In the early morning of February 2, 1989, during a record cold snap, a Montana Rail Link freight train picked up three extra pusher locomotives in Helena, Montana, to help move the train over Mullan Pass. The train then traveled west from Helena. Halfway up the pass, the lead engine developed an electrical problem that caused a loss of power and at about the same time was stopped by a malfunctioning signal. The train crew then parked the train at the Austin siding, on the east side of Mullan Pass. While waiting for the signal to be fixed, the crew uncoupled the engines from the 48-car train to switch the order of the locomotives, setting the air brakes but not the hand brakes on the cars. At about 5:30 a.m., record cold temperatures caused the air brakes to fail on the decoupled cars. The cars then rolled backwards downhill, uncontrolled, into Helena, crashed into a parked work train near the Benton Avenue crossing and Carroll College, caught fire, and exploded.