What was found
AIRCRAFT WAS GROUNDED. RAMP PERSONNEL NOTIFIED CREW OF AUXILIARY POWER UNIT TAILPIPE FIRE. NO INDICATIONS IN THE COCKPIT. APU FIRE BOTTLES WERE BLOWN. APU FAILED. INSPECTION FOUND NO EVIDENCE OF FIRE IN THE APU COMPARTMENT. REMOVED AND REPLACED FIRE EXTINGUISHER BOTTLE PER AMM 26-22-01. OPERATIONAL CHECK GOOD. ENGINEER REQUEST APU REPLACEMENT DUE TO TIME, EGT TREND AND TAIL PIPE FIRE. REMOVED AND REPLACED APU, OPS CHECKED AND LEAK CHECKED GOOD PER MCM CARD 49-94-11.