Flight Background
On September 12, the An-2 aircraft with registration RA-33017 departed Surgut on a special flight to Saranpaul and Arbyn. On board were two pilots and five employees of the Sosvapromgeologya Company. On September 18, the crew was scheduled to return to Surgut but, due to poor weather conditions, decided to divert to Nefteyugansk.
Emergency Landing
Approximately one hour and ten minutes into the flight, while cruising at an altitude of 700 meters, the engine temperature rose to 305°C and the oil temperature to 90°C. Simultaneously, the engine lost power. The crew initiated a descent and attempted an emergency landing. The aircraft crash-landed in a field located 48 kilometers west of Nyagan. There was no fire. All seven occupants were injured, and the aircraft was damaged beyond repair.
Probable Cause
The official investigation determined that the accident was most probably caused by the use of uncoordinated automotive fuel not specified by valid aircraft maintenance engineering documentation. The fuel had a low octane grade and contained mechanical admixtures (rust). This resulted in cylinder-head temperatures increasing beyond operating limits, engine power loss, an unintentional flight altitude decrease, and the need for an emergency landing on saturated terrain. Contributing factors included unsatisfactory management of fuel storage, refueling procedures, and fuel quality inspection at Arbyn Airfield, as well as the pilot-in-command's incorrect decision to continue the flight after detecting deviations in the fuel quick drain sample (color, consistency, mechanical mixtures).