Accident Details
A helicopter experienced a tail boom failure during landing following a practice hovering autorotation. The pilot reported that the accident occurred after the third hovering autorotation landing of the session. He stated that the touchdown was acceptable and would have met check ride criteria. Approximately 2 seconds after touchdown, an "obvious component failure" was felt throughout the airframe, accompanied by severe vibrations and "audible and physical indications" of failure.
Pilot Observations
After exiting the aircraft, the pilot expected to find a problem in the main rotor head and was surprised to discover the tail boom bent downward at the midpoint.
Postaccident Examination
A postaccident examination of the helicopter revealed that the tail boom was fabricated from skins with a thickness of 0.025 inches, as opposed to the skin thickness of 0.032 inches identified in the structural repair manual. The helicopter records showed that the tail boom was originally installed on the new helicopter at the factory and had accumulated 14,053 hours in service.