Accident Narrative
Witnesses reported that the helicopter came apart while in flight. Radar data indicated the aircraft was at an altitude of 2,600 feet when it executed a right turn of approximately 35 degrees over a span of about four seconds. Subsequently, the helicopter sustained general disintegration.
Investigation Findings
Examination of the wreckage revealed that the splines of the tail rotor splined drive sleeve were excessively worn. This wear rendered the component unable to transmit torque to the tail rotor, leading to a loss of tail rotor control. Two other aircraft of the same model (HU-269) were found to have similar wear on the splined sleeve.
Maintenance and Service Bulletin
The 300-hour inspection for this helicopter type requires the removal and inspection of the upper pulley assembly, as well as lubrication of bearings. Additionally, Schweizer Aircraft Corporation had issued Service Bulletin N-219 approximately one month prior to the accident. The bulletin called for retorquing of the spline retaining nut. The accident helicopter was within the required compliance time for this bulletin, but the bulletin had not been performed.