Aviation officials said Tuesday that a preliminary inquiry into the UTair flight disaster that killed 31 people in Siberia showed that the plane's wings had begun rolling wildly before the crash but that the cause remained unclear.
"After taking off, the plane gained a height of about 210 meters, then banked more than 35 degrees to the right and then 50 degrees to the left, at which point it slammed into the ground," the International Aviation Committee said in a statement.
The aircraft broke into three parts after its left engine hit the ground, investigators said.
An examination of the ATR 72 twin turboprop plane's flight recorders showed that the engines had not failed.
"Both engines had been functioning until the plane collided with the ground," the statement read.
Federal Air Transportation Agency chief Alexander Neradko told Interfax on Tuesday that the fact that deicing agent appeared not to have been adequately applied to the plane could not have caused the crash. Industry experts had earlier pointed to ice conditions as a likely cause of the accident.
Investigators also said "no alcohol was found in the pilots' blood." The final inquiry results will be announced in a month.
The plane was carrying 39 passengers and four crew members when it crashed just minutes after takeoff from Tyumen early Monday on its way to oil town Surgut. Twelve people survived, but all remain hospitalized with serious injuries.
UTair announced Tuesday that it was grounding all its ATR 72-200 planes and will replace them with ATR 72-500s made in 2011 until the investigation is finished.
''While we have no doubts about the reliability and technical condition of these aircraft, the decision has been made from a psychological point of view,'' the company's CEO Andrei Martirosov said in a statement.
Martirosov also said that despite being in their 20s, the two pilots were considered experienced.
Surgutneftegaz, Russia's fourth-largest oil producer, confirmed Tuesday that its board member Nikolai Medvedev and five other employees died in the crash.
Three other Surgutneftegaz employees were hospitalized, company spokesman Alexei Artemnenko told Bloomberg.
LUKoil, Russia's second-largest oil producer, lost two employees in the accident. They were identified as geologist Alexander Lebedev and engineer Yury Fyodorov, according to a statement from the company.
Meanwhile, Russia's U.S. Ambassador Michael McFaul Tweeted his condolences.
"Saddened by plane crash in Tyumen. Condolences to Russian people and those who lost loved ones. Prayers for survivors and families," McFaul wrote in a message on Twitter.