NTSB Identification: NYC90LA125.
The docket is stored on NTSB microfiche number 45743.
Accident occurred Tuesday, June 05, 1990 in BROOKVILLE, PA
Probable Cause Approval Date: 03/17/1992
Aircraft: HUGHES 369HS, registration: N8315F
Injuries: 1 Serious,2 Minor.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

DURING A POWER LINE PATROL FLT OVER WOODED TERRIAN, AT ABOUT 60 TO 85 FT AGL, TAILROTOR CONTROL OF THE HELICOPTER WAS LOST. THE HELICOPTER BEGAN TO SPIN TO THE RIGHT AND THE PLT ATTEMPTED A HOVERING AUTOROTATION. THE HELICOPTER BEGAN SPINNING FASTER. SUBSEQUENTLY, IT SETTLED ONTO THE POWER LINE, THEN CRASHED TO THE GROUND. AN EXAM REVEALED THAT THE TAIL ROTOR SWASHPLATE HAD FAILED FROM FATIGUE. THE SWASHPLATE OUTER DIAMETER WAS WORN WITH EVIDENCE OF SPALLING, THE BEARING INNER DIAMETER WAS LIGHTLY SCORED, THE SWASHPLATE THREADS WERE SEVERELY WORN WITH EVIDENCE OF SPALLING DUE TO RELATIVE MOTION WITH THE MATING THREADS OF THE LOCKNUT, AND THE LOCKWASHER TANG HAD WORN A SIGNIFICANT PATTERN IN THE SWASHPLATE KEYWAY.

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

WORN TAIL ROTOR PITCH CONTROL ASSEMBLY, DUE TO IMPROPER MAINTENANCE/INSTALLATION, AND SUBSEQUENT FATIGUE FAILURE OF THE TAIL ROTOR SWASHPLATE.

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