Definition
Rubber coverings bonded to the leading edge of each propeller blade, fed with anti-icing fluid (typically isopropyl alcohol or a glycol-based mixture) through a slinger ring at the propeller hub. Centrifugal force throws the fluid outward along grooves in the boot, coating the blade leading edge and preventing ice from forming or adhering during flight in icing conditions.
Plain English
Rubber strips along the front edge of each propeller blade that get fed a special fluid. As the propeller spins, the fluid spreads along the blade and stops ice from sticking.
Context Anchor
Seen in aircraft anti-ice and deice system discussions, especially when checking or operating propeller ice protection in cold visible moisture.
Derivation
Boot' here is borrowed from the older deice boot terminology -- a protective rubber covering fitted over a part, much like a boot fits over a foot. 'Anti-ice' means it prevents ice from forming, as opposed to 'deice' which removes ice after it forms.
Why Pilots Care
Ice on propeller blades creates imbalance, severe vibration, and reduced thrust; the boots restore smooth operation and prevent these hazards.
Intuition Check
Do not picture a removable boot or a rubber sleeve you put on the propeller. In this context, a boot is a fixed protective strip on the blade, often heated by electricity.
Example Sentence 1
Before entering the icing layer, the pilot switched on the propeller anti-ice system and watched the fluid flow indicator confirm the boots were being fed.
Example Sentence 2
Cycling the propeller anti-ice boots shed the ice and eliminated the vibration.