On September 8, 2025, a P-2002 Sierra RG, registration RA-1304G, was engaged in aerial work near Myachkovo, Moscow Oblast. The pilot-in-command planned several flights involving takeoffs, landings, and taxiing. The aircraft was operating with three passengers on board and contained approximately 75 liters of AI-95 automotive gasoline.
During the flight operations, the Rotax 912 ULS engine experienced a critical failure. An investigation by the Aviation Register of the Russian Federation revealed that the engine seized due to the melting and subsequent destruction of the lower head of the number 4 connecting rod. This failure was a direct result of overheating caused by insufficient oil flow.
The investigation identified the root cause as a non-compliant oil suction hose connecting the oil tank to the engine oil thermostat. The hose used in the RA-1304G did not meet the specifications required by the BRP-Rotax installation manual. Specifically, the hose lost stability and completely blocked the passage when the absolute pressure inside the vacuum line reached 600 mbar.
According to the manufacturer's installation manual, engine oil hoses must be capable of withstanding a vacuum pressure of -500 mbar at an oil temperature of 150 ºC without collapsing. In this instance, the hose failed at a vacuum pressure of -400 mbar, which was 100 mbar less than the required threshold, leading to the loss of oil lubrication.