Accident Overview
On August 8, 2013, at approximately 1430 Alaska daylight time, a restricted category Bell UH-1B helicopter, registration N70NW, sustained substantial damage during a forced landing at Tok Junction Airport, Tok, Alaska. The helicopter was operated by Northern Pioneer Helicopters of Big Lake, Alaska, under 14 CFR Part 133 for external load aerial firefighting. The certificated commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed, and U.S. Forestry Service flight following procedures were in effect.
Flight Narrative
The flight departed Tok Junction Airport around 1400. The pilot reported that the helicopter was dispatched to support U.S. Forestry Service firefighting operations. During the accident flight, the pilot completed a water drop using a water bucket attached to a 100-foot long-line on the helicopter's belly-mounted cargo hook. Immediately after releasing the water at a predetermined site, he noticed a degradation of directional control. He was able to maintain control and returned to Tok Junction Airport with the long-line and bucket still attached. As the helicopter approached the airport, the pilot jettisoned the long-line and bucket before attempting an emergency stuck-pedal run-on landing. During the approach, the helicopter began drifting left toward a stand of trees. Unable to maintain directional control, he initiated a go-around, and the main rotor blades struck the tops of the trees. After realigning with the runway, he performed a slow-speed run-on landing on a gravel area adjacent to the runway. During touchdown, the helicopter bounced multiple times and came to rest upright. Substantial damage occurred to the fuselage, vertical fin, and tail rotor blades.
Examination Findings
The helicopter was equipped with after-market tail rotor blades. An on-scene examination by the operator revealed that the pitch change rod and crosshead bearing retention nut protruded outboard through the tail rotor crosshead. The entire tail rotor gearbox assembly was removed for further examination. On January 14 and 15, 2014, under NTSB supervision, the tail rotor pitch change assembly was examined at Bell Helicopter's field investigation laboratory in Hurst, Texas. The examination showed that the tail rotor crosshead bearing's inboard shoulder of the split inner ring was spalled and completely worn away, allowing the bearing's outboard set of balls to run over the pitch change rod's seating flange for the split inner ring inboard shoulder. The pitch change rod then migrated outboard, machining a hole through the end of the crosshead. As a result, the maximum tail rotor blade pitch change decreased.