What happened
On July 4, 2011, at approximately 1915 Alaska daylight time, a Hughes 500D helicopter, registration N315SH, performed an emergency landing about 3 miles southwest of McGrath, Alaska. The aircraft was operating as a visual flight rules (VFR) on-demand charter flight for Soloy Helicopters LLC, performing a crew change at a remote mine site.
As the pilot began a gradual descent toward McGrath Airport, the engine sound changed abruptly. This was immediately followed by the activation of the engine-out audio horn and a red engine-out annunciator light. The pilot initiated an emergency autorotation and selected an open area containing trees as a landing site. During the touchdown on uneven, tundra-covered terrain, the main rotor blades struck several small trees, resulting in minor damage to the aircraft. There were no injuries to the pilot or the two passengers.
The investigation
Post-incident inspection of the Rolls-Royce 250-C20 series engine revealed a fractured Pc (pneumatic) line on the engine governor. This line provides compressed air from the compressor to the fuel control and governor units; a breach in this line causes the engine to roll back to an idle or near-idle condition.
An examination of the fractured line by a Safety Board metallurgist identified evidence of fatigue cracking originating from the flared portion of the line. While the line met all metallurgical material specifications, the investigation found a bend in a portion of the line that is normally straight. This bend would have placed additional stress on the line during installation. It was not determined when or how this bend was introduced to the component.