Air Conditioning 747-400

Question 1

How is cabin pressure regulated?

Answer 1

Automatically or manually by the outflow valves, and automatically by the overboard valve.

Question 2

Ground exhaust valve open. Is the aircraft ready for flight ?

Answer 2

No. A/C can’t be pressurized.

Question 3

What bleed air is supplied at low engine thrust settings?

Answer 3

HP bleed air only.

IP not supplied due to the check valve in combination with the HP bleed air.

Question 4

What bleed air is provided is the FWSOV is closed?

Answer 4

No bleed air is provided.

Question 5

What are the 4 main pneumatic users?

Answer 5

(HEEL)

1) Hydraulic demand pumps 1 and 4
2) ECS
3) Engine starters
4) Leading edge flaps

Question 6

What additional systems aside of the main one use pneumatic?

Answer 6

WACH-W

1) Wing Anti Ice
2) Aft cargo heat and circulations
3) Cargo smoke detection
4) Hydraulic reservoir pressurization
5) Water tank pressurization

Question 7

Is the air from any single pack supplied to a specific cabin zone?

Answer 7

No. The air of all packs is mixed in the conditioned air manifold, except air for FWD and AFT lower lobe.

Question 8

If the cabin altitude AUTO select is in NORM. How many outflow valves are active normally?

Answer 8

Two, which are controlled by the active controller.

Question 9

During normal operations, the APU bleed air switch is on or off?

Answer 9

On. Works automatically.

Question 10

Where is the lower aft cargo air condition supplied from?

Answer 10

Pack 2, and trim air directly from the bleed air duct.

Question 11

What position should the outflow valves be when on the ground and doors open and why?

Answer 11

Open, to prevent inadvertent cabin pressurization when closing the doors.

Question 12

What position should the engine bleed valve be during engine start?

Answer 12

Open. (Reverse flow protection is inhibited during start.)

• If closed, there will be no bleed air to the starter.

Question 13

What happens to the cabin altitude during takeoff?

Answer 13

When the aircraft passes 65Kias

1) The outflow valves are commanded closed,
2) The cabin altitude decreases slightly with a minor descent rate to avoid cabin pressure bumps at liftoff.

Question 14

What is the scheduled differential pressure?

Answer 14

8. 4 to 8.8 PSI

8. 4 at lower altitudes to minimize strain on the aircraft structure.

Question 15

What will happen if during step climb from cruise, you start climbing without pushing the AFDS alt selector?

Answer 15

The cabin altitude will be maintained until max dif (8.8Psi) and then increase thereafter with up to 2000FPM.

Question 16

What pressure indications and when do the positive pressure relief valves open?

Answer 16

1) Amber above 8.8 Psi
2) Red above 9.1 PSI
3) At 9,4 , positive pressure relief valves open and PACK 2 shuts OFF.

Question 17

The bleed air SYS FAULT light of engine 4 is displayed along with the BLEED 4 message during CLB power. What does it mean?

Answer 17

HP bleed shutoff valve is not closed.

Question 18

What does the APU caution message mean?

Answer 18

Bleed air duct leak / overheat

* No APU restart possible as long as APU is displayed.

Question 19

What happends when Cargo fire switch is armed?

Answer 19

Pack 3 shuts down automatically.

Question 20

What does PRESS RELIEF caution message mean?

Answer 20

Pack 2 fails to shutdown automatically when pressure relief valves open automatically.

Question 21

What does EQUIP COOLING caution message mean?

Answer 21

1) Smoke
2) Overheat
3) Inadequate airflow