Bell 206B N211CS accident near Firebaugh, California

Probable cause

A total loss of engine power due to fuel exhaustion. Contributing to the accident was the improper calibration of the fuel quantity gauge, which led the pilot to believe that there was adequate fuel onboard.

NTSB analysis

The commercial pilot of the helicopter reported that, while conducting an aerial application flight, he heard a loud bang followed by a total loss of engine power. The pilot initiated an autorotation to a plowed field; however, during the landing sequence, the main rotor blades struck the tailboom.

Postaccident examination revealed that, when power was applied, the fuel quantity gauge indicated about 15 gallons of fuel when the actual amount present was about 6.5 gallons. This erroneous fuel level indication led the pilot to believe that more fuel was available than was actually in the fuel tanks. The helicopter flight manual indicated that, due to possible fuel sloshing in unusual attitudes or out-of-trim conditions, and one or both fuel pumps inoperative, the unusable fuel is 10 gallons.

The engine was subsequently installed on a test stand and several test runs revealed no anomalies. Further testing revealed that the aft fuel boost pump was inoperative. The thermal fuse was found open, consistent with overheating due to the lack of fuel being transferred through the pump. It is likely that, during the flight, the attitude of the helicopter was slightly nose-down. This allowed the fuel to transfer to the forward portion of the tank, which resulted in a lack of fuel flow through the aft fuel pump; the subsequent overheating triggered the thermal fuse, which caused the aft fuel pump to become inoperative.

It is likely that the total loss of engine power was the result of fuel exhaustion.

Text from the NTSB. Open the NTSB docket for WPR17LA071 for the full record.