1988 Aeroflot Yakovlev Yak-40 crash. Aeroflot Flight 29674 was a non-scheduled passenger flight from Nizhnevartosk to Bugulma, with a stopover at Tyumen. On January 24, 1988, the Yakovlev Yak-40 operating the flight, crashed after an engine failure caused by unknown causes, crashing near Nizhnevartosk Airport, killing 27 out of the 31 occupants onboard.

Aircraft 
The Yak-40, registration CCCP-87549 (MSN 9531442 - Serial number 42-14), was manufactured at the Saratov Aviation plant in 1975 and transferred to the Ministry of Civil Aviation of the USSR and entered service on August 26, 1975 under the Bugulma Aviation Unit of the Privolzhsk Civil Aviation Directorate. The aircraft was powered by three Ivchenko AI-25 turbofan engines (H5512104, H5432091 and H5822081). At the time of the accident, the aircraft had accumulated 13,978 flight hours and 14,766 flight cycles.

Accident 
Flight 29674 was flown by the Yak-40 (CCCP-87549), flying to Tyumen, under the command of the 343rd flight squadron. At 16:50, the flight began to takeoff from Nizhnevartovsk Airport.

However, during the acceleration on the runway, at a speed of 150 km/h, the flight engineer noticed, according to the cockpit voice recorder, that the "air starter open" light illuminated. Immediately after liftoff, the high-pressure compressor (HPC) RPM of engines No. 2 and 3 (center and right, respectively) dropped, and within a second, engine No. 1 (left) also experienced an RPM drop. Engines No. 1 and 3 then shut down, while engine No. 2's RPM initially fell to 74% but then returned to takeoff power. By this time, the Yak-40 had climbed to an altitude of 35 meters. Losing thrust from two of its three engines, the aircraft began to lose speed and roll. One minute and 31 seconds after takeoff, it crashed into the slope of a ravine 1,800 meters from the runway's end and 18 meters to the right of its axis, hitting a power line and completely disintegrating.

The air temperature at the time was −31 °C. Rescue operations were conducted poorly, and the crash site was only located five hours later. By that time, only four passengers were still alive. The remaining four crew members and 23 passengers had perished.

Causes 
The commission was unable to determine the exact cause of why the engines' RPMs dropped below the level required for horizontal flight in the takeoff configuration. There were only two main hypotheses:
 When the flight engineer noticed the "air starter open" warning light, he might have set the throttle levers of all engines to idle, subsequently shutting down the outer engines by setting the throttle levers to "stop," or the engines might have shut down automatically due to the abrupt change in operating parameters. Since it was not possible to abort the takeoff at that moment, the captain ordered the flight engineer to move the throttle levers to the takeoff position, or he might have done it himself.
 An airlock might have formed in the fuel system due to air ingestion. This could have caused the engines' RPM to drop, leading to their automatic shutdown, or the crew might have moved the throttle levers after noticing the engine failure, which also led to the engines shutting down automatically.

References 

29674
January 1988
Accidents and incidents involving the Yakovlev Yak-40
Aviation accidents and incidents involving controlled flight into terrain
Aviation accidents and incidents in the Soviet Union