Definition
A system that prevents ice from forming on the leading edges of propeller blades and the spinner during flight in icing conditions. It typically works by applying heat through electrically heated elements bonded to the blade leading edges, or by feeding a freezing-point-depressant fluid (such as isopropyl alcohol or a glycol-based fluid) through a slinger ring that distributes the fluid outward along the blades by centrifugal force.
Plain English
A system that stops ice from forming on the propeller blades while you fly through icy conditions, either by warming the blades electrically or by spreading a special fluid along them.
Context Anchor
You will see this term in aircraft systems descriptions, icing procedures, and preflight checks for airplanes equipped for flight near freezing moisture.
Derivation
"Anti-ice" means "against ice" -- the system is designed to keep ice from forming in the first place. This is different from "deice," which removes ice after it has already formed.
Why Pilots Care
Ice accumulation on propeller blades reduces thrust, creates imbalance, and can lead to severe vibration that may force an emergency landing or cause structural damage.
Grounding Statement
If the propeller is spinning in cold, wet air, propeller anti-ice helps stop ice from collecting on the blades in the first place.
Intuition Check
Propeller anti-ice is not the same idea as removing a heavy ice buildup after the fact. In this context, anti-ice means preventing ice from forming or keeping it from getting started.
Example Sentence 1
Before entering the cloud layer, the pilot turned on the propeller anti-ice to keep ice from building up on the blades.
Example Sentence 2
During the preflight briefing the instructor emphasized checking the propeller anti-ice system when icing was forecast along the route.