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In certain leading edge de-icing devices, sequential pneumatic impulses are installed. These:

1) prevent ice formation;
2) can be triggered from the flight deck after icing has become visible;
3) will inflate each pneumatic boot for a few seconds;
4) will repeat more than ten times per second.

  • A
    1 and 3.
  • B
    1 and 4.
  • C
    2 and 3.
  • D
    2 and 4.

Refer to figure.
ICE CONTROL SYSTEMS

Two major categories of ice control systems are pneumatic boots – which expand and break ice off aerofoils; and thermal systems – which use bleed air or electricity to heat protected surfaces and prevent ice.

AEROFOIL ICE CONTROL

To protect wing and tail surface leading edges from icing, most aeroplanes use pneumatic devices. On many reciprocating-engine and turboprop airplanes, de-icing boots are pneumatically inflated for a few seconds to break the ice, which allows it to be carried away by the airstream. A high-pressure de-icing boot is a fabric-reinforced rubber sheet that contains built in inflation tubes. The boots are installed in sections along each leading-edge surface. This system can be triggered from the flight deck.

In another system, primarily used by turbine-powered aeroplanes, heated air is directed through ducting in the aerofoil leading edge, to thermally prevent ice from forming. This is referred to as thermal anti-ice system.

Note: Pneumatic de-icing boots do not prevent ice formation, these are de-icing systems only.

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