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Duct Leak and Overheat Detection System
A bleed duct overheat system is provided to detect leaks. If a duct leak is detected,
the bleed air duct section affected can be isolated by closing the respective
isolation and engine bleed air valves.
Bleed Air System Non-normal Operations
If a bleed duct leak is detected, closing the respective isolation and engine bleed
valves prevents further air loss.
If the center duct section is isolated, pushing the Aft Cargo Heat switch off closes
the electrically operated aft cargo heat valves to prevent cabin air flowing in
reverse through the aft cargo heat supply duct and into the leaking center dect
section. All temperature zones operate in backup temperature control mode
without trim air. Potable water pressurization and cargo smoke detection are not
available.
If the left or right duct section is isolated, the respective leading edge flaps operate
electrically in secondary mode. The respective hydraulic demand pump one or
four is selected OFF to avoid the EICAS alert message HYD PRESS DEMAND
from being displayed during approach. A maximum of one air conditioning pack
on assures sufficient thrust is available from the two engines which supply air to
the unaffected duct sections.
The EICAS alert message BLEED is displayed for bleed overpressure, or PRV or
HP bleed valve failed to close when commanded. If the respective NAI VALVE
message is displayed after pushing the related Nacelle Anti-ice switch ON, the
PRV is closed because the HP bleed valve failed open and nacelle anti-ice is not
available.
December 01, 1999
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
2.40.4 D6-30151-425
Air Systems -
Bleed Air System Description
Bleed Air System Schematic
PRV
PRV
PRECOOLER
FAN
PRECOOLER
FAN
AFT CARGO HT
ON
TEMP
ON
TRIM AIR
3
3
REVERSER
THRUST
REVERSER
THRUST
IP
BLEED
START
VALVE
IP
4
BLEED
4
START
VALVE
BLEED
VALVE
ENGINE
3
OFF
ON
ON
OFF
AUTO
4
NACELLE
ANTI-ICE
VALVE VALVE
3
NORM NORM
OFF A
B
1
L ISLN
OFF
NORM
2
A
B
R ISLN
OFF A
B
ON
AUTO
OFF
AUX
FLAPS
AIR DRIVEN
HYDRAULIC
DEMAND PUMP
DUCT P
PRESSURE
P DUCT
LE
PRESSURE
ENGINES
1 & 2
TO
LEFT
WING
AND
AIR CONDITIONING PACKS
RESERVOIR
PRESS
HYD SYS 4
HYD SYS 3
RESERVOIR
PRESS
ON
OFF
AUTO
3
ANTI-ICE
NACELLE
OFF
ENGINE
BLEED
VALVE
ON
4
HP BLEED
HP BLEED
OFF
AUTO
ON
WING
ANTI-ICE
POTABLE WATER
PRESSURIZATION
DETECTION
CARGO SMOKE
ISOLATION
VALVE
APU BLEED AIR
SOURCES
GRD
APU
VALVE
ON
APU
December 01, 1999
747 Operations Manual
Air Systems Chapter 2
EICAS Messages Section 50
Copyright © The Boeing Company. See title page for details.
D6-30151-425 2.50.1
Air Systems EICAS Messages
The following EICAS messages can be displayed.
EICAS Alert Messages
Message Level Aural Condition
BLD DUCT LEAK
L, C, R
Caution Beeper Bleed air leak or overheat along the left,
center, or right duct section.
Message Level Aural Condition
BLD OVHT/PRV
1, 2, 3, 4
Advisory Engine bleed air overheat or PRV failed
closed.
BLEED 1, 2, 3, 4 Advisory Engine bleed air overpressure, or HP bleed
valve or PRV failed to close when
commanded.
Message Level Aural Condition
>BLEED 1, 2, 3, 4
OFF
Advisory Engine Bleed Air switch OFF, engine
operating, and engine bleed air valve
closed.
BLEED HP ENG
1, 2, 3, 4
Advisory HP bleed valve failed closed.
BLEED ISLN L, R Advisory Isolation Valve switch position and valve
position disagree.
Message Level Aural Condition
>BLEED ISLN
APU
Advisory APU bleed isolation valve position
disagrees with commanded position.
April 01, 2001
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
2.50.2 D6-30151-425
Air Systems -
EICAS Messages
Message Level Aural Condition
CABIN ALT
AUTO
Caution Beeper Both cabin altitude controllers inoperative
or both Outflow Valve Manual switches
　
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