Originally Posted by Ian W
447 however did not enter the stall in the classic straight and level gently slowing down manner. The aircraft was in a rapid climb to above its flight envelope and thrust ceiling converting kinetic energy to potential energy. There is no prestall buffet or normal handling effects if you pull into a hammer-head stall or tail slide this was not far short of that. The resultant loss of aerodynamic lift as the aircraft ballooned over the top with negative g, gave the THS algorithms something perhaps that had never been considered likely.
The aircraft entered the stall on a gently upward sloping flight path of 2.5 degrees, hardly a "hammer-head stall or tail slide". There was considerable pre-stall buffet and never negative g.
Once set up in the stable nose up stall the wrong side of the drag curve in TOGA with a descent speed that was almost as much as the forward speed, there might be insufficient aerodynamic pressure on the elevators even in the down position to get the THS to move. Therefore it would remain fully nose up until (or if) the aircraft responded and started nose down.
Movement of the THS is by hydraulic power and does not depend on "aerodynamic pressure on the elevators" nor on the aircraft going "nose down".