Pneumatics

Question 1

On the SD, when is GND displayed?

Answer 1

Displayed in white when the aircraft is on the ground.

Question 2

How many BMC’s are there? What happens if left or right BMC fails?

Answer 2

• 2
• If one BMC fails, the adjacent BMC takes over the monitoring of the bleed system to issue the following ECAM warnings:
  o Over pressure
  o Over temperature
  o Wing leak.
• BMC 1 lost: (ENG 1) APU leak detection lost.
• BMC 2 lost: (ENG 2) GEN 2 leak detection lost.

Question 3

During normal operation when would you expect to see the HP valve OPEN?

Answer 3

When idle.

• Air is normally bled form the intermediate pressure stage (IP) of engine’s high-pressure (HP) compressor to minimize fuel penalty.
• At low engine speed, when the pressure and temperature of the IP air are to low, the system bleeds air from the HP stage and maintain it at 36+/-4PSI.
• An intermediate pressure check valve downstream of the IP part closes to prevent air from the HP stage from being circulated to the IP stage.

Question 4

How is the Bleed Air Temperature regulated and to what temperature?

Answer 4

• A pre-cooler downstream of the bleed valve regulates the temperature of the bleed air.
• The pre-cooler is an air-to-air heat exchanger than uses cooling air bleed from the engine fan to regulate the temperature to approximately 200 degrees.

Question 5

How is the bleed air pressure regulated? What is the normal pressure?

Answer 5

• The bleed valve, which is downstream of the junction of HP and IP ducting, acts as a shut-off and pressure regulating valve.
• It maintains delivery pressure at 45+/-5PSI.
• May fluctuate between 38 ~ 56PSI with max peak-to-peak pressure of 16PSI) at high engine power to FL100).

Question 6

With the cross-bleed selector in AUTO, what controls the position of the crossbleed valve?

Answer 6

• 2 electric motors, one for automatic, one from manual mode, control the valve.
• In automatic mode, the crossbleed value opens when the system uses APU bleed air. It closes, if the system detects an air leak, except during engine start.

Question 7

What happens if a bleed leak occurs with the crossbleed selector in AUTO?

Answer 7

It closes. Except during engine start.

Question 8

Which bleed (engine or APU) has priority?

Answer 8

APU

Question 9

Does the overhead panel FAULT light extinguish when the temperature drops following a bleed overheat?

Answer 9

The FAULT light goes out when the ENG BLEED p/b switch is OFF if the fault has disappeared.

Question 10

When do the bleed air temperature drops following bleed overheat?

Answer 10

The FAULT light goes out when the ENG BLEED p/b switch is OFF if the fault has disappeared.

Question 11

When do the bleed air temperature and pressure go amber on the S.D?

Answer 11

• Pre-cooler outlet temperature overheat 290 degrees for > 5sec, 270 degrees for > 15sec, 257 degrees for > 55sec, or < 4PSI, or if overpressure detected by BMC (threshold 57-60PSI).

Question 12

Is WAI allowed if only one bleed system is operating?

Answer 12

Yes, if only one pack operating.

Question 13

What should you NOT do if GD LP Air is connected? And the HP air?

Answer 13

LP: Packs 1+2 OFF, to prevent pack contamination.
HP: Do NOT use packs + APU bleed.