Investigation Summary
The flight was a scheduled international service from Beijing to Moscow with an intermediate stop in Irkutsk. As the Tu-104B approached Irkutsk, weather conditions were poor, characterized by rain and a cloud base at approximately 100 meters. The crew was provided with contradictory weather data regarding the cloud tops and was unaware of the actual severity of the low ceiling. During the final approach to runway 29, the aircraft began a premature and sharp descent. The pilots only broke out of the clouds at an altitude of less than 60 meters, leaving insufficient time to recover. The aircraft first struck approach lighting 2,450 meters from the threshold, then impacted a hillside, became briefly airborne, and finally crashed in a left-hand bank. A post-crash fire consumed much of the wreckage. The investigation highlighted a technical failure where moisture ingress into the static system led to erroneous instrument displays, which misled the crew into a dangerous descent profile.
Final Conclusions
The investigation concluded that the primary cause of the accident was the entry of water into the aircraft's static system. This moisture caused the horizontal speed, vertical speed, and altitude instruments to display incorrect readings, leading to a loss of speed and an unintentional descent below the glide slope. Contributing factors included the crew's lack of awareness regarding the actual low cloud cover and the failure of air traffic control to divert the flight despite the deteriorating weather conditions.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Static System
The pneumatic system responsible for providing ambient air pressure to flight instruments; water ingress here caused false altitude and airspeed readings.
Altimeter
The primary instrument for measuring altitude, which provided incorrect data due to static system contamination.
Vertical Speed Indicator (VSI)
An instrument that shows the rate of climb or descent, which failed to accurately reflect the aircraft's sharp descent.
Interesting Facts
- 01The aircraft had accumulated 2,497 flight hours and 1,138 cycles at the time of the accident.
- 02Two passengers survived the crash, while all eight crew members perished.
- 03The victims included citizens from Albania, China, Czechoslovakia, and Colombia.
- 04The Soviet press largely ignored the accident, while a major public burial was held in Beijing for the victims.
- 05The aircraft was powered by Mikulin AM-3M-500 engines.
Safety Actions & Advisories
Static Port Protection
Source ↗Following the investigation into moisture ingress, recommendations were made to improve the sealing and protection of static ports on Tu-104 aircraft to prevent water entry during heavy rain or ground washing.