Originally Posted by
HazelNuts39
Sensor validation;
Does the report say that airspeed fell below stall speed? IIRC it only stated that airspeed fell below VLS (lowest selectable speed).
The report explicitly states that overspeed protection was not invoked.
Rhetorical question I guess but altitude also rose above 'the maximum cruising level displayed on the Flight Management and Guidance System (FMGS)' = FL360+1000ft. So I believe the aircraft was below a speed where it could maintain steady level flight which is one definition of 'stall speed', recovery required 'flying the ballistic trajectory' keeping the nose pointing the right direction to avoid an aerodynamic stall, which was successfully received in the A340.
Capture of alpha-prot means that the FCS maintains an AoA greater than required for level flight, hence loadfactor>1, hence vertical acceleration, increasing v/s and FPA. Since pitch = FPA + AoA, increasing FPA at constant AoA=alphaprot means increasing pitch. Agree that turbulence 'noise' gets into the act too.
EDIT:: I suppose alpha-prot is tied to alpha-max which decreases with increasing Mach. So yes, I would expect that alpha-prot increases with decreasing airspeed, but consider that is a second-order effect. The protection will still keep the airplane a comfortable AoA margin away from the stall, because stall AoA increases also.
My calcs give peak FPA around 8 degrees, so it does all add up. Interesting thought exercise - what would have happened if pilot didn't recover Normal control?