ROCKWELL 690C near Minden, NV — 2008-05-03

Probable cause

The collapse of both main landing gear for undetermined reasons.

NTSB narrative

While beginning a 90-degree right turn onto the active runway for takeoff, both the left and right main landing gear partially collapsed. A Federal Aviation Administration inspector said the airplane's clam shell gear doors remained in the closed position, which is inconsistent with the landing gear being in an intransit operating mode, and the gear select handle was found in the DOWN position. The left main landing gear's inboard clevis, which secures the left gear's inboard hydraulic actuator to the gear's trunnion boss, was fractured. It had been installed incorrectly and had missed the barrel nut, which retains the clevis in the trunnion. When removed, the clevis bolt rotated relatively easily and the nut appeared to be incorrectly located. Maintenance personnel who had installed the clevis during the previous inspection, 26 days and 13 operating hours before the accident, stated that the breakage of the clevis pin would not be caused by the installation. A metallurgical examination of the fracture region revealed that the clevis failed during a single bending overstress event. No preexisting cracks or corrosion were noted at the fracture and the laboratory could not determine an underlying reason for the overstress fracture. The main landing gear is retained in the down and locked position by hydraulic pressure being applied to the inboard main landing gear actuating cylinder, as well as being assisted by the outboard main landing gear (hydraulic-pneumatic) actuating cylinder. Additionally, bungee cords attached to the main landing gear drag braces assures that the main landing gear is locked and retained in the down position. As a result of these redundant features that are designed to ensure that the main landing gear is locked in the down position, the gear collapse cannot be positively attributed to the failure of the clevis. An inspection of the right main landing gear's components failed to reveal any anomalies that would have precluded normal operation. After the failed clevis was replaced, multiple landing gear retraction and extension cycles were performed with no anomalies noted. The reason for the gear collapse was undetermined.

NTSB coding

• Landing gear collapse · Taxi-into takeoff position

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