What was found
AFTER TAKEOFF FROM NKW, EXPERIENCED AN APU FIRE WARNING INDICATION WITH ALL FIRE WARNING LIGHTS BUT NO HORN DURING CLIMB. APU WAS SHUTDOWN BEFORE TAXI. CREW FOLLOWED EMERGENCY PROCEDURES, DISCHARGED THE FIRE BOTTLE AND RETURNED TO UKW. AIRCRAFT LANDED WITHOUT INCIDENT. INSPECTED APU COMPARTMENT AND FIRE LOOPS, NO DAMAGE FOUND. CHECKED ECU AND RESET BPCU. BITE CHECKED AND ALL POWER SYSTEMS CHECKED NORMAL. REMOVED AND REPLACED ENGINE FIRE BOTTLE AND SQUIB. RAN APU FOR 2 HOURS WITH NO FAULTS.