AIRCRAFT SYSTEMS: AIR CONDITIONING / PRESSURIZATION / VENTILATION Flashcards by Rajat Kumar

It provides continuous air renewal and maintains a constant, selected temperature in the following three zones :

COCKPIT, FWD CABIN, AFT CABIN. These three zones are independently controlled.

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Air is supplied by the pneumatic system, via:

‐ Two pack flow control valves,
‐ Two packs,
‐ The mixing unit, which mixes the air that comes from the cabin and the packs.

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In an emergency, a ram air inlet can provide

ambient air to the mixing unit.

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Temperature regulation of the temperature is ensured by

a zone controller and two pack controllers, or two Air Conditioning System Controller (ACSC)

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Temperature regulation is optimized via

the hot air pressure regulating valve, and the trim air valves that add hot air, tapped upstream of the packs, to the air coming from the mixing unit.

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During cruise, the cabin crew can modify each cabin zone temperature that is selected from the cockpit, with a limited authority of

± 2.5 °C.

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The two AIR CONDITIONING PACKS operate automatically and independently of each other. Pack operation is controlled by signals coming from

the pack controller or the Air Conditioning System Controller (ACSC)

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Warm pre-conditioned bleed air enters the cooling path via the pack flow control valve, and is ducted to

the primary heat exchanger.

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PACK FLOW CONTROL VALVE is ___-operated and ___-controlled

pneumatically / electrically

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PACK FLOW CONTROL VALVE regulates the air flow in accordance with signals received from

the pack controllers or the ACSC.
In the absence of air pressure, a spring keeps the valve closed.

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The valve closes automatically in case of

pack overheat (on ground only), engine start, or operation of the fire or ditching pushbutton.

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EMERGENCY RAM AIR
An emergency ram air inlet ventilates the cockpit and cabin to

remove smoke, or if both packs fail.

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The emergency ram air inlet valve is controlled by

the RAM AIR pushbutton on the AIR COND panel.
This pushbutton opens the ram air valve, provided that ditching is not selected.

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When the RAM AIR pushbutton is ON : The outflow valve opens about 50 %, provided that it is under automatic control and ΔP is less than 1 PSI. The outflow valve does not automatically open if

it is under manual control, even if ΔP is less than 1 PSI. If ΔP is greater than 1 PSI, the check valve located downstream the ram air door will not open, even if the ram air door has been selected open. No airflow will then be supplied.

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MIXER UNIT mixes cold fresh air from the packs with the cabin air being recirculated through

recirculation fans.

The mixer unit is also connected to the emergency ram air inlet and the low pressure ground inlets.

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HOT-AIR PRESSURE-REGULATING VALVE regulates the pressure of

hot air, tapped upstream of the packs.

It is pneumatically-operated and electrically-controlled from the HOT AIR pb-sw on the AIR COND panel.
The ACSC 1 regulates this valve.
In the absence of air, a spring keeps the valve closed.

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HOT-AIR PRESSURE-REGULATING VALVE closes automatically, if:

‐ Both lanes of ACSC 1 or ACSC 2 fail, or
‐ The duct overheats, or
‐ At least two trim air valves fail.
The valve remains operative, even if either the forward or aft cabin trim air valve fails.

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TRIM AIR VALVES are electrically-controlled by the zone controller or the ACSC  . A trim air valve, associated with each zone, adjusts

the temperature by adding hot air.

The cockpit trim air valve is controlled by the ACSC 1  , and the cabin trim air valves are controlled by the ACSC 2  .

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Temperature regulation is automatic and controlled by

one zone controller and two pack controllers, or the ACSC  .

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The actual temperature is measured by sensors:
‐ In the cockpit, for the cockpit zone;
‐ for the cabin ___

In the lavatory extraction circuit and galley ventilation system

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OPTIMIZED TEMPERATURE REGULATION
The temperature selection range is from

18 °C to 30 °C

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AIR CONDITIONING SYSTEM CONTROLLERS regulates the temperature of its associated pack, by modulating

the bypass valve and the ram air inlet flap.
The ram air inlet flap closes during takeoff and landing to avoid the ingestion of foreign matter.

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During takeoff, the ram air inlet flap closes when takeoff power is set, and the main landing gear struts are compressed.
During landing, it closes as soon as the main landing gear struts are compressed, as long as speed is at or above

70 kt.
It opens 20 s after the speed drops below 70 kt.

