Pilot’s Manual Learjet 60
6-10 PM-123
Change 6
WINDSHIELD ANTI-ICE
Primary windshield anti-icing is accomplished by directing condi-
tioned engine bleed air through ducting and control valves to external
outlet nozzles forward of the windshield. The windshield anti-ice sys-
tem consists of a shutoff valve, an anti-ice modulating valve, two low-
limit overheat thermoswitches, two high-limit overheat thermoswitch-
es, a green WSHLD HT light, an amber WSHLD OV HT caution light,
a ram air modulating valve, an anti-ice duct temperature sensor, an
anti-ice heat exchanger, two outlet nozzle assemblies, a system control
switch, and associated aircraft wiring and bleed-air ducting. Electrical
power to the control circuits is 28 VDC supplied through the 7.5-amp
WSHLD HEAT circuit breaker on the copilot’s circuit breaker panel.
WSHLD HEAT SWITCH
The windshield anti-ice system is controlled through the WSHLD
HEAT switch in the ANTI-ICE grouping on the center switch panel.
The switch has three positions: WSHLD HEAT (On), HOLD, and OFF.
When power is applied to the aircraft, or the BATTERY switches are set
On, the windshield anti-ice shutoff valve is energized to the open posi-
tion. When open, the shutoff valve allows engine bleed air to the anti-
ice modulating valve downstream. When the WSHLD HEAT switch is
placed in the On position, a circuit is completed to the anti-ice modu-
lating valve and WSHLD HT indicator light. The anti-ice modulating
valve will move toward full open until the valve is fully open or the
WSHLD HEAT switch is set to HOLD. When the switch is in the HOLD
position, the anti-ice modulating valve will remain in its last attained
position, and allow bleed air to the anti-ice heat exchanger. When the
WSHLD HEAT switch is set to OFF, the anti-ice modulating valve will
move towards the closed position until the valve is fully closed or the
WSHLD HEAT switch is set to HOLD. The anti-ice modulating valve
will fully open or close in approximately 15 seconds. The anti-ice heat
exchanger cools the bleed air with ram air regulated by a ram air mod-
ulating valve. This valve is controlled by the downstream anti-ice duct
temperature sensor and regulates the anti-ice bleed air temperature by
varying the amount of ram air allowed into the heat exchanger.
Change 6
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