What was found
PRIOR TO PUSHBACK, APU TAILPIPE FIRE DEVELOPED. AIRCRAFT APU FIRE BOTTLES WERE DISCHARGED AND FLAMES EXTINGUISHED. THE PASSENGERS WERE DEPLANED THROUGHT THE JETWAY WITHOUT INCIDENT. NO SMOKE WAS PRESENT IN CABIN. MAINTENANCE INSPECTED APU AND SURROUNDING STRUCTURE, NO DAMAGE FOUND. FIRE BOTTLES WERE REPLACED AND APU PLACED ON MEL.