Overview
A helicopter conducting a local photography (sightseeing) flight experienced a loss of engine power while hovering at approximately 200 feet above the Potomac River. The pilot initiated an autorotation and deployed the emergency floats. Subsequently, the helicopter impacted the river surface and rolled over, coming to rest upside down but supported by the floats.
Investigation Findings
After the helicopter was recovered, examination revealed no pre-impact part failure or malfunction of the airframe. However, a teardown of the engine disclosed that the spur adapter gearshaft (SAG), part number 6890482, had failed due to wear and subsequent fatigue. The failure occurred at the forward, splined end of the SAG.
Further examination found debris, composed of 82% silicon, inside the oil delivery tube. The oil jets for the number 2 and number 3 bearings were obstructed, but the oil jet for the SAG was not obstructed. The precise nature of the conditions and circumstances that led to the excessive wear on the SAG was not determined.
Operational Considerations
The height/velocity diagram in the flight manual indicated that hovering flight between 10 and 400 feet should be avoided to allow for a successful autorotative landing in the event of a power loss.