Number 90 posted:but, if the train had been fully secured with hand brakes it would remained stationary, even if the brake cylinders on the cars leaked down. That is a given. Period.
Tom,
Yes, one would think that and normally that would be true. However, such is not the case. If, I repeat, if snow had built up between the the brake shoes and the wheels a train will not be able to stay stopped on a grade, even with the train in "emergency" and 100% handbrakes set!
I know this because I was involved in a situation where this happened!
As you correctly said: "There's not enough information in the preliminary report to determine why the emergency brake application occurred"