Ice protection system

Ice protection systems are designed to keep atmospheric ice from accumulating on aircraft surfaces (particularly leading edges), such as wings, propellers, rotor blades, engine intakes, and environmental control intakes. If ice is allowed to build up to a significant thickness it can change the shape of airfoils and flight control surfaces, degrading the performance, control or handling characteristics of the aircraft. An ice protection system either prevents formation of ice, or enables the aircraft to shed the ice before it can grow to a dangerous thickness.

The pneumatic boot is usually made of layers of rubber, with one or more air chambers between the layers. If multiple chambers are used, they are typically shaped as stripes aligned with the long direction of the boot. It is typically placed on the leading edge of an aircraft's wings and stabilizers. The chambers are rapidly inflated and deflated, either simultaneously, or in a pattern of specific chambers only. The rapid change in shape of the boot is designed to break the adhesive force between the ice and the rubber, and allow the ice to be carried away by the relative wind flowing past the aircraft. However, the ice must be carried away cleanly from the trailing portions of the surface, or it could re-freeze behind the protected area. Re-freezing of ice in this manner was a contributing factor to the crash of American Eagle Flight 4184.

Certain older designs of pneumatic boot were subject to a phenomenon known as Ice Bridging. If the ice had not accumulated to a sufficient thickness and fragility, malleable ice could be pushed into a shape out of reach of the inflatable sections of the boot. This problem is mostly solved in modern designs by increasing the speed of inflation/deflation action, and by alternating the timing of inflating/deflating adjacent chambers.

The pneumatic boot is most appropriate for low and medium speed aircraft, especially those without leading edge lift devices such as slats. Therefore, this system is most commonly found on turbo propeller aircraft such as the Saab 340, Embraer EMB 120 Brasilia, and British Aerospace Jetstream 41. Pneumatic De-Icing boots are sometimes found on larger piston prop aircraft, smaller turbojets such as the Cessna Citation V, and some older turbojets. This device is rarely used on modern turbojet aircraft.

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Wikipedia