Accident Overview
An An-2 aircraft on a flight from Us-Khatyn to Suordakh crashed on a rocky mountain slope. The aircraft carried five passengers, two pilots, and a load of 600 kilograms of goods. While cruising at approximately 1,450 meters, the crew encountered moderate atmospheric turbulence and was unable to maintain altitude. The aircraft lost height and collided with a mountain located 15 kilometers southeast of Lake Siljan-Kuel, about 250 kilometers from the destination.
Occupants and Damage
Two passengers were killed in the accident. The other five occupants—three passengers and both pilots—were injured. The aircraft was destroyed.
Investigation Findings
The official investigation determined that the accident was caused by the pilot in command (PIC) failing to maintain a safe flight altitude in mountainous terrain. This led the aircraft to encounter strong downdrafts while flying over the leeward side of a ridge, resulting in an uncontrolled descent and collision with the mountain top. Contributing factors included:
- Insufficient analysis of meteorological conditions and the potential for strong ascending and descending air currents in the mountains.
- Failure of the PIC to take safety measures when flying in mountains and to act when encountering downward air currents while crossing a ridge.
- Use of motor gasoline with an octane rating below 95, which reduced engine power.
- Operating the An-2 without the required procedure to restore skills and obtain clearance for flights on this type after a significant break of approximately 15 years.
Probable Cause
The probable cause, as stated by the official findings, was that the PIC did not maintain a safe flight altitude in mountainous terrain, which led to the aircraft getting into strong downdrafts while flying over the leeward side of the ridge, uncontrolled descent and collision with the top of the mountain. Contributing factors included insufficient analysis of meteorological conditions, failure of the PIC to take safety measures and act when falling into downward air currents, use of low-octane gasoline decreasing engine power, and performance of the mission on the An-2 without skill restoration after a break of about 15 years.