What was found
FLT 701 - FLL-PID - PILOT REPORTED NR 3 ENGINE FIRE DETECTION LIGHTS FLICKERED ON AND OFF DURING CLIMB-OUT. FIRE WARNING TEST INOP SHORT TEST GOOD. AIRCRAFT RETURNED TO GATE, PASSENGERS DEPLANED. OPERATIONAL CHECK OF AIRCRAFT COULD NOT DUPLICATE PROBLEM. REMOVED AND REPLACED FIRE DETECTION CONTROL UNIT. OPS CHECKED NR 3 ENGINE A AND B LOOPS, FOUND MINIMUM RESISTANCE ON 'A' LOOP. REPLACED 'A' LOOP. OPERATIONALLY TESTED SYSTEM, CHECKED OK. AIRCRAFT RETURNED TO SERVICE. (M)