On July 6, 1996, approximately 1440 Pacific daylight time, the Engine Power Out (EPO) warning light and horn activated on a Hughes 369D, N5110Y, operated by Evergreen Helicopters, Inc., of McMinnville, Oregon (a 14 CFR 135 on-demand air taxi certificate holder), while on a 14 CFR 91 maintenance test flight approximately 3 miles northeast of the McMinnville airport. The airline transport pilot (Evergreen's chief pilot) entered an autorotation and landed in a plowed cornfield. The helicopter rolled over during the landing and was substantially damaged, with the pilot and a pilot-rated mechanic crewmember receiving minor injuries. The flight was to have been a local flight out of McMinnville. Visual meteorological conditions prevailed and no flight plan had been filed.

At the request of the NTSB investigator-in-charge (IIC), an on-site investigation was performed by investigators from the FAA, McDonnell Douglas Helicopter Systems (MDHS), and the Allison Engine Company. The MDHS investigator's report noted the following findings. The aircraft had been reassembled following disassembly and shipment from Africa in November 1995, and was undergoing an annual/300-hour inspection at the time of the accident. The maintenance test flight was being flown in order to perform main rotor blade track and balance checks. About 4 minutes after takeoff, while at 400 to 500 feet above ground level in a 45 degree right bank at 100 to 110 knots indicated airspeed and 70 to 80 percent torque, the EPO light and warning horn activated. The pilot rolled level, reduced collective, and entered an autorotative descent, making a right turn of 135 to 140 degrees during the descent to clear trees and land in a clear area. During the descent, the pilot noted that the engine N2 (power turbine) RPM was stabilized at about 88 to 90 percent (the normal range is 102 to 103 percent.) The landing from the autorotation was downwind, with a forward touchdown speed of 20 to 25 MPH, in a level attitude. The aircraft traveled about 30 feet on its skids and then began to "roll/pitch forward over the nose as the aircraft skids sunk into the soft soil of the plowed field..."; the pilot applied aft cyclic in an attempt to stop the pitchover, without effect. The main rotor blades contacted the ground and the aircraft came to rest on its left side. The report stated that at that point, "a small oil fire in the vicinity of the engine starter generator ignited and extinguished itself." Both crew members exited the aircraft unassisted with minor injuries.

The on-site investigators found that the engine N2 RPM governor had been removed and replaced the day before the accident flight. During the examination of the aircraft wreckage, the adjustable governor lever control rod (part number 369A7706-5) was found disconnected at the governor control lever. The nut and washer (part numbers AN320-4 and HS306-327, respectively) specified in the aircraft parts manual for connecting the adjustable governor lever control rod to the governor control lever were found in the bottom of the engine compartment. Investigators reported that they were unable to locate the cotter pin (part number MS24665-151) specified in the aircraft parts manual for safetying the nut and washer installation. The MDHS investigator's report contained the following comments at the end of the narrative:

a. All damage noted was a result of the accident/ground impact sequence and was indicative of a power on condition. There was no evidence of any pre-existing damage that would have caused or contributed to the accident.

b. There was no evidence of any system or component failure or malfunction that would have caused or contributed to the accident.

c. Damage to the main rotor system and drive systems is indicative of at or near full power available at the time of the ground impact/rollover (i.e., drive to all systems was present until ground impact occurred.)

d. Sufficient N2/engine and Nr/main rotor RPM existed for a power on landing.

e. The adjustable governor lever control rod was found to be disconnected between the governor and the N2 control idler bellcrank.

f. Disconnect of the adjustable governor control lever rod resulted in loss of automatic governing of the engine.

Evergreen Helicopters, the aircraft operator, did not furnish a completed NTSB Form 6120.1/2, Pilot/Operator Aircraft Accident Report, or any crewmember statements to the NTSB. However, Evergreen's vice president for maintenance did report to the NTSB by phone that the helicopter had flown an uneventful 1.2-hour maintenance test flight the day before the accident, but that the engine fuel governor had been changed following that flight.

The Hughes 369D operating handbook directs pilots to check the "fuel control, N2 governor, and associated linkages" in the engine compartment during preflight inspection.

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