Prelimianry report released 23 September 2015
At about 0800 on 26 July 2014, the crew of Genesee & Wyoming Australia (GWA) freight train 6DA2 carried out a crew change near Hugh River, Northern Territory. The train then continued its journey south before crossing the South Australia – Northern Territory border. At about the 1056 km mark the train entered a section of track that had a permanent speed restriction of 80 km/h.
Figure 1: Map of derailment location
Source: FreightLink (annotated by ATSB)
The crew reported that train had been handling well when the driver reduced the speed with throttle and dynamic brake applications to enter the 80 km/h section (Figure 1). At about the 1036.530 km mark, the driver had just acknowledged the vigilance indication and was verifying the train’s speed when a ‘large bang’ was heard and the crew felt the lead locomotive jar. The crew commented that the ‘bang’ may have been their passage across a broken rail. The crew looked in the rear view mirrors and could see large volumes of dust rising from derailed wagons about 200 m behind the driver’s cab. At this time, the locomotives started shuddering and the driver made an emergency brake application and moved the throttle back to idle. The lead locomotive stopped about 360 m from the point of derailment.
Events after the derailment
The second driver alighted from the locomotive to check that the crew resting in the crew van were uninjured. When walking back to the crew van, the second driver observed that the wheelsets of the leading bogie on the trailing locomotive and the wheelsets of the trailing bogie on the crew van had also derailed.
Further inspection of the train found that it had separated into two portions, with the locomotives, locomotive refuelling wagon, crew van and one loaded container flat wagon remaining coupled. There was a gap of about 108 m between the front portion of train and the first of the derailed wagons. Various wagon types, freight and containers were scattered either laterally or vertically, for about 250 m along the rail corridor. The rear 930 m of the train, extending north beyond the point of derailment, remained on rail.
The train crew was uninjured during the event, however a number of rail vehicles, containers, freight goods and track infrastructure had sustained significant damage.
The derailment occurred near Marryat (1036.530 km) on the Tarcoola to Darwin railway, about 28 km south of the Northern Territory - South Australia border (Figure 1).
Train and train crew information
Train 6DA2 was a freight service operated by GWA between Darwin and Adelaide. The train consisted of two locomotives (GWU 006 leading and ALF 23 trailing), hauling an in-line fuel wagon, a crew van and 42 freight wagons (including 14 multi-platform wagons). The train was 1543.3 m long and had a trailing mass of 2540.9 t.
Train 6DA2 departed from the Berrimah Freight Terminal, Northern Territory at about 0920 on 25 July with a crew of four drivers. The drivers worked the train in pairs, operating in rotating relay shifts. The drivers operating the train at the time of derailment had about 2.5 and 7 years rail industry experience respectively.
Preliminary examination of the train and locomotive data indicated that there were no anomalies with the train handling or mechanical condition before the derailment. A review of video and audio recordings extracted from leading locomotive GWU 006 supported the drivers report of a ‘large bang’ when they travelled over what they thought was a broken rail (Figure 2).
Figure 2: Location of rail defect & minor ballast displacement near 1036.530 km mark
Source: Genesee & Wyoming – Locomotive GWU 006 video camera
The Bureau of Meteorology weather stations nearest the derailment were located at Kulgera (47 km NNW) and Ernabella (120 km E). On the morning of 26 July, overnight minimum temperatures at these stations were 10.4 °C and 9.4 °C respectively. No rainfall was recorded and winds were light, generally from a northerly direction. On this basis, it was considered unlikely that environmental conditions had contributed to the derailment.
The track infrastructure is owned and maintained by GWA, with the movement of rail traffic controlled from the GWA’s Transport Control Centre located at Dry Creek in South Australia.
The standard gauge (1435 mm) track at the derailment location consisted of 80 lb/yd rail fastened to concrete sleepers by resilient clips. The track formation comprised sand/clay based soil, topped with a capping layer and overlaid with ballast to a nominal design depth of 250 mm. The track bed supported prestressed concrete sleepers spaced at 667 mm centres.
Approaching the derailment site from Kulgera, the track was tangent and the terrain slightly undulating. The derailment occurred within a 68 km section of track where the maximum track speed was 80 km/h.
The ATSB’s examination of the track leading into the derailment site determined the most likely contributor to the derailment was a break in the east rail near the 1036.530 km mark. An inspection of the mating ends from two broken rail sections strewn near the point of derailment identified variable oxidisation levels across the fracture surfaces and a localised feature that was characteristic of an internal material defect (Figure 3).
Figure 3: Broken rail fracture surface
The oxidisation that extended across the rail foot and through the web was noticeably greater than on the fracture surfaces through the rail head. This was consistent with the rail break originating in the rail foot and propagating vertically through the rail web.
Evidence of iron oxide bleed on the top surface of the foot suggested that the fracture had propagated slowly and been in existence for some period – potentially remaining undetected during track inspections and the passage of previous trains.
The rail head at the point of initial fracture showed light battering from train wheels that had traversed the break, before the rail breakup extended into multiple other sections - each about 700 mm long.
The ATSB quarantined four pieces of the broken rail for the purposes of laboratory metallurgical examination and analysis, including:
- Magnetic particle testing to identify and characterise any surface features of relevance to the failure
- Ultrasonic testing to assess internal quality (steel cleanliness) to the relevant standards
- Residual stress measurements on the failed rail section/s (including a like-sample section of rail taken from store stock)
- Examination and characterisation of the fracture surfaces
- Chemical analysis and mechanical testing to assess material properties.
Ongoing investigation activities
The ATSB’s investigation is continuing and will focus on:
- The inspection and maintenance practices for rail and track infrastructure between North Gate, South Australia and Alice Springs, Northern Territory
- The findings from laboratory tests of the quarantined and sample rail sections
- A review of rail and track defects reported by train operators and track inspection staff before the derailment of 6DA2.
 The 24-hour clock is used in this report and is referenced from Central Standard Time (CST), UTC + 9.5 hours.
 Distance in kilometres from the reference point located at Coonamia, South Australia.
 Straight track with no applied cant.