What happened
During a flight intended for an ongoing drug eradication program, the pilot of a Schweizer 269 experienced two vibrations followed by a loud bang from the rear of the aircraft shortly after takeoff. The helicopter yawed to the right, forcing the pilot into an autorotation. The pilot attempted to maneuver toward a small clearing within a wooded area; however, the main rotor blades struck a pine tree approximately 30 feet tall at the edge of the clearing. The aircraft subsequently impacted the ground on its left side. The pilot was not injured.
The investigation
A review of maintenance records showed that the last annual inspection was completed on March 21, 2004, at an airframe total time of 5,506.2 hours. Investigators identified a previously issued Airworthiness Directive (AD) 80-05-05, which required inspections for Schweizer Helicopters Model 269 series aircraft to prevent fatigue failure of the tailboom center support fitting. No logbook entries were found indicating that the required inspections outlined in this AD had been performed.
Examination of the tail rotor assembly revealed that the tailboom saddle attachment was broken. Further inspection showed rubbing on the tail rotor drive shaft near the broken attachment point. The investigation determined that the tailboom support fitting fractured due to fatigue originating at the base of a large corrosion pit on the tip surface of the forward wall. This specific surface, which was in direct contact with the tailboom, contained extensive pitting damage and was only partially covered by paint. Following the fracture of the saddle support fitting, the tailboom dropped and rubbed against the tail drive shaft, causing it to fracture due to overstress.