# NTSB MKC89LA176: Bell 206-B2, N96117, Sebeka, MN, August 4, 1989

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: August 4, 1989, 11:00 local (16:00 UTC)
- Place: Sebeka, MN
- Coordinates: 46.619941, -95.079208 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=46.6199&lon=-95.0792&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 3 uninjured
- Status: Completed, report September 30, 1991
- Report: Approved by Office Director
- NTSB case key (mKey): 34845
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=MKC89LA176
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/34845/pdf
- Page: https://openairdocs.org/ntsb/MKC89LA176

## Probable cause

POWER PLANT FAILURE DUE TO A FRACTURE OF THE FIRST STAGE TURBINE WHEEL, RESULTING IN AN UNCONTROLLED AUTOROTATION.

## Sequence of events

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

- Loss of engine power(total) - mech failure/malf, approach
  - turbine assembly,turbine wheel - fractured (cause)
- Forced landing, landing - flare/touchdown
  - autorotation - uncontrolled, pilot in command (contributing factor)
- Hard landing, landing - flare/touchdown

## Analysis

THE PILOT WAS ON AN APPROACH TO A FIELD SITE WHEN HE HEARD A LOUD 'BANG' FOLLOWED BY AN ENGINE OUT LIGHT AND AUDIO WARNING. THE PILOT EXECUTED A FORCED LANDING, WITH LOSS OF TAIL ROTOR CONTROL, WHICH RESULTED IN A HARD LANDING. TEARDOWN AND EXAMINATION OF THE ENGINE REVEALED THAT THE FIRST STAGE TURBINE WHEEL FRACTURED DUE TO THERMAL FATIGUE CRACKING.

## Aircraft

- Registration: N96117 (not matched to a registry record)
- Reported make and model: BELL 206-B2
- Category: Helicopter
- Serial number: 975
- Airframe hours: 4460
- Engines: ALLISON 250-C20 400 horsepower turbo shaft
- Damage: Substantial damage
- Flight: Aerial observation, Part 91
- Operator: Imperial International Inc.
- Registered owner: Mortenson, Sheldon A.
- Airworthiness certificate: Standard, Normal
- Departed: 18MN, MOTLEY, MN

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 40; commercial, flight instructor; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: right; flight hours: 3,417 total, 1,565 in this make and model, 3,251 as pilot in command, 181 in the last 90 days, 136 in the last 30 days, 1 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 270° at 8 knots
- Visibility: 12 statute miles
- Lowest ceiling: 6,000 ft broken
- Temperature: 82 °F, dew point 64 °F
- Altimeter: 29.00 inHg
- Observed at: PKD, 23 nm away

## 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 19890804037079A](https://openairdocs.org/incident/19890804037079A), Aug 4, 1989: Bell 206B, Sebeka, MN, Substantial damage. Engine failed at low speed and altitude on landing approach. Crashed. Turbine failure.

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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