PNEUMATICS
AIR CONDITIONING
AND PRESSURIZATION
AIRPLANE
OPERATIONS
MANUAL
2-14-15
Page
4
Code
01
REVISION 29
AUTOMATIC PREPRESSURIZATION SEQUENCE ON GROUND
This sequence is initiated and maintained as long as the airplane is on
the ground and the engine 1 thrust lever is set to THRUST SET
position or above. It causes the cabin altitude to descend toward an
altitude equivalent to 0.2 psi (15 mbar) below the takeoff altitude.
The purpose of the automatic prepressurization is to avoid cabin
bumps due to the irregular airflow on the fuselage during rotation and
takeoff and also to keep a controlled cabin altitude just after rotation,
as the cabin altitude tends to follow the airplane altitude.
In the case of takeoff with air conditioning supply, the cabin altitude is
controlled with an altitude rate of descent equal to –450 ft/min.
In the case of takeoff without air conditioning supply, the outflow valves
are closed, also avoiding cabin bump.
TAKEOFF SEQUENCE
This sequence is initiated after the airplane leaves the ground with the
purpose of avoiding reselecting the landing altitude, in case it is
necessary to return to the takeoff airport.
It causes the cabin altitude to continue descending towards the altitude
equivalent to 0.2 psi below the takeoff altitude. If an altitude of 0.2 psi
below the takeoff altitude has already been reached during the
pre-pressurization sequence, the cabin altitude does not change.
The takeoff sequence lasts until the theoretical cabin altitude becomes
greater than the actual cabin altitude, or until 15 minutes have elapsed
since the sequence initiation, whichever occurs first.
FLIGHT SEQUENCE
This sequence is initiated after the takeoff sequence is finished, to
establish a cabin altitude and a cabin altitude rate of change during
flight. The Digital Controller schedules a cabin altitude that is the
greatest value between the theoretical cabin altitude and the selected
landing altitude minus 11 mbar (300 ft at SL).
The cabin altitude rate of change is controlled at different values
depending on the scheduled cabin altitude and the airplane vertical
speed, but is limited to –450 ft/min during descent and as following
while climbing:
− 500 ft/min (for airplanes Pre-Mod. SB 145-21-0006);
− 600 ft/min (for airplanes Post-Mod. SB 145-21-0006 or S/N 145.050
up to 145.362);
− 700 ft/min (for airplanes S/N 145.363 and on).
Barometric correction, when required, is automatically provided by the
Air Data Computer (ADC).
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