on the radome. If necessary, this system may
be used as a backup for the windshield anti-
ice defog system for the pilot’s windshield.
There are two different systems in use. The sys-
tems are operated by DC power routed through
the ALC PUMP circuit breaker.
SNs 24-181 through -349, and
25-003 through -226, and
Earlier Airplanes Modified
for All-Weather Operation
A DC motor-driven pump supplies filtered al-
cohol from a 2 1/4 gallon reservoir to the
radome only or to the radome and pilot’s wind-
shield, depending on the position selected on
the WSHLD & RADOME switch (Figure 10-
11) on the pilot’s anti-icing control panel.
Figure 10-12 illustrates the early system.
When the switch is positioned to RADOME,
the pump is energized and alcohol is delivered
to the radome only. In this position, a fully ser-
viced reservoir should dispense alcohol for
approximately 1 1/2 hours.
When the switch is positioned to WSHLD &
RADOME, the pump is energized and alcohol
is delivered to both surfaces. Flow to the wind-
shield is dispensed through an orifice assem-
bly integrated with the pilot’s defog outlet. In
this position, a fully serviced reservoir should
dispense alcohol for approximately 45 minutes.
A pressure switch installed in the radome supply
line actuates the amber ALC AI light when the
reservoir is empty or if the pump fails. The light
extinguishes when the control switch is turned off.
SNs 24-350 and Subsequent,
and 25-227 and Subsequent
Methyl alcohol is stored in a 1.75-gallon reser-
voir. When the cockpit control switch is po-
s i t i o n e d t o W S H L D & R A D O M E o r t o
RADOME, circuits are completed to position
a three-way valve in the fluid supply line
(Figure 10-13) This position also opens the
shutoff valve and pressure regulator in the
servo bleed-air supply line.
Servo bleed air trapped from the bleed-air
manifold passes through the shutoff valve and
pressure regulator where it is regulated to 2.3
psi. The air is then routed to pressurize the al-
cohol reservoir.
The alcohol is forced through a filter to the
three-way valve which is positioned accord-
ing to the selected switch position.
The pressure relief valve, set to 2.6 psi, relieves
any overpressure in the reservoir should the
pressure regulator fail. Residual pressure bleeds
off when the control switch is turned off.
10-9
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
Figure 10-11.
WSHLD & RADOME Switch
SYSTEM RETURN
LINE
INSTRUCTION PLACARDS
INSTRUCTION
PLACARDS
FILLER CAP
FILLER CAP
CHECK VALVE
VENT LINE
SUPPLY TANK
SUPPLY TANK
OVERBOARD VENT LINE
REGULATED
PRESSURE
LINE
AIRPLANES 25-061, 25-070 THROUGH 25-226
AIRPLANES 25-227 AND SUBSEQUENT, 24-350
AND SUBSEQUENT
Figure 10-10.
Alcohol Reservoir
