Rail Safety Investigation - Runaway and derailment of loaded grain train 3966 - Dombarton - 15 December 2020

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What happened

On Tuesday, 15 December 2020 at 0454, the crew of Qube loaded grain train 3966, consisting of 41 wagons and two CM class locomotives, reported a runaway on the descent of the Moss Vale to Unanderra rail line. The train reached speeds up to 100 km/h on a 30 km/h section of track before it derailed and separated at two points between Dombarton and Farmborough Heights, New South Wales (NSW). Shortly after, the train crew advised they had brought the two locomotives and the remaining two wagons to a stand at Farmborough Heights. The train crew were not physically injured.

What was found

The investigation identified that ineffective braking caused by several factors contributed to the  runaway. The ineffective application of train braking systems was influenced by a heavily loaded train with some overloaded wagons, wagons with variable net brake ratio (NBR), reduced brake cylinder pressure through the train, and train handling and locomotive dynamic braking affected by low track adhesion conditions.



The weight of the train was near, but likely not over, the maximum allowable tonnage limit specified by the Australian Rail Track Corporation (ARTC)’s Train Operating Conditions (TOC) Waiver 16002. It was likely, however, that several individual wagons across the train consist were over the allowable limit for a single wagon.



Measurements of NBR at different times and on different wagons returned varying results ranging from 10.7% to 19.5%. The minimum required NBR for these wagons, specified by Australian Standards was 13%. While modifications were made to improve braking performance on the wagons, the NBR on some wagons continued to change over time. The wagon type test met the NBR requirement when introduced into service and met NBR requirements when tested post  modifications, however there was no requirement for regular testing of NBR, which may have  identified the changes in NBR. 



The mix of wagons with variable NBRs and variability in loading likely reduced braking effort on some of the wagons during the steep descent along the rail line.



During the occurrence, the second automatic brake application made by the driver was made before the brake pipe had fully recharged. This resulted in a reduced amount of available brake cylinder pressure and lessened braking effort on the trailing wagons.



The driver's operation of the train and braking actions did not always conform to the operator (Qube)’s instructions, and it is likely some of the driver’s decisions on the morning of the accident were affected by fatigue.



Once control was lost, the driver elected not to use the emergency brake because they believed, in accordance with Qube’s procedures, that the locomotive braking would have been diminished. This in turn lessened the opportunity to regain control of the train. 



Qube’s operational procedure for train management between Moss Vale and Inner Harbour did not consider locomotive configurations that maintained locomotive dynamic braking during emergency applications. This increased the risk of train drivers not applying the emergency brake  during a runaway event. This assumption was also found to be embedded within other rolling stock operators’ procedures with similarly configured locomotives in NSW.



The conditions on the rail line from Summit Tank to Farmborough Heights on the morning of the incident included wet rail and track contaminant that likely contributed to low track adhesion and also reduced dynamic braking effort by the locomotives. The wheel slip/slide protection system worked as designed to maximise traction through the use of auto sanding to increase friction and derated the dynamic braking effort through the wheels to match the lower adhesion conditions.



Several rail flange lubricators, which provided lubrication to the down and up rail, were less than the 500 m minimum separation requirement specified in ARTC’s engineering practices manual RC2411. A review of these to ensure consistency with the engineering practice and to minimise the risk of excess track lubrication on a steep gradient was warranted.



Finally, the brake pipe charging flow indicator on CM class locomotives only provided a numerical  display without any corresponding audio or visual warning system to alert the driver of its status. This limited the ability of the driver to detect derailment or train separation events and, as in this incident, effectively monitor recharge of main reservoir air into the brake pipe to ensure it was fully charged before making another brake application.

What has been done as a result

During the investigation, a Safety Advisory Notice was issued by the Office of Transport Safety Investigations (OTSI) in collaboration with the ATSB to the rail industry to raise awareness of variable locomotive braking system configurations on locomotives across Australia. Qube and other affected rollingstock operators took immediate actions to review their locomotive configurations, to ensure their locomotive drivers had a clear understanding of the braking systems on the locomotives they were operating.



A forum was chaired by the Office of the National Rail Safety Regulator (ONRSR) in March 2023 with Rail Infrastructure Managers (RIMs) and Rollingstock Operators (RSOs) that operated on the Moss Vale to Unanderra rail line. This provided an opportunity to discuss and communicate the risks of operating on the rail line and how to manage them to mitigate runaway events.



The two RIMs, Sydney Trains and ARTC conducted a review and alignment of Transport for NSW (TfNSW) TOC Manual Illawarra operations and the ARTC Route Access Standard - Section Page D52 Moss Vale - Unanderra. The focus of the review was on providing interoperable train configuration and operating conditions between the two RIM interfaces. Additionally, conditions for managing degraded dynamic brakes and hauling dead attached locomotives were developed. All changes were held in consultation with RSOs, ARTC operations and Network Control stakeholders.



In consultation with TfNSW, ARTC developed joint assessment criterion for Unanderra Trial train configurations, operating conditions, and implementation plans. The RSO will be required to submit supporting documentation as part of a variation to existing approved train configurations.



ARTC has updated NBRs for vehicle classes following physical testing and has worked with others in the rail industry to promote NBR testing as part of preventive maintenance.

Safety message

The rail line between Summit Tank and Unanderra is one of the steepest sections of rail line in NSW. To prevent runaway occurrences on this rail line, operators must regularly review the  effectiveness of their risk controls and proactively manage conditions that present greater risk of runaway.



RSOs should ensure their trains have sufficient braking, are loaded within safe load limits and are operated in accordance with their procedures.



RSOs and RIMs should ensure that risk assessments identify critical operational requirements to safely run trains down such steep sections of track. They should also ensure that there is sufficient error tolerance to enable control of trains on sections of rail line that present increased risks from long and steep descents.



RSOs should review the locomotive specifications and test those locomotives under their control to understand how the braking systems are configured and the associated error tolerance. RSOs must communicate this information through their organisation’s procedures and training material to ensure train crew have knowledge of and competence in operating locomotive braking systems, including emergency braking in the event of a runaway.



The use of two-pipe wagon braking systems significantly reduces the recharge times for the brake pipe after a brake application, but the starting air pressure of a wagon’s auxiliary reservoir remains a critical consideration. For example, low auxiliary reservoir starting pressure at the beginning of an automatic brake application reduces the response of a wagon’s supplementary reservoir, resulting in lower wagon brake cylinder pressure and therefore less effective braking effort.



Finally, while a ‘full service’ automatic brake application typically provides the maximum pneumatic braking force available on a train, in the unique circumstance of a train with low auxiliary reservoir starting pressure, lowering the brake pipe pressure further through the application of the emergency brake, will result in an increase in the available braking force. However, this increased braking force will remain less than that which would have been available in full service had the auxiliary reservoir been fully charged at the time of the brake application.