NTSB Identification: NYC92GA089.
The docket is stored on NTSB microfiche number 47961.
Accident occurred Thursday, April 30, 1992 in MOUNT ZION, KY
Probable Cause Approval Date: 05/26/1993
Aircraft: MCDONNELL DOUGLAS 500E, registration: N97BR
Injuries: 3 Uninjured.

: NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this public aircraft accident report.

WHILE FLYING IN A CRUISE CONFIGURATION AT 1500 FEET MEAN SEA LEVEL, AND ABOUT 10 MINUTES INTO THE FLIGHT THE HELICOPTER STARTED TO VIBRATE. THE PILOT ELECTED TO MAKE A FORCED LANDING IN THE MOST SUITABLE AREA AVAILABLE. DURING THE DESCENT THE VIBRATION CONTINUED TO WORSEN. AT ABOUT 5 FEET ABOVE THE SELECTED LANDING SITE THE PILOT HEARD A LOUD BANG, THE HELICOPTER YAWED TO THE RIGHT AND PITCHED NOSE DOWN. THE PILOT LOWERED THE COLLECTIVE AND PUT THE HELICOPTER ON THE GROUND. METALLURGICAL EXAMINATION DETERMINED THAT THE LOSS OF THE ABRASION STRIP FROM THE LEADING EDGE OF TAIL ROTOR BLADE S/N 5086 INDUCED VIBRATIONAL STRESSES THAT WERE HIGH ENOUGH TO INITIATE FATIGUE FAILURE IN THE TAIL ROTOR GEAR BOX MOUNTING STUDS WHICH RESULTED IN THE SEPARATION OF THE GEAR BOX ASSEMBLY FROM THE HELICOPTER.

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

AN IN-FLIGHT SEPARATION OF THE TAIL ROTOR ASSEMBLY AS THE RESULT OF THE LOSS OF AN ABRASION STRIP FROM THE LEADING EDGE OF ONE OF THE TAIL ROTOR BLADES, WHICH INDUCED VIBRATIONAL STRESSES HIGH ENOUGH TO INITIATE FATIGUE FAILURE IN THE TAIL ROTOR GEAR BOX MOUNTING STUDS.

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