The document provides information on anti-ice and rain protection systems for the Boeing 737 NG, including thermal anti-icing, electrical anti-icing, and windshield wipers. It describes the flight deck window heat, probe and sensor heat, engine anti-ice system, wing anti-ice system, ice detection system, and corresponding controls and indicators. The wing and engine anti-ice systems use bleed air to prevent ice buildup, while probes and sensors are heated electrically. Lights indicate system status and faults like overheat conditions.

1. B 737 NG Ground School.
See the aircraft study guide at www.theorycentre.com
The information contained here is for training purposes only. It is of a general nature it is
unamended and does not relate to any individual aircraft. The FCOM must be consulted for
up to date information on any particular aircraft.

2. ANTI ICE and RAIN POTECTION.

4. Introduction
Thermal anti-icing (TAI), electrical anti-icing, and windshield wipers are the systems
provided for ice and rain protection. The anti-ice and rain systems include:
• Flight Deck Window Heat
• Windshield Wipers
• Probe and Sensor Heat
• Engine Anti-Ice System (TAI)
• Wing Anti-Ice System (TAI)
• Ice Detection System (Option available)
Note; Thermal Anti Ice Uses engine bleed air from the compressor carried in ducts
to heat the engine intake lip and the 3 inboard slats.

5. ANTI ICE and RAIN Controls and Indicators.

6. Window OVERHEAT Lights
Illuminated (amber) – overheat condition is detected.
Note: OVERHEAT lights also illuminate if electrical power to window(s)
is interrupted. Note; Overheat is >63⁰ C
Window Heat ON Lights
Illuminated (green) – window heat is being applied to selected window(s).
Extinguished –
• switch is OFF, or
• an overheat is detected, or
• a system failure has occurred
• system is at correct temperature. Window temperature is above 43⁰ C

7. WINDOW HEAT Switches
ON – window heat is applied to selected window(s).
OFF – window heat not in use.
WINDOW HEAT Test Switch (spring–loaded to neutral)
OVHT – simulates an overheat condition.
PWR TEST – provides a confidence test.
Note: Refer to Supplementary Normal Procedures for Window
Heat Test procedures.

8. PWR TEST is a confidence test
only.
Supplementary Procedures.
Window heat switches ON
If window temperature is above
43⁰ C Green on light will not
illuminate.
Momentary power test will apply
power and bring on the green light.

9. If all GREEN ON lights
illuminated Do not do a
PWR TEST!
If one light is not illuminated
do a PWR TEST. If light
does not come on the power
supply has failed.
Maximum speed 250 Knots.
Below 10,000 Feet.

10. OVHT TEST Simulates an
overheat condition.
Supplementary Procedures.
Overheat is >63⁰ C
Window heat switches ON

11. Test switch to OVHT.
All Green lights OFF
OVERHEAT lights
illuminated

12. After approximately 1
minute.
All lights are OFF.
Window heat
switches OFF then
ON.

13. Window 1 Left and Right.
Window 2
Left and Right
Window 3
Left and Right
Windows
4 and 5
Left and
right as
fitted

14. Flight Deck Window Heat (Various options depending on aircraft)
Flight deck window numbers 1, 2, 4 and 5 consist of glass panes laminated to
each side of a vinyl core. Flight deck window number 4 has an additional vinyl
layer and acrylic sheet laminated to the inside surface. Flight deck window
number 3 consists of two acrylic panes separated by an air space.
A conductive coating on the outer glass pane of window numbers 1 and 2 permits
electrical heating to prevent ice build–up and fogging. A conductive coating on
the inner glass pane of window numbers 4 and 5 permits electrical heating to
prevent fogging. Window number 3 may or may not be electrically heated.
When heated a conductive coating on the inner glass pane of window number 3
permits electrical heating to prevent fogging.
The FWD WINDOW HEAT switches control heat to window number 1. The
SIDE WINDOW HEAT switches control heat to window numbers 2, 3 4 and 5 as
fitted.
Temperature controllers maintain windows numbers 1 and 2 at the correct
temperature to ensure maximum strength of the windows in the event of bird
impact. Power to window numbers 1 and 2 is automatically removed if an
overheat condition is detected.
Thermal switches, located on window number 3, 4 and 5, open and close to
maintain the correct temperature on the windows that are heated .

