Following up a piece in today's Times, I find that the ATSB published their
preliminary report yesterday. The new piece of explanation that's been grabbing the reporters' interest is that the repair crew, who were meant to be working forwards along the train applying handbrakes while the driver was working his way backwards - were working on the wrong train!
There's a lot in the report about the details of the braking systems on the train, which were somewhat more complicated than on your average British train. Exactly why what happened, I can't exactly fathom yet. The train-line cable parted between two cars not far from the front of the train, which caused an emergency brake application. There's a hint that this emergency brake application (120%) may have timed out, leaving the train brake set at 39%, or maybe the air bled off - that's said too. How much of the braking system operates without a continuous train-line is not clear either. There was
ATP▸ that it was hoped would stop the train at the first red signal, and in any case the ATP should detect that the train is moving when the controls aren't telling it to and brake it. So, loads of factors (as usual) to try and understand.