Corrosion cracking caused Korean Air Boeing 777 main gear axle failure on landing…

September 29, 2019

 

Japan Investigators of Korean Air Boeing 777-300 that suffered serious damage to its rear wheel axle of the main landing gear conclude the corrosion attributed to failure.

Incident

On Friday, June 29, 2018, a Korean Air Boeing 777-300, registered HL7573 had the right main landing gear aft axle fractured when landing at Narita international airport. Consequently, the aircraft was forced to halt and was unable to continue taxiing on the taxiway.

The flight 703, from Incheon airport in the Republic of Korea, with 15 crew members and 319 passengers, and arrived at Narita international airport at 12:37. The aircraft touched down, decelerated thereafter and taxied on taxiway without any trouble.

At 12:43, Narita Ground sighted something, which was seemingly smoke, on the right main landing gear aft of the aircraft; and subsequently, the Narita Ground instructed the aircraft to halt at the position where it was.

There were no warning and caution messages appeared on EICAS; however, they confirmed that the temperature of the No. 12 brake was disappeared, the hydraulic quantity on the right system was gradually decreasing, and status messages of “MAIN GEAR STEERING” and “BRAKE TEMP SYS” were appeared.

At 1:10, the tires pointed to the unusual direction caused by the fractured axle and the hydraulic fluid was leaking, that the aircraft could not
continue taxiing.

Findings


Corrosion Inhibitor Coating Situations;
Main landing gear of the aircraft was overhauled in July 2009; however, the corrosion inhibitor was not coated because the CMM at that time required grease either ASG 7 or ASG 33 (MIL-PRF-23827) to be applied when assembling bushings.

Detailed investigation on the fractured axle and the pivot pin revealed, aft fractured surface had a corrosion initiating region on the lubrication passage on the lower side of the pivot bore, which was further developed to SCC. It was observed that the cracking that further progressed afterward

Causes


It is certain that the aircraft had the right main landing gear aft axle fractured when landing in the serious incident, and subsequently, it was forced to halt on taxiway and could not continue taxiing.
It is highly probable that the fractured axle was attributed to the SCC originated from the corrosion generating on the pivot bore and ongoing operations of the aircraft thereafter with cracking occurred.
It is highly probable that the corrosion generated on the pivot bore was contributed by water penetration caused by the torn fillet seal due to rotation of the bushings and corrosion inhibitor that was not applied. 

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