An ATSB investigation has found that high track temperatures, track stability and the movement of rolling stock led to derailments involving Train 6MP4 at Koolyanobbing WA and Train 6SP5 at Booraan WA on the afternoon of 30 January 2005.
Koolyanobbing and Booraan are respectively about 200 kilometres and 360 kilometres west of Kalgoorlie. Both freight trains had been travelling to Perth on the Defined Interstate Rail Network (DIRN), 6MP4 having started its journey in Melbourne and 6SP5 in Sydney.
There were no serious injuries due to either derailment but many wagons from each train sustained extensive damage.
The Australian Transport Safety Bureau investigation determined that the most probable cause for each derailment was track misalignments in the form of track buckles on a very hot day. A number of additional factors combined to contribute to each derailment, any one of which may not have resulted in a derailment in its own right.
Considering how unusual it is for two similar derailments to occur approximately an hour apart and within 200 kilometres of each other, extensive examination and analysis of freight loading, train handling, and rollingstock was also conducted.
There was no evidence or indication of any fault, defect or deficiency in freight loading, train handling, or rollingstock that may have directly contributed to one or both derailments or to the development of a track defect subsequently causing one or both derailments.
In the interest of future safety the ATSB has made recommendations regarding management of track stability and movement, procedures for assessing minor defects and identifying factors that may have contributed to the defect, and documenting of procedures for managing safe operations during periods of high ambient temperature.
Read the report: Derailment of Pacific National 6MP4 and Pacific National 6SP5 Trains