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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Anti-Ice and Deice Systems

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




In the past it was believed that if the boots were cycled too
soon after encountering ice, the ice layer would expand
instead of breaking off, resulting in a condition referred to as
ice "bridging." Consequently, subsequent deice boot cycles
would be ineffective at removing the ice buildup. Although
some residual ice may remain after a boot cycle, "bridging"
does not occur with any modern boots. Pilots can cycle the
boots as soon as an ice accumulation is observed. Consult
the AFM/POH for information on the operation of deice
boots on an aircraft.

Many deicing boot systems use the instrument system suction
gauge and a pneumatic pressure gauge to indicate proper boot
operation. These gauges have range markings that indicate
the operating limits for boot operation. Some systems may
also incorporate an annunciator light to indicate proper boot

Proper maintenance and care of deicing boots are important
for continued operation of this system. They need to be
carefully inspected during preflight

Another type of leading edge protection is the thermal anti-ice
system. Heat provides one of the most effective methods for
preventing ice accumulation on an airfoil. High performance
turbine aircraft often direct hot air from the compressor
section of the engine to the leading edge surfaces. The hot
air heats the leading edge surfaces sufficiently to prevent the
formation of ice. A newer type of thermal anti-ice system
referred to as thermawing uses electrically heated graphite
foil laminate applied to the leading edge of the wing and
horizontal stabilizer. Thermawing systems typically have
two zones of heat application. One zone on the leading edge
receives continuous heat; the second zone further aft receives
heat in cycles to dislodge the ice allowing aerodynamic forces
to remove it. Thermal anti-ice systems should be activated
prior to entering icing conditions.

An alternate type of leading edge protection that is not as
common as thermal anti-ice and deicing boots is known
as a weeping wing. The weeping-wing design uses small
holes located in the leading edge of the wing to prevent
the formation and build-up of ice. An antifreeze solution
is pumped to the leading edge and weeps out through the
holes. Additionally, the weeping wing is capable of deicing
an aircraft. When ice has accumulated on the leading edges,
application of the antifreeze solution chemically breaks down
the bond between the ice and airframe, allowing aerodynamic
forces to remove the ice. [Figure 6-48]

TKS weeping wing anti-ice/deicing system.
Figure 6-49. TKS weeping wing anti-ice/deicing system.

Windscreen Anti-Ice
There are two main types of windscreen anti-ice systems.
The first system directs a .ow of alcohol to the windscreen.
If used early enough, the alcohol will prevent ice from
building up on the windscreen. The rate of alcohol .ow can be
controlled by a dial in the flight deck according to procedures
recommended by the aircraft manufacturer.

Another effective method of anti-icing equipment is the
electric heating method. Small wires or other conductive
material is imbedded in the windscreen. The heater can be
turned on by a switch in the flight deck, causing an electrical
current to be passed across the shield through the wires to
provide sufficient heat to prevent the formation of ice on
the windscreen. The heated windscreen should only be used
during flight Do not leave it on during ground operations, as
it can overheat and cause damage to the windscreen. Warning:
the electrical current can cause compass deviation errors by
as much as 40°.

Propeller Anti-Ice
Propellers are protected from icing by the use of alcohol or
electrically heated elements. Some propellers are equipped
with a discharge nozzle that is pointed toward the root of the
blade. Alcohol is discharged from the nozzles, and centrifugal
force drives the alcohol down the leading edge of the blade.
The boots are also grooved to help direct the flow of alcohol.
This prevents ice from forming on the leading edge of the
propeller. Propellers can also be fitted with propeller anti-ice
boots. The propeller boot is divided into two sections—the
inboard and the outboard sections. The boots are imbedded
with electrical wires that carry current for heating the
propeller. The prop anti-ice system can be monitored for
proper operation by monitoring the prop anti-ice ammeter.
During the preflight inspection, check the propeller boots for
proper operation. If a boot fails to heat one blade, an unequal
blade loading can result, and may cause severe propeller
vibration. [Figure 6-49]