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PACK FLOW CONTROL
Whatever the crew selects, the system delivers higher flow for any of the following circumstances:

‐ In single-pack operation,
‐ When the APU is supplying bleed air.

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ENGINE PRESSURE DEMAND When the cooling demand in one zone cannot be satisfied, if the bleed pressure is too low, the air conditioning system controller sends a pressure demand signal to both Engine Interface Units (EIU) to increase

the minimum idle and to raise the bleed pressure.

APU FLOW DEMAND When the APU bleed valve is open, the air conditioning system controller signals the APU's Electronic Control Box (ECB) to increase

the APU flow output when any zone temperature demand cannot be satisfied.

AIR CONDITIONING - SYSTEM OPERATION UNDER FAILURE CONDITION Each controller is comprised of two lanes. One lane controls the system,

the other takes over full control, in case of an active lane failure.

AIR CONDITIONING - SYSTEM OPERATION UNDER FAILURE CONDITION ONE LANE FAILURE

No effect, as the second lane takes over.

AIR CONDITIONING SYSTEM CONTROLLERS  BOTH LANES FAILURE

The related pack is lost, and the hot air pressure-regulating valve and associated trim air valves close.

AIR CYCLE MACHINE FAILURE If the Air Cycle Machine (ACM) fails (compressor/turbine seizure), the affected pack may be operated in

heat exchanger cooling mode.

HOT AIR PRESSURE REGULATING VALVE FAILURE Failed open : No effect. Failed closed :

Optimized regulation is lost. Trim air valves are driven to the fully closed position. Pack 1 controls the cockpit temperature to the selected value and pack 2 controls the cabin temperature (FWD and AFT) to the mean value of the selected temperatures.

TRIM AIR VALVE FAILURE Optimized temperature regulation of

the corresponding zone is lost.

HOT AIR pb FAULT : The FAULT light comes on amber, along with an associated ECAM caution, when

duct overheat is detected. The valve and trim air valves close automatically.

PACK pb-sw ON : The pack flow control valve is automatically-controlled. Pack flow control valve opens, except in the following cases:

‐ Upstream pressure below minimum ‐ Compressor outlet overheat ‐ Engine start sequence: ‐ FIRE pb, of the engine on the related side, is pressed ‐ Ditching is selected.

PACK pb-sw On ground, reopening of the pack flow control valves is delayed for ___ to avoid a supplementary pack closure cycle during second engine start.

60 s

PACK FLOW selector ‐ Permits the selection of pack valve flow, according to the number of passengers and ambient conditions (smoke removal, hot or wet conditions) LO (___) – NORM (100 %) – HI (___)

80 % / 120 %

PACK FLOW selector ‐ Manual selection is irrelevant in single pack operation, or with APU bleed supply. In these cases, ___ is automatically selected

PACK FLOW selector ‐ If LO is selected, the pack flow can be automatically selected up to ___ when the cooling demand cannot be satisfied.

100 %

RAM AIR pb (guarded) If the DITCHING pb, on the CABIN PRESS panel, is in normal position:

‐ The emergency ram air inlet opens ‐ If Δp ≥ 1 PSI: The outflow valve control remains normal. No emergency ram air flows in ‐ If Δp < 1 PSI: The outflow valve opens to about 50 % when under automatic control. It does not automatically open when it is under manual control. Emergency ram airflow is directly supplied to the mixer unit.

CAB FAN pb ON :

The two cabin fans are on.

The cabin pressurization system has four general functions:

Ground function Prepressurization Pressurization in flight Depressurization

The cabin pressurization system Ground function :

Fully opens the outflow valve on ground

The cabin pressurization system Prepressurization :

During takeoff, increases cabin pressure to avoid a surge in cabin pressure during rotation

The cabin pressurization system Pressurization in flight :

Adjusts cabin altitude, and rate of change to provide passengers with a comfortable flight

The cabin pressurization system Depressurization :

After touchdown, gradually releases residual cabin overpressure before the ground function fully opens the outflow valve.

The cabin pressurization system consists of:

‐ Two Cabin Pressure Controllers (CPC) ‐ One Residual Pressure Control Unit (RPCU) ‐ One outflow valve, with an actuator that incorporates three motors (two for automatic operation, one for manual operation) ‐ One control panel ‐ Two safety valves.

