NTSB Identification: ATL96LA104.
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Accident occurred Thursday, July 11, 1996 in COTTONDALE, FL
Probable Cause Approval Date: 04/29/1997
Aircraft: Hiller UH-12E, registration: N102HT
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

Approximately two minutes into the climbout, the pilots felt a vibration in the airframe followed by a loud bang. The pilots entered an autorotation and selected a field for a forced landing. The pilots reported that, subsequently, as they were attempting to control the helicopter, the flight controls would not respond to inputs. Control of the helicopter was lost, and it impacted the ground inverted. Examination of the helicopter disclosed that the main drive clutch and engine gimble ring with the torsional coupling had failed. Debris from the failed components was not recovered for examination. A review of the maintenance logs showed that the drive coupling assembly had 511 hours of total service since new. Wreckage examination also disclosed that the entire transmission assembly had rotated from its normally installed position, and that the flight control rods were displaced from their normal position.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

failure of the main rotor drive torsional coupling and inner gimbal ring, which resulted in jamming of the flight controls during an attempted autorotation.

Full narrative available

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