Airbus pitch trim
I get the idea that many real pilots here (I am not one) do not understand the Airbus pitch trim. As far as I can see it's not in any sense Trim as we know it Jim.
As I understand it:-
With autopilot off and hands-off the stick in Normal and Alternate Laws the aircraft maintains constant g (hence absent other inputs - pitch attitude). As I understand it the crew of AF447 (and indeed any AB not in direct law) could have wound the pitch trim wheel as much as they liked and as long as the elevator did not run out of travel no aircraft pitch changes would have occured. The computer would have matched the manual THS movements with elevator movements to exactly compensate so that aircraft g (pitch) was maintained.
The Airbus auto-trim merely seeks to keep an adequate range of elevator authority available (zero degrees of elevator deflection?) - however with a long time constant (delay if you like) so that it does not try to follow every little twitch of the stick/elevator. In Normal and Alternate Laws it has *no* influence on aircraft pitch while there remains elevator movement in the required direction.
So:- the THS and auto trim had NO BEARING AT ALL on this incident. Nil, null, zip, nada.
I will allow that perhaps when in the deep stall at extreme AoA (60 deg was it?), certain THS/elevator combinations may have been advantageous but that is strictly in Chuck Yeager territory and in any case no serious attempt was made to get the nose down so artful trim twiddling was never going to be considered by this or probably any other crew.
Of course all is not sunshine and roses. In direct law the pilot must ensure that the THS is positioned manually so as to allow adequate pitch authority. The exact same issue however occurs on Boeings too and Boeings too have crashed as a result. Airbus knockers can just therefore put their toys back in the pram forthwith:-) The issue of extreme THS "trim" and subsequent lack of needed pitch authority in rare circumstances appears to me to be an industry wide problem. It can occur in Boeings on autopilot disconnection and in AB on reversion to Direct Law. The burden of being in an unusual attitude and needing to use manual trim to get adequate pitch authority to recover is surely pushing at the boundaries of The Average Airline Pilot?