NTSB Identification: DEN85FA180.
The docket is stored on NTSB microfiche number 30882.
Accident occurred Saturday, July 06, 1985 in KEYSTONE, SD
Aircraft: HUGHES 369HS, registration: N5410W
Injuries: 4 Fatal,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.

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.

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

ROTOR SYSTEM,MAIN ROTOR BLADE..SEPARATION

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

ROTOR SYSTEM,MAIN ROTOR HUB..SEPARATION

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

MAINTENANCE,OVERHAUL..IMPROPER..OTHER MAINTENANCE PERSONNEL

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