Originally posted by RWA ...
Can anyone with more knowledge of the aircraft and its systems – bearing in mind that the BEA says that auto-trim was still in operation - explain why the THS would have behaved in this (on the face of it, very strange) way?
I believe the outcome is due to the THS being 'g' driven. In other words, the SS command was given that allowed the actuator to take the elevator to maximum NU, but the expected 'g' didn't occur and the THS moved to (try) correct that situation.
In explanation - the THS will always attempt to neutralize the position of the elevator, and if necessary readjust according to elevator demand.
If I am wrong, you will soon find out.