PRESSURIZATION Any one of the three independent electric motors may power the outflow valve. Normally, one of the two cabin pressure controllers operates the outflow valve by means of its

associated automatic motor.

PRESSURIZATION In case of ditching, an override switch on the control panel allows the flight crew to close

the outflow valve and all valves below the flotation line.

Air pressure in the cabin follows external schedules that the system receives as signals from

the Flight Management and Guidance System (FMGS).

When FMGS data is not available for automatic pressurization, the crew only needs to select

the landing field elevation.

In manual mode, the flight crew controls the cabin altitude via

the manual motor of the outflow valves, by operating controls on the pressurization control panel.

Two identical, independent, digital CABIN PRESSURE CONTROLLERS automatically control the system, by signals from the

4 items Air Data Inertial Reference System (ADIRS), the Flight Management and Guidance Computer (FMGC), the Engine Interface Unit (EIU), and the Landing Gear Control Interface Unit (LGCIU).

CABIN PRESSURE CONTROLLERS For operation in manual mode, each controller has a backup section, which is powered by an independent power supply in the controller N°1 position. This section also has a ___ that generates the cabin altitude and pressure signal for the ECAM, when MAN mode is selected.

pressure sensor

The outflow valve is on the ___ side of fuselage, behind the aft cargo compartment and below the flotation line.

right-hand

Two independent pneumatic SAFETY VALVES prevent cabin pressure from going too high ( ___ above ambient) or too low ( ___ below ambient).

8.6 PSI / 1 PSI They are located on the rear pressure bulkhead, above the flotation line.

The RPCU automatically depressurizes the aircraft in case of abnormal residual pressure on ground. It automatically opens the outflow valve, when:

‐ The outflow valve is not fully open, and ‐ Both CPCs are failed, or manual mode is selected, and ‐ The aircraft is on ground, and ‐ All engines are shutdown, or all ADIRS indicate an airspeed below 100 kt.

AUTOMATIC PRESSURE CONTROL MODE CPCs automatic transfer occurs:

* 70 s after each landing. * If the operating system fails.

AUTOMATIC PRESSURE CONTROL MODE ‐ The controller automatically controls the cabin pressure. It limits the cabin pressure to approximately ___ maximum during CRUISE mode and is optimized to support high airfield operations up to a pressure of 14 100 ft during ground, climb and descent phases.

8 000 ft

AUTOMATIC PRESSURE CONTROL MODE ‐ The controller normally uses the landing elevation and the QNH from the ___, and the pressure altitude from ___. If FMGC data are not available, the controller uses the captain BARO Reference from the ADIRS and the LDG ELEV selection.

FMGC / ADIRS

‐ Pressurization is assumed through the following modes: GROUND (GN)

Before takeoff, and 55 s after landing, the outflow valve fully opens to ensure that there is no residual cabin pressure. At touchdown, any remaining cabin pressure is released at a cabin vertical speed of 500 ft/min.

‐ Pressurization is assumed through the following modes: TAKEOFF (TO)

To avoid a pressure surge at rotation, the controller pre-pressurizes the aircraft at a rate of 400 ft/min, until the ΔP reaches 0.1 PSI. At liftoff, the controller initiates the climb phase.

‐ Pressurization is assumed through the following modes: CLIMB (CL)

During climb, the cabin altitude varies according to a fixed pre-programmed law that takes into account the aircraft’s actual rate of climb.

‐ Pressurization is assumed through the following modes: CRUISE (CR)

During cruise, the controller maintains cabin altitude at the level-off value, or at the landing field elevation, whichever is higher, but the cabin altitude target is limited to a maximum of approximately 8 000 ft.

‐ Pressurization is assumed through the following modes: DESCENT (DE)

During descent, the controller maintains a cabin rate of descent, such that the cabin pressure is equal to the landing field pressure +0.1 PSI, shortly before landing. The maximum descent rate is 750 ft/min.

‐ Pressurization is assumed through the following modes: ABORT (AB)

If the aircraft does not climb after takeoff, the abort mode prevents the cabin altitude from climbing. Cabin pressure is set back to the takeoff altitude +0.1 PSI.

MANUAL PRESSURE CONTROL MODE If both automatic systems fail, the flight crew may use the CABIN PRESS control panel to take over manual control of cabin pressurization.

* Release the MODE SEL pushbutton to select MAN, and * Push the MAN V/S CTL switch UP or DN to increase or decrease cabin altitude.

