Robinson Helicopter Company R44 II N247DB accident near Gunnison, Utah

Probable cause

A total loss of engine power for reasons that could not be determined based on the available evidence.

NTSB analysis

The commercial pilot was nearing the end of his second agricultural application pass; about the time that he turned off the spray system, he heard a "pop" and felt a "thump" that shook the helicopter. After he observed chemical spray in the air and along the side of the helicopter, he pushed the "kill" button for the spray pump. As he was doing so, the engine rpm dropped, and the pilot heard the engine "sputtering." The pilot lowered the collective to re-establish main rotor rpm; the engine subsequently experienced a total loss of power. He entered an autorotation between 50 and 75 ft above the ground, and the helicopter landed hard.

The spray system was recently installed, and the helicopter had flown about 16 hours since the installation. The spray system pump was mounted on the right side skid. The engine air filter compartment was located above and behind the spray pump.

A postaccident examination of the spray system revealed that the plastic pipe nipple on the spray system fractured. The initial crack progressed through the wall of the nipple during flight and caused a pesticide leak. Examination of the internal and external surfaces of the engine intake air filter revealed no cake deposits.

Because there was no evidence of chemical residue on the airframe between the engine and the air intake filter and the condition of the air filter was relatively clean, it is unlikely that the engine ingested enough chemical to cause the total loss of power. Additionally, the operator later had the engine successfully run in a test cell with no anomalies noted; therefore, the reason for the loss of engine power could not be determined.

Text from the NTSB. Open the NTSB docket for WPR16LA165 for the full record.