Background
The aircraft was engaged in an ambulance flight from Sangar to Segyan-Kyuel and back. Due to poor weather, the flight was delayed. At the estimated time of departure, weather conditions at Sangar Airport included visibility greater than 10 km, scattered clouds at 800 meters, overcast at 3,000 meters, temperature -22°C, dewpoint -23°C, and pressure 765 mm Hg. The en route weather forecast indicated a few stratocumulus clouds between 1,400 and 1,700 meters and significant altostratus clouds between 2,700 and 3,500 meters. The mountainous area over which the Antonov was to fly was expected to have moderate orographic turbulence in the layer from 900 to 1,700 meters, with possible downdrafts on the lee side of ridges within the same altitude range. These conditions were not reported to the crew.
Passenger and Departure
Medical equipment weighing 400 kg and passengers arrived at the airport by ambulances. The captain expected seven passengers, but three additional passengers arrived without tickets. Their names were added to the passenger list, and the copilot arranged payment for their fares. No seats were available for two of these passengers, so they sat on hand luggage in the aisle. At 04:46 UTC, the aircraft departed from Sangar and climbed toward the mountainous terrain.
Accident Sequence
The highest point along the route was at an elevation of 1,976 meters, with a minimum safe altitude of 2,515 meters. The pilot climbed under visual flight rules (VFR) and maintained visual separation from the snow-covered mountains. At an altitude of 1,300 meters, the Antonov entered an area of strong turbulence and was caught in a downdraft. Power was increased to nominal and then to takeoff power in an attempt to stop the descent. With rising terrain ahead, continuation was impossible. The pilot decided to carry out a 180° turn to the left over downsloping terrain. This turn was performed downwind with a 30° bank instead of the recommended 20°. As a result, the rate of descent increased, and after the aircraft rolled to an angle of 120°, the left lower wing contacted a cliff. The aircraft lost speed and crashed on the snow-covered mountain. All 12 occupants were rescued; four sustained serious injuries. The aircraft was destroyed.
Probable Cause
The official investigation identified the following findings: the crew flew lower than the minimum safe altitude; incorrect estimation of the prevailing situation led to a late decision to return to the departure airport under conditions of orographic turbulence and limited airspace; deficiencies in flight instructions at Sangar Airport, including the absence of an altitude diagram that would have shown the aircraft could not gain sufficient height within 10 km after takeoff; an incorrect weather forecast that did not include orographic turbulence; and erroneous actions during the downwind turn with a 30° bank, which increased the vertical rate of descent.