PPRuNe Forums - View Single Post - Pilot Commands TOGA; A320 lands anyway
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Old 31st May 2001, 22:55
  #29 (permalink)  
Flight Safety
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Heavens Gate, I generally agree with you. If the energy and height required are greater than the energy and height available, then there's nothing you can do except to try and achieve a minimum rate of descent and a flat attitude on impact. Stalling the aircraft in an attempt to recover from windshear is also not helpful, and AOA protection would theoretically be useful in preventing this. But I emphasize the word theoretically.

I also agree that this really has nothing to do with Airbus or any other manufacturer. This is really about an aircraft designed with a particularly unique feature called "Alpha Protection" that has "Alpha Floor" and "Alpha Max" modes.

Apparently during the simulator portion of this accident investigation, it must have been determined that the AOA was not calculated properly due to the sequence of updrafts, downdrafts, and changing airspeeds from gusts and "wind direction inversions" just prior to the flare. If the AOA was not calculated properly, then the "Alpha Protection" is of no help to the pilot, and in fact may hinder his ablility to recover the aircraft if sufficient height and energy ARE available for recovery. I think that's precisely what occurred here, and that's why the investigation has recommended modifying the software to give the pilots more direct control in the flare.

But this software mod poses some interesting questions. On the one hand I see this mod as perhaps partially negating the benefits of AOA protection. On the other hand, if the rapidly changing wind conditions that existed in this accident prevent the possibility of accurately and reliably calculating the AOA, then a switch to Direct Law would be the preferred solution. What I'm not clear on is whether this software mod will cause a reversion to Direct Law in all cases just prior to the flare, or only in cases where rapid changes in wind direction cross a threshold of AOA calculation "unpredictability", thus forcing a reversion to Direct Law in only those instances.

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Safe flying to you...

[This message has been edited by Flight Safety (edited 01 June 2001).]