Medford, OR, USA
N58295
McDonnell Douglas 369D
The helicopter was engaged in fire fighting operation (aerial observation) when the accident occurred. The pilot reported that the helicopter was in a cruise configuration 200 - 400 feet above ground level (AGL) when the engine lost power. The pilot initiated an autorotation and the helicopter descended into heavily wooded terrain. Two days after the accident, before the helicopter could be recovered, the on-going forest fire burned over the helicopter and destroyed the aircraft, engine and associated system components. Examination/teardown of the engine and associated components did not reveal any evidence of a pre-impact part failure or signs of abnormal wear.
On July 22, 2002, approximately 1150 Pacific daylight time, a McDonnell Douglas 369D helicopter, N58295, sustained substantial damage following a sudden loss of power and subsequent collision with trees approximately 18 miles north of Medford, Oregon. The helicopter is owned by the pilot, and was being operated by Timberland Logging Inc, as a visual flight rules (VFR) aerial observation flight under the provisions of Title 14, CFR Part 135. The commercial pilot and passenger (the Air Tactical Group Supervisor) both sustained serious injuries and were airlifted to a local hospital. Visual meteorological conditions prevailed and a flight plan had been activated for the local flight. The flight originated from Beagle Sky Ranch near Medford approximately 20 minutes prior to the accident. The helicopter came to rest in the upright position on sloping, heavily wooded terrain. In a written statement, and subsequent phone interview, the pilot reported that the helicopter was in a cruise configuration 200 - 400 feet above ground level (AGL) when the engine "quit." He stated that there were no unusual vibrations, sounds or other indications of a problem prior to the power failure. A witness reported hearing the pilot of N58295 transmitting "mayday" over his radio prior to the accident helicopter entering the treetops. The witness also reported that he could hear a warning horn in the background noise during the same transmission. After the radio transmission, the witness observed the helicopter descend into heavily wooded terrain. It was later determined that the before mentioned warning horn was the helicopter's low rotor RPM warning horn. At the time of the accident the helicopter was being operated in support of the Timbered Rock fire, managed by the Oregon Department of Forestry. The fire was ignited by a lightning strike on July 13, 2002 and encompassed an area of approximately 27,000 acres. On July 24, two days after the accident, the fire reached, and burned over the accident helicopter. The fire destroyed the aircraft, engine and associated system components (Reference Photo 1&2). On August 29, 2002, the remains of the helicopter wreckage was recovered and moved to a storage facility in Independence, Oregon. Shortly after being recovered, the engine was shipped to Rolls-Royce's facility in Indianapolis, Indiana, for further inspection and teardown. On November 6, 2002, representatives from the Federal Aviation Administration and Rolls-Royce performed an inspection and teardown of the engine and associated engine components. The following is a summary of their findings: The engine case, exterior accessories and interior of the accessory gearbox revealed signs of prolonged heat distress and impact damage, however, there was no evidence of an engine mechanical failure. Soot deposits were noted to the exterior of the compressor, accessory gearbox, turbine and combustion sections of the engine assembly. The gearbox was intact. The clutch assembly was attached to its respective mounting pad and engaged with the power takeoff gear shaft. The clutch flex couplers were fractured (overstress). The fuel nozzle line and engine igniter lead showed signs of heat distress and impact damage, however, their associated coupling nuts were secure. Rotation of the N1 shafting system was attempted by turning the first stage compressor wheel. The shafting system was bound in place. It was later determined that the binding was due to thermal distortion of the compressor case plastic as well as misalignment and distortion of the mating gear and spline surface in the N1 drive train. Rotation of the N2 shafting system was accomplished by turning the fourth stage turbine wheel. Resulting rotation of the power takeoff gear shaft was observed. It was noted that the Pc (compressor discharge pressure) line coupling nut, at the outlet of the Pc filter, was approximately 3/4 of a turn backed off from finger tight. A pneumatic leak check was conducted and air passage was noted in the area of the loose fitting. Leakage was also noted in the Pg line, between the turbine governor and accumulator. It was noted that both areas showed signs of significant heat distress and soot deposits. The turbine bearing oil supply line was found loose. No evidence of oil leakage was noted. The airframe fuel pressure differential switch (where it screws into the fuel pump filter) was found 2.5 flats from finger tight. The fuel control unit throttle lever had full travel from stop to stop. The power turbine governor throttle lever had full travel from stop to stop. The compressor scroll to compressor bleed valve inlet line coupling nut was found to be one flat loose. The following observations were made during the disassembly of the engine: Removal and disassembly of the compressor case revealed significant amounts of molten aluminum and pieces of the plastic case material was present in the first two stages of the compressor. Leading edge damage was noted to several of the compressor blades in the first two compressor stages. No damage was noted to the impeller or rear diffuser. Disassembly of the accessory gearbox revealed that the gearbox housing and gearbox cover was intact. All gear shafts, subassemblies and bearings of the gas producer gear train, as well as the power turbine gear train, were intact. Significant amounts of carbon like material were noted in the oil pump housing and oil transfer tubes. Coke like deposits were noted along the interior and exterior walls of the turbine-to-compressor coupling (N1). The coupling was intact with no apparent damage. After removal of the turbine assembly, the gas producer turbine assembly (N1) rotated freely. Coke like deposits were also noted to the exterior surface of the power turbine coupling (N2). The coupling was intact with no apparent damage. The power turbine rotor was intact and rotated as an assembly. Moderate rub indications were noted to the fourth stage turbine nozzle from the 9 o'clock to 2-3 o'clock position on the outer rim face and from the 9 o'clock to 2 o'clock position on the outer band. A corresponding 360-degree rub mark was observed to the outer rim, forward side of the fourth stage wheel. The fourth stage turbine blade track shows two localized rub indications at the 7 o'clock and 3 o'clock position. The rub marks are less than two inches in length. Rub marks, consistent with turbine blade tip rub, were noted at the 6 o'clock through 12 o'clock position of the third stage blade track. The first stage turbine nozzle was intact with no apparent damage. Erosion to the leading edges of the first stage turbine blades was noted. Following the teardown at Rolls-Royce, the power turbine governor and fuel control unit were shipped to Honeywell Engine Control Systems, South Bend, Indiana, for further examination and testing by representatives from the FAA, Honeywell and Rolls-Royce. During the examination of the fuel control unit, it was determined that the unit could not be functionally tested due to thermal damage sustained during the fire. Disassembly of the unit disclosed that all internal components were intact with no evidence of a pre impact malfunction or failure. Bench testing of the power turbine governor showed that the unit tested within limits with no indication of a malfunction or failure. The examination/teardown of the engine and associated components did not reveal any evidence of a pre-impact part failure or signs of abnormal wear. See attached report for further information. At the conclusion of the investigation, the engine and associated components were shipped to HLM Air Services, Independence, Oregon. On May 15, 2003, the airframe, engine and associated components were released to CTC Services, LAD (Aviation), Inc, Renton, Washington.
Power loss during cruise flight for undetermined reasons. Factors include mountainous terrain and trees.
Source: NTSB Aviation Accident Database
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