aircraft use an electrical solenoid to control a
possibility of inducting chunks of ice into the
pneumatic anti-icing valve. See figure 6-13.
engine. Engine anti-icing systems prevent these
When the aircraft routinely flys in adverse
problems if turned on prior to entering an icing
weather conditions, a fail-safe system may be used
condition. Icing will not normally occur in super-
in the system. The solenoid-actuated air valve is
sonic flight because heat caused by the friction
electrically actuated closed. If the switch is turned
of the aircraft passing through the air is sufficient
on, or if electrical power is lost, the valve is spring
to prevent ice from forming.
loaded to the open position. Some systems anti-
Many types of anti-icing systems are in use
ice the complete inlet duct, while in other systems
today. All systems use bleed air from the engine
only the guide vanes are anti-iced.
to perform the anti-icing function. The use of
bleed air causes engine power loss. Anti-icing will
BLEED-AIR SYSTEMS (AIRFRAME)
be used only when absolutely necessary. Some air-
There are a several airframe systems that rely
craft use a reversible electric motor to open and
on engine bleed air to operate. See figure 6-14.
close an air valve to supply the needed air. Other
Figure 6-13.-Inlet guide vane anti-icing system.