Originally Posted by
Smilin_Ed
Dozy: I agree that they didn't factor the trim system into their troubleshooting.
Because the trim system (following the sidestick input) held the nose up and kept the Angle of Attack in the stall range, the aircraft continued its plunge to the ocean.
Wrong. Look at the timeline A33Zab (I think) posted a while back (post 379 - found it) - the elevators alone took them up to 15+deg pitch and right into stall, the trim followed later (as it is supposed to).
Had the auto trim done
nothing, as far as I can see they would have stayed stalled all the way down from the elevator input.
Why didn't one of the pilots do something about that? It seems apparent that they didn't even notice it.
Why didn't they notice it? It wasn't in their scan because they apparently were trained not to touch the pitch trim wheel(s) since pitch trim is always automatic and since it's automatic, why would you care?
If trim is manual, why on earth would you trim nose-down and hold the stick hard back ?
If they had noticed the trim they would have noticed it was doing as asked - they were asking for full nose-up.
I think autotrim is a complete red-herring and a diversion form the real question (in terms of recovery from stall, not why they ended up there) which is why did PF pull stick hard back through 30s or more of stall warning. I have no answer to that, except to say that in the history of aviation accidents, he is not the only one, and we can't ask any of them "why".
I continue to believe that autotrim should disconnect along with the autopilot. That way, there is no doubt who is in control. That is a pilot's perspective.
Yet doing it that way has killed or nearly killed a lot of people already (schipol, perpignan, bournemouth...) - tyring to recover when the autos have trimmed full up (for whatever reason) and then stick forward doesn't overrider the trim. Based on that accident and incident history, pilots tyring to recover a (approach to or) stall
don't always grasp the need to re-trim.
Look at the pilot action / trim possibilities:
Stick-forward, manual trim
- may not recover unless pilot re-trims, may not have pitch auth to override trim
Stick forward, auto trim
- best chance to recover, without need to re-trim, reducing workload in emergency
Stick backwards - no chance of recovery, whatever the trim does.
What should the a/c designer do ?