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Ventilation
The avionics are cooled through a system that uses two openings and two
electric fans. Conditioned air is also available for backup if needed. Yes, a
computer controls the whole thing (sigh).The intake is on the lower left side
below the cockpit. A blower fan draws air in and the extract fan on the right side
exhausts the air out from a port below the cockpit on the lower right side.
Open configuration: Only for ground operations, both the inlet and outlet vents
are open and both fans operate. Note: during heavy rain operations on ground
select EXTRACT pb to OVRD with both packs operating. This will prevent rain
from entering the avionics bay. Return to normal auto operation once airborne
(see PH 3.2.5 for parameters).
Closed configuration: In-flight mode and very cold ground operations. Both vents
are closed, however both fans run to circulate air past skin heat exchangers that
US Airways Airbus A319, A320, A321 Notes
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are cooled by low outside skin temperatures. Some air exhausted through cargo
underfloor. Also known as the infamous Skin Cooling Config.
Intermediate configuration: Only for use in-flight when warm, same as closed
except reduced opening to allow some additional exhaust of cooling air.
Abnormal configuration: Fault is detected in either the BLOWER or EXTRACT
fan. Blower fan is off but Extract remains ON. Similar to closed except air
conditioned air is added to the circulated air. ECAM will direct configuration.
Smoke configuration: If smoke is detected in avionics both the BLOWER and
EXTRACT fan will have amber FAULT lights on and the GEN 1 LINE pb (on
EMER ELEC PWR panel) has amber SMOKE illuminated. Selecting BOTH fans
to OVRD will cause the blower to stop but the extract to continue operating.
Conditioned air is added to attempt to cool and clear the smoke, then exhausted
overboard.
US Airways Airbus A319, A320, A321 Notes
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Hydraulics, Brakes & Landing Gear
There are three hydraulic systems: green, blue and yellow. All three systems are
independent of each other and do not transfer fluid at any time. Each system has
its own accumulator. Priority valves ensure proper pressure to critical users when
system pressure is low.
Green system – 1 pump: engine driven. Two power sources: engine 1 pump &
PTU
Blue system – 2 pumps: 1 electric and the emergency RAT. Two sources of
power: electric pump & RAT pump.
Yellow system – 3 pumps: 1 engine, 1 electric & 1 hand pump. 4 sources of
power: engine 2 pump, electric pump, hand pump and PTU.
Green is the “heavy” system with landing gear, flaps/slats, nosewheel steering
and Normal Brakes.
Blue is basically for redundancy with the only unique items on it being L & R
spoiler 3 and the Emergency Generator which are “backup” items themselves.
Yellow provides the ground service items of parking brake and cargo door and
also helps power the flaps.
The RAT and Yellow electric pumps do not normally run during flight. The Yellow
electric pump will automatically come on when a cargo door is operated. Other
Yellow system functions are inhibited when automatically activated by a cargo
door. A hand pump is provided on the Yellow system to provide the ability to
open cargo doors with no electric power on the aircraft. Blue electric operates all
the time in-flight and on the ground when at least one engine is operating.
The RAT hydraulic pump is for emergency use only and will only deploy
manually for hydraulic problems. For electrical problems it will deploy
automatically above 100 kts. with loss of all AC. Note: Min RAT speed is 140 kts.
with A319/321 and modified A320 RATs stalling at less than 125 kts. This speed
limit is for electrical power and the RAT will continue to supply hydraulic power to
much slower speeds.
The PTU (Power Transfer Unit) is able to transfer power but not fluid. It transfers
power between the Green and Yellow systems (the two with the engine pumps
and heavy consumers). The PTU can transfer power in either direction and is
activated when a 500 psi differential is sensed between Green and Yellow. The
PTU can also be powered on the ground by the Yellow electric pump to power
Green hydraulic. Allows Yellow electric pump to power Green on ground (for
example to retract slats on ground).
US Airways Airbus A319, A320, A321 Notes
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The PTU is inhibited when:
 First engine is being started. This is identified as when the nosewheel
steering disconnect pin is in and only one ENG MASTER switch is ON. (PTU
operation is tested on second engine start)
 Cargo doors are operated (Yellow electric normally powers cargo doors, this
　
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