# NTSB SEA91LA212: Cessna U206F, N35831, Nimrod, OR, August 19, 1991

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: August 18, 1991, 21:30 local (Aug 19, 1991, 04:30 UTC)
- Place: Nimrod, OR
- Coordinates: 44.129478, -122.41957 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=44.1295&lon=-122.4196&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 2 uninjured
- Status: Completed, report May 7, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 41516
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA91LA212
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/41516/pdf
- Page: https://openairdocs.org/ntsb/SEA91LA212

## Probable cause

THE FRACTURED CRANKSHAFT RESULTING IN ENGINE SEIZURE FOLLOWED BY A FORCED LANDING ON ROUGH AND UNEVEN TERRAIN RESULTING IN SEPARATION OF THE NOSE GEAR.

## 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, cruise - normal
  - engine assembly,crankshaft - fractured (cause)
  - powerplant - seized (cause)
- Forced landing, descent - emergency
- Nose gear collapsed, landing - roll
  - terrain condition - rough/uneven (cause)
  - light condition - dark night (contributing factor)
- Nose over, landing - roll
  - landing gear,nose gear - separation

## Analysis

WHILE IN CRUISE FLIGHT THE ENGINE BEGAN RUNNING ROUGH AND ULTIMATELY SEIZED.  THE PILOT EXECUTED A FORCED LANDING DURING DARK NIGHT CONDITIONS ONTO ROUGH AND UNEVEN TERRAIN WITHIN A LOGGING CLEARCUT AREA.  DURING THE ROLLOUT THE NOSE GEAR WAS SHEARED OFF AND THE AIRCRAFT NOSED OVER TO AN INVERTED POSITION RESULTING IN SUBSTANTIAL DAMAGE.  SUBSEQUENT DISASSEMBLY OF THE ENGINE REVEALED A FATIGUE CRACK WHICH GENERATED INTO A FRACTURE OF THE CRANKSHAFT.  THE CRACK WAS OBSERVED TO EMANATE FROM THE OIL TUBE PASSAGE HOLE IN THE NUMBER FOUR SHORT CHEEK OF THE CRANKSHAFT.

## Aircraft

- Registration: [N35831](https://openairdocs.org/deregistered/N35831-2013-04-10), registration cancelled 2013-04-10, S/N U20602744, built 1975 (OpenAirDocs)
- Reported make and model: CESSNA U206F
- Registry model: [Cessna U206F](https://openairdocs.org/model/cessna-u206f) (registry code 2073333) (OpenAirDocs)
- Registry engine: [Continental IO-520 series](https://openairdocs.org/engine/continental-io-520-series) (registry code 17032, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: U20602744
- Airframe hours: 3116
- Engines: CONTINENTAL IO-520-F 300 horsepower reciprocating
- Damage: Substantial damage
- Flight: Personal, Part 91
- Operator: Evergreen Helicopters
- Registered owner: Evergreen Helicopters
- Last inspection: 100 hour, May 2, 1991, 19 hours before
- Departed: 5S2, CRESCENT LAKE, OR
- Destination: MMV, MCMINNVILLE, OR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 30; flight instructor, airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; flight hours: 4,400 total, 500 in this make and model, 3,650 as pilot in command, 250 in the last 90 days, 80 in the last 30 days, 2 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Night/dark
- Wind: 260° at 10 knots
- Visibility: 15 statute miles
- Lowest ceiling: none
- Temperature: -0 °F, dew point -0 °F
- Observed at: EUG, 34 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 19910818038359A](https://openairdocs.org/incident/19910818038359A), Aug 18, 1991: Cessna U206F, Nimrod, OR, Substantial damage. Engine vibration and oil on windshield power loss and night landing. Fatigue crack in crankshaft near oil tube hole

## Other investigations on N35831 (1)

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.

- [NTSB ANC81DA104](https://openairdocs.org/ntsb/ANC81DA104), Sep 1, 1981: Cessna U206 (N35831), Big River, AK, substantial damage

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.

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.