Accident Overview
On May 3, 2016, at approximately 1230 Alaska daylight time, a tailwheel-equipped Cessna 180 airplane, registration N6479X, experienced a landing gear failure during the landing rollout at Naknek Airport in Naknek, Alaska. The airplane sustained substantial damage. The commercial pilot, who was the sole occupant, was not injured. The aircraft was registered to Skol-Alaska, LLC and operated by the pilot under 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and a Federal Aviation Administration visual flight rules flight plan had been filed and activated.
Sequence of Events
During an interview with the National Transportation Safety Board (NTSB) investigator-in-charge on the same day, the pilot stated that during the landing rollout, 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, causing the left wing and left horizontal stabilizer to strike the runway. The resulting damage was substantial to the left wing and left horizontal stabilizer.
Post-Accident Examination
The fractured wheel axle was sent to the NTSB Materials Laboratory in Washington, D.C. for further examination. The fracture surface exhibited several areas of post-fracture damage. The undamaged portions displayed an optically matte grey, highly textured appearance, consistent with a bending overstress fracture. Radial lines on the fracture indicated a wide area initiation at the outer diameter surface near the inboard end of the axle. High magnification optical examination also revealed several small fatigue cracks within the crack origin area. A Materials Laboratory Factual Report is included in the public docket for this accident.
Weather Information
The closest weather reporting facility is King Salmon Airport, King Salmon, Alaska, approximately 12 miles east of the accident site. At 1154, an aviation routine weather report from King Salmon Airport reported 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, and broken at 20,000 feet AGL; visibility 10 statute miles; temperature 52°F; dewpoint 36°F; barometric pressure 29.70 inHg.