*
Engine bleed air is isolated or off
*
Ground air source is off
*
APU is off.
The third set relates to a pneumatic start for the APU. This set is true if all of these conditions occur:
*
APU fire switch is set to in
*
APU bleed switch is set to AUTO
*
No left wing inboard duct leak
*
No left body duct leak
*
APUC wants to do a pneumatic start of the APU.
The fourth set relates to when the APU is the only air source for the pneumatic system. This set is true if all of these conditions occur:
*
APU fire switch is set to in
*
APU bleed switch is set to AUTO
*
No left wing duct inboard leak
*
No left body duct leak
*
Engine bleed air is isolated or off
*
Ground air is off
*
APU is on.
The fifth set relates to when the APU is used to start the left or right engines. This set is true if all of these conditions occur:
*
APU fire switch is set to in
*
APU bleed switch is set to AUTO
*
No left wing inboard duct leak
EFFECTIVITY BEJ ALL 36-12-00
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -APU SHUTOFF VALVE CONTROL LOGIC
*
No left body duct leak
*
Airplane on the ground
*
Left or right engine start
*
Ground air is off
*
APU is on.
See the duct leak and overheat detection section for more information on wing and body duct leaks (SECTION 26-18).
Valve Closed Control Logic
There are six sets of conditions that cause the ASCPCs to set the APUSOV to close. The valve is set to close if any of these conditions occur:
*
APU bleed switch selected to out (first set)
*
APU fire switch pulled (second set).
The third set relates to when the ASCPCs close the valve to find the location of a duct leak. When the ASCPCs find the location of the leak, the ASCPCs open the valve if it has no effect on the leak or latch the valve close if it does effect the leak. This third set is true if all of these conditions occur:
*
APU is on
*
Valve latched closed logic is not true
*
Hot solenoid cooldown logic is not true
*
ASCPCs want to find the location of a wing inboard or body duct leak.
The fourth set is true if all of these conditions occur:
EFFECTIVITY
BEJ ALL
*
APU is on or transfer buses have power
*
Valve latched closed logic is not true
*
Hot solenoid cooldown logic is not true
*
No pneumatic start for APU
*
Ground air is on.
The fifth set is true if all of these conditions occur:
*
APU is on or transfer buses have power
*
Valve latched closed logic is not true
*
Hot solenoid cooldown logic is not true
*
No pneumatic start for APU
*
No engine start with APU air
*
Engine 1 or 2 bleed air supply systems are on.
The sixth set is true if all of these conditions occur:
*
Transfer busses have power
*
Valve latched closed logic is not true
*
Hot solenoid cooldown logic is not true
*
No pneumatic start for APU
*
APU is off.
Valve Latched Closed Control Logic
The APU shutoff valve is latched closed to isolate a section of duct that has a leak. The valve is latched closed if the APU is on and a duct leak is found in the left wing inboard area or in the left body area.
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AIR SUPPLY DISTRIBUTION -FUNCTIONAL DESCRIPTION -APU SHUTOFF VALVE CONTROL LOGIC
When a duct leak condition occurs, the ASCPCs latch the valve closed only after the location of the leak is known or after a specified quantity of time. These are examples of the time permitted to find the location of a leak:
*
Wing leak, 185 seconds
*
Body leak, 95 seconds.
Training Information Point
The ASCPC has logic that lets the APU isolation valve stay open if the airplane has a wing or body duct leak and any of these conditions occur:
*
Engine start is in progress
*
ADP is on and it is less than three minutes since the airplane has taken off.
This logic lets the engine start complete or makes sure air is available for ADP operate immediately after takeoff. If a wing or body duct leak occurs after the valve is latched close, the valve will not open for engine start or for ADP operation.
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