Air conditioning

Question 1

What are the temperature controlled zones?

Answer 1

The air is distributed into four independently controlled zones, the cockpit, the forward cabin, the mid cabin and the aft cabin.

Question 2

Describe the packs and its components

Answer 2

The main components of the air conditioning system are the two independent, automatically controlled packs.
Each pack is comprised of an air cycle machine, a primary heat exchanger and a main heat exchanger.
The heat exchangers use external ram air to cool the hot pneumatic air; the ram air is then exhausted overboard.

Question 3

Where are the packs located?

Answer 3

The packs are located in the unpressurized belly area, just forward of the main landing gear bay.

Question 4

How do the heat exchangers work?

Answer 4

The heat exchangers use external ram air to cool the hot pneumatic air; the ram air is then exhausted overboard.

Question 5

The pack flow control valve will close automatically if:

Answer 5

The pack flow control valve will close automatically if: pneumatic pressure is low, the pack overheats or during the engine start sequence. The valve will also close if the engine fire or ditching pb switches are operated, or if doors are not closed at engines start.

Question 6

Describe the mixer unit.

Answer 6

The mixer unit mixes temperature regulated air from the packs with re-circulated cabin air drawn in by the cabin fans, which are controlled from the overhead VENTILATION panel.
The mixer unit can also receive conditioned air from an external low pressure air conditioning unit, or ram air from the emergency ram air inlet.

Question 7

How is temperature regulation achieved?

Answer 7

The conditioned air from the mixer unit is temperature regulated by the hot air valves and trim air valves, which use hot pneumatic air tapped upstream of the packs.

Question 8

Describe hot air valves.

Answer 8

The hot air valves are pneumatically operated and electrically controlled by the HOT AIR 1(2) pb sw(s) on the overhead AIR panel.
The valves supply the trim air valves with hot pneumatic air which is tapped upstream of the packs.

Question 9

When will the hot air valves automatically close?

Answer 9

The valves will close automatically if a duct overheats, or in the absence of pneumatic pressure.

Question 10

Function o hot air cross valve.

Answer 10

A hot air cross valve is fitted between the hot air manifolds; normally closed, it opens automatically if one hot air supply has failed.

Question 11

Function of trim air valves.

Answer 11

The trim air valves are electrically controlled by the zone controller to add hot pneumatic air from the hot air manifold to the conditioned air of the mixer unit before it enters the cabin, satisfying the demand for individual zone heating.

Question 12

What controls the temperature and airflow of the air conditioning system?

Answer 12

One zone controller and two pack controllers automatically control the temperature and airflow of the air conditioning system.
The zone and pack controllers are dual channel controllers. Channel 1 normally controls with channel 2 as a backup if channel 1 fails.

Question 13

Describe the pack controllers.

Answer 13

Each pack has an associated pack controller, which controls the airflow of the pack by modulating the pack flow control valve.

Question 14

How do the pack controllers control the temperature of the packs?

Answer 14

The pack controller controls the temperature of the pack by modulating the position of the temperature control valve, and the ram air heat exchanger inlet and outlet flaps.
A signal corresponding to the lowest demanded zone temperature goes to the pack controller, which then makes both packs produce the required outlet temperature.

Question 15

How do the pack controllers help prevent foreign object damage from ingestion by the packs?

Answer 15

The pack controller also closes the ram air heat exchanger inlet and outlet flaps during take-off and landing to prevent foreign object damage from ingestion by the packs.

Question 16

How does the zone controller regulates the temperature?

Answer 16

The zone controller regulates the temperature of the three cabin zones and the cockpit zone by sending signals to the pack controller and trim air valves.
The zone controller uses temperature selector position and cabin temperature information to regulate the pack outlet temperature, and optimizes it with the trim air valves.

Question 17

What signals the zone controller to regulate airflow?

Answer 17

The zone controller regulates the airflow in accordance with the position of the PACK FLOW selector on the overhead AIR panel.

Question 18

What if zone temperature cannot be satisfied by the zone controller?

Answer 18

If the zone temperature cannot be satisfied, the zone controller can automatically increase the output flow of the APU or engine idle to increase bleed pressure.
If a zone cooling demand cannot be met, the zone controller will signal the bleed monitor computer to reduce the bleed temperature.

Question 19

When is bleed temperature reduction by the zone controller inhibited?

Answer 19

If wing anti ice is ON, the bleed temperature reduction demand is inhibited.

Question 20

The cargo ventilation and heating system provides ventilation and heating to what cargos sections?

Answer 20

The forward and bulk cargo compartments. The aft cargo compartment is not ventilated or heated.

Question 21

The isolation valves are closed and the extract fans stopped when…

Answer 21

The isolation valves are closed and the extract fans stopped, by the cargo ventilation controller, when the cargo smoke detection system detects smoke.
and when the DITCHING pb sw on the overhead CABIN PRESS panel is selected ON.

Question 22

Cargo ventilating air is received from…

Answer 22

Cabin air

Question 23

Time limitation without A/C source when pax on board

Answer 23

With passengers on board it is not recommended to exceed 20 min without air conditioning as the lack of fresh air will significantly reduce cabin air quality.

Question 24

Is it allowed to use packs and LP gnd units for conditioned air when it’s too hot?

Answer 24

It is prohibited to use conditioned air simultaneously from packs and low pressure ground units.

Question 25

HP gnd units can be used when APU supplies bleed air?

Answer 25

Do not use high pressure ground unit when APU supplies bleed air to avoid bleed system damage.