Aggravated stall, AKA flat spin is the only thing that could explain this. Stall’s are caused by insufficient air speed. At least they’ve narrowed the scope of what they’re looking for.
BUT ... IIRC the VS was found FAR from the presumed impact area (debris field), leading one to infer that perhaps the VS ‘fell off’ before the ‘flat spin’. who knows
While certainly not the ‘only thing’, the flat spin is a big possibility.
Especially with reports of 100mph updrafts.
Another thing that could cause a flat spin is if the vertical stabilizer breaks off.
Icing shouldn’t have been a problem because the pitot tubes all have heaters on them. Unless they find the FDR we may never know.
.. Considering the “Rudder Limit Reached” was the first fault reported by the ACARS, I would guess that the vertical stabilizer separated right after that, with the aircraft entering a flat spin. A flat spin could explain the resulting speed errors. Remember the Rock-Away crash, the first thing they found/recovered was the intact vertical stab with the rudder attached, the same as in this instance. They blamed that on the copilot inducing rudder movement in response to wake turbulence. I submit that the Airbus FBW system is capable of “uncommanded” full rudder movement resulting in structural failure of the vertical stabilizer attach points