What happened
The helicopter was conducting cruise flight over open ocean water at 130 knots and 800 feet MSL when the pilot experienced a violent jerk or yaw accompanied by a grinding sound originating from the rear of the aircraft. The pilot attempted to use the anti-torque pedals to correct the yaw, but the controls provided no response. As the aircraft continued to yaw to the right and the nose pitched down, the pilot reduced throttle and initiated an autorotation.
The pilot reported that the helicopter completed nearly a 360-degree right turn before making contact with the water at a level pitch attitude with slight forward speed. One of the 4 passengers observed an object falling into the water just prior to the landing. The aircraft remained afloat due to its deployed skid-mounted float system and was recovered on the day of the accident. However, the aft section of the tail boom—including the vertical fin, tail rotor hub, blade assembly, and tail rotor gearbox—was missing at the time of recovery. This missing section was located approximately three months later.
The investigation
Examination of the tail boom separation area between stations 148 and 162 revealed multiple tears and fractures, with no evidence of fatigue found in the fractured metal. Investigators identified four tail rotor blade strikes occurring between tail boom stations 150.9 and 153.2.
One tail rotor blade was fractured approximately 14 to 18 inches from the inboard end, with the outboard portion missing; the metallic leading edge of the remaining section was twisted toward the tail boom. The second blade remained relatively intact but featured an indentation near the leading edge. White paint, matching the tail boom, was found smeared onto the black paint of the tail rotor blade at the site of the indentation. Detailed inspections of the tail rotor mast, controls, drive system, hub assembly, and the 90-degree gearbox mounting system failed to identify the specific cause for the in-flight contact between the blades and the tail boom.