yaw), you would normally trim away those pressures until the controls were neutral. I say "normally" because there are some flying techniques that involve leaving in some control pressures in certain situations, but that is beyond the scope of this discussion. So in reality, you could tape over the index, and as long as you trimmed out the control pressures, then maintaining aircraft control should pose no problem. Again, this is assuming that you do not have an aircraft that is loaded outside its C.G. envelope.
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Thanks for confirming my impression that the crew would not be referencing the absolute trim numbers.
One puzzling feature of the ET (and to some extent LionAir) traces is the failure to fully trim after MCAS inputs.

I wonder if part of this could be due to a 'muscle memory" illusion that after having to pull with a lot of force to counteract the ND trim the relaxed force after the partial re-trim felt less out of trim than actual situation.

The report does not have a collum force trace, just position. Can anyone hazard a guess as to what force might have been required.






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