Ice & Rain Protection

Thermal anti-ice, pneumatic de-ice boots, electrical probe/windshield heating and rain removal.

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Main ideas

ANTI-ICING prevents ice forming; DE-ICING lets a little ice build up and then removes it. Wing and engine-cowl leading edges on jets are usually ANTI-iced with hot engine BLEED AIR (thermal); the surfaces are kept above freezing.
PNEUMATIC BOOTS (mostly on turboprops) are DE-icers: rubber boots on the leading edge inflate to crack off accumulated ice, then deflate — a cyclic system, timed to let ice build before shedding.
ELECTRICAL heating protects pitot/static probes, angle-of-attack and total-air-temperature probes, windshields, water lines and (via slip rings) propellers; windshields also have anti-ice and demist heating films.
RAIN removal uses windshield wipers, chemical rain repellent and hydrophobic coatings; ICE DETECTION (probes/sensors) warns the crew or auto-activates protection.
Fluid (glycol/TKS) systems weep freezing-point depressant through porous panels on some aircraft.
⚠ Exam trap: wing/cowl anti-ice normally uses hot BLEED AIR (thermal, prevents ice); pneumatic BOOTS are cyclic DE-icers that inflate to break ice off after it forms; pitot and static probes are ELECTRICALLY heated.

Solved examples

Why are de-icing boots operated in cycles (allowing ice to build up first) rather than continuously?
A de-icing boot works by inflating to crack the ice off its surface. If run continuously with only a thin layer of ice, the ice can form a shell around the inflated boot and merely lift with it, then re-freeze — 'ice bridging'. Allowing a defined thickness to accumulate before a cycle ensures the ice is brittle enough to crack and shed cleanly when the boot inflates.

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