Originally Posted by
CONF iture
So according to Bechet the airplane has no issue going to alpha max but then, what do you make of the Airbus statement that "the flight protection system operated perfectly and prevented the aircraft from crashing nose first" ?
In addition to HN39's remarks, I should add that "operating perfectly" in this context seems to refer to the fact that it operated as designed - and based on the analysis both of the report and the work done on this thread, that looks like a reasonably accurate statement.
What Bechet seems to have proved (and others here have explained how and why), is that the aircraft will attain Alpha Max as long as speed is sufficient, but the time taken to do so depends on the flight conditions and the mode. Specifically, the time taken to achieve it will be longer if the command (i.e. full back-stick) is given with the aircraft already in HAP mode and decelerating than it will if the aircraft is in pitch command mode when the command is given.
From a systems perspective this makes sense as, when presented with a decelerating aircraft, HAP mode has to constrain rate of movement in the pitch axis (and elsewhere) in order to fulfil the part of its design brief that demands flightpath stability and trajectory be paramount. Pitch command mode is obviously free of those constraints because airspeed deltas are immaterial if pitch (as opposed to AoA) is what's being commanded by the stick.
As to what impact the earlier increase in AoA might have made in that situation - well, we can only speculate. But my speculation based on reading of the graphs (aided immeasurably by other posters' explanations) definitely indicates that there would still have been some impact with the trees, and at that point there are just too many variables involved (particularly with regard to what part of the aircraft hit the trees, at what angle and what damage that would cause) to make even an educated guess. That said, based on the photographic evidence, I do think that the actual path of the aircraft caused the main gear and later the main spar to absorb more of the impact force from the trees, lessening the subsequent forces on the more fragile empennage and tailcone.