Overview
A pilot/owner and a passenger departed on a local flight in a helicopter. Approximately five minutes after takeoff, while the helicopter was orbiting the airport at an altitude of 200 to 300 feet above ground level, the engine lost power. The pilot performed an autorotation, which resulted in the helicopter contacting trees.
Wreckage Examination
Examination of the wreckage revealed that the single-drive dual-magneto had separated from the engine. The two magneto attaching studs on the engine were intact and undamaged; however, no nuts, washers, or flange clamps were attached to the studs. The flange of the magneto was also undamaged. The two flange clamps were found in the debris scattered below the helicopter.
Previous Event and Maintenance
During a previous flight, the pilot had experienced a dual magneto failure and successfully autorotated to a field. Subsequently, the pilot arranged for a mechanic to replace the magneto. The mechanic performed ground runs after the replacement, which were successful. The flight during which the engine power loss occurred was the first flight following the magneto change.