What happened
On 17 December 2023 at 1415 , the TranzAlpine passenger train departed Greymouth on its scheduled service back to Christchurch.
An earlier mechanical issue with one of the two locomotives resulted in two additional locomotives being attached at Otira Station for supplementary power to Arthur’s Pass station.
At approximately 1630 as the train descended into Arthur’s Pass station, the locomotive engineer completed several train brake applications.
As the train came to a stop at the station’s platform, the first two carriages parted by approximately one metre (m), activating the fail-safe braking system .
The train crew members were unaware of the parting until an onboard crew member went to walk between the two carriages. No passengers or crew were injured when the train parted.
Why it happened
A single component of the carriage-coupler system broke, causing the two carriages to part.
The broken component had a pre-existing fracture that had not been identified in regular maintenance inspections by KiwiRail.
It is virtually certain that the train’s configuration of four locomotives operating in throttle position three while applying the train’s brakes to their full capability caused the weakened coupler component to break.
What we can learn
Adequate inspection and maintenance plans for safety-critical components are vital to ensure components remain in a condition fit for their intended purpose.
Preprepared and practised response plans assist in an incident to ensure appropriate action can be undertaken safely.
Who may benefit
Rail operator personnel, transport designers and maintainers of safety-critical components may benefit from the findings in this report.
Any personnel involved in preparing or implementing response plans.
