Alexei Morozov, a deputy IAC chairman, said the accident occurred when the aircraft's captain suffered from spatial disorientation, losing his sense of direction and causing the plane's left wing to tilt in mid-air. The plane then went into a steep descent and crashed.
"Spatial disorientation occurred during a flight on a cloudy night with the auto pilot and auto-throttle switched off," Morozov said, adding that the crew did not have sufficient professional training.
The Boeing-737-500, owned by Russian flagship air carrier Aeroflot, crashed on a Siberian railroad track linking Yekaterinburg and Perm.
"The crew commander's work and rest schedule in the period preceding the air accident contributed to his general tiredness and ran counter to established standards," Morozov added.
Morozov also said that forensic experts had detected traces of alcohol in the captain's blood, but that this was not the primary cause of the crash.