MANUAL PRESSURE CONTROL MODE * Release the MODE SEL pushbutton to select MAN these actions cuts off power to the ___ motors, and enables the MAN motor to control the outflow valve.

AUTO

Due to the slow operation of the outflow valves in manual mode, and the limited resolution of the outflow valves' position on the ECAM, the visual ECAM indication of a change in the outflow valves' position can take up to ___

5 s.

MANUAL PRESSURE CONTROL MODE As the pressurization system is manually-controlled, the outflow valve does not open automatically at

touchdown.

DITCHING To prepare for ditching, the flight crew must press the DITCHING pb on the CABIN PRESS control panel to close

4 items the outflow valve, the emergency ram air inlet, the avionics ventilation inlet and extract valves, the pack flow control valves,

PRESSURIZATION LDG ELEV knob The pressurization schedule does not use the landing elevation from the FMGS, but instead uses the landing elevation selected with this knob ( ___ ) as its reference

from -2 000 to +14 000 ft

PRESSURIZATION Switching the MODE SEL pb to MAN, for at least ___ , then returning it to AUTO will select the other system.

10 s

PRESSURIZATION The pilot may notice a variation in the CAB ALT indication on the ECAM PRESS page, when the system switches from the cabin pressure control AUTO mode to MAN mode, due to the reduced resolution of

the backup pressure sensor.

PRESSURIZATION MAN V/S CTL toggle switch The switch, springloaded to neutral controls the outflow valve position through operation of the MAN motor, when the MODE SEL pb is in the MAN position. UP : The valve moves towards the ___ position. DN : The valve moves towards the ___ position.

open / closed

If the ditching pb is set to ON, with the low pressure ground cart connected and all doors closed, a ___ will build up.

differential pressure

PRESSURIZATION ECAM CAB PRESS PAGE CABIN ALTITUDE It flashes when the cabin altitude reaches 8 800 ft and stop flashing when returning below 8 600 ft. RED Cabin altitude is at or above

9 550 ft.

PRESSURIZATION ECAM CAB PRESS PAGE OUTFLOW VALVE POSITION In automatic mode, the valve opens more than ___ during flight.

95 %

VENTILATION The ventilation system includes ventilation for:

‐ The avionics, controlled by the Avionics Equipment Ventilation Controller (AEVC), ‐ The batteries, ‐ The lavatories and galleys.

AVIONICS VENTILATION It uses ___ electric fans to force the circulation of cooling air.

two

AVIONICS VENTILATION MAIN COMPONENTS 6 items

FANS SKIN AIR INLET AND OUTLET VALVES SKIN EXCHANGE INLET AND OUTLET BYPASS VALVES AIR CONDITIONING INLET VALVE SKIN EXCHANGE ISOLATION VALVE AVIONICS EQUIPMENT VENTILATION CONTROLLER (AEVC)

AVIONICS VENTILATION The Fan Speed Controller (FSC)  controls the avionics ventilation fan speed as a function of temperature:

1. High speed when the ventilation air temperature is above +40 °C 2. Low speed when the ventilation air temperature is below +35 °C

AVIONICS VENTILATION SKIN AIR INLET AND OUTLET VALVES These valves admit air

from outside the aircraft and evacuate hot air from the avionics equipment.

AVIONICS VENTILATION SKIN EXCHANGE INLET AND OUTLET BYPASS VALVES These valves enable air to circulate between the avionics bay and the space under

the cargo compartment floor.

AVIONICS VENTILATION AIR CONDITIONING INLET VALVE This valve opens to enable the air conditioning circuit to supply fresh air to

the avionics bay.

AVIONICS VENTILATION SKIN EXCHANGE ISOLATION VALVE This valve connects or isolates the

skin heat exchanger.

AVIONICS VENTILATION AVIONICS EQUIPMENT VENTILATION CONTROLLER (AEVC) The AEVC controls the operation of

all fans and valves in the avionics ventilation system.

AVIONICS VENTILATION NORMAL OPERATION, OPEN-CIRCUIT CONFIGURATION GROUND OPERATIONS The open-circuit configuration operates when the avionics duct temperature is

equal or above 40 °C (104 °F).

AVIONICS VENTILATION NORMAL OPERATION, CLOSE-CIRCUIT CONFIGURATION GROUND OPERATIONS The close-circuit configuration operates when the avionics duct temperature is below

40 °C

AVIONICS VENTILATION NORMAL OPERATION, CLOSE-CIRCUIT CONFIGURATION FLIGHT OPERATIONS The close-circuit configuration operates when skin temperature is beneath the in-flight threshold.

