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HISTORY OF FLIGHT
On April 14, 1996, at 1155 hours Pacific daylight time, a Hughes 369D, N519BH, owned and operated by the pilot, experienced a loss of engine power during cruise flight. The helicopter was substantially damaged during landing in an open field about 30 miles south of Yerington, Nevada. Neither the private pilot nor the two passengers were injured during the personal flight. Visual meteorological conditions prevailed, and no flight plan was filed. The round robin flight originated at 1110 from the pilot's private airstrip at the Flying M. Ranch in Yerington.
According to the pilot, he experienced a total loss of engine power while cruising between 200 and 300 feet above ground level at an airspeed of 100 knots. The pilot reported that "the engine noise resembled the same whining as if it were in a shut down mode."
The pilot entered an autorotation and landed on a freshly plowed soft dirt field approximately 0.5 miles from his private airstrip. After touchdown, the helicopter rolled onto its right side.
The helicopter was maintained on an annual inspection program and had been operated for about 29 flight hours during the previous year. Since receiving its last annual inspection on October 11, 1995, the helicopter had been operated for about 16.9 hours.
The last recorded engine maintenance was a compressor wash which was completed on February 7, 1996, at 1,785.0 hours. The helicopter's maintenance records were examined by representatives from the Federal Aviation Administration (FAA), McDonnell Douglas Helicopter Systems (MDD), and the Allison Engine Company. None of the parties reported observing any recorded deficiencies pertinent to the accident flight.
WRECKAGE AND IMPACT INFORMATION
Under FAA supervision, the helicopter was examined by the MDD and Allison Engine participants. The parties reported observing skid-like depressions over a 25- to 30-foot-long path between the initial point of ground impact and the main wreckage.
Based upon structural deformation signatures and the wreckage fragmentation pattern, MDD opined that during the landing sequence a main rotor blade contacted and severed the helicopter's tail boom. Tail rotor blade and tail rotor drive shaft components were located over 200 feet from the main wreckage. MDD reported that the physical evidence indicated "at least partial engine power . . . was present at the time (of ground impact). . . . No evidence was found of any preexisting system or component failure or malfunction that would have caused or contributed to the mishap."
TESTS AND RESEARCH
On May 17, 1996, the helicopter's engine was inspected and test run at Allison Engine Company's Indianapolis, Indiana, facilities. In pertinent part, the FAA made the following observations:
". . . Accumulated debris encompassed the nozzle port. It was located towards an area of about 1/4 inch over the air atomizer path. Furthermore, fine dust particles were noted on the outer compressor case. The initial run was normal, but at 4,900 (N1) speed the engine flamed-out. During the second run the engine was operated at take-off power, flight idle, accelerations, decelerations and different power settings." An analysis of the test cell data revealed that during the tests the engine had operated below the targeted torque required for that specific engine model.
According to the Allison Engine Company, during the engine test run power was produced at ". . . a level 7.8 percent below normal performance levels. The compressor was found to be extremely dirty on both blades and vanes throughout all stages." In conclusion, the Allison participant opined that the decreased engine performance was most probably the result of the dirty compressor. Also, during the accident sequence at the point of ground contact, engine power was likely being applied to the main rotor and tail rotor drives.