PIGEON FORGE, TN, USA
N999TV
Bell 206B
The helicopter was refueled before flight. About 1 minute after takeoff, at about 500 feet agl, the engine lost power. The pilot enter an autorotation and established a glide to a field ahead. As he approached the field, he pull up the collective to clear a house and a ditch. Subsequently, the main rotor rpm decreased and the helicopter touched down hard. Postcrash examination of the helicopter revealed the engine PC air line had separated near the attaching nut on the compressor scroll end. Metallurgical examination showed the tube had separated due to fatigue cracking, which was induced by installation damage. No other preaccident failure or malfunction of the engine, helicopter structure, or flight controls was found. Allison Engine Company representatives stated the engine would go to minimum fuel flow after separation of the PC line.
On July 11, 1996, about 1630 eastern daylight time, a Bell 206B, N999TV, registered to Waldens Creek Helicopter Company, and operated by Scenic Helicopter Rides, LTD., as a Title14 CFR Part 91 sightseeing flight, landed hard following loss of engine power near Pigeon Forge, Tennessee. Visual meteorological conditions prevailed at the time and no flight plan was filed for the local flight. The helicopter received substantial damage and the commercial-rated pilot received serious injuries. The four passengers received minor injuries. The flight originated from Pigeon Forge a minute before the accident. The pilot stated that the helicopter was refueled before departure. About 1 minute after takeoff, while at 500 feet agl, the engine failed. He entered autorotation and set up for landing in a field ahead. As he neared the field it became apparent he would hit a house or a ditch if he did not extend his glide. He pulled up on the collective and was able to clear the obstacles; however, main rotor speed was now about 60-70 percent. As he flared for landing he used up the remainder of the rotor speed and the helicopter touched down hard. Postcrash examination of the helicopter was performed by an FAA inspector and representatives of Allison Engine Company. No evidence to indicate precrash mechanical failure or malfunction of the helicopter structure or flight controls was found. Examination of the engine showed the PC air line which runs from the compressor scroll to the engine governor was separated near the attaching nut at the compressor scroll end. No other evidence of failure or malfunction of the engine was found. Metallurgical examination of the separated PC line was performed by the NTSB Materials Laboratory. The line had fractured about .43 inches from the flared end at a location approximately corresponding to the end of the attaching nut ferrule. The outer diameter surface of the tube adjacent to the fracture had severe circumferential scoring and two areas of heavy fretting damage on diametrically opposite sides of the tube. The fracture surfaces revealed fatigue progression emanating from a linear origin area of the outside diameter of the tube which coincided with one of the fretting areas. See Metallurgist's Factual Report. Representatives of the Allison Engine Company stated that upon separation of the PC air line and loss of this pressure to the engine governor, the engine fuel system will go to a minimum fuel flow condition which operates the engine below normal flight idle speed.
fatigue failure of the engine PC line, induced by damage from improper installation, which resulted in a loss of engine power and an autorotative landing to unsuitable terrain.
Source: NTSB Aviation Accident Database
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