Medford, OR, USA
N105RH
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."
HISTORY OF FLIGHT On May 5, 2001, approximately 1654 Pacific daylight time, a Eurocopter (formerly Messerschmitt-Bolkow-Blohm [MBB]) BO-105C helicopter, N105RH, registered to and being operated by TL Forest Products, Inc. of Ashland, Oregon, on a local 14 CFR 135 non-scheduled air ambulance flight from Rogue Valley International-Medford Airport, Medford, Oregon, experienced a failure of the number 1 engine and fire in the number 1 engine compartment. The pilot continued the flight to Rogue Valley International and landed safely, and the fire was extinguished by airport rescue/firefighting (ARFF) personnel. There were no injuries to the airline transport pilot-in-command, two medical crew members, or passenger/patient on board. However, the fire substantially damaged the helicopter, and the helicopter was subsequently removed from the FAA aircraft registry due to being "destroyed" (according to the registry). The accident sequence of events began shortly after the patient was picked up. Visual meteorological conditions were reported at Medford at 1656, and the flight was on a company visual flight rules (VFR) flight plan. The operator's accident report stated that as the helicopter cleared trees after patient pickup, a series of "pops" was heard and the helicopter lost power. The operator's report stated that the pilot initially decided to make an emergency landing in a field as soon as possible, 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 the helicopter on taxiway A at the airport. According to a report of an FAA inspector assigned to assist in the investigation, the fire warning light of the affected engine did not illuminate during the sequence, but the fire warning light of the number 2 engine and the number 1 engine chip detector light did illuminate on landing. The FAA inspector also reported that the pilot reported observing a high turbine outlet temperature (TOT) indication (according to information from Rolls-Royce, the engine's maximum allowable stabilized TOT is 810 degrees C). The aircraft occupants evacuated the helicopter without injury, and ARFF successfully extinguished the fire. DAMAGE TO AIRCRAFT 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. Molten metal and debris were also ingested into the #1 engine compressor. AIRCRAFT INFORMATION The accident helicopter, a BO-105CB4, serial number S-55, was equipped with two Rolls-Royce (formerly Allison) 250-C20B turboshaft engines. According to the operator's accident report, the #1 engine (serial number CAE 835553) had 4,289.3 hours engine total time, and 302.3 hours since overhaul. The aircraft's last inspection was a combined 100-hour/300-hour/annual inspection on March 1, 2001, at 14,324.0 aircraft hours. The operator reported that the aircraft had flown approximately 19 flight hours since this inspection. TESTS AND RESEARCH Post-accident aircraft examinations performed by investigators from the FAA, helicopter manufacturer Eurocopter USA, engine manufacturer Rolls-Royce, and the aircraft operator disclosed that the number 1 engine compartment, and transmission compartment, had been extensively damaged by fire. The engine cowling was fire-damaged, and the outer surfaces of the number 1 engine also showed extensive fire damage. The engine compressor inlet screen and surrounding structure were partially burned. The number 1 engine compressor exhibited evidence of "molten metal and debris [being] ingested into the compressor while it was still operating", according to Rolls-Royce's report of the examination. The number 1 engine compartment contained puddles of oil on the pan below the engine, and the number 1 engine oil tank was found to be empty. The number 1 engine oil out line (a line carrying oil from the engine accessory gearbox to the oil tank) was found to be leaking. According to the FAA investigator's report, the leak was found at a B-nut fitting at one end of the line. Neither the N1 (gas producer/compressor) nor N2 (power) stages of the engine would rotate. Additionally, the FAA investigator reported that he found the engine's right exhaust stack cracked around approximately two-thirds of its circumference at a V-clamp, and the right exhaust extension cracked around approximately one-quarter of its circumference under a V-clamp (note: the 250-C20B engine has two exhaust ducts, one each on the upper left and upper right side of the engine.) Following on-site examination of the helicopter, the N1 gas producer turbine assembly from the number 1 engine was returned to Rolls-Royce facilities in Indianapolis, Indiana, for disassembly and inspection. This examination took place under FAA supervision on July 6, 2001. This examination disclosed that the first-stage nozzle (note: the gas producer turbine assembly comprises two stages) was severely burned consistent with exposure to excessive TOT, and that all blades on the first-stage turbine wheel were also burned consistent with exposure to excessive TOT. The second-stage nozzle and turbine wheel were found to be intact, with the exception of one turbine blade which had a small section of material broken off of the trailing edge tip. Examination of the three main bearings located in the turbine assembly (Nos. 6, 7, and 8) disclosed that the number 8 bearing (at the gas producer turbine inlet) was oiled and rotated freely, the number 6 bearing (at the power turbine inlet) was dry but intact and rotated freely, and that the number 7 bearing (at the gas producer turbine outlet) was dry and slightly notchy but was able to be rotated. The Rolls-Royce accident investigation report concluded, based on the on-site and follow-up turbine section examinations, 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." The number 1 engine oil out line (the one found to have a leak) was partially disassembled and visually examined by the NTSB investigator-in-charge, and subsequently was sent to the NTSB Materials Laboratory in Washington, D.C., for further examination. The Materials Laboratory reported observing a black residue on the outer extremities of the oil line and B-nut fitting at the locations where the two pieces join (the black residue was most prevalent on the B-nut fitting), as well as reddish-brown-colored deposits on the B-nut fitting. Scanning electron microscope/energy dispersive spectroscopy (SEM/EDS) examination of these deposits disclosed major spectral peaks of fluorine, silicon, calcium and carbon consistent with residue from a polytetrafluoroethylene (PTFE) material such as Teflon (TM), and major spectral peaks of carbon and calcium for the reddish-brown deposits.
A leaking engine oil outlet line fitting in the #1 engine compartment, resulting in an oil fire in the engine compartment.
Source: NTSB Aviation Accident Database
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