Under what circumstances would the nose rise with down elevator? Just a few. For one, if, instead of commanding PITCH, the elevators were trimming the THS. How is that possible? Only if the THS had lost integrity with the mount, specifically the jackscrew. Had this occurred, the THS elevator system would perform as an all flying tail, a stabilator.
So IF the Horizontal Stabiliser was not connected to its jackscrew (which "Positions it internally"), it would deflect to whichever angle the elevators put it. This would in turn change the Pitch of the a/c, but opposite to ss input. Down elevator pushes the trailing edge of the HS UP, climbing the a/c.
I'm sure that such severe misbehaviour would stand out in FDR recording. THS diconnected from its jack would be banging up and down dependent on elevators position. This would be accompanied with violent pitch changes and high g loads. If the whole thing would not separate almost immediately. Then how both left and right THS would fail at the same time? Or is there just one jack for both of them?
sebaska. I believe the two motors are positioned on the same jack. Perhaps not.
A I understand each elevator has two jacks (It has been described here recently). Normally one of those is active while the other is in "damping mode" (i.e. gets pulled/pushed instead of pushing/pulling).
THS has one jack with two motors. But I understand it's one for each side. But i could be wrong.