What happened
On 15 August 2019, a Boeing 767-33A (ER), registration N378AX, was performing a commercial flight at Shannon Airport when the crew initiated an aborted takeoff on Runway 24. During the takeoff roll, the pilot heard an increasing, unusual noise and decided to reject the departure. Following the stop, the crew taxied to a holding area to allow the brakes to cool, estimating a required wait time of approximately 44 minutes.
After consulting with the aircraft operator's maintenance department, the crew decided to return to the parking stand for inspection. While taxiing back toward the stand, air traffic controllers observed smoke emerging from the left main landing gear. Shortly thereafter, the fire spread to the landing gear area. The airport fire and rescue service was deployed, and the crew initiated an emergency evacuation of the 145 passengers and 10 crew members via the aircraft's right-side slides. During the evacuation, one passenger sustained a minor injury. The fire was extinguished by rescue services within minutes.
The investigation
Investigators examined the aircraft's flight data recorder and interviewed the flight crew and cabin crew. The investigation focused on the sequence of events from the initial noise heard during the takeoff roll to the ignition of the fire. Technical inspections were conducted on the wheel and brake assemblies by the manufacturer and the FAA.
Data from the flight recorder revealed that the aircraft was actually traveling at approximately 149 kts when the decision to reject the takeoff was made, which was higher than the crew's estimate of 120 kts. The investigation also looked into the maintenance history of the wheels and brakes, noting that certain wheels had been replaced just two days prior due to wear limits. No specific mechanical failure or source of ignition was identified during the disassembly and inspection of the brake units.
Findings
- The crew underestimated the speed of the rejected takeoff, which led to an inaccurate calculation of the necessary brake cooling time.
- The actual speed of 149 kts required a significantly longer cooling period than the 44 minutes the crew had planned for.
- The combination of a high-speed rejected takeoff and subsequent taxiing maneuvers, which involved several left turns and brake applications, likely caused the brake system to overheat.
- The aircraft was not equipped with EICAS indications for monitoring brake temperatures, leaving the crew with no real-time way to monitor the heat levels.
- An unidentified, increasing noise during the takeoff roll acted as a significant distraction, potentially contributing to the crew's underestimation of the aircraft's speed at the moment of the abort.