Pneumatics

Question 1

What are all the sources of pressurized air?

Answer 1

6th or 10th stage (if load requires) engine compressor, APU, and external ground source.

Question 2

Which systems are pneumatically operated?

Answer 2

Engine starting, wing/cowl anti-ice, air conditioning, and pressurization

Question 3

What’s an ACSC?

Answer 3

Air conditioning systems controller

Question 4

With respect to pneumatics, what do the Air Conditioning Systems Controllers do?

Answer 4

They control bleed air source selection, valve operation, and bleed air distribution.

Question 5

What valve connects the engines to the rest of the pneumatic system?

Answer 5

The Engine bleed valves

Question 6

What valve allows the 10th stage to supply bleed air?

Answer 6

The high pressure valve

Question 7

What does the isolation valve do?

Answer 7

Separates the left side from the right side of the pneumatic system. Can be opened to allow air to move between the left and right sides.

Question 8

What does the one way check valve do?

Answer 8

Prevents reverse flow from to the 10th stage (high pressure bleed air) into the 6th stage duct (lower pressure). Also blocks the output of the 6th stage air when the HPV is open.

Question 9

Where is the APU Load Control Valve and what does it do?

Answer 9

It is located just past the the APU bleed air duct which isolates the APU bleed air from the rest of the pneumatic system. Closing the LCV disallows the APU from supplying bleed air. By modulating the LCV the bleed air leaving the APU can be regulated to maintain a constant 45psi in the bleed air duct.

Question 10

What controls the APC Load Control Valve?

Answer 10

The APU Electronic Control Unit (ECU)

Question 11

What is the normal pressure in the bleed air duct?

Answer 11

45PSI

Question 12

Will the ISOL valve be open when the APU is providing bleed air?

Answer 12

Yes

Question 13

On the ground, which bleed source has priority?

Answer 13

APU bleed air

Question 14

Can the APU provide bleed air if anti-ice is on?

Answer 14

No

Question 15

What would happen with the pneumatics in auto mode, APU running, and you select anti-ice on?

Answer 15

The APU Load Control Valve is automatically closed (cuts off all APU bleed air), and the engine bleed valves are commanded open (engines will provide bleed air)

Question 16

What happens with the pneumatics in Manual mode, APU selected as the bleed source, and then anti-ice is selected ON?

Answer 16

• APU Load Control Valve (LCV) is left open (APU continues to provide bleed air)
• Engine bleed valve are kept closed (engines aren’t providing bleed air)
• Wing anti-ice valve are kept closed (no bleed air is sent to the wings)
• BLEED MISCONFIG caution message appears

Question 17

If operating the APU on the ground, with pneumatics in AUTO, when will the bleed source switch from the APU to the engines during takeoff?

Answer 17

Occurs when all of the following have happened.

- Gear up
- Flaps 20º or less
- Thrust retarded from the TOGA detent

Question 18

If operating the APU in the air, with pneumatics in auto mode, when will the bleed air switch from the engine to the APU during the approach?

Answer 18

Occurs when flaps are greater than 20º OR landing gear is extended

Question 19

What happens when the ENG START switchlight is pressed?

Answer 19

Pack valves close
Isolation valve closes
Bleed valves open
Start valve opens
Starter (air turbine starter, ATS) engages

Question 20

What happens to the valves when the engine starter cuts out?

Answer 20

All valves return to their previously selected position

Question 21

What do the dual sensing loops do?

Answer 21

They monitor for leaks in the bleed system. They do this by having two wires (a live and a ground) surrounded by a thermistor material. When the loop heats up, the thermistor materials electrical resistance decreases. This leads to the live wire shorting to ground. This short is detected as an overheat condition. In order to display a warning both loops need to sense an overheat condition.

Question 22

Which areas have dual loops?

Answer 22

Aft equipment bay, wings, center fuselage, bleed air ducts, and anti-ice ducts.

Question 23

How is a leak detected in the cowl anti-ice duct?

Answer 23

A pressure transducer is located in the outer tube of the dual tube anti-ice duct in the cowl. Normally bleed air only passes through the inner tube. If an increased pressure is detected in the outer tube it indicates a leak in the cowl anti-ice.

Question 24

How is a leak or failure detected in the outer portion of slat number 3?

Answer 24

A temperature sensor is located on the outer part of each sides slat number 3 to detect a leak.

Question 25

What are the five zones that can be isolated individually using the SOV’s?

Answer 25

• Left and right bleed zones
• Left and right Cowl anti-ice zones
• Wing anti-ice zones

Question 26

Which valves are closed by the FIRE PUSH switchlights?

Answer 26

Bleed air shut off valve and high pressure valve

Question 27

Which valves are closed by the APU FIRE PUSH switchlight?

Answer 27

APU bleed air load control valve (LCV)

Question 28

What happens when you select the WING A/I CROSS BLEED switch to “FROM LEFT” or “FROM RIGHT”?

Answer 28

It opens the crossbleed valve and closes the opposite side anti-ice valve