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Final Report

Summary

What happened

At about 1404 on 14 May 2014, the fourth wagon from the end of train 3WB3 derailed whilst exiting the Nambucca Heads crossing loop. The train travelled a further 1,397 m before the derailed wagon tipped on its side causing the train to separate and subsequently stop.

What the ATSB found

The ATSB found that the rod-in-coil load had likely shifted, mostly to the left in the direction of travel. The effect of a load shift to the left would have been to transfer vertical forces from the wagon’s right side-bearer to the left side-bearer, causing the right-hand wheels to unload.

At the point of derailment, the track geometry was transitioning out of a left-hand curve which had a relatively high superelevation with respect to the actual speed of train 3WB3 (about 21 km/h). The relatively high superelevation and subsequent twist as the superelevation ramped down through the transition, likely resulted in additional transfer of vertical force from the wagon’s right side-bearer to the left side-bearer, resulting in a further unloading of the right-hand wheels.

The combination of superelevation, twist and (more importantly) uneven lateral loading, combined to unload the right-hand wheels which, when steering through a left-hand curve, resulted in flange climb and derailment of wagon RCOF20375S.

What's been done as a result

Following the occurrence, Pacific National Assets and Infrastructure Services engaged a consultant to conduct an audit of procedures and operational processes relating to the development and implementation of the Freight Loading Manual (FLM). The audit was scoped specifically to include a gap analysis in relation to current steel loading processes.

In addition, PN have advised that they will be arranging an external engineering group to undertake a twist test and/or computer simulation modelling of an RCOF wagon to record its wheel loading performance characteristics during scenarios based on operational data. It is expected that the outcomes of this work will be used to further refine the FLM and associated procedures and loading practices.

Safety message

The ability for a load to shift during transit is an undesirable condition that can affect the dynamic behaviour of the rail vehicle. All rail freight operators should consider the safety implications of shifting/moving loads and should ensure that all loads are restrained and/or enclosed in such a way that prevents movement in any direction relative to the wagon.

 

 

 

The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions

 
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