Definition
A characteristic of a material or component in which its electrical resistance increases as its temperature rises. A resistor or sensor with a positive temperature coefficient will pass less current as it heats up, because its resistance grows with temperature.
Plain English
It means the hotter the part gets, the harder it is for electricity to flow through it. Heat goes up, resistance goes up.
Context Anchor
Seen in aircraft electrical system discussions, especially when describing temperature sensors, circuit protection devices, or parts whose electrical behavior changes with heat.
Derivation
Coefficient comes from the Latin co- (together) and efficere (to bring about) -- a number that describes how one quantity changes together with another. Here, it describes how resistance changes together with temperature. Positive simply means the two move in the same direction: temperature up, resistance up.
Why Pilots Care
Many aircraft electrical components rely on this behaviour. A motor winding with a positive temperature coefficient draws less current as it warms, which helps protect it from overheating. Some self-resetting circuit protectors work the same way -- they heat up under fault current, their resistance climbs, and current is naturally limited.
Intuition Check
Positive does not mean good or safe here. It means the measured value goes up when temperature goes up.
Example Sentence 1
The starter motor windings have a positive temperature coefficient, so as they warm during cranking the current draw gradually decreases.
Example Sentence 2
Maintenance checked the positive temperature coefficient behavior of the heater element during the inspection.