Pneumatics, Air Conditioning & Pressurization (PH 10.x.x)

 

The pneumatic system supplies high pressure air for:

 

Ø      Air conditioning

Ø      Pressurization

Ø      Engine starting

Ø      Wing anti-icing

Ø      Hydraulic reservoir pressurization

Ø      Aft cargo heat

Ø      Water tank pressurization

 

High pressure air can be supplied by:

 

Ø      Engine bleed

Ø      APU load compressor

Ø      High pressure ground connection

 

Controlled by BMC (Bleed Monitoring Computer)

 

Engine Bleeds close automatically when BMC's detect:

 

A         APU bleed valve open

S         Engine Start

O         Over temperature

L          Leak

O         Over pressure

 

The valve will also automatically close pneumatically when:

 

Ø      Low pressure

Ø      Reverse flow

 

And is electrically closed when:

 

Ø      ENG BLEED selected off

Ø      ENG FIRE pb selected

 

The APU bleed will close for leaks

 

The APU is ready for bleed when reaching 95% for two seconds or 99.5%. The AVAIL light will show in the APU start pb and green APU AVAIL will show on EWD display when APU is available for use.

 

The crossbleed valve can be operated in automatic or manual mode. There are two electric motors for the valve, one for each mode. In automatic mode the crossbleed valve opens automatically when using APU bleed air. During normal operation the crossbleed is closed to isolate the two engine bleeds.

 

The crossbleed is manually set OPEN during the engine crossbleed start procedure.

 

The leak detection system uses a single loop for the pylons and APU to detect hot air temps associated with duct leaks. Dual loops are used for the wings. If both of the dual loops detect a leak a warning is given, unless there is a fault on one, then only one loop is required to give a warning.

 

If a leak is detected:

 

Ø      The engine bleed air valve (APU bleed air valve) on that side is closed

Ø      Associated ENG (APU) BLEED FAULT light comes on

Ø      Crossbleed valve closes (except during engine start)

Ø      Left wing leak only – APU bleed air valve closes (except during ENG start)

 

Packs (PH 10.3.x)

 

i Airbus Gotcha’: Do not use external conditioned air when using packs (PH 2.9.3). Unfortunately, there is no cockpit indication of external air connected! You can turn off the cabin fans pb and if air continues to blow from the vents then external air is connected.

 

Pay attention here, many new Airbus pilots fail to understand the way the Zone Temp system works. If you are familiar with the 737-400 this is very similar. Both packs are feeding all three zones. Whichever zone is commanding the coldest temperature will drive BOTH packs to that temp. Hot air is then added to any other zone that is commanding a higher temp. This hot air is called trim air and is how the zone temp system controls temperatures in three zones with only two packs.

 

There are three air conditioning zones: Cockpit, FWD Cabin and AFT Cabin.

The zones are controlled by having the packs deliver all air at the lowest temp requested by any of the three zones. Then hot air is added through the trim air valves to the other two zones as needed to meet temp requirements. A/C zone temp selectors have a range of: Cold 18°C/64°F, 12 o’clock 24°C/76°F, Hot 30°C/86°F

 

The AC pack can bypass bleed air around the air cycle machine (ACM) if the ACM fails and run the bleed air through the primary heat exchanger directly. This allows the pack to operate as a simple heat exchanger with reduced pack flow.

 

Pack flow will revert to HI during single pack operation or APU bleed source regardless of selector position.

 

 The Zone controller can override pilot selected pack flow (HI, NORM and LOW) as needed to meet demands. It can also command higher APU speed or engine idle as needed.

 

One Zone controller with two channels. Failure of the primary channel will result in fixed temperature at 76° F with no optimization. Failure of the secondary as well will result in a fixed temp of 68° F pack 1 and 50° F pack 2.

 

One Pack controller per pack. Two channels per controller. If primary fails the secondary pack air flow will be fixed at the pre-failure setting. No further optimization is available. Further failure of the secondary will result in a fixed pack outlet temp of 59° F.

 

Pack controllers also regulate the cooling air flow through the ACM. During takeoff and touchdown the controllers close the ram air inlet flaps to prevent ingesting debris.

 

Note: The Airbus 319/320 can be dispatched with one pack INOP up to FL310 or below as per MEL 21-5201A

 

RAM air (PH 10.3.6)

 

RAM air is available for cabin ventilation in the event of loss of pressurization or smoke removal. When the RAM AIR pb is selected the RAM air inlet opens.

 

When pressurization differential is less than 1 psi. the outflow valve will open to 50% to allow exhaust. If above 1 psi. then the outflow will remain normal.

 

 

Pressurization (PH 10.5.x)

 

There are two identical independent pressurization systems. Control is normally fully automatic. The system has one control panel, two controllers, one outflow valve and two safety valves. The outflow valve has three DC motors: Primary, Backup and Manual. Controllers can operate in automatic, semi-automatic and manual modes.

 

Automatic:  Controller automatically takes the destination field elevation from the aircraft database. The entire pressurization schedule is optimized by the system.

 

Semi-automatic: If the database is not available for some reason the pilot can select the landing elevation from the LDG ELEV knob by pulling the selector out of the AUTO detent and turning to the needed value.

 

Manual: Normally, the controllers take turns controlling by swapping after each leg. If the active controller fails the backup automatically takes over. If both automatic systems fail the pilot may control manually by pressing the CABIN PRESS MODE SEL to MAN. The primary and backup outflow valve motors are depowered and the manual motor is activated. Now the pilot can select vertical speed on the cabin using the MAN V/S CTL switch.

 

Abort mode: If the aircraft returns after takeoff the system will reset to departure field elevation.

 

Ditching pb: The Ditching pb will close all exterior openings below the flotation line. This pb is also used during deicing to prevent deicing fluid from entering the aircraft.

 

i Airbus Gotcha’: on ground with Ditching pb ON and all doors closed & external low pressure connected a pressurization differential will build (PH 10.6).

 

Note: If the pilot suspects that pressurization is not performing normally but has not yet failed press the MODE SEL pb to MAN for 10 secs. then return to AUTO. This will cause the systems to swap (PH 10.6).

 

Depressurization: When cabin exceeds about 11,000’ the cabin may illuminate and Exit and all cabin signs illuminate automatically. Masks will automatically drop at 14,000’ cabin altitude. (PH 15.1.3, 5.20.1)

 

Ventilation (PH 10.7)

 

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 3a.2 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 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.

 

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