Accident Details
During a local sightseeing flight, the pilot reported that while on final approach for landing, the audio and light for low RPM sounded and illuminated. In response, the helicopter was autorotated. Upon touchdown, the helicopter initially bounced and then landed hard. The engine continued to run after the accident.
Post-Accident Examination
The engine was removed from the helicopter and placed on a test cell for evaluation. All engine parameters, with the exception of seal vent pressure, were found to be within the limits recommended by the manufacturer. The discrepancy in seal vent pressure was addressed by changing the vent orifice from a No. 2 to a No. 4. Following this change, the discrepancy was corrected.
Maintenance Action
The corrective action involved replacing the vent orifice, which resolved the seal vent pressure issue. No other anomalies were identified in the engine's performance during testing.
Conclusion
The accident sequence involved a low RPM warning on final approach, an autorotation, and a hard landing. Post-accident testing isolated a seal vent pressure anomaly, which was rectified by changing the vent orifice size. The engine remained operational throughout the incident and subsequent testing showed all other parameters within limits.