With the airplane in flight and the STAB &
WING HEAT switch in ON, intermittent DC
electrical power is distributed by the sequence
timer to individual heating elements in the
blankets. Power is distributed in a forward-to-
aft sequence of 15 seconds duration each. The
single leading-edge element is suppled with
continuous electrical power. An amber STAB
HEAT light (see “Annunciator Panel” section)
on the glareshield illuminates when power is
lost to the leading-edge wire. The airplane
ammeters reflect a cyclic current drain of ap-
proximately 60 amperes total in 15-second
cycles. This indicates proper operation of the
system.
PITOT, STATIC, AND ANGLE-
OF-ATTACK VANE ANTI-ICE
SYSTEM
Pitot and Angle-of-Attack Vane
Anti-icing
The left and right pitot tubes and angle-of-at-
tack (AOA) vanes (Figure 10-16) contain elec-
trical heating elements.
When the L and R PITOT HEAT switches
(Figure 10-17) located to the pilot’s subpanel
are in ON, both pitot tubes and both stall vanes
are heated. A condensate drain valve is installed
for each system. One is located adjacent to each
nose wheel well door. Some airplanes may have
a light to indicate that a system has failed or that
the PITOT HEAT switch is not turned on.
The static port heaters are wired through the re-
spective PITOT HEAT circuit breakers but not
through the PITOT HEAT switches. Therefore,
static port heat operates when either battery
switch or generator is turned on. The rear static
port on the right side is unheated.
There are two shoulder static ports located on
top of the nose in front of the windshield.
These two static ports provide static pressure
to the autopilot altitude controller. A con-
densate drain valve is installed adjacent to the
left nosewheel gear door.
On aircraft with the Learjet Century III wing,
the shoulder ports are heated whenever a bat-
tery or generator is turned on and the PITOT
HEAT circuit breakers are set.
10-14
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
Figure 10-16.
Pitot Tubes and AOA Vanes
Figure 10-17.
L and R PITOT HEAT
Switches
