What happened
On June 29, 2018, a Korean Airlines Boeing 777-30 and registered HL7573 arrived at Narita International Airport from Incheon, Republic of Korea. The flight, carrying 319 passengers and 15 crew members, landed without incident on runway 16L. However, while taxiing on taxiway K, an aircraft following behind reported seeing what appeared to be smoke emanating from the right main landing gear.
Following instructions from ground control, the pilot halted the aircraft. Upon inspection, the crew noted that the temperature reading for the No. 12 brake had disappeared from the EICAS, and hydraulic fluid was visibly leaking. The right main landing gear tires were also found to be pointing in an unusual direction. The aircraft was unable to proceed, and all passengers and crew were eventually evacuated via bus to the terminal.
The investigation
Investigators examined the damaged components, including the right main landing gear aft axle, truck beam, and steering system. The investigation confirmed that the fracture of the axle had severed hydraulic hoses for both the brake and steering systems, leading to the fluid leak.
Technical analysis of the fractured axle revealed that the metal surface showed evidence of both corrosion and stress corrosion cracking (SCC). The investigation also looked into the maintenance history, noting that the aircraft's landing gear had been overhauled in 2009, prior to a manufacturer revision that introduced a mandatory corrosion inhibitor coating during bushing assembly. Furthermore, investigators examined the condition of the grease within the pivot pin, finding evidence of old, hardened grease that may have impeded the free rotation of the pin.
Findings
- The primary cause of the incident was the fracture of the right main landing gear aft axle due to stress corrosion cracking.
- This cracking originated from corrosion within the pivot bore, which was facilitated by water penetration through a worn fillet seal.
- The rotation of the bushings, which damaged the seal, was likely caused by a combination of factors, including a pivot pin diameter that may have exceeded specifications and the presence of dried, hardened grease that prevented smooth movement.
- The lack of a corrosion inhibitor coating, which was not required during the 2009 overhaul, left the components vulnerable to environmental degradation.
Safety action
Following the incident, the operator performed visual inspections on seven other aircraft that had undergone overhauls prior to the updated maintenance requirements. As a result, the operator replaced 14 main landing gear aft axles across those aircraft. Additionally, the operator updated its maintenance job cards to include specific procedures for ensuring thorough grease distribution and addressing potential blockages during lubrication tasks.