After a wheel on one of its Boeing 737s failed, Virgin Australia implemented new landing gear wheel inspection requirements, while the wheel manufacturer, Safran, updated the relevant component maintenance manual.
The wheel failure event occurred on 4 January 2017 when the 737-800 was holding on taxiway Brisbane Airport B3 when the crew heard a loud noise they thought was a burst tyre. The crew attempted to taxi back to the gate, but were held short when an engineer observed that the left main landing gear main wheel assembly had failed.
The flight was cancelled and passengers disembarked, however the aircraft could not be jacked and towed via the axle due to the damaged wheel. Instead, wing jacks were used to allow a double wheel change on the tarmac. The aircraft was then towed to a maintenance facility for examination.
…There were no mandated inspections suitable for detecting such loosening.
An ATSB investigation found that the wheel had ruptured due to tie bolt assemblies having loosened while in service. This allowed the two wheel halves to move relative to each other, resulting in a fatigue crack and eventual wheel rupture. The loosening was most likely due to the presence of anti-seize compound between the wheel halves, which affected the clamping forces.
“This incident highlights the importance of compliance with all aspects of manufacturers’ maintenance procedures, including the appropriate application of anti‑seize,” said ATSB Director Transport Safety Stuart Macleod. “This is especially important if, as in this case, there is no simple means of detecting the effect that such excess product can have on fastener security.”
The ATSB found that while the bolt assemblies on this single-web wheel-type were more prone to in-service loosening than dual-web wheels, there were no mandated inspections suitable for detecting such loosening. There were also no mandated risk controls to prevent loosening or subsequent rupture.
Virgin has advised that in response to this incident, it has implemented regular inspections to identify and prevent the loosening of tie bolt assemblies. Safran, the wheel manufacturer, updated the wheel’s component maintenance manual with more detailed instructions for applying anti-seize compound.
Finally, Boeing advised 737 NG operators of two possible courses of action to address the issue of potential wheel failures based on two optional service bulletins that it had in place prior to the occurrence.
The particular wheel type was installed on approximately 2,000 737 NG aircraft in service worldwide. Boeing has delivered approximately 7,000 737 NG aircraft in total.