At about 0640 on 20 October 2006, the sixth wagon on express freight Train 237 derailed and entered a crossing loop at Utiku, derailing 9 other wagons and bringing down a section of the overhead electric traction line as well.
The derailment was caused by the dynamics of a permanently coupled pair of wagons and the design of the modified solid drawbar arrangement when the wagons behind bunched and “ran-in” while the train was under braking on a descending gradient.
A safety issue identified was the incomplete process for approving a new design of coupling and monitoring its performance in service.
No new safety recommendations have been made in this report as the safety issue has been raised in previous reports and safety recommendations are still currently open pending corrective action.
