Robinson Helicopter Company R44 II N165RV accident near Columbia, Illinois

Probable cause

A total loss of engine power while maneuvering at low altitude for reasons that could not be determined during postaccident examination.

NTSB analysis

The helicopter experienced a loss of engine power during an agricultural application flight at low altitude. The commercial pilot lowered the collective and increased the throttle but was unable to reestablish engine power, so he made a run-on landing to a field. During landing, the right skid sunk into the mud/wheat, which caused a "slight hop," and the main rotor struck the tailboom.

Postaccident examination of the oil filter revealed no signs of contamination. No mechanical anomalies were noted with the fuel system and the fuel from the carburetor was light blue, typical of 100 low-lead aviation fuel. An unidentified sticky substance, likely agricultural spray, coated the lower half of the throttle flap and the bottom half of the fuel injector body. However, the observed buildup of the substance was not sufficient to restrict the throttle flap from actuating.

The refueling station used for the spraying operations consisted of a large storage tank attached to a trailer, a filtering unit, and a supply hose, which was connected to the refueling tank. The supply hose had been purchased from a farm supply store, and its exterior was stamped with "farm fuel transfer hose w/static wire." According to the manufacturer's packaging label, the supply hose was not designed to dispense aviation fuel. Samples of fuel were collected from inside the refueling tank and the supply hose; the sample from the hose was pale green, indicating that some type of contamination was present, and the sample from the tank was light blue. Laboratory analysis of the fuel samples from the refueling tank and supply hose showed that they were substantially identical; however both had a high "unwashed gum" content from different sources; the unwashed gum content in the hose sample was consistent with an additive used in plastics and rubber hoses; whereas, the unwashed gum content in the fuel tank was consistent with a stabilizing additive common in fuels. However, it could not be determined whether the unwashed gum content from the hose would have affected engine operation.

Text from the NTSB. Open the NTSB docket for CEN15LA231 for the full record.