WING AND HORIZONTAL
STABILIZER ANTI-ICE SYSTEM
Wing Heat
Bleed air is used to prevent ice formation on
the wing leading edges. The bleed air is di-
rected from the bleed-air manifold through a
solenoid-operated pressure-regulator valve
(control valve) (Figure 10-14) to the respec-
tive leading-edge surfaces.
Controls and Indications
The STAB & WING HEAT switch (Figure 10-
14) is located on the pilot’s anti-icing control
panel. When the switch is turned to ON, the
valve is energized open. With the switch in
OFF or if DC power fails, the valve fails to the
closed position.
With the valve open, bleed air is routed through
the wing pressure-regulator valve where it is
regulated to 16 psi and then routed on to tubes
in the leading edges of the wing. After the
bleed air has heated its respective leading
edge, it continues outboard where it is vented
overboard through a scupper drain on the bot-
t o m , o u t e r e d g e o f t h e w i n g . T h e W I N G
OV’HT light (see “Annunciator Panel” section)
on the glareshield illuminates when the right
wing leading-edge structure temperature
reaches 215ºF. The system must not be oper-
ated when the light is illuminated. The ther-
mocouple that operates the light is located at
the right wing fuselage root on the structure.
A wing temperature indicator (Figure 10-15)
located on the pilot’s subpanel has three col-
ored ranges on a round dial. From left to right,
these arcs are red, green, and yellow.
Red arc—Wing temperature is below 35ºF.
Green arc—Wing temperature is above 35ºF
and below 215ºF.
Yellow arc—Wing skin temperature is above
215ºF. (When in the yellow arc, reduce rpm,
and also monitor pressurization.)
NOTE
On SNs 25-260 and 24-358 and sub-
sequent, the red segment has been
changed to blue and the yellow seg-
ment has been changed to red.
Stabilizer Heat
The horizontal stabilizer leading edge is pro-
tected from ice accumulation by an anti-ice
system consisting of two electrical blankets
c o n t r o l l e d b y a S TA B & W I N G H E AT
ON–OFF switch (Figure 10-14) located on
the pilot’s subpanel. With the switch in ON,
electrical power is supplied from the battery-
charging bus through a relay to the sequence
timer which controls the heating elements.
On the ground, stabilizer heat is disabled by
the right squat switch.
10-13
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
Figure 10-15.
Wing Temperature Indicator
