Occurrence
On 19 January 2004, at approximately 1410 eastern standard time, an occurrence involving an Airbus A319, A320, or A321 aircraft prompted a Transportation Safety Board (TSB) investigation. The TSB Engineering Branch examined the nosewheels, fractured nosewheel axle, nose landing gear sliding rod, and flight data recorder (FDR). The FDR data from the occurrence landing and the previous eight landings showed no abnormalities.
Examination of Components
The nose landing gear examined was manufactured by Liebherr, a division of Messier-Dowty (part number D23592020, serial number L2212). The roller bearing was manufactured by the Timken Company (part number 42690H*2-629, not serialized), with the suffix 629 indicating aerospace grade meeting higher design and production standards.
Findings
The investigation determined that the nosewheel right inboard roller bearing failed. It is likely that lack of lubrication, resulting from the grease dam being dislodged from its normal position, was a contributing factor. Friction temperatures generated by the failed roller bearing exceeded the cadmium melting point. Cadmium penetrated and weakened the intergranular structure of the nose landing gear axle, causing it to fail due to liquid metal embrittlement.
Risk
The dislodged inner-bearing grease dam allowed grease to migrate from the inboard roller bearing of the right nosewheel to the inside of the nosewheel assembly. A reduction in lubrication increases cage loads and may lead to bearing failures.
Safety Actions Taken
Air Canada took steps to coat axles for its nose landing gears with SermeTel® to reduce the likelihood of axle failures from cadmium infusion due to high friction heat from bearing failures. Air Canada also issued a maintenance alert and revised its wheel installation job card to stress wheel inspection prior to installation and ensure proper tools and torques per the Aircraft Maintenance Manual. The Air Canada wheel shop manuals were revised to raise awareness of the importance of grease dams and seal installations.
In May 2004, Goodrich released Service Letter 1991 recommending Mobil SHC-100 grease for wheel bearings for its superior adhesion properties, corrosion protection, and bearing lubrication. Goodrich also issued Service Bulletin 3-1531-32-3 in July 2004 with new inspection procedures for bearing grease seals on Airbus A318, A319, A320, and A321 aircraft.
Airbus designed an integrated retaining ring and seal being tested for qualification, including roll and landing tests under different loads and high-pressure water tests to demonstrate enhanced protection of the seal and bearing from external contaminants.
This report concludes the Transportation Safety Board's investigation, authorized for release on 23 February 2005.