Learjet 60 - Normal Pressurization; Pressurization System

Pilot's Manual
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Learjet 60
PRESSURIZATION SYSTEM
Cabin
pressurization is provided by
conditioned air entering the cab-
in through
the air distribution ducts and
controlled by modulating
the amount
of air exhausted from the cabin
. The pressurization sys-
tem consists
of a cabin primary outflow valve,
a cabin secondary out-
flow valve, an
electronic pressurization
controller, a LDG ALT selec-
tor, a MAN
ALT control valve with rate
control, a MODE switch,
an
EMER
DEPRESS switch, a
pressurization vacuum jet
pump, a vacu-
um
regulator, a pressurization
indicator, two emergency
pressuriza-
tion
valves, two emergency
pressurization aneroid switches,
an am-
ber
PRESS SYS caution light, an
amber EMER PRESS
caution light,
and an
aural warning system .
All system controls are
located in the
PRESSURIZATION group
on the copilot's switch
panel . The pressuri-
zation indicators are located
directly above the
system controls . Pow-
er
for the control circuits
is 28 VDC supplied
through the 5-amp CAB-
IN PRESS SYS circuit
breaker on the copilot's
circuit breaker panel .
Power for the pressurization
indicator is 28 VDC
supplied through
the 2-amp CABIN
PRESS IND circuit breaker
on the pilot's circuit
breaker panel
. Automatic and manual
pressurization modes are
avail-
able during
EMER BUSmode . The
pressurization indicator is
opera-
tive during EMER
BUS mode .
NORMAL PRESSURIZATION
Normal
pressurization is controlled
by regulating control pressure to
the
cabin primary and secondary
outflow valves . The control
pres-
sure
may be regulated automatically
by the electronic pressurization
controller or manually by the
MAN ALT control knob . A
pressuriza-
tion vacuum jet pump provides
vacuum (servo pressure) to
operate
the outflow valves . MANUAL
mode operation is completely
indepen-
dent of the aircraft electrical
system . If the cabin-to-ambient differen-
tial pressure reaches 9 .7 psid, the
positive pressure relief metering
section
of the outflow valves will cause
the outflow valves to open
and
maintain a 9 .7 psi differential . The outflow
valves incorporate a
cabin altitude
limiter which limits cabin altitude to
approximately
13,700 (±500) feet
should the system fail to maintain the normal cabin
altitude . Should
the cabin altitude reach approximately 13,700 (±500)
feet, the altitude
limiters will vent cabin pressure to the outflow
valve
control chambers causing the
valves to close . Should a rapid descent
cause a negative pressure
in the cabin, both the primary and secon-
dary outflow valves will open to vent ambient atmospheric
pressure
to the cabin .
6-24
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PM-123
Change 2