NTSB Identification: ATL07LA079
14 CFR Part 133: Rotorcraft Ext. Load
Accident occurred Tuesday, April 24, 2007 in Whiteville, NC
Probable Cause Approval Date: 05/06/2009
Aircraft: HUGHES 369D, registration: N11AS
Injuries: 1 Minor,1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
According to the pilots, the helicopter was at an altitude between 400 and 500 feet above ground level and at an airspeed between 75 and 80 knots when the engine lost power. The instructor-pilot took control of the helicopter, jettisoned the external load, and autorotated to a nearby corn field. He said that the engine "didn't sound like it was running and the engine out was activated." The helicopter touched down and slid 6 to 8 feet when one of the skids dug into the earth. The helicopter turned to the left about 45 degrees and rolled over on its right side. It was later found that the power turbine governor (PTG) spring had fractured in fatigue. The fracture originated from a drawing mark and was the result of deficiencies in the manufacturing process. The PTG spring "provides force opposing those exerted by rotating flyweights on the position of the governor lever. Failure of the spring would result in a false pneumatic signal to the fuel control and a corresponding reduction in fuel flow. The effect of the false pneumatic signal would be a pronounced reduction in fuel flow. At the reduced fuel flow, the engine could not sustain flight, and the symptoms of the reduced fuel flow might easily be interpreted by the pilot as an engine failure."
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A partial loss of engine power due to fatigue fracture of the power turbine governor spring, causing a false pneumatic signal to the fuel control and a corresponding reduction in fuel flow. Full narrative available
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