Aeroflot Flight 6515

Cause

As part of the investigation into the cause of the accident, a recovery operation was carried out from 24 October to 18 November in the 2.5 m deep, murky water, in which all the essential components of the aircraft, including the MSRP-12-9 flight data recorder, were recovered. From the flight data recorder data it was determined that 2–3 minutes before the emergency occurred the aircraft was flying at an altitude of 2450 m at a speed of 400 to 410 km/h. Starting nine minutes before the end of the recording, a loss of speed of 50 km/h and a reduction in oil pressure to 7 kg/cm² were recorded over the following 7.5 minutes. The loss of oil pressure was attributed to progressive icing of the engine air intakes and of the engines themselves. Finally, at 19:40:14, about 1½ minutes before impact, a flameout occurred in both engines 3.5 seconds apart, whereupon both engines failed and the propellers were automatically feathered. The pilots then initiated a left turn towards the coast at a speed of 250 km/h and attempted to restart the left engine. The left engine, however, did not reach the required speed and reverse thrust was produced instead, as a result of which the speed fell to 186 km/h and the aircraft banked 45° to the left. The angle of attack reached a supercritical value, causing a stall, and the aircraft went into a steep spiral dive. The pilots pulled the control columns to operate the elevators, which increased the angular velocity, whereupon the aircraft rotated 360° about its longitudinal axis at an altitude of approx. 500 m. Finally, at 19:41, the aircraft struck the surface at a speed of 490 km/h, a sink rate of 90 m/s and a vertical nose-down attitude of 50°.

The cause of the accident was determined to be the pilots' switching on the engine de-icing system too late. The fact that the flight manual did not take into account the situation of a double engine failure in flight and that the training did not include the correct conduct in similar weather conditions (flight at night in clouds in icing conditions) further aggravated the situation.