BHP Group’s runaway iron ore train saga has taken another twist.

A preliminary report into last year’s calamity in the remote Australian outback has found a rail maintenance crew sent to help the faulty freight train inadvertently worked on the wrong vehicle.

The 2.9 kilometers (1.8 miles)-long train subsequently took off unaccompanied and had to be deliberately derailed after traveling uncontrolled for about 91 kilometers toward Port Hedland, at speeds touching 162 kilometers an hour. The world’s biggest mining company suspended part of its iron ore railroad in Western Australia for five days and lost about four million tons of output.

The Nov. 5 incident began after a problem with an on-board communications system triggered an emergency braking system, prompting the driver to get off to make checks, the Australian Transport Safety Bureau said Tuesday in an interim report.

As the driver made an inspection and manually applied handbrakes from the front of the train, a controller dispatched a maintenance gang from a nearby camp to assist, advising them to start from the opposite end.

At about 4:40 a.m., the driver “heard air venting from the ore car brakes and shortly after noticed the train begin to move forward.” About 20 minutes later, the driver of a second train on an adjacent track contacted controllers to report the maintenance crew had mistakenly applied handbrakes to that vehicle instead, the report said.

Two locomotives, 245 ore cars and two kilometers of track infrastructure were destroyed as the train, weighing about 42,500 tons, was brought to a halt.

An on-going inquiry is examining issues including train-line cable connectors, pneumatic braking systems and risk management processes, the bureau said. BHP, which last month reached a settlement with the train driver, took immediate action to boost safety, had a program of other improvements underway and is planning a longer-term upgrade of automatic train protection systems, according to the report.

The “incident was the result of procedural non-compliance by the driver as well as integration issues with the electronically controlled pneumatic braking system to the rail network,” BHP’s Western Australia iron ore asset president Edgar Basto said in a statement.

The driver “did not apply the automatic brake handle to the emergency position,” and if correct procedures had been followed the train would not have rolled away, Basto said.