Definition
Small electric fans installed in the avionics bay or instrument panel area to draw heat away from radios, navigation equipment, and other electronic units, keeping them within their designed operating temperature range.
Plain English
Little fans that blow air over the airplane's electronic equipment to stop it from overheating.
Context Anchor
A pilot may check these during preflight by listening for fan operation, checking for a warning, or making sure cooling openings are not blocked, depending on the airplane.
Derivation
Avionics' comes from blending 'aviation' and 'electronics' — the electronic gear used in aircraft. Knowing this makes it clear that an avionics cooling fan is specifically for cooling the airplane's electronics, not the engine or cabin.
Why Pilots Care
Overheated avionics can cause instrument failures or automatic shutdowns in flight.
Analogy
It is like the small fan inside a computer: the fan is not the main equipment, but it helps the electronics stay cool enough to work properly.
Intuition Check
Do not think of these as cabin comfort fans. Avionics cooling fans are for protecting aircraft electronic equipment, not for cooling the pilot or passengers.
Example Sentence 1
During preflight, the pilot turned on the avionics master and listened for the avionics cooling fan to confirm it was running.
Example Sentence 2
A failed avionics cooling fan may cause the navigation screens to overheat and blank out.