Investigation Summary
The accident exposed a critical vulnerability in the Tupolev Tu-154B fuel system architecture. The design utilized a single collector tank (sump tank) with a capacity of 3,300 kg that served as the sole source for all three Kuznetsov NK-8-2U engines. There were no redundant fuel lines to bypass this tank. On the day of the accident, fuel transfer from the main wing tanks to the collector tank ceased, leading to the simultaneous flameout of all three engines once the collector tank was empty. Investigators identified two primary possibilities for the failure: a technical malfunction in the automatic fuel transfer electrical circuits (such as a switch or circuit breaker failure) or crew error during a transition to manual fuel transfer mode. If the crew had manually disabled the 'fuel automation' and failed to activate the pumps for the next group of tanks, the collector tank would have drained without replenishment. The investigation also noted that the flight engineer failed to monitor the fuel gauge effectively, and the red warning light intended to signal a critical low level in the collector tank failed to activate. While 130 occupants survived the impact and subsequent fire, 27 of them sustained various injuries.
Final Conclusions
The simultaneous shutdown of all three engines was caused by fuel depletion in the collector tank resulting from a failure in the fuel transfer system. The investigation cited significant design flaws in the Tu-154B fuel system, namely the lack of independent fuel supplies for each engine. Contributing factors included the failure of the low-fuel warning system and the flight engineer's inadequate monitoring of fuel levels during the cruise phase.
Photographic Evidence (1)
Video Analysis
Aeroflot Flight 6709 — A brief overview of the 1978 Aeroflot Flight 6709 accident involving a Tupolev Tu-154B that suffered triple engine failure due to fuel starvation.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Systems & Failure Modes
Fuel Transfer System
Responsible for moving fuel from wing tanks to the central collector tank; its failure led to fuel starvation despite fuel being available in other tanks.
Collector Tank
A single sump tank that supplied all three engines; its depletion caused a total loss of thrust.
Electrical System
Powered by engine-driven generators; the triple engine failure caused a total loss of primary electrical power.
Interesting Facts
- 01The aircraft was only two years old at the time of the accident.
- 02The Tu-154B fuel system relied on a single 3,300 kg collector tank to feed all three engines.
- 03Four passengers were killed, while 27 of the 130 survivors sustained injuries.
- 04The aircraft was completely destroyed by the impact and subsequent fire.
Safety Actions & Advisories
Fuel System Redesign
The investigation highlighted the danger of a single-point failure in the fuel collector system, leading to recommendations for improved redundancy in Tu-154 fuel delivery.