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Old 1st Nov 2011, 23:18
  #1575 (permalink)  
DozyWannabe
 
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@Franzl

You're comparing apples with oranges here, or to be more literal, comparing the conventional, or "way we used to do it" method with the method on the FBW Airbus series, which is intended to be used in a completely different way - unless something has gone so seriously wrong with the aircraft that a drop to Direct Law is necesssary.

The FCPCs may command the physical movements, but it is the pilot that commands the FCPCs in manual flight. As the speed decays under Normal Law, the elevator/trim effect is limited by the AoA protections. Under all load factor laws (i.e everything above Direct) - even without protections, as the speed decays the control mode gradually transfers from "G" command to pitch command, meaning that the autotrim will not trim to stall with stick neutral due to decaying speed alone.

In this case the autotrim was commanded to move as it did to support the demands on the elevators made by the PF, who was - possibly for reasons we will never know - holding the thing between 50-100% back for the majority of the accident sequence. It was for this reason as well that the speed decayed, so in effect both the pitch and airspeed factors of the extreme angle of attack leading to and during the stall sequence were because of the consistent back-pressure on the stick, and for no other reason that I can see.

Last edited by DozyWannabe; 1st Nov 2011 at 23:48.
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