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When the wing thermal anti-ice is used on the ground, the
engine and wing anti-ice control panel (P5-11) energizes the
WTAI solenoid valve. This releases the control pressure from
the precooler control valve actuator. This causes the precooler
control valve to open fully.
The wide open precooler control valve gives maximum cooling
to the engine bleed air. This protects the wing leading edges
from overheat damage.
The wing thermal anti-icing system is made to keep the leading
edge of the wing free of ice accumulation during flight. During
flight there is a large airflow over the wing. This airflow has a
great cooling effect on the leading edges. The wing thermal
anti-icing system heat output is great enough to overcome this
cooling effect.
When the wing thermal anti-icing system is used on the ground,
there is very little cooling airflow over the wing. In these
conditions, the wing thermal anti-icing system heat output can
overheat the wing leading edges. This can damage the heat
treatment of the leading edges devices. To prevent overheat
damage to the wing leading edge, the engine bleed air is given
maximum cooling during ground operations.
ICE AND RAIN PROTECTION - WTAI - WTAI SOLENOID VALVE
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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ICE AND RAIN PROTECTION - WTAI - WTAI SOLENOID VALVE
ICE AND RAIN PROTECTION - WTAI - WTAI SOLENOID VALVE
EFFECTIVITY
GUN ALL 30-11-00
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
30-11-00-008
General
The wing thermal anti-ice (WTAI) system uses 115v ac power to
operate the WTAI shutoff valves and 28v dc for control and
indication. This system operates on the ground and in flight.
The K1 relay connects power to operate the WTAI shutoff
valves. When the relay is energized, it sends 115v ac power to
open the WTAI shutoff valves. When the relay is de-energized, it
sends 115v ac power to close the WTAI shutoff valves.
Ground Operations
When the airplane is on the ground, the K1 relay energizes to
open the WTAI shutoff valves for these conditions:
* WING ANTI-ICE switch (P5-11) is in the ON position
* No overheat conditions (wing anti-icing ground overheat
thermal switches)
* No engine thrust lever is advanced (control stand wing antiice
switches).
Takeoff
When the thrust levers are >60 TRA, the WTAI valves close.
This decreases engine bleed loads and conserves thrust for
climb.
The WING ANTI-ICE switch is a circuit breaker type switch.
Resistance in the K1 energizing circuit keeps current in the
switch below its trip threshold.
During takeoff, a logic circuit in the control panel gives the
switch a low resistance path to ground. This causes an
overcurrent in the switch and the switch trips to the OFF
position. The pilot must select WTAI after takeoff if necessary.
Flight Operations
When the airplane is in the air, the K1 relay energizes to open
the WTAI shutoff valves when the wing anti-ice switch is in the
ON position.
Indication
This is the control panel logic for the dimming diode control of
the blue VALVE OPEN indication lights:
* Light is off - the switch is in the OFF position and the valve is
closed
* Light is dim - the switch is in the ON position and the valve is
open
* Light is bright - the switch position and valve position are not
the same or the valve is in transit.
These things control the bright and dim functions of the VALVE
OPEN lights on anti-ice panel:
* System switch and valve position feedback
* Control panel solid state switch circuits
* Voltage reduction zener diodes (dim mode).
ICE AND RAIN PROTECTION - WTAI - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN ALL 30-11-00
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D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
30-11-00-009
ICE AND RAIN PROTECTION - WTAI - FUNCTIONAL DESCRIPTION
ICE AND RAIN PROTECTION - WTAI - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN ALL 30-11-00
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
30-11-00-009
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D633A101-GUN Oct 10/2002
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