SEA01FA085 · MBB BO-105C

As the helicopter cleared trees after patient pickup, a series of "pops" was heard and the #1 engine lost power. The pilot initially decided to make an emergency landing in a field, but no suitable landing areas were found, and the helicopter's #2 engine was determined to be producing sufficient power to sustain flight. The pilot therefore elected to continue the flight to the airport, and called the Medford tower and requested an emergency landing with fire crews standing by. The medical crew on board the helicopter subsequently reported that they smelled "something burning." Approaching the airport, the Medford tower controller advised the pilot that the aircraft was trailing smoke, and subsequently advised the pilot that the helicopter was on fire. The pilot elected to make a fast run-on landing, and subsequently landed on taxiway A at the airport. The aircraft occupants evacuated the helicopter without injury, and ARFF successfully extinguished the fire. The fire extensively damaged the helicopter's #1 engine compartment, engine cowling, outer surfaces of the #1 engine, and transmission compartment. The fire also partially burned/melted through the main rotor flight control tubes, and molten metal and debris were ingested into the #1 engine compressor. Post-accident examinations disclosed that the fire occurred in the #1 engine compartment, external to the #1 engine. The #1 engine compartment contained puddles of oil on the pan below the engine, and the #1 engine oil tank was found to be empty. The #1 engine oil out line (a line carrying oil from the engine accessory gearbox to the oil tank) was found to be leaking at a B-nut fitting at one end of the line. Additionally, the engine's right exhaust stack and right exhaust extension were found to be cracked around portions of their circumference under a V-clamp. Disassembly examination of the #1 engine N1 gas producer turbine assembly at the engine manufacturer's facilities disclosed that the first-stage nozzle and turbine wheel were burned consistent with exposure to excessive TOT, and that the second-stage nozzle and turbine wheel were generally intact. Examination of the three main bearings located in the turbine assembly (Nos. 6, 7, and 8) disclosed that the number 8 bearing was oiled and rotated freely, the number 6 bearing was dry but intact and rotated freely, and that the number 7 bearing was dry and slightly notchy but was able to be rotated. The Rolls-Royce accident investigation report concluded that "There were no hardware failures on any part of the engine", that "The damages to the 1st stage nozzle and 1st stage turbine wheel were the result of operation at an excessive TOT", and that "The engine was operating with the external fire well advanced as evidenced by the ingestion of fire debris and molten metal into the compressor."

Verbatim NTSB analysis and probable cause from the NTSB dataset