THE HELICOPTER IMPACTED TO THE GROUND AFTER A LOSS OF TAIL ROTOR THRUST DURING AN ATTEMPTED TAKEOFF. INVESTIGATION REVEALED THE INTERMEDIATE FLEX PLATE AND TWO CLUTCH YOKES AND FAILED. A METALLURGICAL EXAMINATION REVEALED THAT THE WASHERS IN ONE OF THE FASTENER JOINTS WERE MISPLACED. A WARNING IN THE MANUFACTURER'S MANUAL STATES: 'A559 NICKEL-PLATED RADIUSED WASHERS ARE REQUIRED ON EACH SIDE OF THE A193 FLEXPLATES OR FRETTING FAILURE MAY OCCUR WITHIN A FEW HOURS.' RECORDS INDICATE THE MOST RECENT ANNUAL INSPECTION WAS SIGNED OFF ON OCTOBER 19, 1989, AND THE AIRCRAFT HAD ACCUMULATED 119 HOURS SINCE THAT TIME. THE HELICOPTER HAD UNDERGONE A PRE-PURCHASE INSPECTION ABOUT ONE MONTH PRIOR TO THE ACCIDENT.

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

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