Investigation Summary
The flight was a multi-leg journey across the Soviet Union. A fresh crew took over the aircraft in Novosibirsk for the leg to Irkutsk. During the instrument approach to Irkutsk, the crew encountered poor weather with a low ceiling of 150 meters and visibility of 1,500 meters. As they descended, the aircraft's airspeed indicators began providing false readings, overstating the actual speed of the jet. Trusting their instruments, the pilots reduced engine thrust to bring the speed down to what they believed was the recommended 300 km/h. In reality, the aircraft slowed to between 270 and 275 km/h. This speed was insufficient to maintain stable flight in the landing configuration, leading to a lateral deviation and a loss of altitude. The aircraft crossed the non-directional beacon at only 85 meters and impacted the terrain 150 meters short of the runway threshold. The force of the hard landing caused the left wing to break off, and the fuselage caught fire as it slid onto the runway.
Final Conclusions
The primary cause of the accident was a malfunction of the airspeed indicators which caused the crew to fly the approach at a critically low speed. Contributing factors included the poor weather conditions (low clouds and limited visibility) and the crew's failure to recognize the instrument error before the aircraft reached a stalled or near-stalled state during the final seconds of the flight.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Pilot in Command
A. V. Ovchinnikov
Navigator
I. V. Shchepkin
Systems & Failure Modes
Airspeed Indicator
The primary flight instruments provided overstated speed readings, leading the crew to reduce thrust to a dangerous level.
Instrument Landing System (ILS)
The crew was utilizing ILS for the approach due to low visibility and cloud cover.
Interesting Facts
- 01The actual approach speed was 270-275 km/h, while the crew believed they were flying faster due to instrument error.
- 02The aircraft struck the ground with a vertical speed of approximately 8 to 10 meters per second.
- 03There were 29 survivors among the 135 people on board.
- 04The left wing broke off upon impact, leading to a massive fuel spill and fire.
Safety Actions & Advisories
Airspeed Indicator Reliability Review
The investigation recommended a technical review of the Tu-104's pitot-static system and airspeed indicators to prevent the overstatement of speed that led the crew to reduce thrust prematurely.
Approach Speed Standardization
Following the crash, Aeroflot and the Soviet Ministry of Civil Aviation reinforced the minimum safe approach speeds for the Tu-104B variant, emphasizing that pilots must not descend below 300 km/h during the final approach phase regardless of instrument fluctuations.