15. FWD switches control
heat to ONLY
window L1 and R 1
Window temperature is
controlled by a
TEMPERATURE
CONTROLLER which
cycles power ON an
OFF

16. The Overheat lights
for the FWD
windows are
controlled by the
Temperature
controllers

17. SIDE switches control
heat to ALL other heated
windows (Aircraft fit)
Window 2 has a
temperature controller

18. The Overheat lights for the
SIDE windows are
controlled by the
Temperature controllers
Window 2 ONLY
SIDE switches control
heat to ALL other heated
windows (Aircraft fit)
Window 2 has a
temperature controller

19. Any other heated window is
protected by a thermal switch only!
Number 3

20. Probe and Sensor Heat
Pitot probes, the total air temperature probe and the alpha vanes are electrically
heated.
Because the Static ports are flush with the fuselage they are not heated.
When operating on standby power, only the captain’s pitot probe may be heated,
however, the CAPT PITOT light does not illuminate for a failure.
Note: The pitot probe for standby airspeed is not heated when the airplane is on
standby power.
The heat for these probes is controlled through probe heater system A:
LEFT (CAPT) PITOT powered by 115V AC Transfer Bus 1
OR
* LEFT (CAPT) PITOT powered by 115V AC Standby Bus 1
* LEFT ELEVATOR PITOT powered by 115V AC Transfer Bus 1
* LEFT ALPHA VANE powered by 115V AC Transfer Bus 1
* TEMPERATURE PROBE powered by 115V AC Transfer Bus 1
The heat for these probes is controlled through probe heater system B:
* UPPER RIGHT (F/O) PITOT powered by 115V AC Transfer Bus 2
* LOWER RIGHT (AUX) PITOT powered by 115V AC Transfer Bus 2
* RIGHT ALPHA VANE powered by 115V AC Transfer Bus 2
* RIGHT ELEVATOR PITOT powered by 115V AC Transfer Bus 2

21. Probes are heated by AC
power.
On some aircraft the
Captains Pitot is heated
from the AC Standby Bus.
Probe heat switches A
controls the Left Probes
Switch B controls Right
Probes.

22. The indicator lights are all
powered from DC BUS 1
On Standby power the
lights are not an indication
of system status!
Static Ports are not
heated on the B737.

23. A Service Bulletin changes The probe heat system.
Off becomes AUTO. Probes are heated as soon as
either engine is running.
PROBE HEAT Switches
ON – power is supplied to heat related system.
AUTO – power is automatically supplied to both A and
B probe heat systems when either engine is running.

24. TAT TEST Switch
Push - Electrical power applied to TEMP PROBE on the ground.
The total air temperature (TAT) probe anti-icing system uses electric power and
resistance-type heating elements. Aircraft with an aspirated TAT probe also have a TAT
TEST button. An aspirated TAT Probe is only heated in flight.
The system uses 115v ac and 28v dc power. The probe heating element uses 115v ac
power. The current detection circuit uses 28v dc power.
On the ground, put the control switch to the ON/AUTO position. This energizes a relay
that stops 115v ac power through the current detection circuit to the probe heater.
The amber TEMP PROBE light does not come on.
Pushing the TEST switch (with control switch in ON position) DE energizes the relay .
This lets 115v ac power through the current detection circuit to the probe heater. If the
probe heater does not use current, the circuit causes the amber TEMP PROBE light to
come on.
The TAT probe is heated with 115 VAC in Air mode.

25. Wing Anti–Ice System
The wing anti–ice system provides protection for the three inboard leading edge
slats by using bleed air. The wing anti–ice system does not include the leading
edge flaps or the outboard leading edge slats.
The wing anti–ice control valves are AC motor–operated. With a valve open, bleed air
flows to the three leading edge inboard slats, and is then exhausted overboard. The
wing anti–ice system is effective with the slats in any position.
Wing Anti–Ice System Operation
On the ground, positioning the WING ANTI–ICE switch ON opens both control valves if
thrust on both engines is below the setting for takeoff warning activation and the
temperature inside both wing distribution ducts is less than the thermal switch activation
temperature.
Both valves close if either engine thrust is above the takeoff warning setting or
either temperature sensor senses a duct over temperature. The valves automatically
reopen if thrust on both engines is reduced and both temperature sensors are cool.
With the air/ground sensor in the ground mode and the WING ANTI–ICE switch
ON, the switch remains in the ON position regardless of control valve position.
The WING ANTI–ICE switch automatically trips OFF at lift–off when the air/ground
sensor goes to the air mode.

