Originally Posted by
Smilin_Ed
I'm the wrong person to ask about that. Someone who is familiar with the actual implementation of the flight control system should answer that. Dozy?
I don't have any numbers, but the question is not so much the speed of actuation (which would be the same), but the speed with which that actuation is demanded. You can crank the manual trim wheel round to neutral in a couple of seconds, and the actuators will catch up, but to do it via autotrim will take sustained nose-down inputs over several seconds, which appears to be something that many pilots aren't comfortable with doing.
Autotrim is designed to take the load off normal control inputs, not recover from extreme THS angles. I think to correct the THS angle with autotrim in time to effect a positive recovery would have required recognition of the situation and corrective action at a considerably higher altitude than with manual trim operation.