NTSB Identification: NYC97LA101.
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Accident occurred Thursday, May 29, 1997 in GRANBY, NY
Probable Cause Approval Date: 12/31/1998
Aircraft: Hiller UH-12E, registration: N4029S
Injuries: 1 Serious.

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 pilot/owner had completed an uneventful aerial application flight, and he began to reposition the helicopter to another site. En route, at 500 feet AGL, the helicopter's engine began to overspeed. The pilot entered autorotation, and the helicopter struck trees and landed hard. Examination revealed the elastomeric torsional coupling inside the transmission, and the secondary steel drive flanges were sheared. The manufacturer's service data for the coupling stated that mandatory replacement of the coupling should occur at 5,000 hours or 5 years from the date embossed on the rubber, or in accordance with maintenance requirements for the coupling, which ever occurred first. The raised numbers on the coupling indicated a date of May 1988, 9 years before the accident.

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

failure of the pilot/owner to replace the torsional clutch as specified by the manufacturer, and subsequent failure of the helicopter's clutch, which resulted in a forced landing (autorotation). A related factor was: the encounter with trees in the emergency landing area.

Full narrative available

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