NTSB Identification: MIA07LA089.
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Accident occurred Friday, April 27, 2007 in Plant City, FL
Probable Cause Approval Date: 12/20/2007
Aircraft: Hiller UH-12C, registration: N92993
Injuries: 1 Serious,1 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.

The flight instructor stated that he was conducting a discovery flight with a student, and all of a sudden, while the helicopter was in cruise flight at an altitude of 600 feet, the engine shook violently, shaking the whole helicopter. He said this lasted for several seconds and then the engine ceased operating. He said he immediately entered autorotation and attempted to affect an autorotative landing. During the landing the helicopter incurred damage. A postcrash examination of the helicopter by an FAA licensed airframe and powerplant mechanic, under the supervision of an FAA airworthiness inspector revealed that the right magneto impulse coupling had failed, and caused the impulse coupling to impact the stud used for starting. According to the inspector, this resulted in the gear train stoppage, and the engine ceasing to operate. The maintenance log revealed that the helicopter had last been given an annual inspection on June 5, 2006.

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

The loss of engine power due to a magneto impulse coupling failure for undetermined reasons.

Full narrative available

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