# NTSB SEA94LA030: Hawkins & Powers UH-1B, N91NW, North Bend, WA, November 12, 1993

- Type: NTSB accident investigation
- Classification: Accident · Minor injuries · Limited investigation · Final report
- Date: November 12, 1993, 11:30 local (19:30 UTC)
- Place: North Bend, WA
- Coordinates: 47.389396, -121.609062 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=47.3894&lon=-121.6091&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: Minor injuries
- Injuries: 1 minor
- Status: Completed, report December 2, 1994
- Report: Approved by Office Director
- NTSB case key (mKey): 41853
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA94LA030
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41853/pdf
- Page: https://openairdocs.org/ntsb/SEA94LA030

## Probable cause

TOTAL FAILURE OF THE INTERMEDIATE GEARBOX.  THE LACK OF SUITABLE TERRAIN FOR AN AUTOROTATION WAS A FACTOR.

## Sequence of events

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

- Airframe/component/system failure/malfunction, maneuvering
  - rotor drive system,intermediate gearbox(42 deg) - failure,total (cause)
- Forced landing, descent - emergency
- In flight collision with terrain/water, landing - flare/touchdown
  - terrain condition - high vegetation (contributing factor)
  - terrain condition - none suitable (cause)

## Analysis

THE PILOT HEARD LOUD GRINDING SOUNDS FROM THE REAR OF THE AIRCRAFT, FOLLOWED BY BANGING SOUNDS AND A LOSS OF DIRECTIONAL CONTROL.  HE JETTISONED HIS LOGS, THEN HIS LONG LINE, AND EXECUTED A POWERED AUTOROTATION INTO THE TREES, SUBSTANTIALLY DAMAGING THE AIRCRAFT.  THE 42 DEGREE INTERMEDIATE GEARBOX WAS EXAMINED AND MULTIPLE ORIGIN FATIGUE CRACKS WERE FOUND IN FRAGMENTS OF THE INPUT PINION GEAR.

## Factual narrative

On November 12, 1993, at 1130 Pacific standard time, a Hawkins and Powers UH-1B, N91NW, operated by Northwest Helicopters, impacted terrain 10 miles south of North Bend, Washington, during an emergency forced landing.  There was no flight plan filed for the external load flight, conducted under 14 CFR 133 in visual meteorological conditions, that was on takeoff when the accident occurred.  The commercial certificated pilot suffered minor injuries in the accident.  The aircraft was substantially damaged.  There was no fire.

The pilot reported he heard a loud growling/grinding noise from the rear of the aircraft, followed by a slow turn to the right, then a banging sound and a violent rotation to the right.  After clearing the choker setters with the load, he jettisoned his external load of logs and attempted to fly the aircraft to a nearby clearcut.  Recognizing that he had neither altitude nor airspeed to make it to the clearcut, he reduced power, jettisoned his long line, and executed a powered autorotation into the trees.  The aircraft was substantially damaged when it impacted the trees and rough terrain.

The 42 degree intermediate gearbox was examined at the NTSB metallurgy laboratory.  Fatigue cracks and overstress fractures were found in the input geat and mating fragments.

## Aircraft

- Registration: N91NW (not matched to a registry record)
- Reported make and model: HAWKINS & POWERS UH-1B
- Category: Helicopter
- Serial number: 62-1915
- Airframe hours: 10106
- Engines: LYCOMING T53-L11D 1100 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Other work use, Part 133
- Operator: Northwest Helicopters, Inc.
- Registered owner: Northwest Helicopters, Inc.
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: 100 hour, November 8, 1993, 25 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 42; commercial; airplane ratings: single-engine land; instrument ratings: helicopter; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 11,800 total, 1,500 in this make and model

## Weather

- Conditions: Visual (VMC), Day
- Visibility: 2 statute miles
- Lowest ceiling: none
- Temperature: 61 °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 19931112042801A](https://openairdocs.org/incident/19931112042801A), Nov 12, 1993: Bell UH1B, Bend, WA, Substantial damage. Grinding noise. Uncontrolled right spin. Jettisoned load. Autorotated into trees. Overstressed gear box fractures.

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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