What was found
CREW NOTICED APU FIRE WARNING LIGHT ILLUMINATED, NO SECONDARY INDICATIONS OF APU OPERATION. FIRE BOTTLE DISCHARGED AS PRECAUTION. AIRCRAFT, APU, AND COMPARTMENT INSPECTED FOR FIRE DAMAGE. NO DAMAGE OR DEFECTS NOTED. APU AND FIRE EXTINGUISHING FOR APU DEFERRED PER KALITTA CHARTERS FAA APPROVED MEL. AIRCRAFT FLOWN BACK TO BASE FOR REPAIRS AND INSPECTION. APU AND FIRE DETECTION SYSTEM INSPECTED AND TESTED I.A.W. THE HAMILTON SUNSTRAND DOC. #T39-1 TGTAPU 49-20-00. FIRE BOTTLE REPLACED WITH SERVICEABLE OVERHAULED BOTTLE, CARTRIDGE'S REPLACED WITH NEW. SATISFACTORY APU AND FIRE WARNING SYSTEMS OPERATIONAL TESTING PERFORMED. NO DEFECTS NOTED. AIRCRAFT RETURNED TO SERVICE.