Definition
The process by which water vapor in the air changes into liquid water, typically when warm, moist air contacts a cooler surface or when the air itself cools below its dew point.
Plain English
When water in the air turns into tiny droplets of liquid water -- like the moisture that forms on the inside of a cold drink glass on a warm day.
Context Anchor
Seen in fuel system discussions, especially when explaining how water can get into fuel tanks before flight.
Derivation
From the Latin condensare, meaning 'to make thick or dense.' Water vapor (a thin, spread-out gas) becomes denser liquid water when it condenses -- the molecules pack together.
Why Pilots Care
Water that collects from condensation in fuel tanks can cause engine stoppage or corrosion if not drained before flight.
Grounding Statement
A cool fuel tank on a humid day can turn moisture in the air into small water drops inside the tank.
Intuition Check
Condensation does not mean fuel is leaking or that rain got into the tank. It means moisture already in the air changed into liquid water because it cooled.
Example Sentence 1
Topping off the fuel tanks after the last flight of the day reduces the air space where condensation can form overnight.
Example Sentence 2
Large day-to-night temperature swings increase the chance of condensation inside partially filled fuel tanks.