A340 / A330 Pneumatics
The pneumatics supply high pressure air, from either engine bleed systems, APU load compressor or 2 HP ground connections, for aircon, engine
starting, wing anti-icing, water pressurisation, hyd reservoir pressurisation and pack bay ventilation turbofan actuation. The engine bleed systems
are interconnected by a crossbleed duct through a crossbleed valve, to which the APU and ground source are connected. The system is controlled
and monitored by 4 / 2 Bleed Monitoring Computers, the pilot overhead control panel and the ECAM. Each engine bleed valve is electrically
controlled and pneumatically operated. Air is normally bled from the IP stage of the HP compressor; when this is insufficient, HP stage air is bled,
which limits pressure to 36/40±4psi. An intermediate pressure check valve downstream of the IP port closes to prevent HP air being passed to the
IP stage. The crossbleed valve is electrically controlled from a rotary selector and is driven by either of 2 motors, one for auto mode and one for
manual. In the automatic mode, the crossbleed valve opens when APU bleed air is used and closes when any air leak is detected except during
Regulation and Limitations
Downstream of the HP/IP ducting air passes through the Bleed Valve which acts as a PRSOV, controlling pressure to 38-48 (44-52)psi, depending
on the flow and on the A340 only, is modulated to balance the flow bled from each engine on the same wing. The pressure can be reduced in case
of over-temperature at the pre-cooler inlet. Pressure is safety limited to 85psi by the overpressure valve; the ECAM goes amber at <4psi and
>60psi. The bleed valve is fully closed pneumatically by upstream pressure <8psi, return flow or engine fire and electrically by the BLEED pb
switch when OFF, the ENG FIRE pb, the BMC (for overtemp, over-pressure, leak, APU bleed ON and starting). Temperature regulation is managed
by a pre-cooler which uses cooling air bled from the engine to achieve 200°C. ECAM goes amber for overheat at 290°C for 5secs, 270/15 or
257/55 or low temperature. Fan airflow is controlled by the Fan Air Valve, which is spring loaded closed in the absence of pressure. When wing
anti-ice is off, the temperature may be 150°C upon zone controller demand.
APU & Ground Air Supply
APU bleed air is controlled by the APU bleed valve selected by the APU BLEED pb switch, which doubles as a shut-off valve. APU bleed air is
available if APU rotor speed > 95%. A check valve near the crossbleed duct protects the APU when air is bled from another source. Leak detection
is ignored during engine start. Air may be supplied by 2 HP ground air connectors. The crossbleed valve must be manually opened to provide air
to both side and all packs, engine and APU bleeds must be deselected to avoid contamination.
Leaks and Failures
Sensing elements are connected to form a single loop for the pylons and APU and a double loop for the wing. A wing system uses modified AND
logic. The system has identical control logic included in each BMC.
For a wing leak, both bleed valves and HP valves on the related side close, both FAULT light on the AIR panel illuminate, the crossbleed valve
closes and the APU bleed valve if it is open, and if the leak is on the left wing, closes .
For a pylon leak, both bleed valves and HP valves on the related side close and the assoc FAULT light for that engine illuminates.
For an APU leak, the APU bleed valve closes, the FAULT light on the APU BLEED pb switch illuminates and the crossbleed valve closes.
In the case of BMC failure, the other one on the same side takes over most of the monitoring functions and provides an ECAM warning of ENG #
BLEED FAULT, WING LEAK or BLEED LO TEMP. The assoc FAULT light is lost and the bleed valve does not auto close. APU leak detection and ENG
BLEED LEAK warning is lost if BMC 2 / 1 fails.
Aircon & Pressurisation
2 packs operate automatically and independently of each other, being controlled by a dual channel zone controller and a pack controller. The pack
valve is auto controlled open except when upstream pressure below minimum, compressor outlet overheat, engine start sequence, any door is not
closed and locked (on the ground with any engine running), FIRE pb depressed for an engine on the related side or ditching selected. During the
engine start sequence, the pack valves close if the ENG selector is set to IGN when on the ground or the ENG selector is set to IGN (or CRANK) and
when on any engine the MASTER switch is set to ON (or the MAN START pb switch is set to ON) and the start valve is open and N2<50%. On the
ground, the valves re-open after 30secs if there has been no subsequent start. Bleed air is pre-cooled by fan air before entering the ACM. A failed
ACM can be bypassed to allow the bleed air to be cooled by the assoc heat exchanger only. Temperature regulation is automatic. The pack
controller responds to zone controller demand signals to modulate the air flow and temperature through its respective control valves, ram air inlet
and outlet flaps. If both packs fail or for smoke ventilation, the ram air inlet may be opened (as long as delta p < 1psi) by the RAM AIR pb switch
provided ditching is not selected: to permit unrestricted ventilation, each outflow valve half opens provided that it is not under manual control.
