*
Temperature limiting.
The backup mode controls the position of the PRSOV for these functions:
*
On/off control
*
Overpressure protection
*
Temperature limiting.
With the engine air supply in backup control, the PRSOV and the HPSOV operate in the pneumatic mode to do pressure regulation and bleed source selection. The FAMV goes to the full open position.
The backup mode gives power to these items:
*
PRSOVC
*
Manifold dual temperature sensor (TM 1)
*
Intermediate pressure sensor.
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The backup mode gets information directly from these sources:
*
Manifold dual temperature sensor (TM 1)
*
Intermediate pressure sensor
*
AIMS
*
DLODS
*
Engine bleed air switch
*
Engine start selector
*
Engine fire switch.
These are some of the data sources and uses in the backup mode:
*
AIMS -engine on/off information for engine air supply on/off
*
DLODS -strut/wing duct leak information for on/off.
Pneumatic Mode
The pneumatic mode does not use the ASCPC for control. It does not use electric power.
The pneumatic mode gives these functions for the engine bleed air supply system:
*
Bleed source selection
*
Pressure regulation.
The HPFAC is mechanically set to cause the FAMV to go full open. The HPFAC also causes the HPSOV to give bleed source selection and pressure regulation at a fixed value.
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The PRSOVC is mechanically set to cause the PRSOV to give pressure regulation at a fixed value.
The engine bleed air system cannot be shut off unless the engine is stopped.
BITE
BITE for the ASCPC has:
*
Continuous BIT
*
Ground test.
Continuous BIT has these functions:
*
Operates when the ASCPC has power and the ground test is not on
*
Uses the HPFAC and PRSOVC to do a preflight test of the FAMV, PRSOV, and HPSOV and the related circuits.
Continuous BIT and ground tests do a check of the pneumatic system LRUs for correct operation. The preflight test and the ground test take approximately 20 seconds.
The preflight test operates when the related engine completes its start. To operate the ground test, select the appropriate test from the MAT.
Indications
A status message (not shown) shows if the primary mode fails. No flight deck effects show if the backup or pneumatic mode fails.
See the indicating system section for more information about indications (SECTION 36-20).
Training Information Point
If the primary mode is off for the left or right ASCPC, it can affect the dispatch of the airplane. If a primary mode is off in one ASCPC, you must make sure the primary mode operates in the other ASCPC and that the backup mode operates in both ASCPCs.
See part II of the airplane maintenance manual for the dispatch deviations guide (DDG) maintenance procedure you use to check the condition of the backup mode.
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General
The primary and backup modes of the ASCPC and the pneumatic mode supply control for the engine air supply system differently. The modes set the position of the HPSOV and PRSOV for these functions:
*
On/off and reverse flow control -primary and backup modes
*
Bleed source selection -primary and pneumatic modes
*
Pressure regulation -primary and pneumatic modes
*
Overpressure protection -primary and backup modes.
On/Off Control -Primary Mode
The following description is based on these conditions: the engine is on and set to idle.
When the engine bleed switch is set to the out (OFF) position, the primary mode commands the HPSOV and the PRSOV to close and the FAMV to open.
The primary mode also closes one or both of the valves, PRSOV and HPSOV if any of these conditions occur:
*
Engine fire switch set to out (PRSOV, HPSOV)
*
ASCPC looking for location of the duct leak (PRSOV)
*
Source loss (PRSOV)
*
This engine start on ground (PRSOV)
*
Ground air source supplies air (PRSOV)
*
Engine off (HPSOV)
* 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：777 AMM 飞机维护手册 气源 Pneumatic(17)
