On May 11, 1990, a Hughes 369E (registration N5217N) was involved in an aviation accident near Firebaugh, CA. Investigators recorded the probable cause as: FAILURE BY COMPANY MAINTENANCE TO PERFORM A MANDATORY COMPRESSOR SECTION INSPECTION THAT RESULTED IN THE UNDETECTED EROSION OF THE COMPRESSOR VANES AND ENGINE FAILURE. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter lost engine power during a climbing left turn after hearing a loud bang. The pilot entered autorotation but could not regain rotor RPM. During the hard landing, the main rotor blades severed the tailboom. Examination revealed a failed third-stage compressor and eroded compressor case plastic, and no evidence of required compressor inspection at 1,750 hours.
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.