Flight and Incident
The pilot was conducting a fire suppression flight. While indicating an airspeed of approximately 100 knots, the empty water bucket, which had been occasionally unstable during the flight, was in use. The pilot heard a "bang," after which the helicopter yawed to the right and the tail rotor ceased spinning. The pilot jettisoned the bucket and, finding no suitable landing location, continued to the dip-point.
Emergency Landing
At the dip-point, the pilot selected an open area that was sloped. Due to uncertainty regarding the helicopter's airworthiness, the pilot did not search for an alternative landing site. He initiated a "needles joined autorotation." As the helicopter slowed, it began to spin to the right. The spin subsequently stopped, and the helicopter impacted the ground, then rolled onto its right side with little or no power applied to the main rotor.
Wreckage Examination
Examination of the wreckage determined that the water bucket had entered the arc of the tail rotor, and the tail-rotor driveshaft had been severed, consistent with overload. The bucket's operating manual noted that the bucket had been proven stable up to an airspeed of approximately 96 knots. Additionally, the manual indicated that a bucket with an overall length greater than the distance from the cargo hook to the front arc of the tail rotor could result in a tail rotor strike.
Emergency Procedures
The established emergency procedure for a complete loss of tail rotor thrust in flight was to reduce throttle to idle and immediately enter autorotation. It further stated that if a suitable landing site was not available, the vertical fin might permit controlled flight to a suitable area.