Rockwell 690C, Minden, Nev., May 2, 2008–The board was unable to determine why both main landing gear collapsed, substantially damaging the Twin Commander while it taxied for takeoff at Minden-Tahoe Airport. An FAA inspector said the landing gear’s clamshell doors remained in the closed position, inconsistent with its being in an in-transit operating mode. The gear select handle was found in the “down” position. Inspection of the right main landing gear’s components failed to identify any causes that would have prevented normal operation, while the left gear’s inboard clevis was fractured. Metallurgical examination of the fracture region showed that it failed during a single bending overstress event. No preexisting cracks
or corrosion were noted, and laboratory analysis failed to determine the cause for the overstress event. After the failed clevis had been replaced, the gear’s retraction and extension cycles were performed with no anomalies noted. At the time of the accident, the airplane had accrued 13 hours since its most recent annual inspection.