Bell 206B accident near Rialto, California, July 31, 1989
On July 31, 1989 at about 8:35 pm local time, a Bell 206B (helicopter), registered N10857, was substantially damaged in an accident near Rialto, California (Rialto Munic. Arpt airport). It was an instructional flight under general aviation rules (Part 91). No one was hurt; 2 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
FAILURE TO INSTALL TWO OF THE FOUR REQUIRED NUTS WHICH RETAIN THE HIGH SPEED COUPLING INPUT DRIVE SHAFT TO THE TRANSMISSION.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 31, 1989 · about 8:35 pm local time
- Place
- Rialto, California · Rialto Munic. Arpt · map
- Type
- Accident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell 206B · all 206Bs on the register
- Registration
- N10857 · no longer on the register · serial 2974
- Damage
- Substantial damage
- Flight
- Instructional flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
DURING A PRACTICE AUTOROTATION WITH A POWER RECOVERY, THE FLIGHT INSTRUCTOR HEARD A NOISE FROM THE REAR OF THE HELICOPTER. WHEN THE POWER RECOVERY WAS ATTEMPTED, THE ENGINE RESPONDED TO THE THROTTLE APPLICATION BUT THE LOW RPM WARNING HORN ACTIVATED AND THE HELICOPTER STRUCK THE GROUND IN A LEVEL ATTITUDE WHICH CAUSED THE MAIN ROTOR BLADES TO SEVER THE TAILBOOM. EXAMINATION OF THE HIGH SPEED OUTPUT DRIVESHAFT COUPLING, TRANSMISSION END, SHOWED THAT THE FOUR BOLTS WERE INSTALLED BUT THE FOUR NUTS AND FOUR WASHERS COULD NOT BE FOUND IN THE ASSEMBLY. TWO NUTS WERE FOUND IN THE SCUPPER DRAIN OF THE TRANSMISSION DECK.
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: multi-engine land; single-engine land; instructor: airplane multi-engine; instructor: airplane single-engine; instructor: helicopter; instrument: airplane; rotorcraft: helicopter
- Flight time: 5,600 hours in all; 1,400 in this make and model; 80 in the last 90 days; 22 in the last 30 days; 3,500 on instruments
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 2,688 hours
- Last inspection: annual inspection, July 20, 1989; 20 hours since
- Maximum gross weight: 3,200 lb
- Seats: 5
- Landing gear: fixed
- Engine: Allison 250-C20-B (turboshaft); 0 hours total
The flight
- Flight plan: none
- Runway 0
- A second pilot was aboard
Weather at the time
- Light: daylight
- Wind: from 240° at 5 knots
- Visibility: 5 statute miles
- Sky: clear
- Temperature: 81°F (27°C), dew point 0°F (-18°C)
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 2 |
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.