Confiture:
The airplane reached 9 deg of AoA when the alpha-protection threshold value was still at 8 deg.
Obviously the alpha-protection threshold value is dependent of the altitude and configuration.
AFAIK those values are nowhere in the Airbus documentation reserved to the pilot. They only appear in the different incident/accident reports.
Well one needs to exceed the alpha-protection threshold to trigger alpha-protect mode doesn't one?
The principle of alpha-protection is well documented though, and it is difficult (for a non-pilot) to see what practical use could be made of a knowledge of the actual numbers since as we all know, AoA is not displayed to the pilot.
Now, how do you call an "attenuation of pilot's controls that accompanies the alpha prot mode which could limit the ability to get more than 9 deg pitch in the time available for flare starting from 50 ft" if not a restriction ?
The very fact that I phrased it in the way I did shows that I accept there was a restriction. [comment on pitch rate limitation removed 26/03]
Let Sully pull another 2 deg of pitch to obtain the recommended attitude for ditching and benefit from it by decreasing his vertical speed at touchdown.
Agreed that if he could have pulled to another 2 deg he could have reduced his vertical speed, but the fuselage crushing loads have two components, one of which is speed/AoA dependent so it is not obvious he would have been significantly better off (if in fact you can be better off than a ditching where everyone gets out OK).
But I note that other pilots, presumably using different flare techniques, managed to achieve the desired low descent rates, which leads me to believe that the control attenuation was a limit on Sully's flare but may not be generally applicable.
Margin is already included, that's why alpha max is not set at alpha stall.
Can you please point me to a reference for that statement? It is not how I understood the system.