What was found
THE APU FIRE WARNING SOUNDED AFTER APU START ON FINAL APPROACH TO ATL. THE BELL WAS SILENCED AND THE APU FIRE CHECKLIST WAS RUN. THE AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND NO EVIDENCE OF FIRE. THE PROBLEM WAS IDENTIFIED AS A FALSE FIRE WARNING AND THE CAUSE WAS DETERMINED TO BE A SHORTED APU LOWER FIRE DETECTION LOOP. THE APU FIRE BOTTLE AND LOWER FIRE LOOP WERE REMOVED AND REPLACED IAW MM 26-15-14 AND 26-22-11. OPERATIONAL CHECKS WERE GOOD.