# NTSB ANC90LA063: Bell 206B3, N1075G, Williamsport, AK, April 21, 1990

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: April 21, 1990, 13:10 local (21:10 UTC)
- Place: Williamsport, AK
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 4 uninjured
- Status: Completed, report December 30, 1992
- Report: Approved by Office Director
- NTSB office: Alaska Regional Office
- NTSB case key (mKey): 5358
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC90LA063
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/5358/pdf
- Page: https://openairdocs.org/ntsb/ANC90LA063

## Probable cause

THE MANUFACTURER'S INADEQUATE PART DESIGN AND THE IMPROPER MAINTENANCE TECHNIQUES BY THE OPERATOR.

## Sequence of events

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

- Loss of engine power(total) - mech failure/malf, climb
  - bleed air system,lines - fractured (cause)
  - maintenance,replacement - improper, company maintenance personnel (cause)
  - acft/equip,inadequate design, manufacturer (cause)
- Forced landing, descent - emergency

## Analysis

THE HELICOPTER PILOT REPORTED A TOTAL LOSS OF POWER AND A SUBSEQUENT HARD AUTOROTATION LANDING. AN EXAMINATION OF THE ENGINE DISCLOSED A FRACTURED PC TUBE FROM THE COMPRESSOR TO THE PC FILTER. FAILURE OF THIS TUBE WILL CAUSE THE ENGINE TO LOSE POWER BELOW IDLE OR FLAME OUT. AN NTSB METALLURGIST WHO EXAMINED THE TUBE BELIEVES THAT THE TUBE FRACTURED DUE TO FRETTING AND FATIGUE, MOST LIKELY PRECIPITATED BY MISALIGNMENT OF THE PC TUBE DURING FIELD MAINTENANCE. ALLISON, THE ENGINE MANUFACTURER, HAS RECENTLY REDESIGNED THE TUBE WITH A THICKER WALL AND A DIFFERENT SHAPE TO FACILITATE MAINTENANCE PROCEDURES IN THE FIELD, AND TO MAKE THE TUBE MORE RESISTANT TO FATIGUE.

## Aircraft

- Registration: N1075G (not matched to a registry record)
- Reported make and model: BELL 206B3
- Category: Helicopter
- Serial number: 2958
- Engines: ALLISON 250-C20B 420 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Part 135
- Registered owner: Maritime Helicopters
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, April 14, 1990, 20 hours before
- Departed: HOM, HOMER, AK
- Destination: HOM, HOMER, AK
- Flight plan: VFR
- Airport: NONE, Iliamna Bay

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 43; airline transport, flight instructor, commercial; airplane ratings: single-engine sea, multi-engine land, single-engine land; instrument ratings: helicopter, airplane; medical: class 1, valid medical--no waivers/lim.; seat: right; flight hours: 7,069 total, 600 in this make and model, 6,626 as pilot in command, 146 in the last 90 days, 146 in the last 30 days, 5 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 115° at 10 knots, gusting 5
- Visibility: 100 statute miles
- Lowest ceiling: none
- Temperature: 39 °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 19900421010399A](https://openairdocs.org/incident/19900421010399A), Apr 21, 1990: Bell 206B, Iliamna, AK, Substantial damage. Engine lost power. Autorotated. Landed hard. Pc filter tube to governor cracked.

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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