Section 21 (2) of the Transport Safety Investigation Act 2003 (TSI Act) empowers the ATSB to discontinue an investigation into a transport safety matter at any time. Section 21 (3) of the TSI Act requires the ATSB to publish a statement setting out the reasons for discontinuing an investigation. This statement is published as a report in accordance with section 25 of the TSI Act, capturing information from the investigation up to the time of discontinuance.
Overview of the investigation
At approximately 0323 on 15 January 2022, the driver of 6MB4 reported losing air on the Up Main at 452.000 km, at Bethungra, NSW. Shortly after, the driver reported that three wagons (RRAY07213S, RRQY08515T and QQCY01120F), in the centre of the consist of 33 wagons, had derailed. The wagons sustained substantial damage with major damage to the track infrastructure. The train crew were uninjured.
Australian Rail Track Corporation was the rail infrastructure manager for the line.
ATSB’s preliminary evidence collection identified that:
- the derailment of train 6MB4 resulted from a screwed journal. The cause of the bearing failure could not be determined due to the large amount of consequential damage sustained, preventing a complete teardown and analysis of the failed bearing
- wheelset 7E3S080144 was fitted to wagon wheelset position 5 of QQCY01120F within bogie QRYE2079. New bearings were installed at the rolling stock maintainer’s facility and released to service on 2 September 2020. Records from the maintainer documented that the bearings fitted were an ‘Class E’ (6” x 11”) packaged bearing manufactured by Timken on 01/2020 and 12/2019. The bearings were fitted new and had not received a reconditioning maintenance event. These bearings covered 370,907 km to the point of failure
- there were no issues identified with the train management of train 6MB4
- there were no identified track defects in the region of or approaching the derailment site
- the condition monitoring equipment available on the operational route did not provide indications of a bearing showing signs of distress.
Reasons for the discontinuation
The ATSB considered the contributing factors to the derailment were a result of a failed bearing. The reasons for that failure were unable to be conclusively determined.
In response to the incident, Pacific National have proposed the following safety actions be initiated:
- work collaboratively with ARTC to implement further Hot Bearing Detector wayside equipment across the Melbourne to Brisbane corridor, to assist with identifying bearing failure modes that do not produce acoustic signals
- undertake a review of the practices and processes at their rolling stock maintenance provider, with particular focus on techniques and tooling used to measure journal diameter.
Based on this information, the ATSB considered it was very unlikely that further investigation would identify any systemic safety issues or identify opportunity for the enhancement of transport safety. Consequently, the ATSB has discontinued this investigation.