Definition
The process of clearing condensation, mist, or frost from the inside surface of an aircraft windshield by directing warm, dry air across the glass. In small airplanes equipped with a combustion heater, defogging is typically accomplished by routing heated air through dedicated windshield outlets at the base of the windscreen.
Plain English
Blowing warm air on the inside of the windshield to clear the fog so the pilot can see out.
Context Anchor
Seen in aircraft heating and ventilation discussions, especially when a cabin heater also provides air to clear the windshield.
Derivation
From 'de-' (to remove) plus 'fog' (a layer of tiny water droplets). Defogging literally means removing the fog — in this case, the moisture that condenses on the inside of the windshield when warm, humid cabin air meets the cold glass.
Why Pilots Care
Fogged windshields reduce visibility and increase workload during critical phases of flight such as takeoff, landing, or instrument approaches.
Grounding Statement
On a cold day, moisture inside the cabin can form a cloudy film on the windshield; windshield defogging clears that film by moving warm air across the surface.
Intuition Check
Windshield defogging does not mean flying out of fog or improving the outside weather. It means clearing the windshield itself so the pilot can see through it.
Example Sentence 1
After descending into warmer, moist air, the pilot opened the windshield defogging vents to clear the condensation forming on the glass.
Example Sentence 2
Effective windshield defogging kept the view clear while flying through a layer of moisture at night.