What happens if only one of the loops in the engine fire detection system is operational?

In an engine fire detection system, the design typically incorporates multiple loops to ensure that fire warnings are reliable and can continue to function even if one loop fails. If only one loop is operational, it is capable of still providing a fire warning if it detects an over-temperature condition indicative of a fire. The system's redundancy is intended to minimize the chances of a failure leading to a lack of detection, and as such, the operational loop will still deliver the necessary indication to alert the crew to a potential fire hazard. This operational resilience allows for continued monitoring despite the failure of one loop, maintaining safety protocols as expected.