Conclusion
The immediate cause of the accident was spatial disorientation of the crew, especially the Captain who was the pilot flying at the final stage of the flight, which led to the left flip-over, a steep descent and the crash of the aircraft. The spatial disorientation was experienced during the night time operation in clouds, with both autopilot and autothrottle disengaged. Contributing to the development of the spatial disorientation and failure to recover from it was a lack of proficiency in aircraft handling, crew resource management and ofskills associated with upset recovery using "western"-type attitude indications that are found on foreign and modern Russianmade aircraft. This type of indication differs from the one used on aircraft types previously flown by the crew (Tupolev 134, Antonov 2).
The cause above was determined on the basis offlight recorders and ATC recorder data analysis, examination of the airframe and engine wreckage, results of the accident flight simulation, findings of the independent expertise conducted by test pilots from State Research Institute of Civil Aviation and Gromov Flight Research Institute as well as line pilots, and also on the basis of all the works conducted with participation of experts from Bermuda, France, Russia, UK and USA in the course of the investigation.
The systemic cause of the accident was insufficient management by the airline of flight and maintenance operations of the Boeing 737 type ofaircraft. These deficiencies in the aircraft maintenance also revealed through safety inspections conducted by the Russian Transport Oversight Authority and the Russian CAA after the accident. Deficiencies in the aircraft maintenance led to a situation when flights were performed for a long time with a throttle stagger that exceeded the limitations in the AMM and when the maintenance staff did not follow the AMM recommended troubleshooting procedures. The need to manage the throttle stagger during the approach increased crew workload.
The forensic medical examination performed inthe State Healthcare Center of Special Status “Perm Regional Forensic Expertise Bureau” confirmed the presence of ethyl alcohol in the Captain’s body before his death. The captain’s recent work schedule during the time period before the accident was conducive to fatigue and did not comply with national regulations.
