Bleed air from the engine compressor section is
delivered to a bleed-air manifold in the
unpressurized aft compartment (tailcone). The
air from this bleed-air manifold is used for
cabin pressurization and heating, wing anti-
icing, windshield anti-icing, pressurization
control (except early 23, 24, and 25 models),
and hydraulic reservoir pressurization on SNs
24-297 and subsequent, 25-135, and 25-181
and subsequent.
SNs 24-350 and subsequent and 25-227 and
subsequent also use servo bleed air from
radome/windshield alcohol anti-icing, operation
of the emergency pressurization valves, and
cabin pressurization and temperature control.
Control of bleed air is accomplished with the left
and right AIR BLEED switches located on the
copilot’s lower instrument panel. Visual
indications of bleed-air duct overtemperatures
are given by illumination of warning lights
on the glareshield annunciator panel (see
“Annunciator Panel” section).
INTRODUCTION
The Lear 20 series pneumatic system uses bleed air extracted from the engine compressor
section. Bleed air is used for cabin pressurization and heating and anti-icing systems on all
airplanes, and servo air is used for hydraulic reservoir pressurization, pressurization control,
temperature control, and radome/windshield alcohol anti-icing on later models. Compressor bleed
air is also used for engine front frame anti-icing. There are two basic pneumatic system
configurations—one for SNs 23-003 through 24-349, and 25-003 through 25-226, and one for
SNs 24-350 and subsequent, and 25-227 and subsequent. The later system incorporates a major
design change including the installation of emergency pressurization valves.
GENERAL
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