FTW01LA036
FTW01LA036

On December 1, 2000, at 1619 central standard time, a Bell 206B helicopter, N222LM, was substantially damaged during a water landing following a loss of engine power near Rockport, Texas. The helicopter was owned and operated by American Helicopters, Inc., of Galveston, Texas. The commercial pilot, sole occupant, was not injured. Visual meteorological conditions prevailed, and a company VFR flight plan was filed for the 14 Code of Federal Regulations Part 91 positioning flight. The flight originated from the Matagorda 603 offshore platform located in the Gulf of Mexico, at 1555, and was destined for the Aransas County Airport, Rockport, Texas.

The pilot reported that he had just made a "5 mile advisory call" announcing his intention to land at the Aransas County Airport when the engine chip light illuminated; this was followed by an immediate loss of engine power. The pilot initiated an autorotation, inflated the floats and made a mayday call with direction, distance from the airport, and the cause of the mayday call. During the descent he had "full [aircraft] control to include tail rotor authority." The helicopter landed on the water and remained upright and afloat. The pilot further reported that he exited the helicopter after the blades came to a stop due to the "waves and wind." After moving away from the helicopter it rolled over. The pilot crawled onto the belly of the helicopter and waited to be rescued. The pilot stated that the wind was from 045 degrees at 15 knots gusting to 25 knots.

An examination of the helicopter by the FAA inspector revealed that the tail rotor drive shaft was severed. Examination of the tail rotor drive shaft by an NTSB investigator revealed that the torsional twisting of the drive shaft was consistent with sudden stoppage of the tail rotor while the main rotor was driving. There was also evidence of a main rotor blade strike to the tail rotor drive shaft cover. Examination of the Allison 250-C20 turbine engine revealed that the N1 gas producer would not turn.

A disassembly examination of the engine was conducted on January 17-18, 2001, at Dallas Airmotive of Dallas, Texas. During the examination the compressor coupling adapter was found fractured. The part was sent to the NTSB Materials Laboratory in Washington, D.C. for further examination.

The examination of the compressor coupling adapter, P/N E23039791, S/N AG6-107, at the NTSB Materials Laboratory revealed fretting on the outer diameter surface where the impeller was press fit onto the adapter. The fretting was only present on the aft portion of the contact surface. Longitudinal scratches were observed around the circumference of the outer diameter surface. One scratch that was examined using scanning electron microscopy (SEM), showed smearing consistent with the aft movement of the compressor coupling adapter relative to the impeller, a relative motion consistent with the disassembly of the components. The aft fracture surface of the compressor coupling adapter was mostly obliterated by post fracture damage. The forward fracture surface had less post fracture damage. The fracture surface was relatively smooth, and crack arrest marks were observed, features typical of fatigue. The fracture was perpendicular to the outer surface and formed a shallow spiral around the longitudinal axis. The spiral was consistent with fatigue propagation with a clockwise (as viewed from aft) loading applied at the aft end relative to the forward end. The fatigue region was present nearly 360 degrees around the circumference. The fatigue features emanated from an origin area at the outer diameter surface in an area of fretting. Some deformation was observed on the faces of the hexagonal hole at the forward end of the compressor coupling adapter. No fretting was observed in that location.

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