I had the problem with an inoperative fire detection loop the other day during my fire check (we have to check all fire detecting devices before we start our first flight of the rotation).
Loop A on engine nr. 1 was inop. Our MEL (737-31S) says about Engine Overheat and Fire Detection System: One Loop (A or B) per engine may be inoperative. According to the Dispatch Deviation Procedures Guide: Except for ER operations beyond 120 minutes, one loop (A or B) per engine may be inoperative.
Denti