Engine and engine nacelle inlet anti-icing
(fig. 1-11) is accomplished by 14th stage bleed air,
which is separated, in each engine pylon, from
14th stage air being used for other environmental
control system (ECS) purposes. The anti-ice
switch on the environmental panel on the center
console, when set to the ENG & PITOT position,
opens both engine anti-icing valves by de-
energizing their solenoids to direct 14th stage bleed
air, regulated to 22.5 ± 2.5 psi, to the engine
nacelle leading edges and engine anti-icing
systems. The position of each anti-ice valve is
shown on the copilot’s advisory panel; 1 A-ICE
ON and 2 A-ICE ON indicator lights come on
whenever the anti-ice valves are open. The engine
anti-ice switch also opens the empennage pressure
regulator valve to provide a source of constant
bleed air to the ram air inlet duct anti-icing shroud
(unless the deice system is being operated, the
empennage cyclic valves will remain inactive/
closed). The engine anti-icing valve activates the
entire deice system. The deice system cannot be
operated until the anti-ice switch is set to the ENG
& PITOT position.
The bleed-air deice/anti-icing system consists
of deice pressure regulating valves, bleed-air
solenoid valves, a WING & EMP deice timing
controller, a probe sensor temperature trans-
mitter, and a deice thermostatic switch.
Deice Pressure Regulating Valve
The system (fig. 1-12) uses three pressure
regulating valves. One pressure regulating valve
Figure 1-11.—Engine anti-icing system.
1-14
