What was found
DURING DESCENT TO MDSG, ENGINE 2 FIRE ALERT. ENGINE FIRE PROCEDURE EXECUTED PER QRH. CORRECTED ACTION (MDSG) INCLUDED VISUALLY INSPECTED NR 2 ENGINE FIRE SYSTEM IAW AMM 26 & PNEUMATIC DUCTS IAW MM 36-00-02. NO DEFECTS NOTED. SWAPPED FIRE BOTTLE FROM APU TO NR 2 ENGINE POSITION IAW AMM 26-21-01. OPS CHECK OK. DEFERRED IAW MEL 26-21-4, CAT C APU CONTAINER. ENGINE NR 2 FIRE DETECTOR LOOP B FAULT ENTERED ON DMI IAW MEL 26-11-1 / CAT C. AIRCRAFT RETURNED TO SERVICE.