What was found
APU FIRE LOOP A ILLUMINATED DURNIG NR 2 ENGINE START. FOLLOWED FIRE DETECTION LOOP LIGHT PROCEDURE, NO TEST FOR LOOP B. MOVED SWITCH TO LOOP A AND OBSERVED APU FIRE LIGHT. FOLLOWED PROCEDURE FOR APU FIRE. LIGHT STAYED ON FOR 30 SECONDS AFTER FIRST BOTTLE, PULLED SECOND BOTTLE SWITCH AND NO HELP. NO EXTERNAL INDICATION FROM RAMP CREW OF FIRE. MAINTENANCE REPLACED RIGHT APU FIRE LOOP. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)