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NTSB Report
July 6, 1985 · Hughes 369HS · N5410W
Keystone, SD
Overview
Report Status
Preliminary report
Event Type
Accident
Date
July 6, 1985
Injury Outcomes
5 injuries (4 fatalities, 1 serious injury)
Location
Keystone, SD
Aircraft
Hughes 369HS
Tail Number
N5410W
Operator
Rushmore Helicopters
Injuries
Fatal
Aircraft Damage
Destroyed
NTSB Number
DEN85FA180
MAIN ROTOR HUB WAS OVERHAULED BY A REPAIR STATION THAT WAS NOT AUTHROIZED BY HUGHES HELICOPTERS FOR HUB OVERHAULS. THE MAIN ROTOR HUB AND BLADES SEPARATED IN-FLT 279 HRS AFTER OVERHAUL. THE ACFT CRASHED IN A DENSILY WOODED AREA. POST ACCIDENT EXAM OF THE MAIN ROTOR SYSTEM REVEALED THE TORSION-TENSION STRAP PACK FAILED DUE TO FATIGUE CRACKING IN THE STAINLESS STEEL LAMINANTS. METALLURGICAL EXAM REVEALED EVIDENCE OF CORROSION PITTING IN THE LAMINANTS. THE CORROSION PITS WERE THE ORIGIN OF FATIGUE CRACKS. THE MAXIMUM ALLOWABLE NUMBER OF LAMINANT FAILURES IN ANY ONE STRAP IS 3. THE FAILED STRAP PACK CONTAINED 9 FATIGUE FAILED LAMINANTS.
Full Narrative
MAIN ROTOR HUB WAS OVERHAULED BY A REPAIR STATION THAT WAS NOT AUTHROIZED BY HUGHES HELICOPTERS FOR HUB OVERHAULS. THE MAIN ROTOR HUB AND BLADES SEPARATED IN-FLT 279 HRS AFTER OVERHAUL. THE ACFT CRASHED IN A DENSILY WOODED AREA. POST ACCIDENT EXAM OF THE MAIN ROTOR SYSTEM REVEALED THE TORSION-TENSION STRAP PACK FAILED DUE TO FATIGUE CRACKING IN THE STAINLESS STEEL LAMINANTS. METALLURGICAL EXAM REVEALED EVIDENCE OF CORROSION PITTING IN THE LAMINANTS. THE CORROSION PITS WERE THE ORIGIN OF FATIGUE CRACKS. THE MAXIMUM ALLOWABLE NUMBER OF LAMINANT FAILURES IN ANY ONE STRAP IS 3. THE FAILED STRAP PACK CONTAINED 9 FATIGUE FAILED LAMINANTS.
Flight
Event TypeAccident
Event Time11:09 MDT
Nearest Airport1nm E
Runway0
Flight Plan FiledNone
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftHughes 369HS
Tail NumberN5410W
Aircraft CategoryHeli
DamageDestroyed
OperatorRushmore Helicopters
Operating RulePart 91
Engines1
Engine TypeTurboshaft
Engine DetailsAllison · 250-C18B · Turboshaft · 278
Seats5
People & Injuries
Injury Summary5 injuries (4 fatalities, 1 serious injury)
Fatal4
Serious1
Minor0
Uninjured0
Total5
Crew 1Age 24 · Second Class
Conditions
ConditionsVMC
LightDaylight
Wind5 kt
Visibility20 sm
CeilingNone
Temperature / Dew Point0 C
Altimeter0
Weather SourceWIT