NTSB Identification: FTW84LA136.
The docket is stored on NTSB microfiche number 24611.
Accident occurred Monday, February 13, 1984 in MORGAN CITY, LA
Aircraft: SIKORSKY S-58E, registration: N70709
Injuries: 1 Serious,3 Minor,1 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.

THE HELICOPTER WAS HOVERING ABOVE TREES AT ABOUT 100 FT AGL WHEN THE TAIL ROTOR CHIP DETECTOR LGT FLICKERED SVRL TIMES, THEN ILLUMINATED STEADILY. THIS WAS FOLLOWED BY A LOUD GRINDING NOISE FROM THE TAIL AREA & THE ACFT YAWED TO THE RIGHT. THE ACFT ENTERED AN AUTOROTATION AFTER MAKING 3 TURNS TO THE RIGHT. IT DESCENDED INTO THE TREES AT WHICH TIME THE MAIN ROTOR BLADES WERE BROKEN OFF. AN EXAM OF THE INTERMEDIATE TAIL ROTOR GEAR BOX DISCLOSED THAT 6 TEETH IN THE INPUT BEVEL PINION GEAR, PN S1635-64114, HAD FAILED IN THE ROOT AREA. A METALLURGICAL EXAM DETERMINED THAT THE FAILURE ZONE HAD FATIGUE INDICATIONS. CRACKS WERE FOUND IN OTHER AREAS OF THE GEAR BOX. SIKORSKY ENGINEERS DETERMINED THAT THE GEAR BOX HAD BEEN SUBJECTED TO HEAVY LOADS. THE GEAR BOX HAD BEEN LAST OPENED IN 1968. ONE GEAR WAS NOT A SIKORSKY PRODUCT.

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

ROTOR DRIVE SYSTEM,INTERMEDIATE GEARBOX(42 DEG)..FATIGUE



Contributing Factors

OBJECT..TREE(S)

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