Whiteville, NC, USA
N11AS
HUGHES 369D
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."
On April 24, 2007 approximately 0840 eastern daylight time, a Hughes 369D, N11AS, registered to and operated by Aerial Solutions, Inc., of Tabor City, North Carolina, was substantially damaged when it rolled over following an autorotation after the engine lost power near Nakina, North Carolina. Visual meteorological conditions prevailed at the time of the accident. The training flight was being conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91, and a company visual flight rules (VFR) flight plan was on file. The instructor-pilot received minor injuries, and the pilot-receiving-instruction was not injured. The cross-country flight originated from a private field near Tabor City approximately 0830, and was en route to Whiteville, North Carolina. The purpose of the flight was to train the pilot in external load operations. To simulate these conditions, two tires were attached to end of a 50-foot cable. According to the instructor-pilot's statement, the helicopter was at an altitude between 400 and 500 feet above ground level (AGL) and at airspeed between 75 and 80 knots when the engine "went to flight idle/loss power (sic)." The instructor-pilot took control of the helicopter, jettisoned the external load, and auto rotated to a nearby corn field. He said 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. One of the skids dug into the earth. The helicopter turned to the left about 45 degrees and rolled over on its right side. The other pilot's statement corroborated what the instructor-pilot reported. On June 13, 2007, the engine was functionally tested at Rolls-Royce in Indianapolis, Indiana. The engine did not start on the first attempt. Engine ignition occurred on the second attempt, but auto shutdown occurred before ground idle speed idle was attained. Engine ignition occurred on the third attempt, but the engine shut down for unknown reasons a "hung start" occurred on the fourth attempt. The engine finally started on the fifth attempt, and accelerated to ground idle. As power was brought up to takeoff, a "whine" could be heard. The power turbine governor (PTG) was removed from the engine and taken to Honeywell Controls in South Bend, Indiana. The PTG spring was found fractured. The fracture originated from a drawing mark on the spring material and was as a result of fatigue. According to Rolls-Royce, the governor 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. 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."
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.
Source: NTSB Aviation Accident Database
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