Incident
During the takeoff roll, the crew noticed a vibration between 135 knots and lift-off. They kept the landing gear extended and were notified that two tires had separated from the right inside main gear truck, a third tire had blown out, and the fourth appeared intact. After dumping fuel, the aircraft landed. Post-flight examination found that the tire failures had resulted in skin damage and broken hydraulic line(s).
Loading Imbalance
Cargo had been loaded with more pallets on the right side; some pallets were not marked to indicate weight or shipping identification. A computer print-out, signed by the captain and the station agent, showed a lateral imbalance of 18,766 pounds. With this imbalance, the gross weight should not have exceeded 744,000 pounds; however, the actual weight was 751,316 pounds. After departing the cargo ramp, the aircraft was taxied approximately three miles in a straight line, then made two left turns onto runway 6R for takeoff.
Previous Loading Criteria
Prior loading criteria provided a 3% allowance for random disposable loads on pallets. In 1969, the FAA issued an exemption from FAR 25.471(b) that allowed Boeing 747 aircraft to be loaded to the design limit, provided instructions were available to ensure symmetrical loading.
Tire Failure Statistics
Of 239 known tire failures, 71 involved Flying Tiger Line, an all-cargo carrier.