Thread: Habsheim
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Old 16th Apr 2014, 08:57
  #789 (permalink)  
737Jock
 
Join Date: Jan 2008
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But the aircraft was flying *faster* than Valphamax throughout - the EFCS didn't have to "reach" anything, and there was no impediment to the aircraft reaching Alpha Max other than time.
You seem to try very hard not to understand me. That is what I said!
They never flew at Valphamax, they never commanded Valphamax until they were about to kiss the trees, evidenced by the lack of full backstick until the last 2 seconds before crash.

What seems to have made the response slower than it might have been was the significant deceleration with the stick half-back and thrust still at idle - then staying half-back until a few seconds after TOGA was commanded, because in that scenario HAP mode restricts pitch rate change to maintain stability and trajectory.
I think this is really far fetched and cannot be reliably be concluded, certainly not from the habsheim plots. And to draw this conclusion from the bechet plots is highly questionable.
They only applied a full aft input on the sidestick in the last 2 seconds. Just in those 2 seconds, loadfactors, engine thrust and wind were changing rapidly. This would lead me to simply think the flight control computers did not have enough time.

If you want to reach Valphamax, the simple matter of fact is that you have to decelerate significantly. If you do this with idle thrust and then smack on toga thrust, the change of force on the airframe will be much more significant then if you had for example 40% N1 on. Lets not forget the pitch-up effect from underslung engines that needs to be compensated for, which happened to really kick in when the sidestick reached full aft position (habsheim).
Combine that with a constantly changing altitude, and you see significant thrust changes and loadfactors.

In more stable conditions (bechet) the FCS will have less of a problem reaching Valphamax (on applying full backstick) as the required output is not constantly changing. P.is he clearly had the benefit of time.

I dont think it has anything to do with some sort of sluggishness of the flightcontrols that only happens after a prolonged time in HAP, it is just the system managing the changing forces as best as it can. Although its a computer it is still a reactive system.
A human certainly could not fly at Valphamax under those circumstances with any accuracy.

Last edited by 737Jock; 16th Apr 2014 at 09:52.
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