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Chapter 3. Air conditioning, pressurisation and ventilation

Table of Contents

3.1. Cabin overpressure
3.2. Excess cabin altitude
3.3. Landing Elevation Fault
3.4. Pack fault
3.5. Pack overheat
3.6. Pack off
3.7. Pack regulator faults
3.8. ACSC single lane failure
3.9. Duct overheat
3.10. Hot air fault
3.11. Trim air faults
3.12. Cabin fan faults
3.13. Lavatory and galley fan faults
3.14. Pressure controller faults
3.15. Low diff pressure
3.16. Outflow valve closed on ground
3.17. Open safety valve
3.18. Blower fault
3.19. Extract fault
3.20. Skin valve fault
3.21. Avionics ventilation system fault

3.1. Cabin overpressure

There is no ECAM in the case of total loss of pressure control leading to an overpressure, so apply the QRH procedure. The basic procedure is to reduce air inflow by turning off one of the packs and put the avionics ventilation system in its smoke removal configuration so that it dumps cabin air overboard. The ΔP is monitored, and the remaining pack is turned off if it exceeds 9 psi. 10 minutes before landing, both packs are turned off and remain off, and the avionics ventilation is returned to its normal configuration.


3.2. Excess cabin altitude

An ECAM warning of excess (>9550ft) cabin altitude should be relied upon, even if not backed up by other indications.

The initial response should be to protect yourself by getting an oxygen mask on. Initiate a descent; if above FL160, this should be according to Section 2.1, “Emergency descent (memory item). Once the descent is established and all relevant checklists are complete, check the position of the outflow valve and, if it is not fully closed, use manual control to close it.


3.3. Landing Elevation Fault

If the landing field elevation is not available from the FMGS, the landing elevation must be manually selected. This is done by pulling out and turning the LDG ELEV knob. The scale on the knob is only a rough indication; use the LDG ELEV displayed on either the CRUISE page or the CAB PRESS SD page instead.


3.4. Pack fault

The PACK FAULT ECAM indicates that the pack valve position disagrees with the selected position or that the pack valve is closed. The affected pack should be turned off. A possible reason for this failure is loss of both channels of an Air Conditioning System Controller (ACSC). If this occurs, the associated hot air trimming will also be lost (cockpit for ACSC 1, cabin for ACSC 2).

If there are simultaneous faults with both packs, ram air must be used. This will necessitate depressurisation of the aircraft, so a descent to FL100 (or MEA if higher) is required. If a PACK button FAULT light subsequently extinguishes, an attempt should be made to reinstate that pack.


3.5. Pack overheat

The associated pack flow control valve closes automatically in the event of a pack overheating (outlet temp > 260°C or outlet temp > 230°C four times in one flight). The remaining pack will automatically go to high flow, and is capable of supplying all of the air conditioning requirement. This system’s automatic response is backed up by turning off the pack. The FAULT light in the PACK button remains illuminated whilst the overheat condition exists. The pack can be turned back on once it has cooled.


3.6. Pack off

A warning is generated if a functional pack is selected off in a phase of flight when it would be expected to be on. This is usually the result of neglecting to re-instate the packs after a packs off takeoff. Unless there is a reason not to, turn the affected pack(s) on.


3.7. Pack regulator faults

A regulator fault is defined as a failure of one of four devices: the bypass valve, the ram air inlet, the compressor outlet temperature sensor or the flow control valve. The ECAM bleed page can be used to determine which device is at fault.

Regardless of the device at fault, the ramification is the same; the pack will continue to operate but there may be a degradation in temperature regulation. If temperatures become uncomfortable, consideration should be given to turning off the affected pack.


3.8. ACSC single lane failure

Each ACSC has two fully redundant “lanes”, so loss of a single “lane” results in loss of redundancy only.


3.9. Duct overheat

A duct overheat is defined as a duct reaching 88°C or a duct reaching 80°C four times in one flight. If this occurs, the hot air pressure regulating valve and trim air valves close automatically and the FAULT light illuminates in the HOT AIR button. This light will extinguish when the temperature drops to 70°C.

Once the duct has cooled, an attempt can be made to recover the hot air system by cycling the HOT AIR button. If recovery is not possible, basic temperature regulation will continue to be provided by the packs.


3.10. Hot air fault

If the hot air pressure regulating valve is not in its commanded position, the effects will depend on its actual position. If it is closed when commanded open, the packs will provide basic temperature regulation. More serious is if it has been commanded closed in response to a duct overheat and it fails to close. Manual control may be effective, but if it is not the only option is to turn off both packs and proceed as per Section 3.4, “Pack fault”.


3.11. Trim air faults

Either a fault with one of the trim air valves or an overpressure downstream of the hot air valve. An associated message indicates which condition exists.

Failure of a trim valve leads to loss of optimised temperature regulation for the corresponding zone; basic temperature regulation is still available.

