Accident Sequence
During a flight, the pilot was orbiting a fishing vessel when a loud bang was heard. The aircraft subsequently pitched forward and entered an uncommanded spin to the right. The pilot responded by lowering the collective control and initiating an emergency autorotation to the water. Control of the helicopter was difficult to maintain, resulting in a hard landing on the water surface.
Post-Accident Inspection
Following the accident, an inspection of the aircraft revealed that the anti-torque rotor and hub were missing. Witnesses reported observing the anti-torque blades and hub separate as a single unit shortly before the accident occurred.
Pilot Report
The pilot stated that previous inspections had not detected any indications of a void on either of the anti-torque blades. Additionally, the aircraft was reported to be in compliance with all applicable airworthiness directives and service information notices at the time of the flight.
Laboratory Findings
A laboratory examination of the remaining portion of the anti-torque system gearbox did not reveal any evidence of preexisting cracks on the fracture surface. The absence of such indications suggests that the failure did not originate from a detectable defect in the gearbox component examined.