Saab 340B, Руководство по эксплуатации

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AIR CONDITIONING AND PRESSURIZATION
Description
Aircraft Operations Manual
2.1
PAGE 1
Jun 01/18
1. GENERAL
1.1 Air conditioning
Air conditioning is furnished by two packs located
under the cabin floor in the wing fairing.
The temperature of the outgoing air is either auto-
matically or manually controlled from the cockpit.
The actual temperature regulation is performed by
mixing hot air directly from the pneumatic system
with air that has been cooled by the main unit of the
pack
− the air cycle machine. The conditioned air
from the left pack is then distributed to the cabin
and from the right unit to the cockpit and cabin.
The two distribution systems are connected by a
cross manifold for transfer purposes, controlled by a
cross valve. The valve may only be open on the
ground. Each distribution system recirculates the air
to improve air flow.
An external air conditioning system can be connec-
ted to the aircraft when parked.
In case of over − temperature, the pneumatic system
bleed valve will close and a DUCT OV TEMP light
in the AIRCOND panel will come on together with
AIRCOND master caution.
1.2 Pressurization
The cabin is pressurized by the two air conditioning
packs. The system is so designed that it is sufficient
with one pack for pressurization up to 31 000 ft.
However, the engine bleed extraction requirement
must be observed above 25 000 ft. (See AOM
17.1.)
The cabin pressure is either automatically controlled
by a pressurization controller, or manually controlled
by means of a control valve operated from the con-
trol panel in the cockpit.
The automatic control system is the one normally
used. It receives power lever position, static pres-
sure, cabin pressure, preselected airfield altitude,
weight on or off wheels and pressure values from
the control panel. These parameters are processed
in a control unit which then electrically regulates the
electro
− pneumatic primary outflow valve to maintain
the correct pressure.
The manually controlled system is an all pneumatic
system. The pilot operates the pneumatic second-
ary outflow valve by adjusting the control valve set-
ting while watching the cabin pressure instruments.
With Mod. No. 1994 installed and in auto mode the
pressurization control system dumps cabin pres-
sure by opening the primary electro
− pneumatic out-
flow valve when on ground, the pneumatic second-
ary outflow valve will remain closed. Both outflow
valves can be opened by means of an emergency
dump switch in the cockpit when on ground. In the
air (flight mode) the dump switch only activates the
primary electro
− pneumatical outflow valve. Both
outflow valves incorporate positive and negative
pressure relief functions.
Without Mod. No. 1994 installed and in auto mode,
the pressurization control system dumps cabin
pressure by opening both outflow valves when on
ground. The electro
− pneumatical outflow valve can
also be opened by means of an emergency dump
switch in the cockpit. Both outflow valves incorpor-
ate positive and negative pressure relief functions.
Cabin pressure is displayed on three indicators in
the cockpit. The indicators show differential pres-
sure, cabin altitude and cabin altitude rate
− of −
change.
A CABIN PRESS master warning on the central
warning panel is activated if cabin climbs above
10 000 ft or if the differential pressure exceeds 7.5.
psi.
2. MAIN COMPONENTS AND SUBSYSTEMS
2.1 Air conditioning system (Fig. 1 and Fig. 2)
Air conditioning pack
Hot air from the pneumatic system is used for
conditioning of the cockpit and cabin. The air condi-
tioning temperature is regulated by two packs.
A dual temperature control valve controls each pack
by modulating the amount of air directed to an air
cycle machine for temperature decrease (pack
valve) and the amount of air bypassing the aircycle
machine (bypass valve). The bypass valve and the
pack valve are linked together and operate in se-
quence so that when the bypass valve is moved