737 Flight Crew Operations Manual
Anti-Ice, Rain -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
D6-27370-866-EGP 3.20.5
Probe and Sensor Heat
Pitot probes, the total air temperature probe and the alpha vanes are electrically
heated. Static ports are not heated.
Note: The pitot probe for standby airspeed is not heated when the airplane is on
standby power.
Engine Anti–Ice System
Engine bleed air thermal anti–icing prevents the formation of ice on the engine
cowl lip. Engine anti–ice operation is controlled by individual ENG ANTI–ICE
switches. The engine anti–ice system may be operated on the ground and in flight.
Engine Anti–Ice System Operation
Each cowl anti–ice valve is electrically controlled and pressure actuated.
Positioning the ENG ANTI–ICE switches to ON:
• allows engine bleed air to flow through the cowl anti–ice valve for cowl
lip anti–icing
• sets stall warning logic for icing conditions.
Note: Stall warning logic adjusts stick shaker and minimum maneuver speed bars
on the airspeed indicator. FMC displayed VREF is not adjusted
automatically.
Note: Stall warning logic, airspeed indications, and minimum maneuver speeds
on the airspeed indicator return to normal when engine anti–ice is
positioned OFF if wing anti–ice has not been used in flight.
If the cowl anti–ice valve fails to move to the position indicated by the ENG
ANTI–ICE switch, the COWL VALVE OPEN light remains illuminated bright
blue and an amber TAI indication illuminates on the CDS after a short delay.
The amber COWL ANTI–ICE light illuminates due to excessive pressure in the
duct leading from the cowl anti–ice valve to the cowl lip.
September 15, 2016
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