Hughes 500D N315SH incident near Mcgrath, Alaska

Probable cause

A fatigue fracture of the governor-to-fuel control Pc line, which resulted in a partial loss of engine power.

NTSB analysis

The pilot reported that during a descent, the helicopter's engine sound changed abruptly and was immediately followed by the engine-out audio horn, and a red engine-out annunciator light. She entered an emergency autorotation, and then selected a mostly open area that contained some trees as an emergency landing site. During the emergency landing, the main rotor blades struck several small trees as the helicopter touched down on the uneven, tundra-covered terrain. A postincident inspection revealed a fatigue fracture in the engine Pc line that provided compressed air to operate the engine governor and fuel control units. The Pc line met the metallurgical material specifications, but there was a bend in a normally straight portion of the line, which would have placed stress on the Pc line when installed. The additional stress likely resulted in the eventual fatigue failure of the line. It could not be determined how or when the bend occurred.

Text from the NTSB. Open the NTSB docket for ANC11IA059 for the full record.