What happened
Following the completion of landing, the flight crew observed a vibration occurring during the landing roll. Upon inspection, it was discovered that the left main gear torque link apex bolt had vibrated out of the torque link. This mechanical failure allowed the main gear truck to rotate 360 degrees while the aircraft was on the ground.
The investigation
An examination of the components revealed that the nut had stripped off the bolt. Laboratory testing of the hardware showed that the torque link attaching pins contained excessive play. When investigators measured both new and old apex bolts, they determined that the bolts failed to pass the most stringent quality control checks regarding correct thread size.
Findings
Investigators concluded that the loose torque links created excessive vibration, which caused the nut to strip off the bolt. Furthermore, because the threads on the undersized apex bolt were incorrect, the nut was able to shear away the bolt pin that was specifically designed to retain it.