What was found
ON APPROACH NR 3 ENGINE FIRE WARNING ILLUM. PUSHED MAST WRN UNABLE TO SILENCE BELL. MASTER WRN EXT, ENG SHUTDOWN IAW POM FIRE WRN DID NOT EXT. LIGHT IN T-HANDLE, FUEL C/O SW, AND LVL 3 ALERT REMAINED ON. COULD NOT GET AGENT LOW LIGHTS WHEN T-HANDLE ROTATED. BELL SILENCED WHEN T-HANDLE PULLED. FDCU-3 FAULTS LOOP A. WHEN ENG 3 LOOP A C/B PULLED ALL FIRE IND NORMAL. SWAP APU FDCU AND ENG 3 FDCU. NOW ALL FIRE IND REST NORMAL. SQUIB FIRE TEST OK. VERIFY GOOD SQUIB VOLTAGE AT BOTTLE 1 AND 2 CONN. RAN ENG PER PFHB, CKS OK. FIRE TEST OK. FDCU-3 REPLACED.