What happened
On 4 May 2010, a Southern Air B747-300SF freighter, registration N749SA, was preparing for a flight from Incheon International Airport to Anchorage, USA. The aircraft was operating at nearly its maximum allowable takeoff weight. During the takeoff roll, as the aircraft reached approximately 150 knots, two tires on the left main body gear disintegrated. The sudden failure caused severe vibrations throughout the airframe.
Recognizing the danger, the captain initiated an immediate rejected takeoff before reaching the decision speed (V1). The crew utilized maximum manual braking and reverse thrust to bring the aircraft to a stop. While the aircraft was holding on taxiway M5, the heat generated during the long taxi and the high-speed braking caused the thermal fuse plugs in the wheels to activate. This resulted in the deflation of 12 of the aircraft's 18 tires. There were no injuries to the three crew members on board, though the aircraft sustained damage to the left wheel well door, a hydraulic return line, and the fuselage skin.
The investigation
The ARAIB examined the aircraft's maintenance history, tire specifications, and the sequence of events leading to the failure. Investigators analyzed the tire fragments and found evidence of heat damage on the casing and tread. The investigation also looked into the taxi route, which involved a significant distance of approximately 8,800 meters from the cargo terminal to the runway.
Findings
- The primary cause of the incident was the rupture of the number 5 tire due to increased pressure from accumulated heat and an uneven load distribution caused by a diameter imbalance between the number 5 and number 6 tires.
- The number 6 tire subsequently failed because it was unable to support the additional load transferred from the failed number 5 tire.
- A contributing factor was the uneven wear on the number 6 tire tread, which increased the load on that specific tire.
- The flight crew was unaware that an exceptionally long taxi distance could lead to sufficient heat buildup to cause tire bursts.
- The aircraft's tire pressure had been inflated to 200–202 psi before cargo loading was complete, which may have led to higher-than-intended pressure once the load was finalized.
Safety action
- The ARAIB recommended that Southern Air Inc. provide crews and controllers with information regarding the risks of heat-induced tire failure during long taxi operations.
- Recommendations were made to improve maintenance procedures, specifically regarding inflating tires to an appropriate pressure that accounts for the final aircraft weight and preventing diameter imbalances between paired tires.
- The ARAIB also suggested that the Boeing Company update flight and maintenance manuals to include specific guidance on taxiing limitations and maximum pressure thresholds relative to aircraft weight.