Accident Description
The pilot reported that while maneuvering at an altitude between 250 and 300 feet and video taping a boat, three dull thumps were heard. Subsequently, the helicopter began to settle and the engine appeared to lose power. The pilot lowered the collective and nosed the helicopter over. With engine power seemingly low, the pilot elected to land on the water.
Postcrash Examination
A postcrash examination of the aircraft structure, aircraft systems, flight controls, engine assembly, and all engine controls revealed no evidence of precrash failure or malfunction. Uncontaminated Jet-A fuel was found in both the airframe and engine fuel systems.
Audio Analysis
Approximately two minutes of audio information from the video camera used by the passenger-photographer on the helicopter was subjected to frequency analysis. The analysis showed that the engine N-1 speed was steady at 92% until 6.99 seconds before water impact, at which point it decreased steadily to flight idle. Rotor speed remained steady at 99.8% until the N-1 speed began to decrease to idle. Rotor speed then dropped to 92.3%, and the low rotor warning horn activated when rotor speed reached 96.3%. No thumps, as reported by the pilot, could be heard on the audio recording.