Pneumatic Systems
Citation Bravo Developed for Training Purposes 5K-25
March 2009
AIR DUCT O'HEAT
Annunciator
The amber AIR DUCT O'HEAT
annunciator advises the pilot that the
temperature in the duct leading to
the cabin exceeds 315 ±8°F. The air
duct overheat sensor is downstream
from the water separator.
Emergency
Pressurization
If the pilot selects EMER pressuriza-
tion on the PRESS SOURCE selec-
tor switch or an overheat condition
occurs in the ACM, the emergency
pressurization valve, off the left
bleed air cluster, is automatically
powered open. Both bleed air flow
control valves are powered closed.
On the ground, the left squat switch
input prevents the emergency pres-
surization valve from opening.
The emergency pressurization valve
routes left engine hot bleed air
through the mixing tube into the
cabin where it mixes with recirculat-
ing air to maintain cabin pressure
during emergency pressurization.
The pilot manually opens the emer-
gency pressurization valve through
the selection of EMER on the
PRESS SOURCE selector switch.
The overheat sensor in the ACM acti-
vates emergency pressurization if the
temperature between the compressor
and the secondary heat exchanger
exceeds 450°F.
If the ACM cools sufficiently within
12 seconds, the system automatically
returns to normal operation. If the tem-
perature does not drop sufficiently
within 12 seconds, rotate the PRESS
SOURCE selector switch to the
EMER position to reset the lockout
relay (make switch match the valve).
Then wait at least one minute before
performing the next step. Rotate the
PRESS SOURCE selector switch to
LH, RH, or NORMAL to return all the
valves to their normal positions. Con-
sider selecting the LH or RH position
to temporarily reduce the volume of
air flow through the ACM.
EMER PRESS ON
Annunciator
The EMER PRESS ON annunciator
illuminates to notify the crew of an
emergency pressurization situation.
The annunciator illuminates through
manual selection of the emergency
pressurization or with automatic acti-
vation due to an ACM overheat. If
emergency pressurization is selected
on the ground, manually or automati-
cally, the annunciator illuminates but
the emergency pressurization valve
does not open.
Mixing Tube
A multi-function mixing tube is
under the aft cabin flooring. During
emergency cabin pressurization
operation, bleed air from the emer-
gency pressurization valve ejects
through a nozzle into the mixing
tube. A check valve assembly allows
cabin air to mix with emergency
pressure bleed air.This lowers the
bleed air temperature as it enters the
air distribution system. Cabin pres-
surization remains without the bene-
fit of the ACM.
Tailcone
Pressurization
The tailcone pressurization system
consists of a ram air scoop, a five-
inch diameter dorsal fin air duct, and
a cover plate over a gap aft of the
vertical fin spar.
The ram air scoops, located in the
dorsal fin provide pressurized air for
the tailcone and fresh air for the cabin
when the cabin is not pressurized.
The cover plate reduces leakage out
of the tailcone, reducing the amount
of required pressurization air.
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