On August 20, 2019, about 1030 mountain daylight time, a Bell 47G-3B-1, N1170W, lost engine power during aerial application near Montrose, Colorado. The commercial pilot was seriously injured, and the helicopter sustained substantial damage to the tail boom and fuselage. The helicopter was registered to and operated by Olathe Spray Service, Inc., Olathe, Colorado, as a Title 14 Code of Federal Regulations Part 137 aerial application flight. Visual meteorological conditions prevailed at the accident site and at the time of the accident, and no visual flight rules flight plan had been filed for the local flight. The local flight departed about 1000. The pilot stated that he had been performing agricultural spray operations in four different locations. He returned to Clifford Field Airport (1CO4), Olathe, Colorado, his home base, to take on additional chemical product. On the three previous trips, pesticide and about 30 gallons of Jet-A fuel were added as the helicopter sat idling. On this, the fourth trip, the helicopter was serviced with chemical, but no fuel was added. Each spray pass was performed about 85 mph and just above the crop in order to achieve optimal product application and spray coverage to the crop. In order to do this the helicopter, at that speed, was flown in a nose-low attitude. The fuel delivery port/tube on both tanks is located at the aft, lower end of each tank, and both tanks deliver fuel to the engine simultaneously. There is no pilot-controlled fuel selector valve in the cockpit. During the aerial application, the helicopter yawed left when the engine flamed out. The pilot slowed the airspeed and the helicopter impacted a cornfield. The helicopter had been resting on its right side in a corn field for several days before a Federal Aviation Administration (FAA) inspector and a representative of the engine manufacturer examined it. As a result, it could not be determined if fuel had drained out of the right fuel tank through a vent line, loose filler cap, or breached tank, but approximately 2/3 to 3/4 gallon of clean, clear, odor-free fuel was drained from of the right tank, and 2-1/2 gallons were drained from the left tank. Fuel was also found from the inlet side of the airframe-mounted fuel filter to the fuel spray nozzle inlet on the engine. The fuel spray nozzle appeared normal with no signs of excessive carbon deposits or blockage. Both the airframe and engine fuel filter bowls contained clean fuel, and both filters were void of contamination. N1 (gas producer) and N2 (power turbine) rotor continuity was confirmed, and both rotors turned smoothly when rotated by hand. Cockpit controls from the throttle and collective back to the engine fuel control unit and power turbine governor were free and continuous. The engine oil system, including the filter and magnetic plugs, was checked and was unremarkable. Further examination revealed no evidence of mechanical malfunction or pre-existing conditions that would have precluded normal engine operation.