Hi predictorM9,
Originally Posted by predictorM9
First: how can the angle of attack can be that high (above 35 degrees)? Is there enough authority from the elevators or THS to maintain such a high angle?
Once stalled, pitch reached about 16 degrees, but AOA increased to above 60 degrees (about 61 at impact time). This change is due to the loss of horizontal speed, not to the THS or elevators position which only maintained the nose up attitude and killed most of the remaining airspeed due to added drag.
Originally Posted by predictorM9
Second: was this stall recoverable at all? If the AOA is that high, shouldn't the elevators be in the wake of the wing (and thus be useless)? Is this some kind of stable stall configuration?
Who know exactly what kind of recovery was attempted? Nonetheless, it seems that some control (roll, pitch) could still be applied with some effects once stalled. We'll see that in detail when more DFDR data would be released.
Originally Posted by predictorM9
Third: How could the captain maintain an almost zero roll (+- a few degrees) in such a stall? I have stalled before in gliders (I know this is not the same size weight altitude etc so it does not fully), and they tend to roll heavily on one side or another (it is very difficult to keep the wings level). I understand the BEA report on the 40 degrees roll oscillations when the stall started (which is for me consistent with a stall), but I don't understand why these large oscillations didn't persist
Oscillations where registered before the stall and there isn't that much info about the later phase once she was effectively stalled, beside indications that the roll tendency was stabilized (likely meaning that ailerons imputs were still effective). The stall warning (SW) start well before entering a stall and it will even start earlier once an Alternate Law is triggered (due to the safe flight enveloppe reduction). Same about an overspeed warning (if airspeed was still computed) which would be reduced from Mach .86 to Mach .82. Despite the early SW (possibly due to pilot imputs or turbulences, hence g-induced in relation to AOA and Mach), she climbed 3,000 ft before effectively beginning to stall.
Originally Posted by predictorM9
Fourth: why did the THS changed its position from +3 to +13 degrees at all? After all, wasn't the autotrim disconnected with the switch to alternate law? How can the computers give up because of lack of data, and still trim the plane (and using what information?)
Alternate Law do not disable auto-trimming in manual pitch as it is only g-load related; consequently, it will follow any pilot pitch imput until an abnormal condition will be declared. On the other hand, FMGECs (flight computers used by autopilot) are not active anymore once ALT2 is triggered due to an unreliable airspeed situation: AP can not be re-engaged until this situation would be cleared (which imply that two ADRs must be valid following their logic).