B747F Bleed Air System
Under what conditions would High Pressure (HP) air be used? - Answer- During descent and other low power setting operations.
Under what conditions would Intermediate Pressure (IP) air be used? - Answer- During high power setting operations.
Which valves does the Engi...
B747F Bleed Air System
Under what conditions would High Pressure (HP) air be used? - Answer- During
descent and other low power setting operations.
Under what conditions would Intermediate Pressure (IP) air be used? - Answer-
During high power setting operations.
Which valves does the Engine Bleed Air Switches control by system logic when
bleed air pressure is available? - Answer- Engine bleed air valve, the HP bleed valve
and the PRV (pressure regulating valve).
Describe the general function of the Pressure Regulating Valve (PRV). - Answer- To
prevent damage to ducting and equipment downstream, the PRV limits bleed air
pressure.
How are the engine bleed air valves actuated, and when do they open for forward
flow? - Answer- The bleed air valves are pressure actuated and remain closed until
engine bleed air pressure causes forward flow.
With the HP valve failed open and the respective bleed air switch OFF, will nacelle
anti-ice be available? - Answer- No.
What does an Engine Bleed Air System (SYS) FAULT light indicate? - Answer-
Bleed air overheat, or
Bleed air overpressure, or
HP bleed valve open when commanded closed
PRV open when commanded closed
What does a bleed duct Isolation (ISLN) VALVE light indicate (amber)? - Answer-
Isolation valve position disagrees with switch position.
What prevents reverse air flow into the engine compressor sections during engine
start? - Answer- The PRV is positively closed to prevent reverse air flow into the
engine compressor sections.
What happens if the engine start valve fails to close? - Answer- Bleed air is isolated
from the engine starter because both the PRV and the engine bleed air valve remain
closed.
What two valves close in the engine if a bleed air overheat is detected? - Answer-
The PRV and HP bleed valves close.
What conditions in the engine bleed air system would prevent nacelle anti-ice
operation when the bleed air switch
is ON? - Answer- The PRV has failed closed or,
the PRV has been closed due to a bleed air overheat, or
the start valve is not closed
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