26. Positioning the WING ANTI–ICE switch to ON in flight:
• opens both control valves
• sets stall warning logic for icing conditions.
Note; Thrust setting logic and duct temperature logic are inhibited in flight.
Note: Stall warning logic adjusts stick shaker and minimum manoeuvre speed
bars on airspeed indications. FMC displayed VREF is not adjusted automatically.
Note: Stall warning logic remains set for icing conditions for the remainder
of the flight, regardless of subsequent WING ANTI–ICE switch position.
Valve position is monitored by the blue VALVE OPEN lights. Duct temperature
and thrust setting logic are disabled and have no affect on control valve operation
in flight.

27. WING ANTI ICE
Lights
Bright blue in Transit
Dim Blue Valve OPEN.
WING ANTI ICE
Switch.
Electrically held in ON
position.

28. ON Ground Operation
Wing Anti Ice Valves are
AC motor operated.
AC TRANSFER BUS 1
Wing ducts are monitored for
temperature only on the
ground.

29. ON Ground Operation
With TO thrust setting the WAI
valves close automatically.
The Switch remains ON.
The Switch is released to OFF with
Air mode.

30. Flight Operation
Only the 3 inboard
slats have WAI
Duct Temperature and Thrust setting logic are inhibited IN FLIGHT
If the switch is on WAI is ON.

31. FUEL FLOW INCREASE 100 PPH or 50 Kg Per Eng = 100 Kg Hr.
Adverse Weather. . . . . . . . . . . . . . . . SP.16
Wing Anti-ice Operation - In Flight
Ice accumulation on the flight deck window frames, windshield
centre post, or on the windshield wiper arm may be used as an
indication of structural icing conditions and the need to turn on wing
anti-ice.
CAUTION: Use of wing anti-ice above approximately FL350 may
cause a dual bleed trip off and possible loss of cabin pressure.
Note: Prolonged operation in icing conditions with the leading edge
and trailing edge flaps extended is not recommended.
Holding in icing conditions with flaps extended is prohibited.

32. ENGINE ANTI ICE

33. ENGINE ANTI ICE
Cowl Anti Ice is available even when the engine bleed valve is closed

34. COWL ANTI–ICE Lights
Illuminated (amber) – indicates an overpressure
condition in duct downstream of
engine cowl anti–ice valve.

35. COWL VALVE OPEN Lights
Illuminated (blue) –
• bright – related cowl anti–ice valve is in transit, or,
cowl anti–ice valve position disagrees with related
ENGINE ANTI–ICE switch position
• dim – related cowl anti–ice valve is open (switch ON).
Extinguished – related cowl anti–ice valve is closed
(switch OFF).

36. 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 manoeuvre speed bars on
the airspeed indicator. FMC displayed VREF is not adjusted automatically.
Note: Stall warning logic, airspeed indications, and minimum manoeuvre 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.

37. TAI indication is a valve OPEN indication.
If switch is ON and valve position disagrees for 8
seconds indication is Amber.
Select CONTINUOUS Ignition before
using TAI. S.P. 16.
Cowl valve lights are Bright
Blue in transit.
Dim Blue valve Open.,
Note; Switch label ENG ANTI-ICE. Lights label COWL and Engine indications TAI These 3
terms all apply to one system. Engine Anti Ice.

