Incident Overview
During an aerial application operation, a helicopter was conducting a procedure turn when a loud explosive noise was heard. Immediately following the noise, the engine RPM exceeded the rotor RPM, indicating a loss of normal power transmission.
Pilot Response
The pilot responded by reducing the throttle and attempting to enter an autorotation. However, the rotor RPM had decayed significantly, preventing a successful autorotative landing. The helicopter subsequently made a hard landing.
Investigation Findings
Investigators examined the helicopter and determined that the most probable cause for the loss of rotor RPM was a disconnect between the engine and the main rotor. The exact reason for this disconnect could not be identified.
Conclusion
The accident involved no other contributing factors beyond the mechanical disconnect. The investigation did not specify the helicopter type, registration, or any injuries.