PNEUMATIC SYSTEM (BLEED AIR)

Question 1

What sources can supply bleed air?

Answer 1

1. The Engines
2. The APU
3. Ground air source

Question 2

List some systems that uses bleed air

Answer 2

Cargo heating
Air driven pumps
Air conditioning packs
HYD reservoir pressurization
Wing anti-ice
Potable water pressurization
Engine and APU starting
Trim air
Engine anti-ice

Question 3

How many bleed air sources are there?

Answer 3

2

From the engines LP and HP sections

Question 4

When is bleed air taken from the LP and the HP sections respectively?

Answer 4

Taken from the LP section normally. Air from the HP section supplements low pressure air during low thrust settings.

Question 5

What controlls the engine bleed air system?

Answer 5

The ASCPC (Air Supply Cabin Pressure Controller)

Question 6

How does the ASCPC regulate bleed air?

Answer 6

It controlls the HP bleed valve.
Regulates total bleed pressure via the PRSOV valve and gets temp info from a temp probe so that total bleed pressure can be regulated if it is too hot.

Question 7

How is engine anti-ice air supplied?

Answer 7

LP stage is used during low power settings

Question 8

When is higher pressure air required from the engines?

Answer 8

During descent and other low engine power operations

Question 9

When are the engine bleed air valves closed automatically?

Answer 9

During start
For bleed source loss
Bleed air over temp and pressure
A bleed duct leak
When the engine fire handle is pulled
When a ground cart  is supplying air

Question 10

Up to what altitude is APU bleed air available?

Answer 10

Approximately 22’000 ft

Question 11

Is ground bleed air High pressure or Low pressure air?

Answer 11

It is high pressure air

Question 12

What is the normal position of the three isolation valves?

Answer 12

Left and Right open

Center is closed

Question 13

How does the system isolate a duct leak?

Answer 13

Using automatic isolation logic

Question 14

What EICAS message will indicate a leak?

Answer 14

BLEED LEAK

Question 15

What EICAS message will indicate that the leak has been isolated?

Answer 15

BLEED LOSS

Question 16

What is APU bleed air used for?

Answer 16

Air conditioning on the ground and for engine starting

Question 17

What happens to the isolation valves when the APU is started and in AUTO with Engines not running?

Answer 17

All 3 isolation valves open

Question 18

Describe the start sequence with regard to how the APU and bleed system operates?

Answer 18

To start first Engine APU bleed air is used. Once the Engine is running the APU bleed valve closes and all isolation vales are open so that that Engine supplies the whole system.
To start second Engine the APU valve opens again and the Engine bleed valve closes.
When second Engine is started the APU bleed valve closes and the Center isolation valve also closes