(The ram air inlet flaps are closed for TO and landing). The pack flow can be selected by the crew according to pax load (LO when total pax < 140
in EY) and external conditions: whatever the setting, high flow is auto-selected when in single pack operation (which increases cruise fuel burn by
1.0% / 0.5% [3.05.15 p19] or with APU bleed supply. The zone controller provides temperature regulation of the three cabin zones and the
cockpit. The cockpit is supplied with fresh air from the mixer unit. The cabin air receives mixer unit air mixed with recirculated cabin air. If low
flow is insufficient, the zone controller will produce an ECAM advisory (PACK LO FLOW). If the cooling demand in one zone is too high for that
bleed pressure, the zone controller demand both engines EIU to increase idle speed, or the APU ECB to increase outflow. If the cooling demand
cannot be satisfied, the zone controller signals the BMC to decrease bleed temperature, through the fan air pre-cooler, from 200°C to 150°C unless
wing anti-ice is on.
Reference temperature is selected in the cockpit and cabin temperatures may be modified through the Flight Attendants' Panel. Cabin temperature
is adjusted for an automatic altitude correction. The selectable temperature range is 18°C to 30°C and is controlled by one zone controller and 2
pack controllers. 2 Hot Air valves, controlled by HOT AIR 1/2 pb, regulate the pressure of hot air upstream of the packs. A Hot Air crossbleed valve
is fitted between the 2 hot air manifolds, which is normally closed but opens automatically when one hot air supply fails. 2 Trim Air valves for the
cabin and one for the cockpit (although the other does also feed the cockpit!) optimise the temperature by adding hot air from the air manifold.
Failures & Warnings
Failure of a single pack or zone controller channel has no effect. A double pack controller channel failure causes the anti-ice valve to add hot air at
the turbine outlet and controls the pack outlet temperature to a fixed value of 5°C±4°. ECAM signals from that pack are lost. The flow control
valve regulates the flow pneumatically to the NORM value. A zone controller double channel failure causes loss of optimised temperature
regulation, trim air valves freeze position, a PACK REG ECAM message and pack outlet temperature is fixed at 20°C. The compressor outlet
temperature becomes amber >230°C, the pack outlet temperature becomes amber >95°C. The pack trips for outlet temperature exceedance
for the compressor at >260°C and for the pack outlet itself >95°C. Pack FAULT light illuminates when pack control valve position disagrees with
selected position, compressor outlet overtemp or pack outlet overheat and then remains on until temperature is within limits. If the zone duct
temperature > 88°C, the assoc Hot Air valves and Trim Air valves close, an ECAM amber temperature warning appears on both COND & CRZ pages
and loss of half zone temperature regulation occurs. In the absence of electrical power, air pressure or duct overheat the Hot Air valves are closed.
A (pulsing) PACK LO FLOW indicates that the flow is insufficient to reach the selected temperature. The DITCHING pb closes the outflow valves
(unless under MAN control), emergency ram air inlet, avionics vent OVBD valve, cargo compartment isolation valves and pack flow control and
stops the bulk extract fans.
The pressurisation system is either fully automatic, semi-automatic or manual. It uses the pressure output from the 2 packs with 2 aft/forward
outflow valves. In fully auto, no crew action is required. In semi auto, the crew must select the landing field elevation. There are 2 crosslinked
Cabin Pressure Controllers (CPC) which use input signals from ADIRS, FMGC, EIU, LGCIU, PSCU and pack controllers and, in the automatic mode,
one is active and one is in standby. The CPCs switch roles 80secs after each landing. In manual mode, CPC 1 uses a back-up section with its own
power supply, which contains a pressure sensor to generate the excess cabin altitude and pressure outputs for the ECAM. The outflow valves are
driven by 3 motors, 2 when in auto and one in manual at one fifth rate. The valves will close if the cabin altitude exceeds 15kft or, if selected, to
close for ditching. When one pack is off (provided that delta p > 4psi), the aft outflow valve closes and the cabin pressure is controlled by the
forward valve. 2 independent safety valves, on the rear bulkhead, avoid excessive positive (+8.85psi) or negative (-1 / -¼ psi) differential
pressure. The safety valves open when the cabin differential pressure is between 8.75 and 8.95psi. One negative relief valve below the floor aft of
the L1 door assists the safety valves in protecting the negative differential pressure. Pressurisation assumes 9 separate modes: ground before TO,
TO, abort, climb internal, climb external, cruise, descent internal, descent external and ground after landing (1.21.20 p4). At TO, the controller pre-
pressurises the cabin at -328fpm to 200ft below airfield datum. At lift-off, the climb phase is initiated. During descent, the cabin is again over-
pressured to 200ft below airfield datum then released at touchdown at +750fpm.
