Description

Engine Fire Protection has two components, detection and extinguishing.

Engine Fire Detection

Detection is achieved by various means. Some older aircraft use a thermal switch system or a thermocouple system. Thermal switches are heat-sensitive units that complete electrical circuits at a certain temperature. Thermocouple systems activate based on the rate of temperature increase. 

Other aircraft use pneumatic detection systems. In pneumatic systems, the sensing element consists of a helium-filled tube connected to an internal switch. As heat rises, the gas pressure inside the tube increases until it closes the switch to activate a fire warning.

Most modern commercial airliners use continuous-loop detector systems. Continuous-loop systems operate similarly to thermal switch systems in that they complete electrical circuits at a certain temperature. They are not sensitive to the rate of temperature increase. These systems use inconel tubing that contains heat-sensitive conducting elements.