controls to activate one or both fire-extinguisher
bottles. There is a test function for the fire de-
tection system. One or two portable fire extin-
guishers are stowed inside the airplane.
The airplane pneumatic system uses bleed air
extracted from the engine compressor sec-
tions. It includes controls for regulation and
distribution of air for heating, cooling, venti-
lation, pressurization, and anti-icing.
ICE AND RAIN PROTECTION
The anti-icing systems use engine bleed air,
electric heating, and alcohol.
Bleed air is used to heat the wing leading
edge, the windshields, and engine front frame.
Bleed air is also used to remove rain from the
windshield.
Electrically heated systems include the hori-
zontal stabilizer leading edge, nacelle lips,
pitot tubes, static ports, and the stall warning
vanes. Airplanes not certified for flight in
known icing do not have stabilizer heat.
An alcohol system is used for radome anti-
icing and to back up the pilot’s windshield
bleed-air anti-icing. Airplanes that are not
certified for flight in known icing supply al-
cohol to both the pilot and copilot windshields
and not to the radome. The Learjet 23 does not
have an alcohol system.
AIR CONDITIONING
AND PRESSURIZATION
The Freon refrigeration system is used for
ground cooling, in-flight cooling, and cabin
air dehumidification. Cabin heating is pro-
vided by electric cabin heat (optional) and
engine compressor bleed air used for cabin
pressurization.
Pressurization is provided by engine bleed
air. Cabin altitude is maintained by regulat-
ing the outflow of air from the cabin. The
pressurization module provides either auto-
matic or manual control of cabin pressuriza-
tion while airborne.
HYDRAULIC POWER SYSTEMS
The hydraulic system supplies pressure for
the operation of the landing gear, gear doors,
brakes, flaps, spoilers, and thrust reversers, if
installed. A single reservoir supplies fluid to
the two engine-driven pumps through the hy-
draulic shutoff valves. An electric auxiliary
pump in the tailcone is used for hydraulic
pressure on the ground when the engines are
not operating and in flight during a hydraulic
failure. It will supply pressure to all hydrauli-
cally operated systems on the airplane.
LANDING GEAR AND BRAKES
Learjet 20 models have retractable tricycle
landing gear which is electrically controlled
and hydraulically operated.
An emergency air bottle, located in the right side
of the nose compartment, can be used to extend
the landing gear or for emergency braking, or
both, in case of hydraulic or electrical failure.
The self-centering nose gear has a single wheel
and incorporates an electrical nosewheel steer-
ing system which has either variable or non-
variable authority, depending upon airplane
model and serial number.
Each main gear has dual wheels, each equipped
with multiple-disc brakes. Hydraulic braking
is controlled from either the pilot’s or copilot’s
station. An antiskid system provides maxi-
mum braking performance while protecting
against skids.
FLIGHT CONTROLS
Learjet 20 models use manually actuated pri-
mary flight controls. Pilot inputs are transmit-
ted via cables, bellcranks, and pushrods to the
ailerons, rudder, and elevators. There are no
hydraulic or electric power boosts for these
systems. Primary control trim is electrically
controlled and operated.
Secondary flight controls (spoiler and flaps) are
electrically controlled and hydraulically operated.
1-17
FOR TRAINING PURPOSES ONLY
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