Definition
A fire detection system that uses thermocouples to sense a rapid rise in temperature in an engine compartment or other monitored area. A thermocouple is a junction of two dissimilar metals that produces a small voltage proportional to its temperature. The system compares the voltage from a sensing thermocouple, exposed to the area being monitored, against a reference thermocouple shielded from rapid temperature change. A normal, gradual temperature rise heats both thermocouples roughly equally and produces no warning. A sudden temperature rise from a fire heats the sensing thermocouple much faster than the reference, creating a voltage difference that triggers the fire warning.
Plain English
A fire warning system that watches for sudden jumps in temperature, not high temperature itself. Two small metal sensors are compared against each other; if one heats up much faster than the other, the system signals a fire.
Context Anchor
Seen in aircraft fire protection systems, especially around engines, APUs, and other areas where a fire warning must reach the cockpit quickly.
Derivation
Thermocouple comes from 'thermo-' (Greek for heat) and 'couple' (a pair). The name reflects the device's design: a pair of dissimilar metals joined together that produce voltage when heated.
Why Pilots Care
Provides reliable early warning of engine fires so the crew can shut down the engine or discharge extinguishers before damage spreads.
Grounding Statement
If a fire starts near an engine, the heated thermocouple creates an electrical signal that can trigger the cockpit fire warning.
Intuition Check
Do not think of this as a smoke detector. A thermocouple fire detection system senses heat, especially a rapid temperature rise, not smoke.
Example Sentence 1
The thermocouple fire detection system illuminated the engine fire warning light shortly after the pilot heard a loud bang from the right nacelle.
Example Sentence 2
Maintenance tested the thermocouple fire detection system by applying a heat source to verify the cockpit warning activated.