The TRIM AIR HIGH PR message may be disregarded if triggered when all the trim air valves are closed. This occurs during the first 30 seconds after the packs are selected on and in flight if all zone heating demands are fulfilled.[15]


3.12. Cabin fan faults

If both cabin fans fail, their flow should be replaced by increasing the pack flow to HI.


3.13. Lavatory and galley fan faults

The cabin zone temperature sensors are normally ventilated by air extracted by these fans. Loss of the fans therefore leads to loss of accurate zone temperature indication.

On older aircraft, temperature control reverts to maintenance of a fixed cabin zone inlet duct temperature of 15°C.

On newer aircraft the temperature controls for the cabin revert to controlling temperature in the ducts. If ACSC 2 has also failed, the duct temperatures are maintained at the same level as the cockpit duct temperature, and may therefore be controlled with the cockpit temperature selector.


3.14. Pressure controller faults

Loss of a single cabin pressure controller leads to loss of redundancy only.

If both pressure controllers are lost, use manual control. The outflow valve reacts slowly in manual mode, and it may be 10 seconds before positive control of the outflow valve can be verified. It may also react too slowly to prevent a temporary depressurisation.

Manual pressurisation control is activated by pressing the MODE SEL button. This allows the MAN V/S CTL toggle switch to directly control the outflow valve. Moving the toggle to DN closes the outflow valve causing the cabin altitude to descend, whilst moving the toggle to UP opens the outflow valve causing the cabin altitude to climb. The target climb and descent rates are 500fpm and 300fpm, these being displayed on the status page for easy reference.

A table of FL versus ‘CAB ALT TGT’ is also provided on the status page; no guidance is given for the interpretation of this table. The final action of the procedure is to fully open the outflow valve when 2500ft QFE in preparation for an unpressurised landing, so to avoid large pressurisation changes during this action, the final cabin altitude target needs to be aerodrome elevation plus 2500ft . This gives an indication of how ‘CAB ALT TGT’ should be interpreted: it is the lowest cabin altitude that results in a safe ΔP at a given FL. A cabin altitude greater then ‘CAB ALT TGT’ is always acceptable[16] and, moreover, for the final stages of the approach, it is necessary. The method is therefore to avoid cabin altitudes below ‘CAB ALT TGT’ for your actual FL while ensuring that a cabin altitude of aerodrome elevation plus 2500ft will be achieved by the time you need to fully open the outflow valve.

Ensure cabin diff pressure is zero before attempting to open the doors.


3.15. Low diff pressure

High rates of descent may lead to the aircraft descending through the cabin altitude when more than 3000ft above the landing altitude. An ECAM warning indicates that this situation is projected to occur within the next 1½ minutes. If the rate of descent of the aircraft is not reduced, the pressure controllers will have to resort to high rates of change of cabin altitude, which may cause passenger discomfort. The aircraft’s vertical speed should be reduced unless there is a pressing reason not to.


3.16. Outflow valve closed on ground

If the outflow valve fails to automatically open on the ground, manual control should be attempted. If that doesn’t work, depressurise the aircraft by turning off both packs.


3.17. Open safety valve

There are safety valves for both cabin overpressure and negative differential pressure; the associated ECAM message does not distinguish between the two.

If diff pressure is above 8psi, it is the overpressure valve that has opened. Attempt manual pressurisation control and if that fails, reduce aircraft altitude.

If diff pressure is below zero, it is the negative differential valve. Reduce aircraft vertical speed or expect high cabin rates.


3.18. Blower fault

Defined as low blowing pressure or duct overheat. Unless there is a DC ESS Bus fault, the blower fan should be set to OVRD. This puts the avionics ventilation into closed configuration and adds cooling air from the air conditioning system.


3.19. Extract fault

Defined as low extract pressure. The extract fan should be put in OVRD. This puts the avionics ventilation into closed configuration and adds cooling air from the air conditioning system.


3.20. Skin valve fault

Defined as one of three faults: the inlet valve is not fully closed in flight, the extract valve is fully open in flight or the extract valve did not automatically close on application of take-off power. The ECAM Cab Press page will differentiate.

If the fault is with the inlet valve, no action is required since it incorporates a non-return valve.

If the extract valve is affected, the system should be put into smoke configuration; this sends additional close signals to the extract valve. If this fails, the aircraft must be depressurised.


3.21. Avionics ventilation system fault

Defined as either a valve not in its commanded position or the Avionics Equipment Ventilation Controller (AEVC) being either unpowered or failing its power-up test. The system will automatically default to a safe configuration similar to smoke configuration. No crew action is required.


[15] The FCOM is not very informative regarding response to overpressure when this does not apply. However the MEL operating procedures for dispatch with this condition indicate that turning the HOT AIR pb-sw off is probably a good idea.

[16] A reasonable maximum cabin altitude is 8800ft, which is when the CAB ALTITUDE advisory triggers.