On Thursday 9 February 2006 at about 0351 an XPT passenger train travelling from Melbourne to Sydney derailed near Harden in New South Wales. An inspection by the driver found one wheel on the trailing bogie of the leading power car had derailed. During recovery operations the axle of the derailed wheel was found to have completely sheared with a crack in the radius relief area between the gear and wheel seats.

The ATSB's investigation concluded that impacts from track ballast from unknown location(s) had led to the formation of the cracks in the axles. The investigation also concluded that routine testing of the axles carried out by the operator's maintenance contractor, using magnetic particle inspection (MPI), was ineffective and resulted in the fatigue cracks going undetected for a considerable period of time.

A number of safety actions have been undertaken by RailCorp and the Independent Transport Safety and Reliability Regulator of New South Wales which include measures aimed at the early detection and prevention of axle fatigue cracks in XPT and other diesel fleet rail vehicles to limit the risk of further axle failures. Additionally, the Australian Transport Safety Bureau has issued a safety advisory notice to all rail vehicle operators in Australia that they should consider the risks associated with axle failures as a result of fatigue cracks initiated by ballast strikes and review their maintenance practices accordingly.