Bell 206B accident near San Francisco, California, July 12, 2001
On July 12, 2001 at about 8:30 pm local time, a Bell 206B (helicopter), registered N474SF, was substantially damaged in an accident near San Francisco, California (San Francisco International airport). It was a business flight under general aviation rules (Part 91). No one was hurt; 4 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The failure of the accessory gearbox 2 1/2 bearing in fatigue resulting in the complete loss of engine power and a subsequent forced landing. The pilot's failure to maintain directional control during the autorotational flare maneuver is also causal. The operator's failure to comply with the recommendations in the engine service manual regarding removal of the engine from service for detailed inspection is a factor.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 12, 2001 · about 8:30 pm local time
- Place
- San Francisco, California · San Francisco International · map
- Type
- Accident
- Injuries
- No one was hurt; 4 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell 206B · all 206Bs on the register
- Registration
- N474SF · no longer on the register · serial 1526
- Damage
- Substantial damage
- Flight
- Business flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The helicopter made a hard landing and severed the tail boom after an in-flight engine failure and autorotation. The pilot reported seeing an engine chip light and hearing a whining sound in the engine about 700 feet agl. An engine out light followed by a complete engine failure occurred about 1 minute later. The pilot had been descending to land in an open field by that time. The collective was lowered to enter an autorotation and aft cyclic applied to slow the forward airspeed. As he neared the bottom of the maneuver, he pulled collective pitch to cushion the landing; however, the helicopter abruptly spun 90 degrees to the left. The main rotor blades struck the tail boom and the ground. The tail boom was separated from the helicopter. After an inspection and teardown of the engine, the 2 1/2 bearing was found to have failed in fatigue. Records revealed that a chip light had been reported in the same helicopter on a flight (4) days prior. Before being returned to service, a magnetic plug inspection/cleaning and an engine ground test run were performed. According to the Allision 250 Series Operation and Maintenance Manual, when either a chip light is encountered after a gearbox flush and a second ground test run has been performed or when a total of (4) chip lights have been encountered within 50 hours of engine operation, the engine must be removed from service and sent to the manufacturer's authorized maintenance center.
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: commercial pilot
- Ratings: multi-engine land; single-engine land; instrument: airplane; instrument: helicopter; rotorcraft: helicopter
- Flight time: 1,305 hours in all; 860 in this make and model; 134 in the last 90 days; 44 in the last 30 days; 1,000 as pilot in command
- Last flight review: July 27, 2000
- Medical certificate: Class 1 (valid medical--no waivers/lim.)
- Seat: rgt
- Injury: no injuries
The aircraft
- Airframe total time: 5,876 hours
- Last inspection: 100-hour inspection, April 25, 2001; 99.5 hours since
- Maximum gross weight: 3,200 lb
- Seats: 5
- Landing gear: fixed
- Engine: Allison 250-C20 (turboshaft); 0 hours total
The flight
- Departed from: SFO San Francisco CA at 8:17 pm
- Destination: SFO San Francisco CA
Weather at the time
- Light: daylight
- Wind: from 250° at 7 knots
- Visibility: 10 statute miles
- Sky: overcast at 1,800 ft; clear
- Temperature: 64°F (18°C), dew point 54°F (12°C)
- Altimeter: 30.09 inHg
- Observation at 7:56 pm from KSFO
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 3 |
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.