# NTSB ANC16LA024: Cessna 180, N6479X, Naknek, AK, May 3, 2016 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: May 3, 2016, 12:30 local (20:30 UTC) - Place: Naknek, AK - Coordinates: 58.735, -157.021942 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=58.7350&lon=-157.0219&mi=10 - Phase of flight: [Landing](https://openairdocs.org/ntsb-phases/550) (OpenAirDocs' grouping) - Defining event: [Landing-landing roll: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report July 26, 2017 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - Parties: FAA - NTSB case key (mKey): 93139 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC16LA024 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/93139/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=93139 - Page: https://openairdocs.org/ntsb/ANC16LA024 ## Probable cause The overstress fracture and subsequent separation of the left main landing gear axle due to a hard landing, which resulted in the pilot’s inability to maintain directional control of the airplane. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Landing gear system: main gear strut/axle/truck](https://openairdocs.org/ntsb-findings/01023213): Aircraft › Aircraft systems · Capability exceeded (probable cause); cases with it: [Cessna 180D, 1 case](https://openairdocs.org/ntsb-findings/01023213/cases.md?model=2072610), [All aircraft, 86 cases](https://openairdocs.org/ntsb-findings/01023213/cases.md) - [Landing gear system: main gear strut/axle/truck](https://openairdocs.org/ntsb-findings/01023213): Aircraft › Aircraft systems · Failure (probable cause); cases with it: [Cessna 180D, 1 case](https://openairdocs.org/ntsb-findings/01023213/cases.md?model=2072610), [All aircraft, 86 cases](https://openairdocs.org/ntsb-findings/01023213/cases.md) - [Performance/control parameters: directional control](https://openairdocs.org/ntsb-findings/01062020): Aircraft › Aircraft oper/perf/capability · Attain/maintain not possible (probable cause); cases with it: [Cessna 180D, 5 cases](https://openairdocs.org/ntsb-findings/01062020/cases.md?model=2072610), [All aircraft, 3,958 cases](https://openairdocs.org/ntsb-findings/01062020/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Landing-flare/touchdown: Abnormal runway contact](https://openairdocs.org/ntsb-events/090); cases with it: [Cessna 180D, 1 case](https://openairdocs.org/ntsb-events/090/sequence.md?model=2072610), [All aircraft, 1,506 cases](https://openairdocs.org/ntsb-events/090/sequence.md) - [Landing-landing roll: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) (defining event); cases with it: [Cessna 180D, 1 case](https://openairdocs.org/ntsb-events/338/sequence.md?model=2072610), [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) ## Analysis The commercial pilot stated that, during the landing rollout in the tailwheel-equipped airplane, the left wheel axle fractured and separated from the airplane with the wheel attached. The left landing gear leg then dug into the runway surface, the airplane made a sudden left turn, and the left wing and left horizontal stabilizer struck the runway. An examination of the fractured left axle revealed features consistent with a bending overstress fracture. High magnification optical examination of the fracture also revealed several small fatigue cracks within the crack origin area. Although several fatigue initiation sites were present along the fracture origin area, none of them were large enough to have led to the failure or to have significantly lowered the ultimate strength of the axle enough for a bending overstress failure to occur under normal loading conditions. Therefore, it is likely the landing gear axle failed as a result of bending overstress due to a hard landing. ## Factual narrative On May 3, 2016, about 1230 Alaska daylight time, a tailwheel-equipped Cessna 180 airplane, N6479X, sustained substantial damage following a separation of the left main wheel and axle from the landing gear strut during the landing rollout at the Naknek airport, Naknek, Alaska. The commercial pilot and sole occupant were not injured. The airplane was registered to Skol-Alaska, LLC and operated by the pilot under the provisions of 14 Code of Federal Regulations (CFR) Part 91 as a personal flight. Visual meteorological conditions prevailed at the time of the accident and a Federal Aviation Administration (FAA) visual flight rules (VFR) flight plan had been filed and activated. During an interview with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on May 3, 2016, the pilot stated that during the landing roll out, the left wheel axle fractured and separated from the airplane with the wheel attached. As the left landing gear leg dug into the runway surface, the airplane made a sudden left turn, and the left wing and left horizontal stabilizer struck the runway. The airplane sustained substantial damage to the left wing and left horizontal stabilizer. The fractured wheel axle was sent to the NTSB Materials Laboratory in Washington, D.C. for further examination. The fracture surface showed several areas of post-fracture damage. The undamaged portions of the fracture surface were optically, matte grey and highly textured consistent with a bending overstress fracture. Radial lines visible on the fracture indicated a wide area initiation at the outer diameter surface near the inboard end of the axle. High magnification optical examination of the fracture also revealed several small fatigue cracks within the crack origin area. A Materials Laboratory Factual Report is located in the public docket for this accident. The closest weather reporting facility is King Salmon Airport, King Salmon, Alaska, about 12 miles east of the accident site. At 1154, an aviation routine weather report (METAR) from the King Salmon Airport was reporting in part: wind from 080 degrees at 4 knots; sky condition, scattered at 2,700 feet AGL, broken at 5,000 feet AGL, broken at 7,500 feet AGL, broken at 20,000 AGL; visibility, 10 statute miles; temperature 52° F; dewpoint 36° F; barometric pressure 29.70 inHG. ## Aircraft - Registration: [N6479X](https://openairdocs.org/aircraft/N6479X), registered now, S/N 18050979, built 1961 (OpenAirDocs) - Reported make and model: CESSNA 180 - Registry model: [Cessna 180D](https://openairdocs.org/model/cessna-180d) (registry code 2072610) (OpenAirDocs) - Registry engine: [Continental O-470 series](https://openairdocs.org/engine/continental-o-470-series) (registry code 17026, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 18050979 - Year built: 1961 - Airframe hours: 3369 - Engines: CONT MOTOR O-470 SERIES 225 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, March 21, 2016, 34 hours before - Departed: SXQ, SOLDOTNA, AK - Destination: 5NK, Naknek, AK - Flight plan: VFR - Airport: 5NK, Naknek, runway 08, 1,950 × 50 ft, gravel - Equipment: None ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 51; injuries: none; commercial; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 3, with waivers/limitations; last flight review April 23, 2015; seat: left; flight hours: 4,374.6 total, 760 in this make and model, 4,374.6 as pilot in command, 34 in the last 90 days, 2.7 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 80° at 4 knots - Visibility: 10 statute miles - Lowest ceiling: 5,000 ft broken - Temperature: 52 °F, dew point 36 °F - Altimeter: 29.70 inHg - Observed at: PAKN, 12 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 20160503013479A](https://openairdocs.org/incident/20160503013479A), May 3, 2016: Cessna 180D, Naknek, AK, Substantial damage. The event occurred around 1230L on may 3, 2016. The PIC had recently purchased the aircraft and flown it back from new jersey. The previous pilot had owned the… ## Docket (3 files) The files NTSB released with the investigation on June 5, 2017, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=93139. 1.9 MB in all. - Materials Laboratory Factual Report 16-068 (item 1, .PDF, 861 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40452847&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2016-068-Master.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 2, .PDF, 995 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40452848&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Record of Conversation (Pilot) (item 3, .PDF, 30 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40452849&FileExtension=.PDF&FileName=Record%20of%20Conversation%20(Pilot)-Master.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.