"The data available to the commission indicate that after landing the aircraft's brake system failed, causing the failure of the system's other mechanisms. As a result, the aircraft became uncontrollable after landing," the source said.
An Airbus 310-300, owned by Novosibirsk-based S7, formerly Sibir, was making a routine flight from Moscow to the city of Irkutsk, about 3,000 miles east of the capital and the home airport for popular tourist destination Lake Baikal. The airliner veered off the runway on landing and burst into flames after hitting a concrete wall.
The source said the exact reason for the tragedy would be established after the plane's flight recorders were deciphered.
According to the Russian Emergency Situations Ministry, there were 204 people on board the airbus, including 193 passengers and eight crewmembers, and three more people were taken on board "off the list."
The ministry said 122 people had died in the air crash, while 70 people were alive, of whom 58 were being treated in the hospital.