What happened
On August 20, 2019, at approximately 1030 mountain daylight time, a Bell 47G-3B-1 helicopter, registration N1170W, experienced a loss of engine power while performing aerial application near Montrose, Colorado. The aircraft was being operated by Olathe Spray Service, Inc. for a Part 137 agricultural flight.
The pilot had been conducting spray operations at four different locations that day. After three previous trips where both pesticide and approximately 30 gallons of Jet-A fuel were added while the engine idled, the pilot returned to Clifford Field Airport (1CO4) to reload chemical product. On this fourth trip, the helicopter was serviced with chemicals, but no fuel was added.
To achieve optimal coverage, the pilot performed spray passes at approximately 85 mph in a nose-low attitude just above the crops. During the application, the engine flamed out, causing the helicopter to yaw left. The pilot reduced airspeed, and the aircraft impacted a cornfield. The crash resulted in one serious injury to the pilot and substantial damage to the helicopter's fuselage and tail boom.
The investigation
An examination of the aircraft was conducted by an FAA inspector and an engine manufacturer representative. Investigators found that approximately 2.5 gallons of fuel remained in the left tank and between 2/3 to 3/4 gallon in the right tank. Fuel was also present from the airframe-mounted fuel filter to the engine fuel spray nozzle inlet. The fuel spray nozzle showed no signs of blockage or excessive carbon deposits, and both fuel filters were free of contamination.
Mechanical inspections of the engine revealed that the N1 and N2 rotor continuity was confirmed and both rotors rotated smoothly by hand. Cockpit controls, including the throttle and collective, were found to be free and continuous through to the engine fuel control unit and power turbine governor. The engine oil system, including the magnetic plugs, showed no abnormalities. No mechanical malfunctions or pre-existing conditions were identified that would have prevented normal engine operation.