Communications mix up may have led to November 5 BHP train derailment.
Driver was sacked before Christmas for his part in the derailment.
Rio Tinto document shows it has several levels of additional redundancy.
Train derailed on February 6, damaging 2km of track.
Train derailment hits BHP's productivity hard.
BHP finally says something about the train derailment that stopped it in its tracks
BHP already put in place learnings from a train derailment two years ago.
Another day, another iron ore train crash in WA
BHP mops up last weeks train wreck
BHP's runaway train on a one way track
Coal line out of action for several days.