Event ATL91IA134

1991-07-16 SAVANNAH, Georgia, United States Airport · SAV None 1 aircraft Status: Completed

Registry · N922HA

FAA Aircraft Registry record.

Make / Model

HILLER UH-12E

TCDS

4H11 · SIAM HILLER HOLDINGS INC

Engine

LYCOMING VO-540-C2A (315 hp)

Seats / Engines

4 seats · 1 engine

Last airworthiness date

20150917

ADS-B equipped

Yes — Mode-S ACC648

Registrant of record

HILLER AVIATION GROUP INC

Source: FAA Aircraft Registry (releasable master file).

Aircraft involved

N922HA de Havilland DHC-8-102 None

Probable cause & findings

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.

Factual narrative

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. Source: NTSB Aviation Accident Database (Pre-2008 Archive) Retrieved: 2026-02-12

Verbatim from NTSB's published report. Source file NTSB_1991_ATL91IA134.txt. Findings + structured fields enriched from FAA avall.mdb. Full investigation docket on data.ntsb.gov ↗.

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