Lisunov LI-2

The aircraft has been subject to technical modifications on part of the Aeroflot technicians few days prior to the accident and converted to a cargo version capable to carry a maximum of 9 passengers. It was reported that several mistakes were done during this conversion, especially concerning the ventilation system air inlet that was installed in a wrong position, just behind the cockpit window instead of lower or higher. Investigations revealed that the fire spread quickly because the insulating material used failed to respond to the requirements and was unimpregnated wadding. The aircraft accumulated 73 flying hours since this conversion.

It was determined that the failure of the right engine was caused by an act of sabotage. A nut was found in the fuel line which caused the fuel pump to fail during initial climb. A similar case was detected eight days prior to the crash.

It was determined that the flaps were deployed at 25° for takeoff, too much for this procedure. Thus, the aircraft's speed after rotation was too low, deteriorating its stability and its lateral control. Investigations were able to determine that the flying crew failed to identify and eliminate the abnormal behavior of the aircraft during initial climb, probably because his attention was diverted. This situation led the aircraft to stall and the distance between the aircraft and the ground was insufficient to expect a recovery. At the time of the accident, the crew was on duty since 13 hours and 40 minutes and the day before, it observed a ON duty period of 17 hours. Thus, it is believed that fatigue accumulated during these two consecutive days, which could be considered as a contributing factor.

The radio navigator mistook two outer markers when the crew started the approach to Yuzhno-Sakhalinsk Airport, and referred to the outer marker of the Korsakov Airbase (frequency 684 kHz) instead of the outer marker of the civil airport of Yuzhno-Sakhalinsk-Bolchaya Yelan (frequency 670 kHz). Investigations reported that these two outer markers were too close from each other (13,5 km) with close frequency as well, which contributed to the mistake. The following factors were also pointed out: lack of visibility caused by low clouds (the crew failed to distinguish the mountain); the crew failed to use the radio altimeter and an abnormal action on part of the crew regarding the direction finder unit.

It was determined that both engines failed due to a fuel exhaustion. Investigations confirmed that the fuel selector was connected to the left rear fuel tank that was empty. At the time of the accident, one of the passenger was seating at the copilot seat, against the published procedures. Also, it appears that most of the crew members were intoxicated, which was considered as contributory factors.

It was determined that the aircraft was, at the time of impact, off course about 18 km due to strong winds. Investigations reported that the crew failed to prepare the mission according to procedures and miscalculated the flight trajectory. Also, it was determined that the crew did not receive any information about the wind component prior to the flight and failed to use the ADF system properly, which was considered as contributory factor. While cruising in clouds, the pilots were unable to distinguish the mountain struck by the aircraft.

It was determined that the crew adopted a wrong approach configuration and that both engine were running at idle when the pilot wanted to avoid obstacles. Poor approach techniques on part of the flying crew and against the published procedures according to the weather conditions.