# NTSB SEA90LA010: Hughes 369D, N9163F, Neah Bay, WA, October 27, 1989

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: October 27, 1989, 11:30 local (19:30 UTC)
- Place: Neah Bay, WA
- Coordinates: 48.329326, -124.630706 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=48.3293&lon=-124.6307&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report October 7, 1992
- Report: Approved by Office Director
- ADs cited in the narratives: [AD 88-17-09 R1](https://openairdocs.org/ad/88-17-09-R1) (OpenAirDocs)
- NTSB case key (mKey): 41142
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA90LA010
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41142/pdf
- Page: https://openairdocs.org/ntsb/SEA90LA010

## Probable cause

FATIGUE FAILURE OF ALL FOUR ATTACHMENT STUDS OF THE TAILROTOR GEARBOX RESULTING IN SEPARATION OF THE GEAR BOX, AND INADEQUATE MAINTENANCE INSPECTION.

## Sequence of events

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

- Airframe/component/system failure/malfunction, climb
  - rotor drive system,tail rotor gearbox(90 deg) - fatigue (cause)
  - maintenance,inspection - inadequate, company maintenance personnel (cause)
  - rotor drive system,tail rotor gearbox(90 deg) - separation
- Forced landing, landing - flare/touchdown
- In flight collision with terrain/water, landing
  - terrain condition - rough/uneven (contributing factor)

## Analysis

DURING AN EXTERNAL LOAD OPERATION, THE PILOT HAD JUST RELEASED THE LOAD AND WAS TRANSITIONING TO A CLIMB ATTITUDE WHEN THE TAIL ROTOR GEARBOX SEPARATED FROM THE TAIL BOOM. THE PILOT WAS UNABLE TO MAINTAIN CONTROL AND THE HELICOPTER COLLIDED INTO THE ROUGH TERRAIN. THE GEARBOX WAS METALLURGICALLY EXAMINED, REVEALING THAT ALL FOUR ATTACHMENT STUDS HAD FAILED DUE TO FATIGUE. FURTHER EXAMINATION REVEALED CONTAMINANTS ON THE GEARBOX MOUNTING PADS BETWEEN THE TAIL ROTOR GEARBOX AND THE TAIL BOOM; FRETTING WAS NOTED. AD88-17-09 AND SERVICE INFORMATION NOTICE DN-151/EN-39/FN-28 BOTH MANDATE INITIAL AND RECURRENT INSPECTION (EVERY FLIGHT) OF THE GEARBOX ATTACHMENT AREA.

## Aircraft

- Registration: [N9163F](https://openairdocs.org/deregistered/N9163F-1998-03-14), registration cancelled 1998-03-14, S/N 690540D (OpenAirDocs)
- Reported make and model: HUGHES 369D
- Registry model: [Hughes Helicopters HUGHES 369D](https://openairdocs.org/model/hughes-helicopters-hughes-369d) (registry code 4470706) (OpenAirDocs)
- Category: Helicopter
- Serial number: 690540D
- Airframe hours: 8187
- Engines: ALLISON 250-C20B 375 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Other work use, Part 133
- Registered owner: Eagle Air Helicopters, Inc.
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, May 9, 1989, 96 hours before
- Flight plan: Company VFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 41; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; flight hours: 9,796 total, 3,512 in this make and model, 9,505 as pilot in command, 332 in the last 90 days, 11 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: calm
- Visibility: 40 statute miles
- Lowest ceiling: none
- Temperature: -0 °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 19891027043679A](https://openairdocs.org/incident/19891027043679A), Oct 27, 1989: Hughes 369D, Neah Bay, WA, Substantial damage. Tail rotor gear box separated. Crash landed. Marks indicate gear box and fatigue cracks on studes existed long time

## Other investigations on N9163F (1)

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.

- [NTSB IAD80FLQ10](https://openairdocs.org/ntsb/IAD80FLQ10), Jan 11, 1980: Hughes 500D (N9163F), Dione, KY, destroyed

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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