Airbus A320 Air Conditioning (ATA 21)

Question 0

What does the Pack Bypass valve do and what controls it?

Answer 0

It determines how much air passes through the Pack Air Cycle Machine and Main Heat Exchanger & how much bypasses them.
This determines Pack output temperature.

The Bypass Valve is controlled by the two channel Pack Controller.

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Question 1

What is the function of a pack & how does it achieve this?

Answer 1

Function - to cool hot pneumatic bleed air.

Achieved by; Energy is removed by an Air Cycle Machine and also by Heat Exchangers which are themselves cooled by Ram Air.

Question 2

What does the Pack Flow Control Valve do?

How is it operated?

Which component controls it?

Answer 2

• it varies the rate of Air-flow to the pack
• Electrically signalled closed (engine start, Fire p/b, o/heat,) Pneumatically opened by Upstream Pneumatic Pressure.
• it is controlled by the onside Pack Controller

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Question 3

What components are controlled by the Pack Controllers?

Answer 3

• Pack Flow Control Valve

- Pack heat exchanger ram air inlets.

Question 4

To where does the Emergency Ram Air inlet connect and what condition must be satisfied before it will open?

Answer 4

• mixer unit

- Delta P < 1 psi

Question 5

How is the Hot Air Pressure Regulating Valve Operated?

Answer 5

Electrically signalled, Pneumatically opened by Upstream Air Pressure.

Question 6

How are the Trim Air Valves operated; what controls them?

Answer 6

• Electrically signalled & operated.

- All 3 TAVs are controlled by the single Zone Controller.

Question 7

When do Pack Ram Air Inlet Flaps Open & Close?

Answer 7

• CLOSE for Take-off when TOGA/FLEX thrust set
• OPEN at Lift Off
• CLOSE on Landing on touchdown
• OPEN at 70 knots +20 seconds.

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Question 8

With Pack Flow Rate selected to NORM;

Give two occasions when Pack Flow rate will be HIGH.

Answer 8

• Single Pack Operations
• APU supplying Bleed Air

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Question 9

In Normal Operations, what temperature demand is signalled by the Zone Controller to the Pack Controllers?

Answer 9

That the packs both output air at the lowest demanded zone temperatures.

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Question 10

What happens to zones requiring warmer air than the lowest demanded zone temperature?

Answer 10

Trim Air Valves will open to add Hot Air to the Air supplied to that zone.

Question 11

What is the temperature range of the Flight Deck temperature controls?

Answer 11

18 deg C to 30 deg C.

Question 12

The Zone Controller has two channels: Primary & Secondary.

What happens if the Primary Channel Fails?

What is this mode of Temperature Regulation called & how is it shown?

Answer 12

• The Secondary channel is unable to read the Flight Deck Temp Selectors or control the TAVs, although it can sense zone ambient temperatures. It assumes that all zones should be at 24 deg C, so commands the Pack Controllers to Output Air at appropriate temperatures to achieve this.
• This is called ALTN MODE
• Indicated by caption ALTN MODE on the COND SD.

NB: When in ALTN mode control, the two packs may be running at different temperatures.

REF: cannot find an official one (Alteon Question Pack.)

Question 13

What happens if the Zone Controller Secondary Channel (only) fails?

Answer 13

Redundancy is lost, but System Temperature Control is not otherwise affected.

Question 14

What happens if both Zone Controller Channels fail?

What is this mode of Temperature Regulation called & how is it shown?

Answer 14

• The Zone Controller is unable to send control signals to the Pack Controllers. In the absence of such incoming signals, the Left Pack outputs air at a fixed 20 deg C and the Right at 10 deg C. There are no ECAM AirCond parameters.
• This is called PACK REG
• Annotated as PACK REG on the COND SD.

Question 15

Each Pack Controller has two channels: Primary and Secondary.

What is the effect of failure of the Primary?

Answer 15

The secondary channel continues to control the pack to the Temp signalled by the Zone Controller.

However, Pack Valve Flow Rate will be fixed at the current setting.

Question 16

What is the effect of Failure of the Secondary Pack Controller Channel?

Answer 16

Pack Parameters are lost from the BLEED SD. That is all.

Question 17

What is the effect of Failure of the Primary and Secondary Pack Controller Channels?

Answer 17

In the absence of any incoming control signals from its Controller, the Pack itself will run at a ‘suitable temperature’ (believed to be between 5 deg C & 30 deg C) in a process that involves pneumo-mechanical control of the Pack Anti-ice Valve.

Pack Flow Rate is Fixed.

No Pack Function parameters on ECAM.

Question 18

What is the effect of Failure of the Hot Air PRV?

Answer 18

• The Trim Air Valves will all close.
• The Zone Controller will signal the Packs to run at appropriate (and, if necessary, different) temperatures to maintain the Selected Temperature in the Flight-deck and the average of the two selected temps in the cabin.

Question 19

What does a FAULT light in the Hot Air p/b mean and what happens if it illuminates?

Answer 19

• Duct Overheat downstream of the Trim Air Valves.

- If such a condition is detected, the Hot Air PRV and all 3 Trim Air Valves close.

Question 20

If the Pack Valve has insufficient upstream pressure, it will not open.

However, in what circumstances will it be Electrically signalled closed?

Answer 20

• COMPRESSOR Outlet Overheat
• During Engine Start
• Fire p/b pressed
• Ditching p/b pressed.

Question 21

What does a FAULT light in a Pack Valve p/b indicate?

Answer 21

• PACK Outlet Temperature Overheat
• COMPRESSOR Outlet Temperature Overheat
• valve out of selected position

Note: If Compressor Outlet Overheat is detected, the valve closes;
The procedure requires it to be switched off & left switched off.
However, if there is a Pack Outlet Overheat, the valve is not commanded closed.
This action is taken by Pilots, who may re-instate the pack when it has cooled.

Question 22

What 4 Pack Parameters are shown on the BLEED SD?

Answer 22

• Flow Rate
• Internal Temp (Compressor Outlet : This is the hottest part of the Pack)
• Bypass valve position
• Pack Outlet Temp

Question 23

How is Re-circulating Fan Failure displayed on ECAM?

Answer 23

An amber FAN caption on the COND SD

Question 24

What parameters are shown on the COND page?

Answer 24

• HOT AIR PRV Position
• Trim Air Valve Positions
• Air Supply Duct Temp
• Cabin Temps
• ALTN MODE or PACK REG caption
• FAN fail captions

Question 25

Where else are Cabin Temps displayed?

Answer 25

The CRUISE SD

Question 26

The Emergency Ram Air Valve (or, more precisely, a check valve just downstream of it) should not open if Delta P > 1psi.

May we rely on this mechanical protection and press the Ram Air p/b at any time?

Answer 26

No.

Open Ram Air to provide Ventilation only if Delta P < 1 PSI.