Fort Worth, TX, USA
N10375
HUGHES 269A
The certified flight instructor (CFI) and pilot receiving instruction were practicing hovering autorotations on a taxiway. With the skids on the ground for about 20 seconds after completing a hovering autorotation and with the engine at 2,000 rpm, the helicopter began to vibrate and violently shake, consistent with ground resonance. The vibrations and shaking continued to increase and lasted about 15 to 30 seconds. After the shaking stopped, the CFI shut down the helicopter. A postaccident examination of the helicopter revealed that the tail rotor and gearbox separated, and the fuselage was bent and deformed. No preimpact mechanical malfunctions or failures with the helicopter were noted that would have precluded normal operation.
After practicing some flight and landing maneuvers, the certified flight instructor and pilot receiving instruction decided to practice some hovering autorotations on a taxiway. With the skids on the ground for approximately 20 seconds after completing a hovering autorotation and the engine at 2,000 RPM, the helicopter began to vibrate and violently shake. The vibrations and shaking continued to increase and lasted approximately 15 to 30 seconds. After the shaking stopped, the certified flight instructor shutdown the helicopter. Postaccident examination of the helicopter revealed the tail rotor and gearbox separated, and the fuselage was bent and deformed. No preimpact mechanical malfunctions or failures with the helicopter were noted that would have precluded normal operation.
The inadvertent entry into ground resonance after a hovering autorotation.
Source: NTSB Aviation Accident Database
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