What happened
The pilot reported that the engine's revolutions per minute began to deteriorate while climbing toward cruise altitude. In response to the loss of power, he returned to the departure site. As the aircraft approached the landing area, the engine RPM decayed to flight idle. The pilot initiated an autorotation and executed a hard landing.
The investigation
Post-accident examination revealed that the engine operated for one hour in a test cell without evidence of malfunction. The fuel speed governor was removed and tested, functioning normally. However, during removal of the fuel metering system, a fragment of an O-ring was discovered lodged in a spring near the fuel ports.
Findings
The O-ring fragment likely blocked one of the fuel ports, causing the RPM to drop to flight idle. This mechanical obstruction led to the power loss and subsequent hard landing.