Accident Sequence
While cruising, the pilot detected airframe buffeting followed by a left yaw. Engine instruments showed decreasing power output and a high turbine outlet temperature. The engine chip and failure lights illuminated. The pilot executed an autorotation and had to extend the glide to reach the only suitable landing area, resulting in a downwind landing. As the helicopter slid to a stop, the main rotor severed the tail boom.
Previous Maintenance Issues
A review of the operator's daily flight sheets for the accident helicopter revealed that an engine chip light had illuminated on the preceding flight. The corrective action taken was to clean the chip plug and reinstall it. No test flight or further inspection of the plug was performed as required by the maintenance manuals.
Engine Examination
Disassembly of the engine revealed that bearings number 1 and 2 in the compressor module had failed. Further review of maintenance records showed that the compressor module had previously been installed in an engine involved in a helicopter accident in May 1992. At that time, the compressor module was not disassembled for inspection as required by the overhaul and maintenance manual, nor was it signed off for return to service. The module was subsequently installed by the operator into the accident helicopter's engine on November 21, 1992.