Both engines on the crashed UTAir ATR 72-200 at Tyumen were operating before the impact shortly after take-off, but the aircraft exhibited instability in the roll axis beforehand.
Investigators from the Interstate Aviation Committee (MAK) state that the turboprop reached an altitude of 210m (690ft) then banked sharply to the right, about 35°.
It then rolled in the opposite direction, reaching a left bank of more than 50° at the point of impact, says MAK.
Both of the Pratt & Whitney Canada PW124 engines "operated up to the collision with the ground", it adds.
One local report, quoting the deputy director of Tyumen airport, states that the ATR crew opted against de-icing before departure.
Twelve of the 43 occupants were initially listed as having survived the accident. The aircraft had been operating a domestic service to Surgut when it came down yesterday.