On December 27, 2021, a Mi-2 helicopter, registration RA-15671, was performing a pipeline survey mission for JSC Transneft – Prikamye. The flight originated from Izhevsk Airport, where the pilot-in-command had completed a pre-flight medical examination and reviewed meteorological information. The aircraft was carrying one passenger and 10 kg of cargo, with a takeoff weight of 3550 kg.
Post-accident investigations focused on the mechanical condition of the transmission systems. While the intermediate gearbox and tail gearbox were found to be in working order without signs of failure, investigators identified significant wear on the universal joint components. Specifically, traces of false brinelling were found on the working surfaces of the pins and yokes of the main shaft transmission from the left engine.
The investigation of the aircraft, RA-15671, determined that these wear patterns resulted from torque being transmitted under conditions of insufficient or contaminated lubrication. Additionally, carbon deposits were observed on the oil sight glass of the intermediate gearbox, which could lead to inaccurate oil level readings.
The accident resulted in two fatalities. The investigation concluded that the maintenance of the universal joints did not adhere to the required lubrication intervals specified in the helicopter's maintenance manual.