The report said the TAIC was pursuing the possibility that two split pins were left off during maintenance in March this year, allowing a parking brake assembly to work loose, fall and derail the train.
However, the inquiry had yet to reach firm conclusions.
Chief TAIC commissioner John Marshall QC said there were two safety issues identified with the Wellington maintenance depot processes.
``First, there were no individual task instructions describing how each safety-critical job was to be done, and secondly there was no check sheet associated with each task to record that important steps and checks for the task had been completed. Instead, the depot relied on the knowledge of the depot staff to complete each task satisfactorily,'' he said.
TAIC has issued an urgent recommendation for Kiwirail to ensure that its maintenance is in accordance with good railway engineering practice. This includes documentation of maintenance processes and safety-critical components, and requiring work on safety critical components to be signed off by qualified staff other than the worker who had done the job.
KiwiRail chief executive Jim Quinn said the company accepted the report's findings.
"In a safety critical environment like this, such an oversight is of significant concern,'' he said.
"We can confirm that TAIC's preliminary view aligns with our own investigation and a thorough review of depot practises has been undertaken.''
All of TAIC's recommendations had already been implemented at its Wellington depot.
The New Zealand Transport Agency said it would work closely with KiwiRail to ensure that all of the Commission's recommendations were fully addressed.
