Incident Overview
During a flight en route to a practice area, the helicopter's crew felt a slight vibration through the airframe. Moments later, the vibration level became severe. The certified flight instructor (CFI) immediately entered an autorotation. During the descent, the CFI looked back and observed that the tail rotor was disabled. The autorotation was completed to a field without further incident.
Post-Accident Examination
A metallurgical examination conducted after the accident revealed that the center aft mast support tube had fractured in flight. The fracture surface exhibited characteristics consistent with fatigue, indicating a progressive failure over time.
Sequence of Events
The in-flight fracture of the center aft mast support tube led to a loss of structural integrity, causing the severe vibrations and subsequent tail rotor disablement. The CFI's prompt decision to enter autorotation and land in a field prevented further escalation. No other details regarding aircraft type, registration, or injuries were provided in the investigation source.