Hawker 800 XP Pilot Training Manual Download

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GENERAL

When pressurization and air conditioning are
in use, a supply of air is fed into the pressure
cabin. Outflow is controlled by a cabin pres-
sure controller and by two outflow/safety
valves. The pressure controller regulates both
the discharge of the air and the discharge rate.
The rate control affects the cabin rate of
climb/descent.

The pressurization system can maintain a cabin
altitude of 8,000 feet at an airplane altitude of
43,000 feet at 8.55 psi maximum cabin dif-
ferential pressure.

If a crewmember selects a cabin differential
greater than 8.55 psi, a safety device on the out-
flow/safety valve prevents the cabin pressure
from exceeding 8.6 to 8.8 psi. If an attempt is
made to position the airplane so that the 8.55
psi cabin differential pressure is exceeded, the
same safety device causes the cabin pressure to
decrease at the same rate the airplane climbs.

During a rapid descent, if the ambient pressure
exceeds cabin pressure, another safety device
allows ambient pressure to enter the cabin,
preventing a negative cabin differential pres-
sure from exceeding 0.5 psi.

The 8,000 feet cabin altitude ensures that no pas-
senger discomfort associated with hypoxia is ex-
perienced during normal high-altitude flight.

DESCRIPTION

The pressurization system (Figure 12-l) in-
cludes a CABIN CONTROLLER, two out-
flow safety valves, two pneumatic relays, a
venturi, an air jet pump, two pressure regula-
tors, a fan-operated venturi, and controls and
indicators. Two controls labeled “MANUAL
CABIN ALTITUDE CONTROL” and “PRES-
SURIZATION CONTROL” permit manual
control of the system.

CABIN CONTROLLER

The CABIN CONTROLLER (pressure con-
troller) (Figure 12-1), located on the copilot’s
i n s t r u m e n t p a n e l , e n s u r e s t h a t t h e
outflow/safety valves maintain a selected cabin
altitude and that the cabin air pressure changes
at an acceptable rate during climb or descent.
The controller has two knobs. The center knob
is labeled “CABIN”; the knob on the lower left
is labeled “RATE.”

The CABIN knob controls rotation of a dial
containing an inner and outer scale. Both
scales indicate altitude and are graduated in
feet x 1,000. The outer scale displays the se-
lected cabin altitude. With the cabin altitude
selected, the airplane’s altitude at which the
maximum cabin differential will be reached is
displayed on the inner scale. This provides
an 8,000 feet cabin altitude at an actual airplane
altitude of 43,000 feet.

The RATE knob is used to adjust cabin alti-
tude rate of change. This range is from ap-
proximately 2,000 fpm (MAX setting) to 50
fpm (MIN setting). Positioning the arrow ver-
tically provides a rate of change of approxi-
mately 500 fpm.

OUTFLOW/SAFETY VALVES

Controlled by the pressure controller, the two
outflow/safety valves permit a controlled dis-
charge of cabin air. The valves incorporate
s a f e t y d ev i c e s w h i c h p r eve n t a p r e s s u r e
buildup in excess of the maximum cabin dif-
ferential of 8.6 to 8.8 psi and of the negative
pressure differential of 0.5 psi. They are lo-
cated on the rear pressure bulkhead.

PNEUMATIC RELAYS

Two identical pneumatic relays sense pressure
changes within the controller and transmit
these changes to the outflow/safety valves.
The relays are located on the rear pressure
bulkhead. They amplify the pressure changes
from the controller located in the cockpit,
thus improving system response.

Hawker 800 XP, Pilot Training Manual

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