Accident Summary
A helicopter was being operated at approximately 100 feet above ground level with a hopper extended from a cable. Witnesses reported hearing a loud popping sound and observed that the tail rotor was not turning, with one blade appearing to hang. The pilot stated there was no warning of an impending anti-torque control problem before losing control of the helicopter. The aircraft subsequently collided with trees and crashed.
Investigation Findings
Examination of maintenance records revealed that the pilot had reported an oil leak from the 90-degree gearbox on April 11, 1989. The company mechanic replaced the gearbox, and a functional test flight was completed. The accident occurred after approximately six additional hours of operation.
Inspection of the tail rotor assembly showed that one of the two retention bolts was missing from the tail rotor pitch change crosshead. Threaded imprints were found inside the respective crosshead retention thru-bolt hole. The retention bolt, nut, washer, and cotter pin were not recovered.
Both tail rotor blades contained chordwise marks that corresponded to marks on the vertical fin, located opposite the tail rotor tip path plane. This indicates contact between the blade and fin after separation.