Originally Posted by
up_down_n_out
Honestly, I'm not really convinced it was the tail plane.
The Sequence of disengaging autopilot followed by significant roll excursions would rather lead me to believe it was primarily the main plane. Maybe with some contribution from the back.
But it seems it occured upon flap retraction. Flap retraction reduces the load on the tailplane, thereby it should be reducing the effect of any icing.
but the contrary appeared to be the case:
Apparently the effect increased/set on after retraction, therefore I would rather look to the main wing.
Edit: Tail plane icing would be particularly critical on the underside.
Leaving the plane outside on the ground in snowing/freezing conditions would rather lead to build up on the upper side. This is where the main plane is much more susceptible.