Pneumatics

Question 1

What are the three sources of HP air?

Answer 1

Engines, APU, and an HP ground cart.

Question 2

Which (6) systems use the pneumatic system?

Answer 2

Water pressurization, hydraulic pressurization, engine start, air conditioning packs, air conditioning compartment ventilation, and wing anti-ice.

Question 3

How is the pneumatic system controlled and operated?

Answer 3

It is electrically controlled and pneumatically operated.

Question 4

How many BMCs are there, and what do they monitor?

Answer 4

There are two BMCs, one for each engine.

Question 5

What happens if one BMC fails, and how do they interact?

Answer 5

The other BMC automatically takes over its functions, as they continuously exchange data with each other.

Question 6

How is the air prepared before being supplied to the pneumatic system?

Answer 6

It is pressure and temperature regulated.

Question 7

From which stages of the High-Pressure Compressor (HPC) is HP air tapped?

Answer 7

HP air is tapped from two HPC stages:
1- The Intermediate Pressure (IP) stage
2- The High Pressure (HP) stage

Question 8

What valves control the bleed air supply from the HPC stages?

Answer 8

The Intermediate Pressure Check Valve (IPC) and the High-Pressure Valve (HPV) control the bleed air supply.

Question 9

When is the HP stage used for bleed air, and when does the IP stage kick in?

Answer 9

The HP stage is used only when the engine is at low power. Once IP pressure is sufficient, the HPV closes, and the IPC opens, allowing air from the IP stage instead.

Question 10

What valve regulates engine bleed air pressure before it enters the pneumatic system and what are its functions?

Answer 10

The Pressure Regulating Valve (PRV):
1- Regulates the system pressure
2- Acts as a shut-off valve

Question 11

What monitors system pressure and shuts down engine bleed if overpressure occurs?

Answer 11

The BMC monitors system pressure & will shut down engine bleed if an over-pressure is detected.

Question 12

What protects the aircraft pneumatic system from overpressure downstream of the PRV?

Answer 12

The Over Pressure Valve (OPV) is installed downstream of the PRV to protect the pneumatic system if overpressure is detected.

Question 13

What is the purpose of the Precooler in the bleed air system?

Answer 13

The Precooler is an air-to-air heat exchanger that cools hot bleed air before it enters the pneumatic system.

Question 14

How is the Precooler cooled?

Answer 14

Fan discharge air is used to cool the precooler. The Fan Air Valve (FAV) modulates the amount of fan air that flows across the precooler to maintain bleed air temperature within limits.

Question 15

What happens if the bleed air temperature exceeds safe limits?

Answer 15

The Bleed Monitoring Computer (BMC) monitors system temperature and will shut down engine bleed if an over-temperature is detected.

Question 16

When is APU bleed air mainly used?

Answer 16

APU bleed air is primarily used on the ground for:
1- Air conditioning
2-Engine start

It can also be used in flight but only below a certain altitude:
1- During climb up to 23,000 ft
2- During descent from 21,000 ft

Question 17

To which part of the pneumatic system is APU bleed air connected?

Answer 17

APU bleed air is connected to the left-hand side of the Cross-Bleed Valve.

Question 18

What happens to the Cross-Bleed Valve when APU bleed air is turned on?

Answer 18

The Cross-Bleed Valve opens automatically when APU bleed is on, allowing pneumatics to supply both sides of the aircraft.

Question 19

Where is the Ground Cart Supply connected in the pneumatic system?

Answer 19

The Ground Cart Supply is connected to the left-hand side of the Cross-Bleed Valve

Question 20

How can pneumatic air be supplied to the right-hand side of the system when using ground air?

Answer 20

By manually opening the Cross-Bleed Valve using the cockpit pushbutton, pneumatic air can be supplied to the right-hand side.

Question 21

Where are the HP ground air connections located?

Answer 21

There are two physical HP ground connections located at the bottom left of the belly fairing.

Question 22

What prevents backflow at the HP ground air connections?

Answer 22

Each HP ground connection is fitted with a non-return valve to prevent backflow.

Question 23

Where are Leak Detection Elements installed in the pneumatic system?

Answer 23

Leak Detection Elements are installed along the pneumatic supply ducts and are monitored by the Bleed Monitoring Computers (BMCs).

Question 24

How are the Leak Detection Loops designed?

Answer 24

The loops consist of multiple sensing elements connected in series.
There are two loops (A & B) routed in parallel along the pneumatic ducts.

Question 25

How do the BMCs detect a pneumatic leak while avoiding false warnings?

Answer 25

The BMCs use AND logic, meaning both Loop A and Loop B must detect a leak before triggering a warning, reducing spurious alerts.

Question 26

Where is the Dual Loop Detection System installed?

Answer 26

The Dual Loop Detection System is installed along: 1- The APU supply duct 2- The wings 3- The fuselage 4- The air conditioning compartments

Question 27

Where is the Single Loop Detection System installed?

Answer 27

The Single Loop Detection System is installed in each engine pylon and is monitored by its respective BMC.

Question 28

What does the white "GND" indication on the pneumatic system display mean?

Answer 28

The white "GND" indication appears only when the aircraft is on the ground and serves as informational only. It indicates that: 1- Ground pressure connects to the left-hand side of the pneumatic system. 2- It does NOT mean that bleed air is connected or that the ground air door is open.