What was found
FLT NR 1523 - IAH - TWENTY MINUTES INTO THE FLIGHT, AFTER THE APU HAD BEEN SHUT DOWN. THE APU FIRE LIGHT ILLUMINATED WITH FIRE BELL. THE FIRE HANDLE WAS PULLED AND THE WARNING CEASED WITHIN 3-4 MINUTES. MAINTENANCE FOUND THE APU FIRE DETECTION LOOP SHORTING AGINST LOWER SHROUD. THE LOOP WAS REPOSITIONED AND THE FALSE FIRE INDICATION WAS ELIMINATED. IN ADDITION, A HOLE WAS DISCOVERED IN THE APU MUFFLER. THE APU HAD BEEN PLACARDED INOPERATIVE, DUE TO THE FIRE DETECTION PROBLEM, AND THE PLACARD WILL REMAIN PENDING EXHAUST SHROUD REPLACEMENT. (M)