Incident Overview
A helicopter experienced an in-flight separation of its tailboom assembly during a maintenance test flight. The pilot, who was also a certificated airframe and powerplant mechanic, had recently replaced the tailboom assembly. At the time of the accident, the pilot was conducting a maintenance test flight.
Sequence of Events
The pilot executed one autorotation with a power recovery and then reentered the traffic pattern. Ground witnesses reported that as the helicopter entered the base leg, they heard an explosive sound, followed by the tailboom assembly separating from the helicopter.
Post-Accident Examination
Examination of the wreckage revealed that the main rotor blade had struck the tailboom. Subsequently, the tail rotor blades went out of track and struck the vertical fins, resulting in the separation of the upper vertical fin. The main rotor blades exhibited damage consistent with low rotor RPM. No evidence of any preexisting malfunctions was found.