Accident Overview
A pilot conducting sightseeing flights from a rodeo and fairground area experienced a tail rotor blade separation during a critical phase of takeoff. The loss of directional control prompted the pilot to attempt an autorotative landing. After spinning approximately three times, the pilot pulled full collective just before the helicopter impacted the ground. The helicopter sustained substantial damage.
Investigation Findings
Post-accident examination of the tail rotor assembly revealed that the tension-torsion (T-T) bar assembly, part number 24-55106, had failed at the location where the attachment bolt passes through the T-T straps. A metallurgical examination identified chlorine-rich deposits in the fracture area. The grease from the T-T bar cavity had darkened, and the cavity for the other set of T-T straps contained a small amount of fluid with an unpleasant odor. Analysis of the grease showed excessive amounts of chlorine.
Probable Cause
The evidence indicated that water and chlorine contamination resulted in stress corrosion, leading to the eventual failure of the T-T bar assembly.