Regional Jet 200 ER/LR (CRJ200)
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Workload; Confusion
Aircraft Equipment Problem Critical
Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Shortly before dusk we were pushing back for a flight.  As we started to pushback; about 40 yards into the push; the tug driver reported he could see fluid coming from the back of the aircraft.  I requested he tow us back into the gate; so I could investigate.  Once back into the gate I ask the First Officer to brief the passengers that we are checking out a possible fluid leak.  I then went to the aft of the airplane and noticed the fluid was fuel.  My concern at this point was to get the APU shut down to prevent a fire. I went back to the cockpit and briefed the First Officer.  We asked to have ground power hooked up. While this was taking place the First Officer went to look at the leak. I was preparing to shutdown the APU.  The APU then shutdown on its own and a LO APU BTL light caution message appeared.  I then wanted to evacuate the passengers.  I ask ground personnel if we could have the passengers use the outside stairs. I was informed security had to open that door.  I could see this would take too much time. I had them hook up the jet bridge and deplane. They did so. At no time did I see or have a fire indication other than the BTL LO message.  The First Officer reported to me that he heard the bottle pop.  He also did not see the fire. This happened very quickly and we had the people off as fast as possible. The entire event took around 6 minutes.  I then called our Dispatcher and was transferred to Maintenance Control.  I reported the situation to them and Dispatch. At this point I still did not know we had a fire but thought there may have been.  I talked with Contract Maintenance and they said the did not see a fire or signs of a fire.  We were then released and sent to the hotel for the night.
A CRJ-200 ground crew reported an aft fuselage fluid drainage during pushback so the Captain requested a tow to the gate where an apparent APU fuel leak was detected followed by an APU auto-shutdown and a LO APU BTL alert.