RO-2007-114 Derailment caused by a wheel-bearing failure, Huntly, 19 October 2007, and 11 subsequent wheel-bearing failures at various locations during the following 12 month period

Between Friday 19 October 2007 and Sunday 5 October 2008, there were 12 occurrences when wheel-bearings failed on wagons travelling on express freight trains at various locations in the North and South Island.
Seven of the 12 wheel-bearing failures resulted in the affected wagon derailing, and causing a number of following wagons to also derail. The derailments caused extensive damage to the rolling stock, freight it was conveying and the rail network. On 2 occasions, molten metal from the failed wheel-bearings resulted in fires in trackside foliage and across adjacent land.
No-one was injured in any of the derailments.
The Commission determined that wheel-bearings were critical items, the failure of which had the potential to result in a derailment. The derailments usually resulted in substantial damage to track and infrastructure, and have the potential to cause injury to third parties if the derailment occurs adjacent to populated areas or other infrastructure.
The reason for the failures of the wheel-bearings could not be conclusively determined because the bearings had usually catastrophically failed, destroying the evidence and historically inadequate record-keeping for maintenance and service life of the bearings that could not support probable cause investigation.
Because the impending failure of wheel-bearings can be difficult to detect through traditional inspection procedures, the Commission recommended to the Chief Executive of the Land Transport NZ (predecessor to NZ Transport Agency) on 8 March 2008 that he address the safety issue where the New Zealand rail network had not been protected with a track-side acoustic wheel-bearing monitoring system in line with current international best practice.
In the latter half of 2010, KiwiRail was completing the installation of an integrated acoustic wheel-bearing monitoring, coupled in motion weighbridge, wheel impact and automatic vehicle identification system at strategic sites on its network. The Safety Action section of the report shows a number of other initiatives that have been taken by KiwiRail since 2008, which together with the acoustic wheel-bearing monitoring system appears to have reduced the number of reported bearing related occurrences.