Incident Overview
A helicopter was in cruise flight over open ocean water at an altitude of 800 feet MSL and a speed of 130 knots when the pilot felt a "violent jerk or yaw" and heard a grinding sound emanating from the rear of the aircraft. The pilot attempted to correct the yaw using the anti-torque pedals but received no response, and the helicopter continued to yaw to the right while the nose pitched down.
Emergency Maneuver
The pilot reduced the throttle and initiated an autorotation. According to the pilot, the helicopter made "almost" a 360-degree right turn before contacting the water at a level pitch attitude with "slight" forward speed. One of the four passengers recalled seeing an object fall and hit the water, "leaving a circular motion" on the surface, just prior to landing.
Post-Accident Recovery
The helicopter remained afloat on its deployed skid-mounted float system and was recovered on the day of the accident, except for the aft section of the tail boom (including the tail rotor gearbox, vertical fin, and tail rotor hub and blade assembly), which was missing. This section was recovered approximately three months later.
Examination Findings
Detailed examination of the tail boom separation area revealed multiple fractures and tears between tail boom stations 148 and 162. No evidence of fatigue was found in the fractured area. There was evidence of four tail rotor blade strikes between tail boom stations 150.9 and 153.2.
One tail rotor blade was fractured approximately 14 to 18 inches from its inboard end, with the outboard section missing. The metallic leading edge of the remaining inboard section was deformed and twisted toward the tail boom. The other tail rotor blade was relatively intact, with an indentation near the leading edge on the side facing the tail boom, located about 18 inches from the inboard end. White paint, similar to that on the tail boom, was found smeared onto the blade's black paint in the area of the indentation.
Component Inspection
Detailed examinations of the tail rotor hub and blade assembly, tail rotor mast, tail rotor controls, tail rotor drive system, and the 90-degree gearbox mounting system did not reveal the reason for the in-flight contact of the tail rotor blades with the tail boom.