Downer EDI 3550 Class

The 3550 class, often called the 3551 class, are rebuilt 3900 class locos. The 3900s were built for passenger and general freight work between Brisbane and Rockhampton, but due to various problems with them leading in general freight service they ended up working as slave/remote locos on the Central Queensland coal trains. The 3900s placed in coal traffic were fitted with access ladders and identified with a 'C' suffix.

With more locos needed on the coal lines, Downer EDI won a contract in 2003 to rebuild 3900s for coal traffic. They were renumbered into the 3500 series, so 3901 became 3551, 3903 became 3553 and so on. There's no 3552, as 3902 had already been scrapped after a collision at Beerburrum in 1994. The modifications included new 3500 class bogies with axle hung traction motors and lower gearing, with speed limited to 80km/h. 3556 (ex 3906, damaged in the Petrie derailment) was the prototype.

In all 18 3900s were rebuilt: 3551, 3553 to 3567, 3569 and 3573. They work alongside the 3500/3600s for Aurizon, and as of May 2025 thirteen were still operational, with 3554, 3556, 3560, 3564 and 3569 scrapped.

References

'Aurizon electric locomotives', Wikipedia (accessed October 2026)
'Queensland Railways 3900 class', Wikipedia (accessed October 2026)
'Queensland 3900 Class', Australian Locomotive Rosters, May 2025