Which of the following is a continuous loop fire detection system used in DoD aircraft?

• A. Helium
• B. Pneumatic detectors
• C. Optical detectors
• D. Inconel loop

Answer: (D)

Continuous loop fire detection in DoD aircraft uses a sensing loop that is continuously monitored for heat-induced changes. The loop is typically made from a high-temperature alloy like Inconel, forming a closed circuit around the area to be protected. When a fire heats the loop, its electrical resistance changes rapidly, triggering the fire alert. This approach is favored because the Inconel loop can withstand harsh aircraft environments and provide reliable, fast detection along extended areas.

Helium isn’t a detector at all; it’s just a gas. Pneumatic detectors rely on pressure changes rather than a heat-sensitive loop. Optical detectors sense flame radiation, not the heating of a loop. Therefore, the loop made of Inconel is the continuous-loop fire detection system used in DoD aircraft.