McGrath, AK, USA
N315SH
HUGHES 500D
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.
On July 4, 2011, about 1915 Alaska daylight time, a Hughes 500D (369D) helicopter, N315SH, sustained minor damage following a partial loss of engine power and subsequent emergency landing, about 3 miles southwest of McGrath, Alaska. The helicopter was operated as a visual flight rules (VFR) on-demand charter flight under the provisions of 14 CFR Part 135. The helicopter was operated by Soloy Helicopters LLC., Wasilla, Alaska. The airline transport pilot and two passengers were not injured. Visual meteorological conditions prevailed, and VFR company flight following procedures were in effect. The main rotor blades were damaged during the emergency landing. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on July 4, the operator's president/director of operations reported that the helicopter was being used for a crew change at a remote mine site, about 15 miles southwest of McGrath. He said that as the pilot began a gradual descent to the McGrath Airport, the engine sound changed abruptly, which was immediately followed by the engine out audio horn, and a red engine out annunciator light. The pilot entered an emergency autorotation, turned the helicopter left, and selected a mostly open area that contained some trees as an emergency landing site. During the descent, the helicopter's main rotor blades struck several small trees as it touched down on the uneven, tundra-covered terrain. The helicopter was equipped with a Rolls-Royce 250-C20 series engine. A postincident inspection of the helicopter's engine revealed a fractured Pc (pneumatic) line on the engine governor. According to the engine manufacturer, the Pc line provides compressed air (bleed air) from the compressor to the fuel control and governor units, and if it becomes disconnected or breached, the engine will roll back to an idle, or near idle condition. During a follow-up telephone conversation with the NTSB IIC on March 28, 2012, the operator's president/director of operations reported that he had recently leased the incident helicopter, and a new Pc line was installed by the owner. He said that the new Pc line was installed on April 28, 2011, and it had accumulated 233.7 hours before the incident. He noted that the Pc line had not been removed by his maintenance personnel. During the manufacturing process, the Pc line is bent and manipulated to specific drawing specifications, allowing the rigid Pc line to be connected to the threaded compression T fitting on the engine governor and a threaded compression fitting on the engine fuel control. The fractured Pc line was sent to the NTSB's Materials Laboratory for examination. A senior Safety Board metallurgist reported that the separated Pc line displayed evidence of fatigue cracking that emanated from the flared portion of the line. In use, a B-nut and sleeve seals the flared portion of the line to the threaded T fitting on the engine governor. The fracture surface was found within the sleeve, and adjacent to the flared radius of the Pc line. The Safety Board metallurgist noted that the Pc line met the metallurgical material specifications, but his examination revealed a bend in a normally straight portion of the line, which would have placed stress on the Pc line when installed. It could not be determined when or how the bend occurred. A copy of the Safety Board metallurgist's report is included in the public docket for this incident.
A fatigue fracture of the governor-to-fuel control Pc line, which resulted in a partial loss of engine power.
Source: NTSB Aviation Accident Database
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