A B737-300 ON TURNING OFF RWY ONTO TXWY HAD #3 MAIN TIRE AND WHEEL ASSEMBLY DEPART THE ACFT. POSSIBLY CAUSED BY A FAILED INNER BEARING.

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I WAS CALLED OUT TO HELP CHANGE A TIRE ON ACFT X. MYSELF AND MR X WENT OUT TO HELP. MR X HELPED BY GRABBING THE TIRE CHANGE CART. MY PART IN THE TIRE CHANGE WAS TO GO GRAB THE LOGBOOK AND I SPOKE TO MAINT CTL TO FIND WHERE ACFT X ROUTINE OVERNIGHT CHK STATION WAS. I DID NOT SEE THE TIRE CHANGE OTHER THAN SEEING THE ORIGINAL TIRE ON THE ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FAA IS INVESTIGATING THE INCIDENT OF #3 TIRE AND WHEEL ASSEMBLY DEPARTING THE ACFT AFTER LNDG AND TURNING ONTO A TXWY. THE FAA CONTENDS THE AXLE NUT RETAINING RING WAS IMPROPERLY INSTALLED AND ALLOWED THE AXLE NUT TO ROTATE OFF. THE TECHNICIANS AND THE COMPANY SAY THE WHEEL ASSEMBLY INNER BEARING FAILED AND FORCED THE WHEEL TO MOVE INWARD ALLOWING THE HUBCAP RIVETS TO TEAR UP THE AXLE RETAINING RING WHICH WAS FOUND. THE INNER BEARING AND PIECES OF THE INNER BEARING WERE NEVER FOUND. THE TIRE AND WHEEL ASSEMBLY WERE BUILT UP AT A CONTRACT MAINT SHOP. THE BEARINGS ARE NOT TIME LIMITED AND ARE INSPECTED AND REPLACED ON CONDITION ONLY.