Engine Bleed System

Question 1

Under what conditions would High Pressure (HP) air be used?

Answer 1

• Descent
• Other low power setting operations
FCOM, VOL 2. 2.40.1

Question 2

Under what conditions would Intermediate Pressure (IP) air be used?

Answer 2

• High power setting operations.

FCOM, VOL 2; 2.40.1

Question 3

The Engine Bleed Air Switches control which valves, when bleed air pressure is available?

Answer 3

• Engine bleed air valve
• PRV
• HP bleed valve
FCOM, VOL 2; 2.10.25

Question 4

Describe the general function of pressure regulating valve (PRV)?

Answer 4

• Prevents damage to ducting and equipment downstream, by limiting
bleed air pressure.

FCOM, VOL 2; 2.40.1

Question 5

How are the engine bleed air valves actuated, and when do they open for forward flow?

Answer 5

• The bleed air valves are pressure actuated.
• They remain closed until engine bleed air pressure causes
forward flow.
- When the engine start switch is pulled, the valve opens to allow reverse flow
from the centre bleed duct, to open the start valve.

FCOM, VOL 2; 2.40.1

Question 6

With the HP valve failed open and the respective bleed air switch OFF, will nacelle anti-ice be available?

Answer 6

• No
- The HP air will be too great for the engine duct, so the PRV will remain
positively closed, this will prevent nacelle anti ice operation.

FCOM, VOL 2; 2.40.2

Question 7

An Engine Bleed Air System (SYS FAULT) light indicates what?

Answer 7

• Bleed air overheat
• Bleed air overpressure
• HP bleed valve open when commanded closed
• PRV open when commanded closed
   FCOM, VOL 2; 2.10.25

Question 8

What does a bleed duct Isolation (ISLN) VALVE light indicate (amber)?

Answer 8

• Isolation valve position disagrees with switch position

FCOM, VOL 2; 2.10.34

Question 9

What prevents reverse air flow into the engine compressor sections during engine start?

Answer 9

• The PRV is positively closed

FCOM, VOL 2; 2.40.1

Question 10

What happens if the engine start valve fails to close?

Answer 10

• Bleed air is isolated from the engine starter
• The PRV remains positively closed
• The engine bleed air valve remains closed.
• Nacelle anti-ice and thrust reverse are not available for the
respective engine.
FCOM, VOL 2; 2.40.2

Question 11

What two valves close in the engine if a bleed air overheat is detected?

Answer 11

• PRV
• HP valve
- Pushing the bleed air switch OFF to ON, resets the ENG bleed fault
detection system.

FCOM, VOL 2; 2.40.2

Question 12

What conditions in the engine bleed air system would prevent nacelle anti ice operation when the bleed air switch is ON?

Answer 12

• The PRV has failed closed, or
• The PRV has been closed due to a bleed air overheat, or
• The start valve is not closed
FCOM, VOL 2; 2.40.2

Question 13

How would you isolate a bleed air duct section in the event of a bleed duct leak is detected?

Answer 13

• Close the respective isolation valve
• Close the engine bleed air valves.
FCOM, VOL 2; 2.40.4

Question 14

Do we normally operate with the Isolation Valves open or closed?

Answer 14

• Open

FCOM, VOL 2; 2.40.3

Question 15

If the center duct is isolated, how is temperature controlled in all temperature zones?

Answer 15

• All temperature zones operate in backup temperature control mode
• Trim air is unavailable.
FCOM, VOL 2; 2.40.4

Question 16

With a left or right duct isolated, how would the leading edge flaps extend on the affected side, and what EICAS Advisory message would display?

Answer 16

• The respective LEF operate electrically in secondary mode.
• FLAPS PRIMARY (until LEF extended)
FCOM, VOL 2; 2.40.3/9.30.1

Question 17

How does an isolated left or right duct affect the hydraulic systems?

Answer 17

• The respective hydraulic demand pump 1 or 4 is turned off, this avoids
The EICAS alert message HYD PRESS DEM on approach.

FCOM, VOL 2; 2.40.4

Question 18

What two systems use engine bleed air downstream in the engine duct prior to the engine bleed valve?

Answer 18

• Nacelle anti-ice
• Thrust reverse
FCOM, VOL 2; 2.40.5 (diagram)

Question 19

What systems use the (R) WING bleed air duct?

Answer 19

• Packs
• Hydraulic system 3 & 4 reservoir pressurisation
• Hydraulic demand pump 4
• Wing anti ice
• Leading edge flaps

Question 20

What systems use the (L) WING bleed air duct?

Answer 20

• Pack 1
• Hydraulic system 1 & 2 reservoir pressurisation
• Wing Anti ice
• Leading edge Flaps
• HYD SYS 1 demand pump.

Question 21

What systems use the (C) bleed air duct?

Answer 21

• Pack 2
• Trim Air
• Aft cargo heat
• Cargo smoke detection
• potable water pressurisation
• Lower lobe cargo air conditioning trim air.

Question 22

ENGINE BLEED air switches ON and OFF functions?

Answer 22

ON
- Engine bleed air valve will open for engine start, and
- Engine bleed air valve, PRV and HP valve open by system logic when
bleed air pressure is available.
OFF
- Engine bleed air valve, PRV and HP bleed valve close.
- PRV opens for nacelle anti-ice on, unless the PRV closed by,
- Prior or present bleed air overheat,
- PRV failed closed,
- Start valve not closed, or
- HP bleed valve failed open.
GE
- HP bleed valve and PRV open for thrust reverse , unless PRV closed by,
- Prior or present bleed air overheat, or
- PRV failed closed,
- Start valve not closed.

Question 23

APU BLEED air switch ON/ OFF logic?

Answer 23

ON
- Valve commanded open when EICAS memo message APU RUNNING 
  is displayed.
OFF
 - Valve closed.

Question 24

APU BLEED air Amber VALVE light means?

Answer 24

• APU bleed air isolation valve position disagrees with the switch position.

Question 25

PACKS control selector functions, OFF/NORM/A/ B?

Answer 25

OFF
- pack valve closed,
- Extinguishes pack SYS FAULT light for selected pack, and
- Resets pack fault detection system
NORM
- Pack controller A or B selected for alternate flights,
- Selected pack controller is primary other secondary.
A
- Selects controller A as primary, selects B if A fails.
B
- Selects controller B as primary, selects A if B fails.