NTSB Identification: ATL88FA213.
The docket is stored on NTSB microfiche number 38697.
Accident occurred Tuesday, July 12, 1988 in WALTERBORO, SC
Probable Cause Approval Date: 10/06/1989
Aircraft: BELL TH-1L, registration: N465JR
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 MILITARY SURPLUS HELICOPTER EXPERIENCED A 42 DEGREE GEAR BOX FAILURE WHILE LIFTING A LOAD OF LOGS. THE HELICOPTER SUBSEQUENTLY LANDED HARD AS THE PLT WAS ATTEMPTING TO AUTOROTATE TO A LDG. METALLURGICAL EXAMINATION OF THE GEARBOX REVEALED THAT A GEAR TOOTH ON THE INPUT QUILL PINION HAD FAILED DUE TO FATIGUE. NO EVIDENCE OF PREEXISTING DAMAGE OR IMPROPER OVERHAUL PROCEDURES WAS FOUND. THE GEARBOX TSO WAS ABOUT 440 HRS. THE 42 DEG GEAR BOX MAY BE OVER- HAULED ON CONDITION. INVESTIGATION REVEALED THAT THE HELICOPTER HAD EXPERIENCED IN EXCESS OF 13,000 LIFT CYCLES IN 380 HRS SINCE IT WAS PLACED IN SERVICE IN A LOGGING OPERATION. THE HELICOPTER HAD BEEN FAA-CERTIFICATED IN THE RESTRICTED CATEGORY FOR EXTERNAL LOAD OPERATIONS; HOWEVER, BELL RPTS THAT THE ACFT WAS NOT DESIGNED FOR REPEATED HEAVY LIFTING. THERE HAVE BEEN AT LEAST 2 OTHER SIMILAR FAILURES INVOLVING SURPLUS UH-1/TH-1 HELICOPTERS USED IN LOGGING OPERATIONS. THE LANDING SITE WAS STREWN WITH CUT TIMBER AND SMALL TREES.

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

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

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

ROTOR DRIVE SYSTEM,INTERMEDIATE GEARBOX(42 DEG)..FAILURE,TOTAL




Contributing Factors

OBJECT..TREE(S)


Contributing Factors

ACFT/EQUIP,INADEQUATE DESIGN..MANUFACTURER


Contributing Factors

INADEQUATE CERTIFICATION/APPROVAL,AIRCRAFT..FAA(ORGANIZATION)

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