Definition
A temperature-sensitive electrical switch that automatically opens or closes a circuit when the temperature it monitors reaches a preset value. In aircraft systems it is commonly used to trigger warning lights, activate cooling or heating equipment, or shut off a system if a temperature limit is exceeded.
Plain English
An on/off switch that is operated by heat instead of by a person. When the temperature reaches a set point, the switch flips by itself.
Context Anchor
Seen in aircraft engine and electrical system maintenance, especially where a temperature change must trigger a light, warning, or automatic action.
Derivation
From 'thermo-' (Greek therme, meaning heat) plus 'switch.' The name describes exactly what it is: a switch operated by heat.
Why Pilots Care
It provides automatic warning or protective action when critical engine temperatures are exceeded, reducing the risk of fire or component failure.
Intuition Check
A thermoswitch is not a thermometer. It does not show the temperature; it changes an electrical circuit when a set temperature is reached.
Example Sentence 1
When the engine bay temperature climbed past the limit, the thermoswitch closed the circuit and illuminated the overheat warning light on the panel.
Example Sentence 2
The thermoswitch in the nacelle activated the cooling fan once the engine compartment reached its limit temperature.