# NTSB LAX92LA319: Bell UH-1B, N89NW, Hayfork, CA, July 28, 1992

- Type: NTSB accident investigation
- Classification: Accident · Minor injuries · Limited investigation · Final report
- Date: July 28, 1992, 08:00 local (15:00 UTC)
- Place: Hayfork, CA
- Coordinates: 40.500545, -123.18991 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=40.5005&lon=-123.1899&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: Minor injuries
- Injuries: 1 minor
- Status: Completed, report September 14, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 27705
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX92LA319
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/27705/pdf
- Page: https://openairdocs.org/ntsb/LAX92LA319

## Probable cause

THE FAILURE OF THE MAIN ROTOR DRIVE SHAFT DUE TO THE IMPROPER INSTALLATION BY COMPANY MAINTENANCE PERSONNEL OF AN 'O' RING SEAL, WHICH ALLOWED THE PACKING GREASE TO ESCAPE AND CAUSED THE OVER TEMPERATURE FAILURE OF THE DRIVE SHAFT.  A FACTOR IN THE ACCIDENT WAS THE LACK OF SUITABLE TERRAIN IN WHICH TO PERFORM AN AUTOROTATION.

## Sequence of events

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

- Airframe/component/system failure/malfunction, hover
  - lubricating system,oil seal - loose (cause)
  - lubricating system,oil seal - leak (cause)
  - maintenance,installation - improper, company maintenance personnel (cause)
  - rotor drive system,engine to transmission drive - overtemperature (cause)
  - rotor drive system,engine to transmission drive - failure,total (cause)
- Forced landing, descent - emergency
  - autorotation - initiated, pilot in command
  - terrain condition - none suitable (contributing factor)
  - terrain condition - mountainous/hilly (contributing factor)
  - terrain condition - tree(s) (contributing factor)
- In flight collision with terrain/water, descent - emergency

## Analysis

THE PILOT HAD JUST DROPPED OFF A LOAD OF LOGS AND WAS EN ROUTE BACK TO THE CUTTING AREA WHEN HE HEARD A LOUD BANG CONCURRENT WITH A LEFT YAW AND A RAPID LOSS OF ROTOR SPEED. THE PILOT ENTERED AN AUTOROTATION AND COLLIDED WITH TREES DURING THE DESCENT. EXAMINATION REVEALED THAT THE MAIN ROTOR DRIVE SHAFT HAD FAILED. EXAMINATION OF THE SHAFT REVEALED EVIDENCE OF A LOSS OF GREASE FROM THE SHAFT'S BOOT, WHICH RESULTED IN AN OVERHEATING CONDITION AND CATASTROPHIC FAILURE OF THE UNIT. THE 'O' RING, WHICH PROVIDES THE GREASE SEAL FOR THE SHAFT BOOT, WAS FOUND DEFORMED WITH EVIDENCE THAT GREASE HAD BEEN SLUNG FROM THE BOOT. THE MAIN ROTOR DRIVE SHAFT HAD BEEN REMOVED FOR MAINTENANCE AND REPLACED THREE DAYS AND 6 HOURS PRIOR TO THE ACCIDENT. THE MAINTENANCE INSTRUCTIONS CALL FOR A NEW 'O' RING TO BE INSTALLED WHEN THE DRIVE SHAFT AND BOOT ARE REASSEMBLED. ACORDING TO THE BELL LABORATORY, THE 'O' RING APPEARED TO HAVE NOT BEEN REPLACED.

## Aircraft

- Registration: N89NW (not matched to a registry record)
- Reported make and model: BELL UH-1B
- Category: Helicopter
- Serial number: 62-4576
- Airframe hours: 5496
- Engines: LYCOMING T53-L110 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, July 27, 1992, 6 hours before

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 41; flight instructor, commercial; airplane ratings: single-engine land; instrument ratings: helicopter, airplane; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 13,000 total, 3,000 in this make and model, 12,700 as pilot in command, 300 in the last 90 days, 73 in the last 30 days, 7 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Visibility: 20 statute miles
- Lowest ceiling: none
- Temperature: 81 °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 19920728027929A](https://openairdocs.org/incident/19920728027929A), Jul 28, 1992: Bell UH1B, Hayfork, CA, Substantial damage. Loud bang trailing long line. Autorotated into trees. Main rotor drive shaft failed. Old o ring used in maintenance

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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