Actually, with Alaska 261, once the jackscrew cut loose from the acme nut, the THS was driven
fully leading-edge up (nose down) by the aerodynamic forces.
And beyond - it actually tilted leading-edge up so far and so hard that the leading edge ripped right through the motor fairing (the bulge on the tip of the MD vertical stabilizer), to 25° or more (normal limit was 2.1°). Resulting in unrecoverable nose-down aircraft pitch. In fact that aircraft performed a half-outside-loop (English Bunt) and was flying inverted on the reciprocal heading when it hit the water.
(There's a little NTSB video presentation on the failure progression here:
https://en.wikipedia.org/wiki/Alaska...nes_Flight_261 )
767 may, of course, have different structural geometry -
tdracer would probably know.
I'd rate a failed THS jackscrew mechanism in
this incident as conceivable and possible, but, thus far, of unknown probability. Effects of a possible turbulence encounter on a weakened jackscrew unit, or switching from auto to manual control at that phase of flight, are suggestive, however.