On November 15, 2017, a Let L-410 (registration RA-67047) operated by Khabarovsk Airlines (KhabAvia) was involved in an aviation accident near Nelkan, Russia during landing or approach. 6 people were killed. Investigators recorded the probable cause as: The direct cause was an uncommanded inflight setting of the right-hand engine propeller blades to minus 1.8°, significantly below the minimum inflight pitch angle of 13.5°, with thrust control levers set to forward thrust. This summary draws on records from the Bureau of Aircraft Accidents Archives (B3A).
On 15 November 2017, an L-410UVP-E20 RA-67047 operated by Khabarovsk Airlines crashed near Nelkan after an uncommanded right propeller pitch change. Five people were killed, including the crew and four passengers.
Flight Details and Pre-Departure Preparations On 14 November 2017, Khabarovsk Airlines submitted a flight request for L-410UVP-E20 RA-67047, designated NI 463, to the Joint ATM System Khabarovsk regional unit. The flight was originally planned from Khabarovsk to Nikolayevsk-on-Amur and then to Nelkan. Preflight preparation began at 22:00 local time on 14 November 2017, which corresponded to 08:00 on 15 November 2017. During this preparation, the crew learned that Nikolayevsk-on-Amur airport was closed for runway snow removal. After coordination with air traffic control, the route was changed to Khabarovsk – Chyumican – Nelkan. The crew completed all required preflight procedures before boarding. Khabarovsk Airlines technicians performed a line maintenance check using Maintenance Job Card #687 and reported no findings related to the aircraft or its systems. The aircraft carried 1,250 kg of fuel. The crew received actual and forecast weather information during the preflight briefing. The weather at the departure aerodrome, along the route, and at the destination and alternate aerodromes met the requirements of FAP-128 items 5.30 and 5.38 and did not prevent the pilot-in-command from deciding to depart. The aircraft carried two crew members, five passengers, and 410 kg of cargo consisting of personal luggage and mail. The takeoff mass was 6,368 kg, and the center of gravity was at 25.5% MAC, within the limits specified in the aircraft flight manual. The aircraft took off from Khabarovsk airport at 23:33. ## Inflight Route Change and Approach Fifty minutes before the planned approach to Chyumican aerodrome, the flight crew checked the remaining fuel and requested a route change from Khabarovsk air traffic control. The crew asked to follow airway B226 to Nelkan after passing the OGUMI waypoint, without stopping at Chyumican. Under the original flight plan, the stop at Chyumican was intended only for refueling. At 01:47 on 15 November 2017, Khabarovsk air traffic control approved the route change. At 02:35, the crew contacted Nelkan Tower and received approach conditions and actual weather at the landing site. During the approach, at a true height of about 100 m and an indicated airspeed of about 100 knots, the aircraft developed an aggressive right roll and lost altitude. It left the descending glidepath, struck the ground, and was destroyed. ## Casualties and Accident Site The crew and four passengers were killed. A child aged three and a half years was taken to hospital with serious injuries. No people on the ground were killed, and there was no damage on the ground. The accident area was described as mountainous and marshy, with broad-leaved and needle-leaved trees. In winter, the area is covered with snow about 50 to 100 cm deep. The accident site had an elevation of 304 m above sea level, and the magnetic dip was minus 15°. ## Official Probable Cause The official findings identified the direct cause as an uncommanded inflight setting of the right-hand engine propeller blades to minus 1.8°, a value significantly below the minimum inflight pitch angle of 13.5°, while the thrust control levers were set to forward thrust. This condition produced significant rolling and turning moments, caused loss of speed and controllability, and led to the collision with the ground. The propeller blades’ movement to negative angles was attributed to failures of two systems: the BETA Feedback system and the Pitch Lock system. The findings stated that components of the Propeller Pitch Lock system that are tested during the PITCH LOCK TEST most probably did not contribute to the malfunction. Therefore, it was considered unlikely that any crew deviation from the PITCH LOCK TEST procedure would have affected detection of the malfunction before the flight. The situation had been classified as extremely improbable during aircraft type certification, so the aircraft flight manual did not require specific crew actions for such a condition, and corresponding crew training was not required.