38. Cowl Anti-Ice Valve is a pressure regulating valve
that controls duct pressure to 50 PSI maximum.

39. Cowl Anti-Ice AMBER light is an Indication of
excessive duct pressure. (65psi)

40. Cowl Anti-Ice AMBER light is an Indication of
excessive duct pressure. (65psi)
QRH Action

41. FUEL FLOW INCREASE 200 PPH or 100 Kg Per Eng = 200 Kg Hr.
Adverse Weather. . . . . . . . . . . . . . . . SP.16
Engine Anti-Ice Operation - In Flight
Engine anti–ice must be ON during all flight operations when icing
conditions exist or are anticipated, except during climb and cruise
when the temperature is below -40 C SAT. Engine anti–ice must be
ON before, and during descent in all icing conditions, including
temperatures below -40 C SAT.
When operating in areas of possible icing, activate engine anti–ice
before entering icing conditions.
When engine anti-ice is needed:
ENGINE START switches .....................................CONT PM
ENGINE ANTI-ICE switches ....................................ON PM

42. NOTE; Total fuel Engine and wing anti ice approximately
300 kg hr.
FUEL FLOW INCREASE 200 PPH or 100 Kg Per Eng = 200 Kg Hr.
Adverse Weather. . . . . . . . . . . . . . . . SP.16
Engine Anti-Ice Operation - In Flight
Engine anti–ice must be ON during all flight operations when icing
conditions exist or are anticipated, except during climb and cruise when
the temperature is below -40°C SAT. Engine anti–ice must be ON before,
and during descent in all icing conditions, including temperatures below
-40°C SAT.
When operating in areas of possible icing, activate engine anti–ice before
entering icing conditions.
When engine anti-ice is needed:
ENGINE START switches .....................................CONT PM
ENGINE ANTI-ICE switches ....................................ON PM

43. S.P.16.1
Icing conditions exist when OAT (on the ground) or TAT (in flight) is 10 C or below
and any of the following exist:
• visible moisture (clouds, fog with visibility of one statute mile (1600m) or less,
rain, snow, sleet, ice crystals, and so on) is present, or
• ice, snow, slush or standing water is present on the ramps, taxiways, or runways.
CAUTION: Do not use engine or wing anti–ice when OAT (on the ground) or
TAT (in flight) is above 10 C.

44. WARNING: Do not rely on airframe visual icing cues before activating engine
anti–ice. Use the temperature and visible moisture criteria because late
activation of engine anti-ice may allow excessive ingestion of ice and result in
engine damage or failure.
CAUTION: Do not use engine anti-ice when TAT is above 10 C
CAUTION: Avoid prolonged operation in moderate to severe icing conditions.

45. Ice Detection System (Option)
An advisory only ice detection system detects airplane icing in flight. The system
consists of a probe located on the forward left fuselage and advisory lights located
on the left forward panel.
When the probe senses ice build–up inflight, the ICING light illuminates. When ice has
previously been detected and the probe is no longer detecting ice, the ICING light will
extinguish and the NO ICE light will illuminate. The ICING light and the NO ICE light do
not illuminate simultaneously.
Note: Residual ice may remain on the window areas with the NO ICE light illuminated.
The ICE DETECTOR light, located on the forward overhead panel, will illuminate if the ice
detection system fails. Illumination of the ICE DETECTOR light also illuminates the
MASTER CAUTION and ANTI–ICE system annunciator lights.

46. ICING Light
Illuminated (amber) –
• ice detector is detecting ice
• light is inhibited on the ground.
Press – extinguishes light, if illuminated.
NO ICE Light
Illuminated (white) –
• ice detector is not detecting ice, and the ice detector
probe had previously detected ice
• light is inhibited on the ground.
Press – extinguishes light, if illuminated.

48. WINDSHIELD WIPERS

49. Windshield Wipers
The rain removal system for the forward windows consists of windshield wipers
and a permanent rain repellent coating on the windows.
CAUTION: Windshield scratching will occur if the windshield wipers are
operated on a dry windshield.
Windshield WIPER Selectors
PARK – turns off wiper motors and stows wiper blades.
INT – seven second intermittent operation.
LOW – low speed operation.
HIGH – high speed operation.
DC Power from DC bus 1.

50. HYDROPHOBIC WINDSHIELD COATING
The hydrophobic windshield coating improves visibility in heavy rain.
Hydrophobic windshield coatings are on the outside surface of the left and right
number 1 flight compartment windows.
Hydrophobic (water repellent) windshield coatings are transparent films. The coatings
repel water. This causes water drops to bead up and roll off the windshields. The
coatings do not affect windshield strength or optical clarity.
The hydrophobic coatings wear down over time. Wear depends on these things:
* Wiper use
* Route structure
* Windshield maintenance practices.
As the coatings wear, they do not repel water droplets as satisfactorily. When this
happens, A new hydrophobic coating is applied to the windshield.
Caution This coating will be damaged if the wipers are operated on a dry windshield.
The Windshield must be cleaned only using approved processes and materials.

