NTSB Identification: MIA06LA126.
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Accident occurred Thursday, June 08, 2006 in Navarre, FL
Probable Cause Approval Date: 11/29/2007
Aircraft: Fairchild Hiller FH-1100, registration: N4035G
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.
While flying in straight and level flight at 600 feet and approximately 100 miles-per-hour, undetected fatigue cracks in the stainless steel plates of one of the tail rotor blade tension-torsion bars resulted in in-flight separation of one tail rotor blade, and subsequent structural separation of a portion of the ventral fin. The pilot executed an autorotative landing to shallow water and there were no injuries to the pilot or pilot-rated passenger. Eight of the 11 stainless steel plates of the tension-torsion bar assembly exhibited fatigue which originated from stress risers created during the manufacturing process (punching) of the holes of the plates. Reaming of the holes did not eliminate the surface created during the punching process. This problem was previously noted to exist and corrective action was taken in the form of an airworthiness directive (AD), but the AD was not applicable to the accident helicopter because the serial number of the accident tension-torsion bars was outside of the scope of the AD.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The inadequate manufacturing of the plates of the tail rotor tension-torsion bar assembly resulting in fatigue failure. Full narrative available
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