Definition
Aircraft systems designed either to prevent the formation of ice on critical surfaces (anti-icing) or to remove ice that has already formed (deicing). Anti-icing systems are activated before ice accumulates and work continuously to keep surfaces clean, while deicing systems are activated after ice has built up and act to break it off. Common installations include heated leading edges, pneumatic boots on wings and tail, heated pitot tubes, heated propellers or windshields, and fluid-based weeping wing systems.
Plain English
Equipment fitted to an aircraft that either stops ice from forming on it or knocks ice off once it has formed. Anti-icing keeps ice from sticking in the first place; deicing gets rid of ice already there.
Context Anchor
Seen in instrument flying and thunderstorm-avoidance discussions, especially when a pilot may encounter cold clouds, rain, or ice during flight.
Derivation
The prefix 'anti-' comes from Greek meaning 'against,' so anti-icing means 'working against ice forming.' 'De-' comes from Latin meaning 'remove' or 'undo,' so deicing means 'removing ice.' The two prefixes capture the key operational difference: prevention versus removal.
Why Pilots Care
Ice on wings or other surfaces changes their shape, reduces lift, and increases drag, which can make the aircraft difficult or impossible to control.
Intuition Check
Do not assume this equipment makes the airplane ice-proof. It protects only the parts and conditions approved for that aircraft, and thunderstorms can still produce ice or turbulence beyond what the equipment can safely handle.
Example Sentence 1
Before entering the cloud layer at freezing temperatures, the pilot turned on the anti-icing equipment to keep the wings clean.
Example Sentence 2
Deicing boots inflated and deflated in sequence to crack and shed the ice that had formed on the leading edges.