What happened
On November 15, 2017, a Khabarovsk Airlines flight, identified as NI 463, departed from Khabarovsk for a planned route including Nikolayevsk-on-Amur and Nelkan. During preflight preparations, the crew learned that Nikolayevsk-on-Amur airport was closed due to snow removal operations on the runway. Consequently, the flight plan was modified to fly via Chyumican to reach the final destination of Nelkan.
The L-410UVP-E20, registration RA-67047, departed Khabarovsk at 23:33. The aircraft was carrying two crew members, 5 passengers, and 410 kg of cargo, with a takeoff mass of 6368 kg. Approximately 50 minutes before reaching Chyumikan, the crew requested an amended flight information లే (AFIL) to bypass the intended refueling stop at Chyumikan and proceed directly to Nelkan, which was approved by air traffic control.
During the approach phase near Chyumikan, the aircraft was flying at an altitude of approximately 100 meters with an indicated airspeed of roughly 100 knots. The aircraft suddenly experienced an aggressive right roll and a loss of altitude, deviating from its glidepath. The aircraft struck the ground in a mountainous, forested area and was destroyed. The accident resulted in 5 fatalities among the crew and passengers, while one child sustained serious injuries.
Findings
The investigation determined that the primary cause of the crash was an uncommanded change in the right engine propeller blade pitch. Specifically, the blades moved to an angle of minus 1.8°, which was far below the minimum required inflight pitch angle of 13.5% while the thrust levers were set to forward position. This mechanical failure induced severe rolling and turning moments, leading to a loss of airspeed and control.
The malfunction was attributed to the simultaneous failure of both the BETA Feedback system and the Pitch Lock system. Investigators noted that because the components involved in the Pitch Lock Test likely did not contribute to the failure, it is unlikely that any errors in the crew's preflight testing procedures would have detected the malfunction. Furthermore, since this specific failure mode was considered extremely improbable during aircraft certification, no specific pilot training or emergency procedures were required in the aircraft flight manual for such an event.