# NTSB ANC83FA131: Cessna U206, N4661Z, Near Iliamna, AK, July 25, 1983

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Field investigation · Final report
- Date: July 24, 1983, 21:30 local (Jul 25, 1983, 05:30 UTC)
- Place: Near Iliamna, AK
- Coordinates: 59.850887, -154.559219 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=59.8509&lon=-154.5592&mi=10
- Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 3 uninjured
- Status: Completed
- Report: Approved by Office Director
- NTSB office: Alaska Regional Office
- Safety recommendations: Yes
- NTSB case key (mKey): 4042
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC83FA131
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/4042/pdf
- Page: https://openairdocs.org/ntsb/ANC83FA131

## Sequence of events

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

- Loss of engine power(partial) - mech failure/malf, takeoff - initial climb
  - induction air control/system - inadequate (cause)
  - aircraft/equipment inadequate, manufacturer (cause)
  - induction air control/system - fatigue (cause)
  - induction air control/system - failure,partial (cause)
  - induction air control/system - separation (cause)
  - engine assembly,valve,intake - foreign object damage (cause)
- Forced landing, landing - flare/touchdown
- Other gear collapsed, landing - flare/touchdown
  - terrain condition - none suitable (contributing factor)
  - landing gear,float assembly - overload (contributing factor)

## Analysis

THE ENG LOST POWER JUST AFTER A WATER TAKEOFF. THE ACFT LANDED STRAIGHT AHEAD IN MUSKEG & TUNDRA COLLAPSING THE FLOATS. ENG TEARDOWN REVEALED A METALLIC 'NUGGET' IN THE LEFT INTAKE MANIFOLD BETWEEN THE #4 & #6 PORTS. NUMEROUS MARKS WERE FOUND ON THE INSIDE OF BOTH INTAKE MANIFOLDS. THERE WAS MINOR DENTING, SCRATCHING & PEENING ON THE INTERIOR OF THE 90 DEG ELBOWS FROM BOTH ENDS OF THE CROSSOVER TUBE, INTAKE VALVE PORTS, SEATS & VALVE FACES OF CYLS 4,5 & 6. THE NUGGET WAS COMPOSED OF THE SAME MATERIAL AS THE AIRBOX ASS'Y, CESSNA P/N 1250705, WHICH CONTAINED TWO HOLES APRX 2-1/2 SQUARE INCHES EACH IN THE AIRBOX WALL. THE HOLES WERE CAUSED BY FATIGUE CRACKS. THE SOURCE OF LOADING CAUSING THE FATIGUE CRACKPROPAGATION WAS DUE TO MEMBRANE &/OR BENDING LOADS IN THE AIRBOX WALL CAUSED BY OUT-OF-PLANE DEFORMATION. THESE DEFORMATION WERE MOST LIKELY CAUSED BY EXCITING A NATURAL MODE OF VIBRATION IN THE WALL. THREE DUCT FAILURES WERE REPORTED TO THE FAA IN 1983, TWO OF WHICH WERE IN C-210 ACFT.

## Aircraft

- Registration: [N4661Z](https://openairdocs.org/aircraft/N4661Z), registered now, S/N U20605998, built 1980 (OpenAirDocs)
- Reported make and model: CESSNA U206
- Registry model: [Cessna U206G](https://openairdocs.org/model/cessna-u206g) (registry code 2073356) (OpenAirDocs)
- Registry engine: [Continental IO-520 series](https://openairdocs.org/engine/continental-io-520-series) (registry code 17032, reciprocating) (OpenAirDocs)
- Category: Airplane
- Serial number: U20605998
- Airframe hours: 325
- Engines: CONTINENTAL IO-520-F 300 horsepower reciprocating
- Damage: Substantial damage
- Flight: Part 135
- Registered owner: Rust'S Flying Service
- Airworthiness certificate: Standard, Normal
- Last inspection: 100 hour, July 13, 1983, 31 hours before
- Destination: LAKE CLARK, AK
- Flight plan: Company VFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 37; commercial; airplane ratings: single-engine sea, single-engine land; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; seat: left; flight hours: 5,809 total, 1,869 in this make and model, 5,714 as pilot in command, 233 in the last 90 days, 3 in the last 24 hours

## Weather

- Conditions: Visual (VMC), Day
- Wind: 80° at 20 knots, gusting 25
- Visibility: 5 statute miles
- Lowest ceiling: 1,500 ft overcast
- Temperature: 55 °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 19830724037139A](https://openairdocs.org/incident/19830724037139A), Jul 24, 1983: Cessna U206, Iliamna, AK, Substantial damage. Engine failed on climbout. Crash landed in tundra and muskeg. Air intake duct failure ingested pieces into engine.

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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