What happened
On the day of the accident, a helicopter operating under contract for the U.S. Forest Service, based at Krassel Helibase (24K), Idaho, was tasked with transporting a relief Fire Lookout to a tower on Williams Peak. The flight involved a 4 nautical mile distance and an elevation gain of 2,844 feet. At the time, several forest fires were active in the area, and visibility in the lower valley was approximately 1 nautical mile; however, the passenger noted that visibility improved while flying up the ridge.
The aircraft was carrying two Forest Service personnel to assist with loading and unloading equipment and supplies from two open-top external cargo baskets secured to the skid gear via bungee cords. The return flight was planned to fly directly into the late afternoon sun. During the flight, the helicopter struck a 90-foot tall dead conifer (snag) on the ridgetop. Debris found at the site included thirteen cubitainers, two large plastic refuse bags, yellow crepe paper, and green paint chips. Following the initial impact with the tree, the aircraft continued down the mountainside, eventually crashing on a forest service road approximately 2,000 feet below the initial impact site and 1,230 feet lower in elevation.
The investigation
Investigators located a tail rotor paddle that had separated from its cuff further down the mountainside. Examination of the wreckage revealed that 11 of the water containers from one cargo basket had sustained 3 to 9 inch slashes caused by the tail rotor. A post-accident examination of the engine showed that the power turbine blades had been sheared from their disc, indicating an overspeed event. This condition was consistent with a sudden stoppage or main rotor blade strike that compromised the engine-to-main-rotor power train. No pre-impact anomalies regarding the engine or airframe were identified.
Findings
Interviews with Helitack crew members revealed that the pilot occasionally performed maneuvers described as "showy," including a maneuver known as a "sleigh ride," which involved topping a ridge and then dropping the collective and the nose. There were no injuries or fatalities reported in the source text, though the aircraft was destroyed.