As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING PUSHBACK FOR DEPARTURE A LOUD BANG WAS HEARD AND THE CENTER GEAR STARTED TO RETRACT. THE TOP PORTION OF THE CLG OUTER CYLINDER FRACTURED AND LIBERATED FROM THE MAIN BODY OF THE OUTER CYLINDER. THE LIBERATED PORTION OF THE OUTER CYLINDER WAS FORCED UPWARD DUE TO THE INTERNAL PRESSURE IN THE CYLINDER CAUSING IT TO CONTRACT AND FRACTURE THE UPPER LOCK LINK. REASON FOR FRACTURE FAILURE OF THE OUTER CYLINDER IS AWAITING FURTHER ANALYSIS OF THE FAILED PARTS.