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A3.1.3 Mechanical de-icing boots
They are typically used for propeller aircraft. The boots are rubber tubes, which are installed on the leading edges of the wing. As soon as ice accretes, the boots are inflated by pressurized air. The change of their shape breaks the ice layers. Mechanical boots ice protection systems are de-icing systems designed to remove already accreted ice. De-icing boots are not used on Airbus aircraft.
A3.2 Airbus procedures for flight in icing condition
The AFM/FCOM states that icing conditions may be expected when the OAT (on the ground and for takeoff) or when TAT (in flight) is at or below 10°C, and there is visible moisture in the air (such as clouds, fog with low visibility of one mile or less, rain, snow, sleet, ice crystals) or standing water, slush, ice or snow is present on the taxiways or runways.
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These are conservative limits defined by airworthiness authorities to guide pilots in
selecting anti-ice systems without necessarily guaranteeing that they will encounter icing conditions
The engine ice protection system (Nacelle Anti-Ice: NAI) must be immediately activated when encountering the above-noted icing condition. This procedure prevents any ice accretion (anti-icing) on the air intakes of the engines, thus protecting the fan blades from damage due to ingested ice plates (FOD). When the Static Air Temperature (SAT) is below -40°C the NAI must only be ‘ON’ when the aircraft enters cumulonimbus clouds, or when the Advisory Ice Detection System - if installed - annunciates ICE DETECTED (refer to section A3.3).
As stated above, the wings are more tolerant to ice accumulation. The FCOM requires the activation of Wing Anti-Ice System (WAI) whenever there is an indication of airframe ice accumulation. The activation of the WAI system can be used to prevent any ice formation (anti-ice) or to remove an ice accumulation from the wing leading edges. Ice accumulation on the airframe can be evident either from an ice build-up on the windshield wipers or on the ice detector pin (visual cue), located between the two front windshields. If a Dual Advisory Ice Detection System is installed (see section A3.3),
the WAI system must be activated, when SEVERE ICE DETECTED is annunciated through a dedicated warning. It should be noted that detection through the ice detection system may appear later than actual ice accretion on the wipers, due to the fact that the wipers in certain conditions are more sensitive to ice build-up. The detectors have been calibrated during extensive flight and wind tunnel testing, so that the severe ice warning corresponds to an amount of ice on the leading edge, which is not critical for the aircraft’s aerodynamic performance or handling qualities. However, the ice detection system being advisory, the flight crew must not wait for the severe ice detection signal to appear, but should activate WAI according to the FCOM. The AFM recommends avoiding extended flight in icing conditions with extended slats and flaps, as accreted ice may block the retraction of the high lift devices causing mechanical damage to the slat / flap system. If the pilot suspects that ice is accumulating on the protected surfaces (WAI inoperative), or if the pilot suspects that a significant amount of ice is accumulating on the unprotected parts of the wing, VLS must be increased as specified in the AFM/FCOM. In all cases the decision to activate and de-activate the Nacelle and Wing Anti-ice systems is in the responsibility of the flight crew, based on the above FCOM criteria.
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