Accident Description
A helicopter was in a climbing left turn at approximately 125 feet above ground level after releasing an external load when the pilot heard a loud bang. The engine then lost power and the pilot entered autorotation. The pilot noted that the main rotor RPM was low and was unable to regain any main rotor RPM before the landing flare. At touchdown, the main rotor blades flexed downward and severed the tailboom.
Engine Examination
Post-accident examination of the engine revealed that the third stage compressor had failed, and the failure damaged the remaining stages of the compressor. The compressor case plastic was eroded.
Maintenance History
The engine had undergone major maintenance at 1,774.5 hours, which required removal of the turbine section. According to the engine logbooks, there was no evidence that the compressor section had been inspected at 1,750 hours as required by the manufacturer. The engine maintenance manual warns that erosion will cause damage to compressor blades and vanes.