# NTSB ANC92FA159: Hughes 369D, N8697F, Nunavaugaluk Lk, AK, September 9, 1992

- Type: NTSB accident investigation
- Classification: Accident · Serious injuries · Field investigation · Final report
- Date: September 9, 1992, 10:10 local (18:10 UTC)
- Place: Nunavaugaluk Lk, AK
- Coordinates: 58.819282, -157.859024 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=58.8193&lon=-157.8590&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: Serious injuries
- Injuries: 2 serious
- Status: Completed, report September 29, 1993
- Report: Approved by Office Director
- NTSB office: Alaska Regional Office
- NTSB case key (mKey): 5649
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC92FA159
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/5649/pdf
- Page: https://openairdocs.org/ntsb/ANC92FA159

## Probable cause

THE SEPARATION OF THE TAIL ROTOR ABRASION STRIP AND THE SUBSEQUENT TOTAL LOSS OF THE TAIL ROTOR. FACTORS CONTRIBUTING TO THE ACCIDENT WERE: INSUFFICIENT MANUFACTURER'S MAINTENANCE DESIGN CHANGES, INADEQUATE AIRCRAFT EQUIPMENT DESIGN BY THE MANUFACTURER AND INSUFFICIENT STANDARDS OF THE FAA CERTIFICATION ORGANIZATION.

## Sequence of events

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

- Airframe/component/system failure/malfunction, cruise - normal
  - rotor system,tail rotor blade abrasion strip - separation (cause)
  - maintenance,design change - information insufficient, manufacturer (contributing factor)
  - acft/equip,inadequate design, manufacturer (contributing factor)
  - insufficient standards/requirements,manufacturer, faa(organization) (contributing factor)
  - rotor system,tail rotor blade - separation (cause)
- Forced landing, landing
  - autorotation - performed, pilot in command
- Loss of control - in flight, landing
- In flight collision with terrain/water, landing

## Analysis

SHORTLY AFTER TAKEOFF, AT 1,000 FT AGL, THE PILOT EXPERIENCED AIRFRAME VIBRATION AND A GRINDING SOUND. HE ENTERED AUTOROTATION, AND AT 200 FT AGL THE TAIL ROTOR AND PART OF THE T/R GEAR BOX SEPARATED FROM THE HELICOPTER. IT THEN ROTATED APPROXIMATELY 720 DEG AND IMPACTED THE GROUND. ONE OF THE T/R BLADES WAS MISSING THE ABRASION STRIP. AN AIRWORTHINESS DIRECTIVE (AD) & SERVICE BULLETIN (SB) WERE IN EFFECT DIRECTING INSTALLATION OF RIVETS WITHIN 300 HRS TO PREVENT POSSIBLE LOSS OF TAILROTOR CONTROL. DUE TO SEASONAL USE, HELICOPTER HAD LESS THAN 160 HRS SINCE ISSUANCE OF THE AD. TAIL ROTOR BLADE FOUND INTACT WAS 40% DEBONDED, BUT WOULD PASS A 'TAP TEST' IAW MANUFACTURER'S SB. FAILED BLADE ESTIMATED TO BE 90% DEBONDED. DAILY VISUAL INSPECTION REQUIRED BY SB REPORTEDLY DID NOT DETECT DEBONDING IN PROGRESS.

## Aircraft

- Registration: [N8697F](https://openairdocs.org/deregistered/N8697F-2013-03-07), registration cancelled 2013-03-07, S/N 1170221D, built 1977 (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)
- Registry engine: [Allison 250 SER 400HP](https://openairdocs.org/engine/allison-250-ser-400hp) (registry code 03013, turbo-shaft) (OpenAirDocs)
- Category: Helicopter
- Serial number: 1170221D
- Airframe hours: 3527
- Engines: ALLISON 250-C20B 375 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Business, Part 91
- Operator: Eberle, Terrance, doing business as Whirlwind Aviation Ltd
- Registered owner: Eberle, Terrance
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, May 16, 1992, 152 hours before
- Departed: CRYSTAL CR LODG, AK
- Destination: KOKWOK RIVER, AK
- Flight plan: Company VFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 39; private; airplane ratings: single-engine sea, single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 1,679 total, 500 in this make and model, 1,400 as pilot in command, 150 in the last 90 days, 50 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 340° at 8 knots
- Temperature: 45 °F, dew point 34 °F
- Altimeter: 29.00 inHg

## 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 19920909035639A](https://openairdocs.org/incident/19920909035639A), Sep 9, 1992: Hughes 369D, Dillingham, AK, Substantial damage. Lost tail rotor blades. Hard impact on landing. Suffered abrasion strip debonding. AD920515 not complied.

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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