Aeroflot Flight 11

Aeroflot Flight 11 (flight number: SU11) was a regional scheduled Aeroflot flight from Semipalatinsk to Abai in the Kazakh Soviet Socialist Republic. On 10 December 1960 this flight was operated with an Antonov An-2T, which went out of control in flight and crashed. All 12 people on board were killed in the accident.

Flight and accident sequence

At 8:10 local time, the captain of the aircraft, together with other pilots of the airline, was briefed on the meteorological conditions along the planned flight route. The validity of the weather report extended from 8:30 to 9:30 local time, with this weather forecast being stated in the flight plan as “indicative”. When the captain submitted the flight plan, the air traffic controller on duty refused permission to take off, because the form had been written out under a different name and did not correspond to the validity period of the weather forecast required for the flight. The duty manager was then called in. Although he recognised the note on the weather report, he did not take any action to request a valid weather report. Instead, he made the decision to clear the pilot for the flight without a valid weather forecast in the flight plan form.

The single-engine aircraft took off from Semipalatinsk at 9:17 local time. The flight was conducted in difficult weather conditions, which deteriorated further en route. After takeoff, the captain had climbed the aircraft to a flight altitude of 650 metres and was in constant contact with air traffic control. He reported that visibility was two to four kilometres. At a distance of 45 kilometres from Semipalatinsk Airport he reported visibility of two kilometres. Air traffic control then instructed the captain, after 15 minutes of flight time and thus two minutes after the validity of the weather report had expired, to return to the departure airport, since a safe flight could not be accomplished under the prevailing meteorological conditions. At 9:36 local time, radio contact with the aircraft was lost.

Accident investigation

After radio contact with the aircraft had been lost, the search for the wreck began. It was found at 13:03 local time at a distance of 45 kilometres on a heading of 186 degrees from Semipalatinsk Airport, near the village of Repinka.

A sudden loss of speed and stall of the aircraft following a loss of pitch controllability was established as the immediate cause of the accident. This event was said to have occurred after the aircraft's centre of gravity had shifted aft in flight beyond 40–42 %. This incorrect weight distribution was said to have come about after several passengers had gone to the rear part of the aircraft, where the toilet was located. Corresponding marks on the structural elements of the tail section and the empennage supported this finding. When the aircraft's angle of attack began to increase, the rest of the passengers could have slid into the rear part of the cabin owing to insufficiently reliable fixing of the seats and the absence of seat belts. In addition, flying the reversal turn to return to Semipalatinsk could have contributed to the stall. After the loss of speed, at a relatively low altitude of about 500 metres, the crew was no longer able to recover the tail-heavy aircraft from the stall. This was also made more difficult by the restricted visibility and the horizon, which was not clearly discernible due to the weather, under whiteout conditions.

The main cause of the accident was identified as the poor organisation and dispatch of the flight at Semipalatinsk Airport, which made it possible for the aircraft to receive takeoff clearance and depart even though there was no valid weather forecast for the route and the destination airport. The poor meteorological advice at Semipalatinsk Airport was counted among the contributing factors, since a weather report had been issued forecasting weather above the weather minima, which did not correspond to the actual conditions along the route. Furthermore, the deficient cooperation between the civil aviation weather service AMSG and air traffic control in Semipalatinsk was criticised, as was the weak meteorological infrastructure for determining weather forecasts for the region around Semipalatinsk.