At 1500 on 30 January 2005, Pacific National freight train 6MP4 derailed at Koolyanobbing, approximately 200 kilometres west of Kalgoorlie, Western Australia. Freight train 6MP4 consisted of two locomotives leading 48 freight wagons, was 4108 tonnes in total train weight and 1685 metres in length. A total of 23 wagons (a train length of 803 metres) derailed, with the main wreckage located over a turn-out and a road level crossing.

On the same day at 1605, Pacific National freight train 6SP5 derailed near Booraan, approximately 360 kilometres west of Kalgoorlie. Freight train 6SP5 consisted of two locomotives leading 46 freight wagons, was 3739 tonnes in total train weight and 1740 metres in length. A total of 19 wagons (a train length of 605 metres) derailed, with the main wreckage located to the east of a road level crossing. 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. Both derailments occurred on the section of DIRN managed by WestNet Rail. No serious injuries were sustained due to either derailment.

The investigation determined that the most probable cause for each derailment was track misalignments in the form of track buckles on a very hot day. The investigation also determined that a number of factors combined to contribute to each derailment, any one of which may not have resulted in a derailment in its own right.

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