A spokesman for the watchdog Rostransnadzor told the Izvestiya newspaper weather had caused icing on the UTair ATR 72 plane but it did not undergo deicing, RIA Novosti reported.
The flight, bound for Surgut, crashed on takeoff from Tyumen in Western Siberia, killing 32 people and severely injuring 11 others. Another passenger died in a hospital weeks later.
A Rostransnadzor investigation found a number of UTair planes had not been deiced. Rostransnadzor also found violations of working time, training failures and lapses in maintenance, RIA Novosti said.
On April 9, Rostransnadzor issued a notice advising UTair against operating all ATR 72 variants.
Rostransnadzor said the plane waited for its flight for about 6 hours overnight on the apron at Tyumen's Roshchino airport. It had been snowing and raining at the time.
Two earlier fatal crashes of ATR 72 planes were attributed to icing, RIA Novosti said.