Originally Posted by
Chris Scott
Even a neutral (in pitch) stick would have resulted in full up-elevator, because the FBW would have still been trying to achieve (maintain) 1G, and the THS seems to have reached full nose-up trim (13NU) at around the apogee-point. Normally, Pitch-Alternate has a stall-protection function, based on AoA. But the AoA readings had been ruled invalid earlier because of the (false) low-airspeed data.
Although it was inevitably unsuccessful in maintaining 1G, and the aircraft's trajectory had become semi-ballistic, the system would have tried its best. In so doing, it would have selected full up-elevator. It no longer had recourse to the THS, which had reached full-travel.
Hi Chris,
I still find it hard to believe that given the amount of thought put into systems degradation upon loss of air data the "G-loading" system would still be in effect (after all, loss of air data will disconnect the FMC because it can no longer function reliably - I find it hard to believe they'd still have the FCU systems trying to work with spurious data). We'd need someone who worked on the system directly to clarify though, as I have no data. On the other thread we discussed the behaviour of the control laws as speed decays, where "stick-neutral" gradually transitions from "G-loading" to "zero pitch". There's also the BEA note which seems to be pretty sure that the PF was commanding a lot of nose-up.