Aeroflot Flight 04

Investigation

Investigation showed that the aircraft remained intact until it crashed into the forest, ruling out a decompression. Two Tupolev Tu-16 bombers flying approximately 150 - 200 km north of the route of flight 4 between 11000 and 12000 m reported the presence of strong updrafts within cumulonimbus clouds. The weight of the Tu-104 at takeoff was 66 tons, which limited the maximum safe altitude for flight to be 11700 m at standard engine power; altitudes of 12000 m could only be safely achieved by the Tu-104 in calm weather. Weather conditions in the Birobidzhan - Arkhara - Magdagachi region were more complex than the description received by the crew described, with cumulonimbus clouds reaching altitudes of over 12000 m. In attempts to avoid the clouds the airliner increased altitude to levels unsafe for the aircraft at the current weight, and combined with the updrafts present in the clouds, the aircraft stalled, during which the engines flamed out and the landing gear was extended. The failure of the engines and disorientation of the crew, from accompanied failure of the artificial horizons, rendered recovery nearly impossible.

Secondary causes of the accident were cited as follows:

Failure of the air traffic controllers and the pilot in command to thoroughly analyze weather conditions at the time, causing the flight to fly into dangerous weather in violation of the flight manual.

The three hour and 35 minutes delay of the departure of the flight from Khabarovsk, during which weather conditions deteriorated considerably.

Insufficient preparation for departure on part of the navigators.

The weather forecast provided to the flight crew did not specify the maximum altitude of the clouds.

There were no clear indicators for the maximum safe altitude of the Tu-104 with the given takeoff weight.

There were no defined procedures in place in the event of a stall.

Later accidents demonstrated that when a Tu-104 flew in certain atmospheric conditions, both clear weather and near thunderstorms, the aircraft was prone to losing longitudinal stability, that could be followed by the landing gear dropping, engine failure, and artificial horizon failure. At the time, the issues with the Tu-104's high stall speed facilitated by weak mechanization of the wing and the other mechanical issues mentioned were not well known.