# NTSB LAX89LA253: Bell 206B, N10857, Rialto, CA, July 31, 1989

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: July 31, 1989, 13:35 local (20:35 UTC)
- Place: Rialto, CA
- Coordinates: 34.100719, -117.379394 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=34.1007&lon=-117.3794&mi=10
- Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed, report March 29, 1991
- Report: Approved by Office Director
- NTSB case key (mKey): 26458
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX89LA253
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/26458/pdf
- Page: https://openairdocs.org/ntsb/LAX89LA253

## Probable cause

FAILURE TO INSTALL TWO OF THE FOUR REQUIRED NUTS WHICH RETAIN THE HIGH SPEED COUPLING INPUT DRIVE SHAFT TO THE TRANSMISSION.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Hard landing, landing - flare/touchdown
  - rotor drive system,engine to transmission drive - separation (cause)
  - power on landing - not possible, pilot in command (contributing factor)
  - maintenance,installation - improper, company maintenance personnel (cause)
  - misc rotorcraft,tail boom - sheared

## Analysis

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.

## Aircraft

- Registration: N10857 (not matched to a registry record)
- Reported make and model: Bell 206B
- Category: Helicopter
- Serial number: 2974
- Airframe hours: 2688
- Engines: ALLISON 250-C20-B 420 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Instructional, Part 91
- Operator: Ca. Amer. Research Information
- Registered owner: California American Research
- Airworthiness certificate: Standard, Normal
- Last inspection: Annual, July 20, 1989, 20 hours before
- Airport: L67, Rialto Munic. Arpt

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 41; commercial, flight instructor; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 5,600 total, 1,400 in this make and model, 80 in the last 90 days, 22 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 240° at 5 knots
- Visibility: 5 statute miles
- Lowest ceiling: none
- Temperature: 81 °F

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19890731026159A](https://openairdocs.org/incident/19890731026159A), Jul 31, 1989: Bell 206B, Rialto, CA, Substantial damage. Driveshaft coupling separated from transmission on flair to hover autorotation. Coupling was improperly secured.

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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