Incident Overview
During taxi from landing following a post-annual inspection flight, the right main landing gear collapsed. The event occurred as the aircraft was moving on the ground, shortly after the inspection flight had been completed.
Maintenance Findings
Maintenance records revealed that during the gear rigging process, both main landing gear push-pull tubes had been removed. The applicable service manual, however, specifies that the drive tubes—not the push-pull tubes—should be disconnected for such adjustments. Additionally, examination of the left push-pull tube indicated that it had been installed upside down and was not properly aligned with its mating components.
Mechanical Failure Analysis
The improper installation led to the aircraft's load being transmitted directly to the center pivot on the main landing gear bellcrank. This stress caused the bellcrank to fail. The National Transportation Safety Board's Materials Laboratory examined the failed components and identified a "ductile overstress fracture in direct shear" on the bolt, which resulted in an instantaneous overload. This fracture pattern is consistent with a sudden application of force exceeding the bolt's capacity.