Bell UH-1B accident near Hayfork, California, July 28, 1992
On July 28, 1992 at about 3:00 pm local time, a Bell UH-1B (helicopter), registered N89NW, was substantially damaged in an accident near Hayfork, California. It was an other work-use flight under external-load helicopter rules (Part 133). 1 person had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 28, 1992 · about 3:00 pm local time
- Place
- Hayfork, California · map
- Type
- Accident
- Injuries
- 1 person had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell UH-1B · all UH-1Bs on the register
- Registration
- N89NW · registry record · serial 62-4576
- Damage
- Substantial damage
- Flight
- Other work-use flight · external-load helicopter rules (Part 133)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
Pilot
- Certificate: flight instructor, commercial pilot
- Ratings: single-engine land; instructor: airplane single-engine; instructor: helicopter; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Flight time: 13,000 hours in all; 3,000 in this make and model; 300 in the last 90 days; 73 in the last 30 days; 12,700 as pilot in command; 200 on instruments
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 5,496 hours
- Last inspection: 100-hour inspection, July 27, 1992; 6 hours since
- Maximum gross weight: 8,500 lb
- Seats: 2
- Landing gear: fixed
- Engine: Lycoming T53-L110 (turboshaft); 0 hours total
- Operator: Northwest Helicopters, INC.
The flight
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Visibility: 20 statute miles
- Sky: clear
- Temperature: 81°F (27°C), dew point 0°F (-18°C)
- Altimeter: 29.00 inHg
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.