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Final report

Summary

What happened

On 14 May 2014, train 4413 – a bulk iron ore service operated by Aurizon, derailed on the Defined Interstate Rail Network (DIRN) between Stewart and Bonnie Vale, about 54 km west of Kalgoorlie in Western Australia. As a result of the derailment there was significant damage to track and rolling stock. There were no injuries.

What the ATSB found

The ATSB determined that the derailment of train 4413 was most likely initiated by lateral harmonic vehicle oscillation induced by a combination of minor cyclic cross-level and lateral track irregularities just in advance of the point of derailment. As a result of these irregularities, it was likely that the roll of wagon WOE33548K caused the left hand wheels to unload at a time when the leading left wheel came into contact with the left rail face – resulting in flange climb and derailment.

While the wagon type that derailed (WOE class) had passed prescribed dynamic performance testing, and the wagons and track complied with mandated engineering requirements, post-derailment computer modelling showed the onset of lateral harmonic wagon oscillation of sufficient magnitude to increase the likelihood of derailment at this location. Simulations showed that iron ore wagons, with their short length, react more severely to 22 m wavelength cyclic irregularities (as evident at this site) than do the typically longer intermodal wagons. The ATSB concluded that undertaking computer modelling when changing rolling stock and/or track working conditions offers rail transport operators an opportunity to identify potential areas of risk exposure before implementing new service arrangements.

Track maintenance and inspection was found to be in compliance with engineering requirements, however the track leading into the derailment site was known (to train drivers) as an area of rough ride. It was found that the systems in place between the train operator and track maintainer for the reporting of track irregularities (in particular the rough riding of trains) was ineffective, and hence the opportunity was lost to check for uncharacteristic track qualities through the derailment site – before such qualities contributed to a derailment.

While not influencing the derailment, it was noted that the loss of the train’s brake pipe integrity (loss of air), including activation of the end-of-train monitor, had not resulted in the immediate and full automatic activation of the train brake.

What's been done as a result

Brookfield Rail and Aurizon have developed enhanced procedures for reporting track irregularities and have jointly committed, through the Rail Industry Safety and Standards Board, to ongoing industry support and research into the cause of this type of derailment. Aurizon is examining, with the intent of rectifying, the train braking irregularity (brakes not activating) that occurred following the loss of brake pipe integrity.

Safety message

To reduce the potential for unforeseen dynamic stability issues affecting the safety of rolling stock operations, it is essential that train operators and track maintainers:

Appropriately test and model rolling stock dynamic characteristics and the effects of changed track conditions before implementing new service arrangements.

Develop proactive interface management strategies that promote the prompt reporting, capture and feedback of uncharacteristic track qualities.

The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions

 
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