NTSB Identification: ATL91IA134.
The docket is stored on NTSB microfiche number 46303.
Scheduled 14 CFR operation of HENSON AIRLINES
Incident occurred Tuesday, July 16, 1991 in SAVANNAH, GA
Probable Cause Approval Date: 03/09/1993
Aircraft: de Havilland DHC-8-102, registration: N922HA
Injuries: 5 Uninjured.

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

AFTER FLT 4317 TOOK OFF, THE MAIN LNDG GEAR DID NOT RETRACT. THE FLT CREW ACCOMPLISHED THE EMERG CHECKLIST, EXTDD THE LNDG GEAR & MADE AN UNEVENTFUL LNDG. AN EXAM OF THE ACFT DISCLOSED THAT THE RGT LNDG GEAR RETRACTION FITTING HAD FAILED & A HYDRAULIC LINE WAS SEVERED. ALSO, THE QUANTITY LIMITING VALVE(S) WERE CORRODED & THE RESPECTIVE PISTON MOVEMENT WAS RESTRICTED. SUBSEQUENTLY, BOTH HYDRAULIC SYSTEMS WERE DRAIN OF FLUID. AN EXAM OF THE FITTING ATTACHMENT BOLTS REVEALED THE TOP BOLT LOST TORQUE & THE BOLT FAILED IN FATIGUE; THE BOTTOM BOLTS FAILED IN OVERLOAD. ADNLY, THE FITTING SPIGOT FAILED DUE TO HYDROGEN EMBRITTLEMENT; AN IMPROVED FITTING HAS BEEN PRODUCED TO CORRECT HYDROGEN EMBRITTLEMENT PROBLEMS. THE OPER CONDUCTED A FLEET CAMPAIGN & FND 13 LOOSE BOLTS IN OTHER 100 SERIES ACFT. SVRL AIRWORTHINESS DIRECTIVES WERE ISSUED TO CORRECT THE LOSS OF TORQUE ON ATTACHMENT BOLTS, WHICH INCLUDED CHECKING THE TORQUE AT THE 300 HR LNDG GEAR INSPN.

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

THE INADEQUATE INSPECTION PROCEDURES WHICH ALLOWED THE LOSS OF TORQUE ON THE TOP RETRACTION FITTING ATTACHMENT BOLT WHICH SUBSEQUENTLY FAILED IN FATIGUE. FACTORS WERE THE LOSS OF HYDRAULIC FLUID THROUGH A SEVERED LINE, AND THE CORROSION OF A HYDRAULIC QUANTITY LIMITING VALVE.

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