NTSB Identification: CHI89FA071.
The docket is stored on NTSB microfiche number 41859.
Accident occurred Tuesday, April 11, 1989 in MILWAUKEE, WI
Probable Cause Approval Date: 06/30/1992
Aircraft: SIKORSKY S-58T, registration: N4247U
Injuries: 1 Serious.

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 aircraft accident report.

THE ACCIDENT HELICOPTER DESCENDED INTO SLOPING TERRAIN AND ROLLED OVER WHILE PERFORMING EXTERNAL LOAD OPERATIONS. THE HELICOPTER HAD JUST PICKED UP A LOAD AND WAS MOVING LATERALLY WHEN IT SUSTAINED A LOSS OF ANTI-TORQUE CONTROL AND THE FUSELAGE STARTED AN UNCOMMANDED AND UNCONTROLLED ROTATION TO THE RIGHT. THE PIC WAS ABLE TO JETTISON HIS EXTERNAL LOAD INTO A CLEAR AREA AND MOVE THE HELICOPTER AWAY FROM OBSTRUCTIONS BEFORE INITIATING AN OUT OF GROUND EFFECT HOVERING AUTOROTATION.

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

DISCONNECT OF THE TAILROTOR DRIVE SHAFT COUPLING.

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