Accident Overview
On July 27, 2019, at approximately 1617 central daylight time, a Ryan Navion B airplane, registered N27AW, sustained substantial damage during a landing accident at Chicago Midway International Airport (MDW), Chicago, Illinois. The private pilot and three passengers were not injured. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
The pilot reported that as the airplane touched down on the dry concrete of runway 31R, a snap noise was heard. Despite a crosswind from the southwest, the landing was described as smooth and normal. After touchdown, the pilot taxied the entire length of the runway for rollout but encountered difficulty maintaining straight taxi. Initially suspecting a flat tire, the pilot exited the airplane and discovered a failure of the left side main landing gear (MLG).
Examination Findings
The left side MLG includes an upper side brace assembly with part number 143-33165-20. This assembly consists of a middle tube welded to a clevis-shaped fork at the inboard end and a scoop-shaped fitting at the outboard end. The fracture occurred in the middle of the circumferential weld between the middle tube and the fork. This failure resulted in the left MLG strut being displaced outboard toward the wingtip, causing substantial damage to the underside of the left wing.
Postaccident examination of the upper side brace assembly revealed portions of the fracture surface exhibited a flat fracture in a plane perpendicular to the tube axis, with a smoothly curving boundary—features consistent with fatigue. The fatigue regions were located on the upper and lower sides of the side brace, indicative of reverse bending fatigue. Crack arrest lines were observed, and the shape of the fatigue regions and arrest lines was consistent with fatigue cracks propagating radially outward from the interior surface of the tube. However, the fatigue regions did not intersect the outer surface.
Engineering drawings for the fork showed a fillet radius at the welded joint location. The interior surface of the middle tube adjacent to the fracture was machined at an angle consistent with a chamfer, and the location of the chamfered end corresponded to the location of the fillet radius in the fork when fitted together at the circumferential weld. The presence of a chamfer on the interior surface was consistent with incomplete penetration of the weld, which was observed around approximately 90% of the circumference. The weld was performed during initial production of the component. The chamfer was consumed by the weld bead on the aft side of the tube, where the weld bead pattern was consistent with the start and stop points for the circumferential weld.
Maintenance and Inspection
A visual inspection is conducted during preflight and maintenance inspections to detect weld defects and cracks in the MLG, including the upper side brace assembly. However, there is no non-destructive inspection method requirement from the manufacturer for this component.