Which statement accurately describes the two widely used continuous loop systems in DoD aircraft?

• A. The Inconel loop and the Systron Donner system are the two widely used continuous loop systems
• B. The Inconel loop is the only one used
• C. Pneumatic principle is used in all loop systems
• D. Optical detectors are used for loops

Answer: (A)

Continuous-loop fire detectors rely on a loop of conductor that senses heat in areas like engines and compartments. The two widely used implementations in DoD aircraft are the Inconel loop and the Systron Donner system. The Inconel loop uses a robust metal conductor that forms a continuous circuit; when exposed to high heat, the loop or its insulation reaches a fuse-like condition and the circuit opens, triggering the fire warning. The Systron Donner system employs a different loop design and sensing electronics, but it serves the same purpose—detecting abnormal heat along the loop and producing an alarm. These systems are electrical, not pneumatic, and they are not optical detectors.