Originally Posted by
A-FLOOR
With regards to Airbus vs. Boeing: the Airbus overspeed mode was commanding an increase in pitch through the flight directors, which was followed religiously at least until the aircraft reached its apogee at 38000ft. This continuous backpressure on the stick caused the THS to trim all the way up, leading to the deep stall.
Hmm, I'm afraid I'm not sure to which case you are referring?
In case of the A340 Zoom Climb it was overspeed protection that send the aircraft into a climb but it did not stall. AoA protection law kicked in and kept it at Alpha_Prot. No stall here, and no alternate law either.
If you are referring to AF447, there was no overspeed event, it was in alternate law 2 due to the ADIRU's signalling Unareliable airspeed (Icing of pitots) and it was sustained NU commands by the manually flying PF that caused the THS to finally support his efforts and go to a significant NU Trim setting. This combined with further mainly NU commands on the sidestick kept it in the stall.
Alpha_Max is a HARD protection which cannot be overriden as long as it's active (not the case in AF447 due to Alt2). High speed protection might win against Alpha_Prot but not against Alpha_Max
It is not THAT easy to fool the Airbus protections. That takes much more finesse and or bad luck (stuck AoA vanes in Perpignan).
@flyburg: Apologies for also taking part in the AF447 thread hijacking ;-)