What happened
On July 17, 2006, a Boeing 747-200F freighter, registration N516MC, was performing a scheduled cargo flight from Amsterdam Airport Schiphol to Atlanta. During the take-off roll on runway 36L, the crew felt vibrations that they initially attributed to nose wheel shimmy. As the aircraft accelerated, the aft tires on the left-hand body gear (LHBG) ruptured, followed by the failure of the wheel rims and one forward tire.
Debris from the bursting tires and fractured rims struck the aircraft's fuselage and flap system. This impact caused a flap asymmetry, where the left inboard flap position differed from the right, creating a roll moment. The crew declared an emergency, dumped fuel, and returned to Schiphol. During the landing on runway 06, the remaining forward tire on the LHBG also ruptured. The incident resulted in major damage to the aircraft and substantial damage to both runways due to the wheel flanges contacting the pavement.
The investigation
The Dutch Safety Board (DSB) examined the fractured wheel assemblies, brakes, and tire remnants. Laboratory analysis at Boeing's facility in the United States revealed that the tire fragments showed evidence of a burst under pressure. Specifically, the two aft tires showed signs of intense heat, including bluing and melted nylon, which is consistent with being operated in an over-deflected or underinflated state.
Investigators also reviewed the aircraft's maintenance logs, noting that a week prior, the aircraft had undergone a rejected take-off in Miami, which involved high brake temperatures and the replacement of a brake metering valve. While the investigation looked into the possibility of a link between the previous overheating event and the Schiphol incident, a definitive connection could not be established.
Findings
- The primary cause was that one or both of the aft tires on the left-hand body gear were operated in an underinflated or overdeflected condition prior to the flight.
- This underinflation led to excessive internal heat generation and heat degradation of the tire's physical properties.
- The combination of pre-existing heat damage, a long taxi distance, and a high take-off weight caused the aft tires to rupture during the take-off roll.
- The subsequent failure of the wheel rims and the loss of tire pressure caused the forward inboard tire to fail due to debris and overload.
- The failure of the forward outboard tire occurred during the landing roll due to the effects of foreign object debris (FOD) and/or overload.