What happened
On August 12, 2024, an Atlas Air Inc. Boeing 747-400F, registration N404KZ, was taxiing for departure from Narita International Airport toward Los Angeles. During the taxi phase near Taxiway A, the flight crew noted a vibration and heard sounds resembling explosions. Shortly after takeoff from Runway 16R, the aircraft's Engine Indicating and Crew Alerting System (EICAS) signaled a low quantity in the No. 4 hydraulic system.
As the aircraft climbed, a secondary issue emerged when the cabin altitude warning activated, indicating a loss of cabin pressure. The crew subsequently decided to return to Narita. During the process of reducing weight via fuel jettisoning, the No. 1 hydraulic system also experienced a loss of pressure. Upon landing, the crew had to utilize manual brakes due to the loss of steering and automatic braking functions. No injuries were reported among the seven people on board.
The investigation
The JTSB investigation focused on the sequence of events starting from the taxi phase. Investigators examined video footage, which captured tire fragments rotating with the wheel and white smoke emitting from the landing gear during the takeoff roll. Post-flight inspections of the Boeing 747-400F revealed substantial damage, including punctures in the landing gear wheel well ceiling, damaged wheel assemblies (No. 7 and No. 8), and numerous cracks and dents on the fuselage and horizontal stabilizer.
Analysis of the No. 7 tire revealed extensive damage, including tread ply exfoliation and nylon dissolution. While the cause of the initial pressure reduction in the No. 7 tire remained unidentified, investigators determined that the tire likely burst while taxiing. This failure caused debris to strike the aircraft's internal structure when the landing gear was retracted. This impact damaged the hydraulic lines, leading to the subsequent fluid leaks and system failures.
Findings
- The primary cause of the mechanical failure was the bursting of the No. 7 tire during taxiing.
- Debris from the damaged wheels and the bursting tire struck the arched pressure deck in the wheel well during gear retraction, causing structural damage and cabin depressurization.
- The damage to the No. 7 tire caused subsequent damage to the No. 8 tire due to increased load and contact with fragments.
- The destruction of hydraulic tubes during the takeoff roll led to the loss of both the No. 1 and No. 4 hydraulic systems.
- The aircraft was not equipped with a Tire Pressure Indication System (TPIS), which would have allowed the crew to detect the abnormal pressure during taxi.