Learjet 60 - Page 244

Pilot's Manual

Learjet 60
When the system is in the automatic mode, the electronic controller
maintains cabin pressure based on air data from the aircraft's
air
data
computers,
landing field elevation selected on the LDG ALT
selector,
position of the thrust
levers, position of the landing gear squat switch,
and the system's
preprogrammed climb and descent schedules . The
electronic controller features
built-in test equipment which performs
fault detection and
annunciation routines during ground and
flight
operation . Should
a fault be detected, the FAULT
annunciator on the
mode switch will
illuminate and the system will
automatically revert
to manual mode .
Depressing the mode switch
will extinguish the
FAULT
annunciator and illuminate the MANUAL
annunciator .
When
the system is in the manual or
fault modes, the crew maintains
the
desired cabin pressure using
the MAN ALT and MAN RATE con-
trols to position the outflow
valves . Moving the MAN ALT control to
UP or DN controls the
outflow valves directly causing them to open
or close as appropriate
until the MAN ALT control is moved to the
center position . The
desired cabin altitude is then controlled by the
crew by reference
to the pressurization indicator . The rate
at which
the outflow
valves will respond to MAN ALT control
movement is
controlled
by rotating the MAN RATE knob from MIN to
MAX as de-
sired
.
EMERGENCY PRESSURIZATION
In the event of normal
cabin airflow malfunction, emergency pressuri-
zation is provided
by routing low pressure engine bleed air directly
into the cabin through
the emergency pressurization valves . Emergen-
cy pressurization is
accomplished automatically by opening the emer-
gency
pressurization valves in response to signals from the aneroid
switches when the cabin altitude increases to 9500 (±250) feet or man-
ually by setting the BLEED AIR switches to EMER . When the aircraft
is below 25,000 feet pressure altitude and the system is in automatic
mode with a takeoff or landing field elevation greater than 8000 feet
specified, the aneroid switches will not trigger the emergency pressur-
ization unless the cabin altitude increases to 14,500 (±250) feet . Emer-
gency pressurization is provided by two independent circuits - left
and
right
. If
triggered automatically, the left and right
circuits
will
ac-
tivate approximately at the same time in response to the aneroid
switch signals . If triggered manually, the left and right circuits may be
activated separately . When emergency pressurization is triggered the
following events occur :
6-26
"

Emergency pressurization valve opens
"

The bleed-air mix valve
goes
to the
low-pressure bleed port
PM-123
Change 3