- Date
- July 28, 1992, 08:00 local (15:00 UTC)
- Place
- Hayfork, CA
- Injuries
- 1 minor
- Damage
- Substantial damage
- Phase of flight
- Maneuvering
- Aircraft
- N89NWBell UH-1B
- Weather
- Visual (VMC) · Day
- Status
- Completed · report September 14, 1993
- Report
- Approved by Office Director
- FAA report
- 19920728027929A
- Case key
- 27705
From the NTSB’s public API. By law, NTSB reports can’t be used as evidence in lawsuits over the accident.
On this page
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
NTSB’s coding before 2008: each occurrence and phase of flight, and the causes and factors under it. The codes are defined in NTSB’s coding manual.
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
- Reported as
- Bell UH-1B
- Category
- Helicopter
- Serial number
- 62-4576
- Airframe hours
- 5,496
- Engine
- Lycoming T53-L110, 1,100 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.
- Role
- Pilot
- Age
- 41
- Certificates
- 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.