The Tu-134 jet liner, en route from the West Siberian town of Surgut, had 50 passengers and seven crewmen on board when it crash-landed in foggy weather in Samara Saturday morning. Twenty people, including four crewmen, were hospitalized.
Prosecutors said that although they were considering all possible versions of the accident, they were inclined to think that the tragedy had happened due to a crew mistake. The Prosecutor General's Office opened a criminal case.
But the Transportation Ministry said different factors might have simultaneously caused the accident.
"First, we should consider bad weather conditions. Besides, we cannot rule out a technical malfunction - in the chassis or any other unit," a ministry spokesperson said.
The source said that the fleet of Tu-134 jet liners was outdated, and the service life of almost all of them had expired.
The Tu-134 was launched in 1967 to become the most widely used airliner in the Soviet Union. It is capable of carrying 76 passengers.
The spokesperson did not rule out the crew's possible mistake. "Whether the crew is to blame for the crash or not will be established after investigation is completed."
UTAir, a Siberia-based owner of the airliner and Russia's fifth largest carrier, said the aircraft had been in good technical condition and that foggy weather was likely to have caused the accident. The company also said the crew was well-skilled and had long experience.
Irina Andrianova, head of the press service of the Ministry of Emergency Situations, said that the plane had touched the earth with a wing on landing and that the ministry did not have any information that the plane had had a chassis malfunction as it was reported earlier.
Anatoly Ilyin, director of the Samara airport's control center, said the plane had landed beyond the landing strip and overturned. He said six and not seven people had been killed. Samara health officials said 29 people had been hospitalized.
The Transportation Ministry said UNAir had decided to pay $75,000 to each family of those killed in the crash.
Transportation Minister Igor Levitin said in February the aging Russian medium-haul airliners Tu-154 and Tu-134 would be phased out of commercial use within the next five years.
The Russian government has recently launched projects to replace the old Tu-154 and Tu-134 models with more technologically advanced SuperJet-100 and MS-21 mid-haulers. But these aircraft will not enter service until 2012.