To the unsuspecting eye it is merely a pile of junk in a scrap metal yard greeting motorists arriving and leaving Port Hedland on Great Northern Highway.

At best it is a blight on the landscape, but to BHP it represents a public relations train wreck after two locomotives and 268 carriages carrying 30,000 tonnes of iron ore crashed into the red dirt near the Pilbara town in November.

BHP attributed the runaway train derailment to mechanical failure and human error.

The company released the details of its preliminary investigation of the incident on November 5, saying the train careered driverless for 50 minutes at an average speed of 110km/h before it was deliberately derailed about 120km south of Port Hedland.

BHP WA iron ore asset president Edgar Basto said initial findings showed that before the incident the train had stopped automatically because a braking system control cable became disconnected.

The driver was advised by BHP’s remote operations centre to get out and manually apply brakes, assuming he had already applied an emergency air brake inside the cabin.

“Our initial findings show that the emergency air brake for the entire train was not engaged as required by the relevant operating procedure,” Mr Basto said.

“In addition, the electric braking system that initially stopped the train automatically released after an hour while the driver was still outside.”

BHP has resumed rail operations after clearing the track and repairing the damaged section.

Mr Basto said investigations by regulators including the Australian Transport Safety Bureau and the Office of the National Rail Safety Regulator were continuing and the company was working with them.