In flight threshold = +35 °C, temperature increasing, or +32 °C, temperature decreasing.

AVIONICS VENTILATION NORMAL OPERATION, INTERMEDIATE CONFIGURATION FLIGHT OPERATIONS The intermediate configuration operates when skin temperature is above the in-flight threshold.

In flight threshold = +35 °C (95 °F), temperature increasing, or +32 °C (90 °F), temperature decreasing.

AVIONICS VENTILATION The measuring range of the skin temperature sensed is between -50 °C and 80 °C. Outside of this range, the AEVC sets the avionics ventilation configuration to the intermediate configuration (partially open) until

the temperature is within the operation range again.

AVIONICS VENTILATION ABNORMAL OPERATION BLOWER FAULT OR EXTRACT FAULT ALERT When the BLOWER or the EXTRACT pushbutton switch is set at the OVRD (override) position, the system is in

closed-circuit configuration and adds air from the air conditioning system to the ventilation air.

AVIONICS VENTILATION ABNORMAL OPERATION BLOWER FAULT OR EXTRACT FAULT ALERT When the BLOWER pushbutton switch is set at OVRD, the blower fan is

stopped and the extract fan continues to run.

AVIONICS VENTILATION ABNORMAL OPERATION BLOWER FAULT OR EXTRACT FAULT ALERT When the EXTRACT pushbutton switch is set at OVRD, the extract fan is controlled directly from the

pushbutton. Both fans continue to run.

AVIONICS VENTILATION ABNORMAL OPERATION SMOKE CONFIGURATION When the smoke detector detects smoke in the avionics ventilation air the BLOWER and the EXTRACT FAULT lights come on. When both the BLOWER and the EXTRACT pushbuttons are set to the OVRD position,

the air conditioning system supplies cooling air, which is then exhausted overboard. The blower fan stops.

AVIONICS VENTILATION ABNORMAL OPERATION CONTROLLER FAILURE In case of a controller failure, the BLOWER and the EXTRACT FAULT lights come on and both the BLOWER and the EXTRACT push-buttons are set to the OVRD position. The skin air inlet valve, the skin exchange isolation valve and the skin exchange outlet bypass valve remain in

the last position checked before the failure occurred. The extract fan keeps running.

BATTERY VENTILATION A venturi in the skin of the aircraft draws air from the space around the batteries and vents it

overboard. The resulting airflow ventilates the batteries.

LAVATORY AND GALLEY VENTILATION An extraction fan draws ambient cabin air through the lavatories and galleys and exhausts it near

the outflow valve. The extraction fan runs continually when electric power is available.

VENTILATION BLOWER pb-sw and EXTRACT pb-sw When both pushbutton switches are on AUTO: ‐ On the ground before the application of TO power, the ventilation system is in

open circuit configuration (closed configuration when the skin temperature is below the ground threshold).

VENTILATION BLOWER pb-sw and EXTRACT pb-sw When both pushbutton switches are on AUTO: ‐ On the ground after the application of TO power, and in flight, the ventilation system is in

closed circuit configuration.

VENTILATION BLOWER pb-sw and EXTRACT pb-sw When either pushbutton switch is on OVRD:

‐ The system goes to closed circuit configuration. ‐ Air from the air conditioning system is added to ventilation air. (The blower fan stops if the BLOWER pushbutton switch is in the OVRD position).

VENTILATION BLOWER pb-sw and EXTRACT pb-sw When both pushbutton switches are on OVRD:

‐ Air flows from the air conditioning system and then overboard. ‐ The extract fan continues to run.

VENTILATION BLOWER pb-sw and EXTRACT pb-sw FAULT Lights up amber (and ECAM activates) in the blower switch, if :

‐ blowing pressure is low (See *) ‐ duct overheats (See *) ‐ computer power supply fails ‐ smoke warning is activated * If the warning occurs on the ground when the engines are stopped, the external horn sounds.

VENTILATION BLOWER pb-sw and EXTRACT pb-sw FAULT Lights up amber (and ECAM activates) in the extract switch, if :

‐ extract pressure is low (See *) ‐ computer power supply fails ‐ smoke warning is activated. * If the warning occurs on the ground when the engines are stopped, the external horn sounds.