Bell 47G N1170W accident near Montrose, Colorado

Probable cause

A loss of engine power due to fuel starvation, which resulted from attitude-induced unporting of the fuel.

NTSB analysis

Before the pilot performed an aerial application, the helicopter was serviced with pesticide, but no fuel was added; fuel had been added before the three previous flights. During one of the aerial application passes, the engine lost power; the pilot conducted a forced landing to a field, and the helicopter’s tailboom and fuselage were substantially damaged. Following the accident, about 3/4 gallon of fuel was recovered from the right fuel tank and 2 1/2 gallons of fuel were recovered from the left fuel tank. There was no evidence of mechanical malfunction of failure that would have precluded normal engine operations.

Each spray pass is made at an airspeed of about 85 mph and directly above the crop to achieve optimal product application and spray coverage to the crop. At that speed, the helicopter flies in a nose-low attitude. The fuel delivery port or tube on both tanks is located at the aft, lower end of each tank, and both tanks deliver fuel to the engine simultaneously. It is likely that the limited fuel in the tanks moved away from the fuel ports due to the helicopter's nose-low attitude, resulting in fuel starvation.

Text from the NTSB. Open the NTSB docket for CEN19TA280 for the full record.