51. Windshield/Foot Air Controls

52. FOOT AIR Controls
PULL – supplies conditioned air to pilots’ leg positions.
WINDSHIELD AIR Controls
PULL – supplies conditioned air to number 1 windows for defogging.
Captain
First Officer

53. Which windows are heated with the LEFT FWD WINDOW HEAT switch selected ON.

54. Which windows are heated with the LEFT FWD WINDOW HEAT switch selected ON.
L1 only.

55. The wing anti-ice system provides protection for which components?

56. The wing anti-ice system provides protection for which components?
Only the three inboard slats.
The wing anti–ice system provides protection for the three
inboard leading edge slats by using bleed air. The wing
anti–ice system does not include the leading edge flaps or
the outboard leading edge slats.

57. The cowl ANTI-ICE light on the overhead panel indicates what malfunction?

58. The cowl ANTI-ICE light on the overhead panel indicates what malfunction?
The pressure in the cowl lip duct exceeds limits.

59. The wing anti-ice valves are powered by what?

60. The wing anti-ice valves are powered by what?
AC motor operated.
The wing anti–ice control valves are AC motor–operated. With a valve
open, bleed air flows to the three leading edge inboard slats, and is then
exhausted overboard. The wing anti–ice system is effective with the
slats in any position.

61. The aircraft is in flight. Wing anti-Ice is selected ON with TAT at + 15°C. What will
happen to the wing anti-ice control valves?

62. The aircraft is in flight. Wing anti-Ice is selected ON with TAT at + 15°C. What will happen to
the wing anti-ice control valves?
The valves will open as duct temperature and thrust setting logic are disabled in
flight.
Positioning the WING ANTI–ICE switch to ON in flight:
• opens both control valves
• sets stall warning logic for icing conditions.
Note; Thrust setting logic and duct temperature logic are inhibited in flight.

63. The following Items are Non AFM and have no Flight deck controls or indicators
WATER LINE AND DRAIN MAST HEATERS
The water and toilet drain anti-ice system prevents ice formation in theses areas:
* Potable water system service and supply components
* Grey water system drain components
• Vacuum waste system drain and service components.
Potable Water Fill Fitting
The potable water fill fitting has a built in heater element. The fitting heater uses
28v dc power. A circuit breaker controls power to the fitting. Heat is constant and
automatic when power is on the airplane.
Potable Water Fill Hose The potable water fill hose has a built-in heater element.
The hose heater element uses 115v ac power. A circuit breaker controls power to
the hose. Heat is constant and automatic when power is on the airplane.

64. Potable Water Supply Hoses
Some of the potable water supply hoses have built-in heater elements. The hoses
use 115v ac power. Thermostatic switch in the hose controls heat to the hoses.
Heat to the hoses is automatic when power is on the airplane.
Potable Water Tank Heater Blankets
The potable water tank heater blanket prevents freezing and provides regulated
heat to the bottom of the water storage tanks within specified temperature limits.
Water tank heaters use electrical power to keep tanks from freezing both in flight
and on the ground.
The heater blankets use 115 vac power, 400 watts maximum and is controlled by a
primary thermostat opening at 24 to 29 degrees C (75 to 85 degrees F). and closes
at 4 to 10 degrees C (40 to 50 degrees F).
A manually reset backup thermostat opens at 50 to 59 C (122 to 138 degrees F).
and closes at 29 degrees C (85 degrees F.)

65. Grey Water Drain Valve/Lines
Tape heaters warm the grey water drain lines.
The tape heaters use 115v ac power. Circuit breakers control electric power to
the tape heaters. Heat is constant and automatic when power is on the
airplane.
An in-line thermostatic switch controls heat to the drain mast inlet line.
Drain Masts
The drain masts have integral electric heater elements.
Heat to the mast is constant and automatic when power is on the airplane.
The drain mast heating elements operate on these two
voltages:
* 115v ac in flight
• 28v ac on the ground.
The drain mast heat uses a reduced voltage on the ground to prevent a burn
hazard to personnel. This also extends the drain mast service life.

66. Anti Ice and Rain Protection.
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