Use of Sidestick (continued)
Quote from Linktrained:
From the threads that I have read inly a few mm of movement would cause the THS to try to compensate by increasing from the initial cruising figure of 3 or 4 NU.
I don’t think much would happen to the THS during the initial rotation from level flight, as it would have required little up-elevator to enter the climb. Once the 7000ft/min had been achieved, the trajectory would be maintained by the EFCS even with no back-stick. As the speed started to drop, more up-elevator would need to be introduced by the EFCS to maintain 1g, and it would then start to trim the THS a bit to retain full elevator authority. Once the aircraft got on to the back end of the drag curve, however, this process would proceed rapidly.
In fact the PF arrested most of the climb at FL375, by “nose down control inputs...”, so some down-elevator may have been used briefly by the EFCS at this point. This partial recovery was to be short-lived, as the PF seems to have reacted to a stall warning by selecting TOGA (causing a pitch-up) and resuming “nose-up inputs”. Resuming the climb at that point, on the wrong side of the drag curve, was when the EFCS had to start using up-elevator and nose-up trim (THS) in earnest, in order to try and maintain the trajectory it thought the PF wanted.
Quote:
“It has also been suggested that the PF may have inadvertently gripped the SS with his fingers gently, (more strongly than with his whole hand ?). C
Rather the reverse, in my opinion. In Normal and Alternate laws, the best way to avoid over-controlling with the sidestick is to make brief inputs, in between which you do not touch the stick. The exceptions are rotation on take-off, and the landing flare. The inputs are best made with fingers and thumb only. If you keep the stick permanently in the palm of your hand, as some do, it’s difficult not to move it accidentally − particularly in turbulence.
But this aircraft was degraded to ALT 2 law: a combination of Direct law for roll (stick-to-aileron/spoiler) and Alternate law for pitch, the latter without any high-AoA protection.
In trying to cope with the roll-control problems described (but not yet explained) by the BEA, it is almost inevitable that the PF was making continuous roll inputs, and probably had the stick in the palm of his hand. This would have made accurate pitch control difficult.