If both auto systems fail, manual control is assumed by selecting MODE SEL pb switch to MAN and MAN V/S CTL switch to UP/DOWN. Both or one
outflow valve can be manually controlled. If only one valve is selected, the other remains under auto control. Delta P goes amber at <-0.2psi or
>8.85psi. A max delta p limiter function, in auto mode, limits delta p to 8.70 / 8.42 psi by fully opening the outflow valves at max speed resulting
in a very high cabin V/S [1.21.20 p8/10]. GOTCHA: CAB PRESS ADV - see 3.02.80 p15, this is the only advisory that really requires action: select
CABIN PRES MODE SEL to MAN then after 3 secs AUTO for V/S errors or leave it for ALT and DIFF PRESS errors.
2 computers, the Avionics Equipment Ventilation Controller controls the inboard and overboard valves and the Ventilation Controller controls the
cabin fans and lavatory/galley vents to auto ventilate the avionics bay, the batteries, the lavatories and galleys and the pack bay. The 2 cabin fans
(CABIN FANS off pb) and EXTRACT fan operate continuously, as long as the aircraft is electrically supplied, recirculating air from the cabin to the
avionics compartment and flight deck instrument panels. If the Cabin Fans fail, fresh air is blown from the packs. With the EXTRACT fan in AUTO
air is blown, on the ground, through the overboard extract valve (fuselage surface, EXTRACT when abnormal), the underfloor extract valve
(internal) being closed or, both in flight & on the ground with the inner / both engines only running, through the underfloor extract valve and then
out through the outflow valve (the OVBD extract valve being closed). ECAM: VENT indicates normal air flow, or VENT in case of extract low flow.
If OVRD is selected on the EXTRACT pb switch, air is blown through the overboard extract valve which is partially open and the underfloor extract
valve closes. Battery ventilation is by ambient air being drawn around the batteries and then vented overboard via a venturi in the skin. Lavatory
and galley ventilation is from the main cabin distribution system and is discharged overboard through a venturi. On the ground when delta p <
1psi, it is extracted by an electrical fan controlled by the VC. If the fan fails on the ground, there is no airflow over the cabin temperature sensors:
erroneous indications are possible. Pack bay ventilation is from a NACA air inlet into the pack bay, which is assisted on the ground by a turbo-fan
driven by bleed air controlled by the AEVC: the fan starts operation when the aircraft is on the ground. An ECAM message, PACK BAY VENT FAULT,
with external horn occurs 30secs after a turbofan failure.
The system provides ventilation and heating to the cargo area controlled by the 2 channel VC. Normal ventilation starts when the isolation valves
are fully open as selected by the BULK ISOL VALVE pb. The extract fan starts to operate continuously. The VC will close the isolation valves and
stop the fan when the BULK ISOL VALVE pb is off, the bulk cargo smoke detection system is triggered or the DITCHING pb switch is ON. An
overheat causes the extract fan to stop and the OVHT COND FANS RESET FAULT light to illuminate. The bulk cargo area is heated by an electrical
fan heater with the necessary temperature being set from the cockpit by the HOT AIR pb and the temperature selector; the heater is switched off
when the bulk cargo door is open.
ECAM - other:
Cabin diff pressure flashes GRN if delta p > 1.5psi during final approach
Cabin diff pressure goes amber at <-0.2psi or >8.85psi
Cabin V/S pulses when greater than ±1800fpm.
Cabin altitude flashes GRN >8800ft and RED >9550ft
Outflow valve position MAN when under manual pilot control
Outflow FWD and AFT are white becoming FWD/AFT when >95% open in flight or failed under auto control.
c:\…\21AIRPRESS.doc - created: 19 January 1995 - last saved: 14 August 2011