Event Description
Shortly after touchdown during a landing, the left main landing gear collapsed. The aircraft subsequently veered off the left side of the runway and struck a ditch. Following impact with the ditch, the right main and nose landing gears also collapsed.
Examination Findings
An examination of the left landing gear assembly revealed that a bolt in the left bellcrank assembly, part number 5041001-5, had sheared. Additionally, one ear of the lower clevis on the bellcrank had broken.
Metallurgical Analysis
Metallurgical examination of the fractured components indicated that the fracture characteristics were consistent with an overstress separation. Research into the Cessna 421B landing gear system indicated that such a failure mode could occur if the landing gear mechanism is improperly rigged. However, no determination was made regarding the adequacy of the aircraft inspections.