Ice may have been a factor in a Russian plane crash that killed 31 people in Siberia Monday.
A twin-engine turboprop ATR-72 crashed four minutes after take-off from Roshchino International Airport in Tyumen, 1,000 miles east of Moscow. There were 39 passengers and four crew members on board.
All four crew members were killed.
The exact cause of the crash is not yet clear, but news reports suggest ice may have played a role.
The plane was not treated with de-icer before takeoff, the Telegraph reported.
Ice and frost can trigger problems in flight.
The Associated Press said government officials denied ice triggered the crash. While officials acknowledged the plane was not properly de-iced, they told the AP a technical failure likely brought down flight UT 120.
Mistakes by pilots or air traffic controllers have not been ruled out, the AP said.
The UTAir flight caught fire and broke into pieces on impact. It was headed to Surgut, an oil town to the north. Most passengers were residents of the two Siberian towns, the Telegraph said.
A witness told the AP smoke was spotted coming from the plane's engines and that pilots appeared to be trying to return to the airport when the plane crashed in a snowy field about 25 miles from the Tyumen airport.
At least six people likely burned to death in the crash, a police official told the news agency. The 12 passengers who survived the crash also suffered severe burns.
The crash is the latest in a string that have plagued the Russian skies in recent years.
A plane crash last year killed an entire hockey team as they departed for their first match of the season.
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