# NTSB SEA86FA137: Bell UH-1L, N4964N, Wenatchee, WA, May 31, 1986

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Field investigation · Final report
- Date: May 31, 1986, 07:10 local (14:10 UTC)
- Place: Wenatchee, WA
- Coordinates: 47.369552, -120.350425 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=47.3696&lon=-120.3504&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 1 fatal
- Status: Completed
- Report: Approved by Office Director
- NTSB case key (mKey): 40284
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA86FA137
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/40284/pdf
- Page: https://openairdocs.org/ntsb/SEA86FA137

## Sequence of events

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

- Airframe/component/system failure/malfunction, hover
  - rotor drive system,intermediate gearbox(42 deg) - fatigue (cause)
- In flight collision with terrain/water, descent - uncontrolled
  - terrain condition - none suitable (cause)
  - autorotation - not possible, pilot in command

## Analysis

N4964N, A BELL UH-1L, WAS BEING OPERATED IN LOGGING OPS BY AN EXPERIENCED, MILITARY TRAINED PLT WHO POSSESSED 6000 HRS OF FLT EXPERIENCE IN MODEL. WHILE LIFTING A SLING LOAD GND CREW RPTD SMOKE FROM THE TAIL ROTOR AREA. PLT RELEASED SLING LOAD & ACKNOWLEDGED THE WARNING RADIOING HIS INTENTIONS TO LAND NEARBY. THE SUBSEQUENT LOSS OF TAIL ROTOR/DIRECTNL CNTRL PLACED ROTORCRAFT IN A CONDITION WHEREBY AN AUTOROTATION WAS NOT POSSBL & A RUN ON LNDG WAS NECESSARY. UNSUITABLE TERRAIN LEFT THE PLT WITH ONLY TWO FORCED LNDG OPTIONS, ONE ON CURVING, HILLY HWY WITH POTENTIAL FOR A COLLISION WITH AUTO TRAFFIC, OR THE OTHER INTO HEAVILY TREED TERRAIN. THE PLT APPEARS TO HAVE CHOSEN THE LATTER. IT IS NOT APPARENT WHY HE CHOSE THIS OPTION RATHER THAN DIVERTING TO A NEARBY AIRSTRIP OR SOME OTHER LEVEL FORCED LNDG AREA. THE 42 DEGREE GEARBOX, WHICH HAD BEEN OVERHAULED AND INSTALLED 195 HRS PREVIOUSLY IN ACFT, WAS FOUND TO HAVE FAILED WHEN THE INPUT PINION GEAR FRACTURED IN FATIGUE ORIGINATING FROM CORROSION.

## Aircraft

- Registration: [N4964N](https://openairdocs.org/deregistered/N4964N-1990-05-31), registration cancelled 1990-05-31, S/N 157854 (OpenAirDocs)
- Reported make and model: BELL UH-1L
- Registry model: [Bell UH-1L](https://openairdocs.org/model/bell-uh-1l) (registry code 1181401) (OpenAirDocs)
- Category: Helicopter
- Serial number: 157854
- Airframe hours: 7899
- Engines: LYCOMING T53-L13B 1250 horsepower turbo shaft
- Damage: Destroyed
- Fire: On-Ground
- Flight: Part 133
- Registered owner: A.M. Mcdowell & Associates
- Airworthiness certificate: Special, Restricted (Special)
- Last inspection: 100 hour, May 18, 1986, 41 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 39; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane, helicopter; medical: class 2, valid medical--no waivers/lim.; seat: left; toxicology performed; flight hours: 11,250 total, 6,000 in this make and model, 1 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 260° at 8 knots
- Visibility: 30 statute miles
- Lowest ceiling: none
- Temperature: 66 °F, dew point 52 °F
- Altimeter: 29.00 inHg
- Observed at: EAT, 15 nm away

## 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 19860531019929A](https://openairdocs.org/incident/19860531019929A), May 31, 1986: Bell UH1M, Wenatchee, WA, Destroyed. The helicopter impacted trees after losing control. Corrosion in the 42 degree gearbox caused metal fatigue.

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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