Definition
The temperature of the metal at the top of an engine cylinder, measured by a sensor mounted on or near the cylinder head and displayed in the cockpit. It is monitored to ensure the engine is operating within its designed thermal limits during all phases of flight.
Plain English
How hot the top part of an engine cylinder is getting. Pilots watch this gauge to make sure the engine is not running too hot or too cold.
Context Anchor
Seen on engine instruments and in discussions of engine cooling, climbs, cruise power settings, and fuel-air mixture management.
Derivation
Cylinder comes from the Greek kylindros, meaning a roller or rolling shape, which is what an engine cylinder looks like inside. The head is simply the top end of that cylinder. So the term literally describes the temperature at the top of the cylinder, which is where combustion happens and where heat is highest.
Why Pilots Care
Monitoring cylinder head temperature lets the pilot adjust mixture and power settings to avoid overheating that can cause detonation or engine damage.
Intuition Check
Do not read this as the temperature of the whole engine. Cylinder head temperature is specifically the heat measured at the cylinder head, which is one of the hottest and most important parts to monitor.
Example Sentence 1
During the climb, the pilot adjusted the mixture to keep the cylinder head temperature within the green range.
Example Sentence 2
In cruise the pilot leaned the mixture until cylinder head temperature stabilized at the recommended value for best economy.