# NTSB ANC18LA064: Cessna 207, N7379U, Iliamna, AK, August 7, 2018 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: August 7, 2018, 12:15 local (20:15 UTC) - Place: Iliamna, AK - Coordinates: 59.745834, -154.91749 - Nearby events: https://openairdocs.org/map.md?lat=59.7458&lon=-154.9175&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Alaska Regional Office - Parties: Continental Motors, Federal Aviation Administration - NTSB case key (mKey): 98036 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC18LA064 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/98036/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=98036 - Page: https://openairdocs.org/ntsb/ANC18LA064 ## Probable cause A total loss of engine power due to detonation/preignition damage of the No. 2 cylinder and piston for reasons that could not be determined. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Damaged/degraded (probable cause); cases with it: [Cessna 207A, 1 case](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=2073605), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) - [Aircraft](https://openairdocs.org/ntsb-findings/01050000): Aircraft › Aircraft power plant · Failure; cases with it: [Cessna 207A, 1 case](https://openairdocs.org/ntsb-findings/01050000/cases.md?model=2073605), [All aircraft, 151 cases](https://openairdocs.org/ntsb-findings/01050000/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Cessna 207A, 2 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=2073605), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Emergency descent: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341); cases with it: [Cessna 207A, 2 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=2073605), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Cessna 207A, 7 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=2073605), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot reported that shortly after takeoff, as he began to configure the airplane for cruise flight, the engine began to run rough and lose power, and he elected to immediately return to the airport. The engine subsequently lost total power and the pilot performed a forced landing on tundra-covered terrain, during which the airplane sustained substantial damage. Examination revealed that the No. 2 piston was eroded on the bottom side, and a hole was burned through. The No. 2 piston and cylinder head were mechanically damaged by loose piston ring debris. Closer examination of the No. 2 cylinder head revealed re-solidified molten metal around the bottom Heli-Coil tang notch. All damage discovered was consistent with a pre-ignition/detonation event; however, the cause of the pre-ignition and/or detonation could not be determined based on the available information. ## Factual narrative On August 7, 2018, about 1215 Alaska daylight time, a Cessna 207 airplane, N7379U, was substantially damaged when it was involved in an accident near Iliamna, Alaska. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 135 flight. The pilot reported that, after takeoff, he started a climbing left turn toward his destination. As the airplane reached his intended altitude of 1,000 ft mean sea level, and as he began to configure the airplane for cruise flight, the engine began to run rough and lose power, so he elected to immediately return to the departure airport. He switched fuel tanks and activated the auxiliary fuel pump in an effort to restore full engine power. He noted that the engine roughness improved momentarily, followed by a severe engine vibration and complete loss of engine power. The pilot selected a forced landing area on tundra-covered terrain, during which the airplane sustained substantial damage to the fuselage and wings. The airplane was subsequently recovered and returned to the operator’s base. A Federal Aviation Administration inspector reported that there was no obvious damage to the engine, and an engine run was attempted. Although the engine eventually started, it ran very rough and began to vibrate and the test was discontinued. The engine was sent to the manufacturer’s facility for further examination. The examination revealed that the No. 2 piston was eroded on the bottom side, and a hole was burned through. The No. 2 piston and cylinder head were mechanically damaged by loose piston ring debris. Closer examination of the No. 2 cylinder head revealed re-solidified molten metal around the bottom Heli-Coil tang notch. All damage discovered was consistent with a pre-ignition/detonation event. The cause of the preignition and/or detonation could not be determined. 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.” ## Aircraft - Registration: [N7379U](https://openairdocs.org/aircraft/N7379U), registered now, S/N 20700427, built 1978 (OpenAirDocs) - Reported make and model: Cessna 207 - Registry model: [Cessna 207A](https://openairdocs.org/model/cessna-207a) (registry code 2073604) (OpenAirDocs) - Registry engine: [Continental IO-520 series](https://openairdocs.org/engine/continental-io-520-series) (registry code 17032, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 20700427 - Year built: 1978 - Airframe hours: 18642.1 - Engines: Continental IO 520 SERIES 285 horsepower reciprocating - Damage: Substantial damage - Flight: Part 135 - Operator: Iliamna Air Taxi Inc - Registered owner: Iliamna Air Taxi Inc - Airworthiness certificate: Standard, Normal - Destination: 9K2, Kokhanok, AK - Flight plan: Company VFR - Airport: PAIL, Iliamna Airport - Equipment: None ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 60; injuries: none; airline transport; airplane ratings: multi-engine land, single-engine sea, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; seat: left; restraint: 4-point; flight hours: 10,000 total, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 320° at 10 knots - Visibility: 10 statute miles - Lowest ceiling: 6,500 ft broken - Temperature: 55 °F - Altimeter: 29.75 inHg - Observed at: IlI, 1 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 20180807010599A](https://openairdocs.org/incident/20180807010599A), Aug 7, 2018: Cessna 207F, Iliamna, AK, Substantial damage. Took-off from Iliamna Airport runway 35, left down wind departure. Two minutes after take off, experienced engine failure, turned back towards airport and… ## Docket (5 files) The files NTSB released with the investigation on March 16, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=98036. 10.7 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 6.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13274115&FileExtension=pdf&FileName=ANC18LA064%206120_Redacted-Rel.pdf - Airframe and engine examination (item 2, PDF, 8 pages, 759 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=14128953&FileExtension=pdf&FileName=ANC18LA064%20Engine%20exam%2012-19-18-Rel.pdf - Continental motors engine examination report (item 3, PDF, 12 pages, 1.8 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13135045&FileExtension=pdf&FileName=ANC18LA064%20Continental%20Motors%20Engine%20Examination%20Report%20N7379U_Redacted-Rel.pdf - Statement of party representatives to NTSB investigation (item 4, PDF, 1 page, 310 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13134322&FileExtension=pdf&FileName=Cert%20of%20Party%20Rep%20ANC18LA064%20CM%20-%20Charnon_Redacted-Rel.pdf - Photos (courtesy of FAA) (item 5, PDF, 3 pages, 3 photos, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13137780&FileExtension=pdf&FileName=ANC18LA064%20Photos-Rel.pdf 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.