Icing
Ofcourse there is no idea of speculate of the reason but similar accidents have happened before. We had one in Sweden (Stockholm) long time ago where a 4 eng turboprop (vickers vicount) nosedived on short approach. That was due to heavy icing on the tail and when crew selected landingflaps the center of gravity changes rapidly and the tail could not support that with the icing and just nosedived into ground killing all omboard.
Weather that has something to do with this time will tell.
But a sad day for aviation is it nevertheless
Wings 1011