Bell 206B accident near Chualar, California, August 4, 2013
On August 4, 2013 at about 5:30 pm local time, a 1975 Bell 206B (helicopter), registered N90146, was substantially damaged in an accident during maneuvering (low-alt flying) near Chualar, California. It was an aerial application (crop spraying) flight under agricultural flying rules (Part 137). 1 person had minor injuries. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
Maintenance personnel's failure to properly tighten the bolts securing the main driveshaft to the transmission, which resulted in fatigue failure of the bolts and disconnection of the driveshaft during low-altitude flight.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- August 4, 2013 · about 5:30 pm local time
- Place
- Chualar, California · map
- Type
- Accident
- Injuries
- 1 person had minor injuries.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell 206B III, built 1975 · all 206Bs on the register
- Registration
- N90146 · no longer on the register · serial 1614
- Damage
- Substantial damage
- Flight
- Aerial application (crop spraying) flight · agricultural flying rules (Part 137)
The NTSB's narrative final · quoted from the NTSB record
The pilot stated that he was operating the helicopter at a low altitude when he heard a loud boom and then noted a decrease in main rotor rpm. During the ensuing emergency landing, the helicopter impacted the ground, the tail boom separated from the fuselage, and the helicopter rolled onto its right side. Postaccident examination revealed that the main driveshaft had disconnected and that the bolts attaching the forward coupling to the transmission had failed. Portions of two of the four bolts that attached the forward coupling to the transmission were found, and the fractured threaded remnants (with nuts attached) were examined. One of the remnants was fractured through its entire cross-section due to fatigue, and the other remnant fractured through about 75% of its cross-section due to fatigue; the remainder of the failure on this remnant occurred in overload. Both fracture faces had multiple fatigue origins around about 1/4 of their circumferences, indicating relatively high stresses. No mechanical damage was noted at the fatigue origin locations. One of the remnants displayed smearing of adjacent threads and decreased height of the nut, suggesting this bolt had a relatively large amount of play. It is likely that the large amount of play was due to improper torqueing of the bolts when the driveshaft was reinstalled after extensive maintenance that was performed on the helicopter about 3 months and 197 flight hours before the accident.
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
What happened, in order
- Powerplant sys/comp malf/fail during maneuvering
- Low altitude operation/event during maneuvering (low-alt flying) defining event
The NTSB's findings
- cause Aircraft › Aircraft power plant › Accessory gear › boxes › (general) › Failure
- cause Personnel issues › Task performance › Maintenance › Scheduled/routine maintenance › Maintenance personnel
Pilot
- Certificate: commercial pilot, private
- Ratings: single-engine land; instrument: airplane; rotorcraft: helicopter
- Flight time: 16,000 hours in all; 5,000 in this make and model; 130 in the last 90 days; 50 in the last 30 days
- Medical certificate: Class 2 (with waivers/limitations)
- Seat: rgt
- Injury: minor injuries
The aircraft
- Airframe total time: 18,985 hours
- Last inspection: 100-hour inspection, July 10, 2013
- Maximum gross weight: 3,350 lb
- Seats: 2
- Landing gear: fixed
- Engine: Allison 250-C20B (turboshaft); 197 hours total
- Operator: R And B Helicopters INC
The flight
- Departed from: Chualar CA at 5:20 pm
- Destination: Chualar CA
- Flight plan: none
Weather at the time
- Light: daylight
- Visibility: 10 statute miles
- Sky: broken clouds at 600 ft
- Temperature: 55°F (13°C), dew point 52°F (11°C)
- Altimeter: 30.04 inHg
- Observation at 4:53 pm from SNS, 8 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Flight 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.