What happened
Witnesses reported that the HU-269 aircraft came apart while in flight. Radar data tracked the aircraft at an altitude of 2,600 feet when it performed a right turn of approximately 35 degrees over a duration of about four seconds. Following this maneuver, the aircraft underwent general disintegration.
The investigation
Mechanical examination of the wreckage revealed that the splines of the tail rotor splined drive sleeve were excessively worn. This wear resulted in a loss of torque transmission to the tail rotor. Investigators noted that two other HU-269 aircraft exhibited similar wear patterns on their splined sleeves.
Maintenance records indicated that a 300-hour inspection requires the removal and inspection of the upper pulley assembly, as well as the lubrication of bearings. Additionally, Schweizer Aircraft Corp had issued Service Bulletin N-219 one month prior to the accident, which mandated the retorquing of the spline retaining nut. While the aircraft was still within the required compliance window for this bulletin, the task had not yet been performed.