Originally Posted by
KRviator
If ATP is configured to work exclusively with ECP when ECP is active it would not function to command a pneumatic emergency brake.
If an ECP cable separates, this will trigger an ECP Emergency brake - 120% of braking capacity - but it will not reduce Brake Pipe Pressure. The potential problem with this, is the ECP cars *not* talking to the locomotive now start a timer, and after a pre-configured delay (usually an hour, depends on the operator), revert to standard pneumatic braking. IF the Brake Pipe is still charged, the brakes will release in pneumatic on those wagons, and you are then relying on the front X number of wagons to try to hold the train stationary. IF he was 50 back fixing the cable, only 50 cars with brakes isn't likely enough to hold a full train on a grade like that. Without knowing BHP's procedures, I'd think they would require the Driver command a full pneumatic emergency brake application before getting off the loco to guard against a fault like this - which if forgotten could lead to such a scenario as they had.
It seems this hypothesis has been confirmed by
BHP's press release, with the company saying the ECP Cable separated which triggered the initial ECP Emergency brake application, but the Driver didn't apply a pneumatic emergency application before walking the train. This kept the brake pipe charged such that when the out-of-comm wagons reverted to pneumatic braking, they released the emergency application and away she went - and as their ATP was only configured to work with ECP it couldn't stop the train.
This has concerned the rail regulator enough for them to put out a
Safety Alert highlighting the risks of this happening. It shouldn't be the case that a single-point failure - a Driver remembering procedure 100%, 100% of the time - has led to this, but this is what happens when you don't utilise all available safeguards...