Definition
A specified length of time during which a combustion heater is run with the fuel shut off but the ventilating fan still operating, allowing residual heat to be carried away from the heater components before the fan is switched off.
Plain English
After turning off a cabin heater, you keep the fan running for a set time so the leftover heat is blown out of the heater before everything is shut down.
Context Anchor
Seen in combustion heater operating procedures, especially during heater shutdown and before securing the aircraft.
Why Pilots Care
Skipping the cool-down period can overheat the heater assembly, damage the combustion chamber or heat exchanger, and create a fire hazard on the ground.
Grounding Statement
The flame may be out, but the heater metal can still be very hot and needs airflow to carry that heat away.
Intuition Check
Do not think of the cool-down period as time for the cabin to become cooler. Here it means a safety interval that lets the heater itself cool before final shutdown.
Example Sentence 1
After turning off the combustion heater, the pilot left the ventilation fan running for the full cool-down period before shutting it off.
Example Sentence 2
The emergency checklist calls for a five-minute cool-down period if the heater is shut down in flight due to a malfunction.