What happened
On September 8, 2006, a Qatar Airways Airbus A300-600, registration A7-ABV, was taxiing at Madrid-Barajas Airport for an international passenger flight. During the taxi sequence, the crew noticed asymmetric heating in the left main landing gear. Specifically, temperatures on wheels 5 and 6 rose significantly, triggering an ECAM warning of brakes exceeding 300 °C.
Despite the high temperatures, the crew attempted to manage the situation by stopping periodically to allow the brakes to cool. They eventually decided to cancel the takeoff and return to their original parking stand. However, as the aircraft continued to taxi, the temperatures continued to climb, reaching 500 °C. During the return journey, the aircraft experienced two heavy bumps, indicating the tires had deflated. Shortly thereafter, other aircraft in the vicinity reported seeing fire beneath the left landing gear.
The captain ordered an emergency evacuation via the right-side doors. While the fire brigade arrived quickly and extinguished the flames, the evacuation resulted in one serious injury and several minor injuries among the 204 passengers and 13 crew members.
The investigation
The CIAIAC investigation focused on the cause of the extreme brake heating and the subsequent fire. Investigators examined the aircraft's hydraulic systems, the brake assemblies, and the servovalve in the alternate braking system. Technical analysis of the servovalve revealed a large scratch on the internal spool, suggesting that a high-hardness particle, such as a grain of sand, had caused an obstruction.
Flight data recorder analysis confirmed that the crew followed taxi instructions but noted that the aircraft had traveled a long distance, which contributed to the prolonged heat exposure. The investigation also reviewed the communication between the crew and Air Traffic Control (ATC), noting frequent frequency changes and the use of Spanish by other aircraft, which hindered the crew's awareness of the fire reported by third parties.
Findings
- The primary cause of the overheating was residual pressure trapped in the alternate brake system, caused by a stuck servovalve due to contamination by a high-hardness particle in the hydraulic fluid.
- The fire likely initiated after the tires deflated, as the extreme heat caused the fusible plugs to melt, and the subsequent friction of the rims on the ground may have ignited combustible materials.
- The crew's decision to continue taxiing, while within the absolute 600 °C limit, contributed to the prolonged heating event.
- Frequent changes in radio frequencies and the use of a language (Spanish) not understood by the crew delayed the transmission of critical fire warnings.
- The airport's lack of a nearby parking area for aircraft with technical issues forced the aircraft to continue taxiing through a long route, exacerbating the heat buildup.