777 AMM 飞机维护手册 发动机起动 Engine Starting PW 777 AIRCRAFT MAINTENANCE MANUAL(5)

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Magnetic Probe
The magnetic probe catches ferrous contamination in the starter oil system. The probe has threads that attach it to a removal check valve. The valve screws into the bottom of the starter. The valve keeps the oil in the starter when you remove the magnetic probe for inspection.
You remove the valve to drain the oil from the starter.
Training Information Point
When you add oil to the starter, the correct oil level shows when oil goes out of the overflow port. Do not use the oil level sightglass to get the correct oil level.
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PW4000 SERIES ENGINES

777 AIRCRAFT MAINTENANCE MANUAL

ENGINE STARTING -STARTER SERVICING

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PW4000 SERIES ENGINES

777 AIRCRAFT MAINTENANCE MANUAL

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ENGINE STARTING -FUNCTIONAL DESCRIPTION

General
You control the engine starting system with the autostart switch and the start/ignition selector. The EEC automatically controls the starter air valve (SAV).
Autostart Switch
The position of the autostart switch goes to the EEC digitally. When the switch is in the ON position, it arms the EEC to do an autostart operation.
Start/Ignition Selector
When you put the start/ignition selector in the START position, it sends signals to these systems and components:
*
ELMS

*
ASCPC

*
EEC

*
AIMS.

ELMS Power
The ELMS supplies 28v dc power from the captain’s flight instrument bus to energize the engine start control relay. This lets 28v dc power go through the EEC to energize the SAV solenoid.
ASCPC
The ASCPC uses the start signal to control the pressure regulating and shutoff valve (PRSOV) and the isolation valves in the pneumatic system. During an engine start, the ASCPC closes the related PRSOV and opens the applicable isolation valve(s). See the engine air supply section for more information about the ASCPC ENGINE AIR SUPPLY, SECTION 36-11.
EEC
The EEC gets an analog start signal directly from the start/ ignition selector. It also gets a digital start signal through the EDIU. These signals tell the EEC that there is a command to open the SAV.
When you put the start/ignition selector in the START position, 28v dc power goes through the ERU to energize the SAV solenoid.
The SAV logic in the EEC opens the switch in the ERU to remove the 28v dc power from the SAV solenoid. This occurs at the starter cutout speed (approximately 41 percent N2). The loss of power to the SAV solenoid causes the SAV to close.
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