# NTSB DEN85FA180: Hughes 369HS, N5410W, Keystone, SD, July 6, 1985

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Field investigation · Final report
- Date: July 6, 1985, 11:09 local (17:09 UTC)
- Place: Keystone, SD
- Coordinates: 43.889007, -103.420616 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=43.8890&lon=-103.4206&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 4 fatal, 1 serious
- Status: Completed
- Report: Approved by Office Director
- NTSB case key (mKey): 16544
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN85FA180
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/16544/pdf
- Page: https://openairdocs.org/ntsb/DEN85FA180

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, approach - vfr pattern - base turn
  - rotor system,main rotor blade - separation (cause)
  - rotor system,main rotor hub - separation (cause)
  - maintenance,overhaul - improper, other maintenance personnel (cause)
- Loss of control - in flight, approach - vfr pattern - base turn
- In flight collision with object, descent - uncontrolled
  - object - tree(s)

## Analysis

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.

## Aircraft

- Registration: [N5410W](https://openairdocs.org/deregistered/N5410W-1991-03-28), registration cancelled 1991-03-28, S/N 900255S (OpenAirDocs)
- Reported make and model: HUGHES 369HS
- Registry model: [Hughes 369HS](https://openairdocs.org/model/hughes-369hs) (registry code 4470728) (OpenAirDocs)
- Category: Helicopter
- Serial number: 900255S
- Airframe hours: 7007
- Engines: ALLISON 250-C18B 278 horsepower turbo shaft
- Damage: Destroyed
- Flight: Part 91
- Operator: Rushmore Helicopters, Inc.
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, September 5, 1984, 100 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 24; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 1,479 total, 500 in this make and model, 1,389 as pilot in command, 87 in the last 90 days, 3 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: variable at 5 knots
- Visibility: 20 statute miles
- Lowest ceiling: none
- Temperature: 84 °F

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19850706033369A](https://openairdocs.org/incident/19850706033369A), Jul 6, 1985: Hughes 369HS, Keystone, SD, Destroyed, 4 fatal. The rotors separated from the helicopter. Straps failed from fatigue. Unapproved parts and improper maintenance.

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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