Incident Overview
A pilot was conducting a flight to enable passengers to photograph a boat off the coast of Beaufort, North Carolina. The helicopter was following the boat at an airspeed of 50 knots and an altitude between 100 and 150 feet above ground level (AGL) when a loud pop was heard. The pilot immediately checked all engine instruments, which indicated normal parameters.
Warning and Engine Response
Shortly after the pop, the low rotor warning light illuminated and the associated audio horn activated. The engine and rotor rpm began to decrease. The pilot increased throttle input, but the engine did not respond. In response, the pilot lowered the collective pitch control and initiated an autorotation to the water.
Post-Incident Examination
Following the water landing, the airframe, flight controls, engine assembly, and all accessories were examined. The inspection revealed no anomalies or malfunctions.
Pilot Actions
The pilot reported that the engine instruments remained normal after the pop, and that the throttle increase did not produce any change in engine performance. The decision to autorotate was made when the low rotor warning persisted and rpm decay continued.