Accident Overview
On February 13, 2016, at about 0930 Pacific standard time, a Cessna 140G airplane (registration N3625V) experienced a left main landing gear axle fracture during landing at Independence State Airport, Independence, Oregon. The aircraft subsequently ground looped, resulting in substantial damage to the right wing and fuselage. The private pilot and one passenger were not injured. The flight was operated under 14 CFR Part 91 as a personal cross-country trip. Visual meteorological conditions prevailed, and no flight plan was filed.
Events During Landing
The pilot reported that the approach and touchdown were normal. Immediately after touchdown, he felt a bump and the airplane began drifting left. Suspecting a flat tire, he attempted corrective measures, but the drift continued. The aircraft exited the left side of the runway into dirt and ground looped.
Post-Accident Examination
A Federal Aviation Administration inspector from the Portland Flight Standards District Office examined the aircraft at the accident scene and found that the left main landing gear axle had fractured, causing the wheel assembly to separate. The NTSB materials laboratory performed a detailed examination of the fractured axle. The fracture was located near the inboard end, just outboard of the axle attachment flange. Portions of the fracture surface exhibited smooth features oriented perpendicular to the outer surface, consistent with fatigue. The fatigue cracks initiated at a fillet corner where the axle outer diameter changed.
Maintenance History
According to a Cessna representative, inspections of the main landing gear axle should follow Section 2A of the 100-series Maintenance Manual. The axles require inspection for cracks and corrosion initially after 10 years or 4,000 hours, and thereafter at intervals of 3 years or 1,000 hours. The inspection involves removing the wheel for a visual check; if a crack is suspected, an eddy current inspection is needed. The airplane was manufactured in 1948. The owner reported that the last annual inspection occurred about 7 months prior, at a total airframe time of 6,314.5 hours. However, no airframe logbooks were located during the investigation, so it could not be determined when the last axle inspection was performed.