What happened
During the takeoff roll, the right main outboard wheel departed from the aircraft. Following the separation, the tower notified the flight crew of the event. The crew reported that all cockpit indications remained normal during the remainder of the operation. The airplane subsequently landed at its destination without any further incident.
The investigation
An examination of the outboard wheel bearing revealed a failure that caused the bearing cage to lose its ability to retain the rollers. Investigators found that both bolts used to secure the retainer nut to the axle were properly in place.
Further inspection showed that the wheel spacer had seized to the inner race of the outer bearing, and a distinct ridge was visible on the damaged spacer. A metallurgical examination conducted by the NTSB determined that the spacer was rotating on the axle, though the specific orientation of the spacer could not be determined. Additionally, the outboard wheel bearing showed evidence of overheating.