Incident Overview
During a training flight, a helicopter was being operated by a certified flight instructor and a pilot receiving instruction. After practicing various flight and landing maneuvers, the duo decided to practice hovering autorotations on a taxiway. Upon completing one such autorotation, the helicopter's skids remained on the ground for approximately 20 seconds with the engine running at 2,000 RPM. At that point, the helicopter began to experience vibration and violent shaking, which intensified over a period of 15 to 30 seconds.
Response and Examination
Once the shaking subsided, the certified flight instructor shut down the helicopter. A postaccident examination revealed that the tail rotor and gearbox had separated from the aircraft, and the fuselage was bent and deformed. Investigators found no evidence of preimpact mechanical malfunctions or failures that would have prevented normal operation.
Technical Details
The accident occurred during a training exercise focused on hovering autorotations, a maneuver designed to simulate engine failure at low altitude. The helicopter was on the ground with the engine at a reduced power setting when the vibrations began. The exact cause of the tail rotor separation was not determined from the examination, but no preexisting mechanical issues were noted.