Moscow: Russian officials on Tuesday were trying to nail down the cause of a plane crash in Siberia which killed 31, amid reports that the craft may have become uncontrollable after icing over.
The turboprop ATR-72 went down moments after taking off from the Tyumen airport Monday and disintegrated on impact two kilometres (just over a mile) away from the runway.
Twelve people out of 43 survived and were being treated in Tyumen and Moscow.
Russia's Interstate Aviation Committee, which is now deciphering the plane's in-flight recorders, said Tuesday that "the craft's engines have been working up to the moment of impact" on the snow-covered field.
However "after the plane gained an altitude of 210 metres, it began to list, first by 35 degrees to the right, and then to the left by over 50 degrees", at which point it crashed, the committee said.
Russia's Kommersant newspaper said Tuesday that the French-Italian ATR-72 was the only outgoing plane whose captain refused to treat the plane with antifreeze on a day with intermittent clouds and low temperatures.
"The plane may have iced over even during taxiing and acceleration, which took 10 minutes," the report said, adding that the young and inexperienced crew members may not have been aware of the process.
Head of the plane's operator UTair, Andrei Martirosov, said Monday that the 27-year-old captain's 2,500 hours of flight time was adequate experience. The second-in-command was only 23, but had all the necessary training, he said.
Russia's investigators on Tuesday said the plane disintegrated after hitting the ground with its left engine during what appears to have been an emergency manoeuvre. "No alcohol has been found in the pilots' blood," the Investigative Committee said in a statement.
Earlier investigators said the main suspected cause of the accident was a technical problem with the plane, based on accounts of witnesses that noticed smoke coming out of the engines.
The city of Tyumen lies 1,700 kilometres (more than 1,000 miles) east of Moscow and is the capital of one of Russia's biggest oil producing regions of the same name.
The plane was flying to Surgut -- the heart of the Surgutneftegaz energy company and one of Russia's largest oil and natural gas producers.