What was found
THE MAINTENANCE TEAM DISCOVERED DURING POSTFLIGHT CHECKS THE APU FIRE ANNUNCIATOR WOULD NOT ILLUMINATE DURING TEST. THE APU SYSTEM WAS DISABLED AND THE MAINTENANCE WAS DEFERRED, OPERATIONS CONTINUED UNDER MEL 49-20-01. DURING THE MAINTENANCE CORRECTIVE ACTIONS, THE MAINTENANCE TEAM DETERMINED THE APU FIRE LOOP SENSOR WAS DEFECTIVE. THE UNIT WAS REMOVED AND REPLACED WITH A NEW SENSOR. OPS CHECKS WERE SATISFACTORY AND THE AIRCRAFT WAS RETURNED TO SERVICE.