AIR CONDITIONING AND PRESSURIZATION
Description
Aircraft Operations Manual
2.1
PAGE
5
Jun 01/18
sec. a timer will give a control command driving
the valve to fully open position.
With Mod. No. 1994 installed:
The primary electro
−
pneumatical outflow valve is
modulated towards its closed position permitting
cabin pressurization at a rate of 300 ft/min (at
detent position) to 140 ft below actual cabin alti-
tude existing prior to power levers advancement.
If both power levers are retarded below the min.
takeoff power position the primary electro
−
pneu-
matic valve modulates a cabin uprate of 500 ft/
min. After 20 sec. a timer will give a control com-
mand driving the valve to fully open position.
−
Climb mode
At Liftoff as sensed by the weight
on wheel switches the system transfers to climb
mode. The pneumatic outflow valve will remain
closed and the electro
−
pneumatical valve is regu-
lated by the controller. The controller computes
the barometric corrected selected LDG ALT and
the sensed aircraft altitude. These parameters
are compared with the computed auto
−
schedule
to establish a control point for cabin pressure
regulation. The rate of change is set to 500 ft/min
(at detent position) for uprate and a zero descent
rate. If the actual takeoff altitude is less than the
selected LDG ALT, the control point is initially set
to the LDG ALT. The controller starts to uprate
the cabin until it intercepts the auto
−
schedule
when it change control point and follows the
auto
−
schedule.
If the actual takeoff altitude is greater than the
selected LGD ALT, the takeoff altitude will be
maintained until the auto
−
schedule exceeds the
takeoff altitude. As the aircraft climb and the
auto
−
schedule exceed the takeoff altitude, the
controller switch will effect an uprate and follow
the auto
−
schedule.
If the system fails to switch to flight mode at lift-
off, a backup feature in the pressurization con-
troller will transfer the system to flight mode
when aircraft altitude exceeds 15 000 ft. In addi-
tion the controller will ensure that the differential
pressure never exceeds 7.1 psi. At takeoff with
both BLD VALVES switched off both outflow
valves will be closed. When switching on the first
BLD VALVE the pressurization system goes di-
rectly into climb mode.
−
Cruise mode
When the aircraft reaches its cruis-
ing level and the altitude change is less than 200
ft per minute the system transfers to cruise
mode. Setting the cruise mode effects two
changes in the control logic:
the down rate limit is revised from zero to 300
ft/min at detent position.
the cabin altitude is clamped at the control
point, the cabin altitude will remain unchanged
for flight disturbances not exceeding 100 ft
climb and 200 ft descend in aircraft altitude.
However a change in LDG ALT or barometric
setting will cause either an up or down rate of
cabin altitude. When the aircraft climbs more
than 100 ft or descends more than 200ft below
the clamped altitude the clamp will be deleted
and a new control point will be established
when the altitude change again is less than 100
ft per minute.
−
Descent mode
When the aircraft descends 200
ft in less then one minute or descends more than
500 ft regardless of time the system transfers to
descent mode. The cruise clamp is deleted and a
new control point is established which is the high-
er of either selected LDG ALT or the auto
−
sched-
uled altitude. The controller starts to downrate
the cabin and maintains the new control point.
−
Landing mode
When the controller receives sig-
nals from the weight on wheel switches at touch
down, and aircraft altitude is less than 15000 ft,
the system is transferred to landing mode.
Without Mod. No. 1994 installed, the pneumatic
outflow valve will go to fully open position and the
electro
−
pneumatic valve will modulate a cabin
uprate of 500 ft/min.
With Mod. No. 1994 installed, the pneumatic out-
flow valve will remain closed and the electro
−
pneumatic valve modulates a cabin uprate of 500
ft/min.
After 20 sec. a timer will give a control command
driving the valve to fully open position, the 20
sec. cabin uprate is to eliminate any error in se-
lected LDG ALT or barometric correction.
