Incident Overview
A pilot reported that shortly after takeoff, at approximately 800 feet above ground level (AGL), the helicopter experienced a violent vibration lasting 2 to 3 seconds. The pilot then re-entered the downwind leg to the airport, during which the vibration occurred again. Subsequently, the aircraft entered an uncontrollable spiral to the right and contacted the ground.
Post-Accident Inspection
Examination of the tail assembly revealed an in-flight separation of the tail rotor drive shaft. Evidence of fatigue fracture was noted in the tail assembly attach points.
Observations
The incident occurred during a flight that began with a takeoff from an airport. The pilot's actions after the initial vibration included returning to the airport pattern. The second vibration preceded the loss of control.
No further details regarding the aircraft type, registration, operator, date, location, occupants, injuries, or environmental conditions were provided in the source.