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June 7, 2024 · Cessna 206 · N756CL

King Salmon, AK

Overview

Report Status
Final with probable cause
Event Type
Accident
Date
June 7, 2024
Injury Outcomes
No injuries (2 uninjured)
Location
King Salmon, AK
Aircraft
Cessna 206 (1977)
Tail Number
N756CL
Operator
Egli Air Haul Service
Injuries
None
Aircraft Damage
Substantial
NTSB Number
ANC24LA045

The pilot reported that, shortly after takeoff, he observed high engine oil temperature and began to turn back to the airport. The engine began losing power, and the pilot performed a forced landing in the tundra, which resulted in substantial damage to the horizontal stabilizer and elevator. Examination of the engine revealed that the No. 1 piston was eroded down to the steel ring lands and scuff marks were observed on the side of the piston skirt. The No. 1 cylinder upper and lower spark plugs had molten aluminum deposits covering the electrodes and insulators. The crankshaft rod journals exhibited evidence of foreign material contamination in the oil. The Nos. 2 and 5 crankshaft rod journals had severe thermal discoloration. All connecting rod bearings exhibited abnormal wear. Connecting rod bearings No. 2 and 5 were severely damaged. The observed damage was consistent with a detonation/pre-ignition event; however, the reasons for the detonation/pre-ignition could not be determined based on the available information.

NTSB Probable Cause

A partial loss of engine power due to detonation/preignition of the No. 1 cylinder for reasons that could not be determined.

Full Narrative

On June 7, 2024, about 1505 Alaska daylight time, a Cessna 206 airplane, N756CL, sustained substantial damage when it was involved in an accident near King Salmon, Alaska. Both pilots onboard were uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 flight. The pilot reported that, shortly after takeoff, he observed a high engine oil temperature indication and initiated a turn back to the airport. The engine began losing power and the pilot performed a forced landing to the tundra, which resulted in substantial damage to the horizontal stabilizer and elevator. The engine was rebuilt by Continental Motors in February 2018, and had accrued about 1,282 hours since the overhaul. A preliminary engine examination revealed that the oil filter media contained a considerable amount of metal. The engine was shipped to Continental Motors in Mobile, Alabama, for further examination, which revealed that the No. 1 piston was eroded down to the steel ring lands and scuff marks were observed on the side of the piston skirt. The upper and lower spark plugs in cylinder No. 1 had molten aluminum deposits covering the electrodes and insulators. The upper and lower spark plugs from cylinder No. 3 and the top spark plug from cylinder No. 4 displayed chipped porcelain insulators at the electrodes. All spark plugs were found worn beyond limits in accordance with the Champion Check-A-Plug chart. The crankshaft rod journals exhibited signs of foreign material contamination in the oil. Dark oil was observed in the sump case when it was drained. The No. 2 and No. 5 crankshaft rod journals had severe thermal discoloration. All connecting rod bearings exhibited abnormal wear. Connecting rod bearings Nos. 2 and 5 were severely damaged. All damage discovered was consistent with a pre-ignition/detonation event. The Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25B), states, in part: Detonation is an uncontrolled, explosive ignition of the fuel/air mixture within the cylinder's combustion chamber. It causes excessive temperatures and pressures which, if not corrected, can quickly lead to a failure of the piston, cylinder, or valves. In less severe cases, detonation causes engine overheating, roughness, or loss of power. Preignition occurs when the fuel/air mixture ignites prior to the engine's normal ignition event. Premature burning is usually caused by a residual hot spot in the combustion chamber, often created by a small carbon deposit on a spark plug, a cracked spark plug insulator, or other damage to the cylinder that causes a part to heat sufficiently to ignite the fuel/air charge.

Flight

Event TypeAccident
Event Time15:05 AKDT
Nearest Airport0nm
Flight Plan FiledCvfr
Flight Plan ActivatedYes
Aircraft FireNo
Aircraft ExplosionNo

Aircraft

AircraftCessna 206
Tail NumberN756CL
Aircraft CategoryAir
DamageSubstantial
OperatorEgli Air Haul Service
Operating RulePart 91
Engines1
Engine TypeReciprocating
Engine DetailsContinental · IO550F17B · Reciprocating · 300
Seats2

People & Injuries

Injury SummaryNo injuries (2 uninjured)
Fatal0
Serious0
Minor0
Uninjured2
Total2
Crew 1Age 47 · First Class · None
Crew 2Age 72 · First Class · None

Conditions

ConditionsVMC
LightDaylight
Wind90° @ 20 kt, gusting 32 kt
Visibility10 sm
CeilingBroken clouds 6500 ft
Temperature / Dew Point54 F / 34 F
Altimeter29.98 inHg
Observation Time15:54
Weather SourceWFAC

Appendix: Source Data