BPalmer
My own A330 simulator trials of recovery after the stab trim was full nose up and the stall fully developed was that a prolonged nose down input did help—but only initially. However, as the angle of attack reduced and the speed increased, apparently the full nose up stab was more than the elevator could overcome and the airplane pitched up regardless of the nose-down stick position.
It's not clear if the autopitch trim was operational with questionable airspeed inputs, but despite high bank angles in an attempt to keep the nose low, recovery was not achieved until I reduced the stab trim manually. Once trim was reduced manually, pitch control resumed and recovery was possible.
First I'm cautious concerning the extent of reality of present flight sims concerning stall behaviour and reaction of the sim on flight control inputs in this untested flight regime.
But looking from a logical point, why should the THS trim start running nose down right away after applying SS nose down?
The position of the SS commands a loadfactor (g) demand, not a pitch demand. With SS neutral the value is known to be 1 g. SS Nose down demands less than 1 g, SS nose up demands more than 1 g. At low speeds the command is a pitch rate change.
AFAIK we still do not know, what the preset rates for those changes are per unit SS deflection, and how the speed changes the preset gains. In case of lost speeds, what value of speed is used by the FBW system to transfer a SS command to the appropriate elevator deflection? And does it change again when the speeds are valid again? Was the FBW system using low speed gains during the stall, high speed gains or preset gains, did the SS stick command a loadfactor or a pitchrate change during stall, or was it a mix with changing gains?
Looking at the FDR and the simulation video i would assume the result was more loadfactor than pitch rate driven. Look at the g values during the stall, due to the increasing sinkrate the value was less than one g most of the time, despite the full nose up elevators and despite the nose up driving THS trim. Both inputs could not arrest the descent and thus could not deliver 1 g or more with full deflection.
SS nose down would command a value of less than one g, or if low speed gains would be used a pitchrate change to nose down. I am pretty sure that the system is set up very sensible for nose down inputs to not spill coffee and bisquits all over the place during normal operation, and it would not know that the aircraft is stalled and therefore a quick change is necessary. As the loadfactor was already below 1 g most of the time, small elevator deflection to less than full nose up elevator would be sufficient to decrease the loadfactor within the allowed gains and values. That's what happened when the SS was kept forward and the elevators went from full nose up to about 1/2 nose up. The THS trim would only react with a Nose down travel to remove a prolonged nose down elevator position, which never happened. It would happen in the end if the SS is held down long enough, but imho that time was very quickly running out.
To expedite the process of reducing the AOA in the available time would only be to use manual nose down THS trim, thus avoiding the comfort gains of the FBW system. How cautious this has to be done in order not to overstress the airframe in the low g or even negative g region i dont't know.