777 AIRCRAFT MAINTENANCE MANUAL
IGNITION -ENGINE COMPONENT LOCATIONS
EFFECTIVITY BEJ ALL 74-00-00
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D633W101-BEJ Sep 05/2002
IGNITION -IGNITION EXCITER
The ignition exciter changes 115v ac input power to pulsing high voltage output power. The high voltage power operates the igniter plug.
Each exciter is a sealed unit inside a removable, two piece heat shield. Fan air cools the exciter, cable and igniter plug.
Functional Description
115v ac power from the engine relay unit (ERU) energizes the ignition system.
The exciter uses capacitive discharge to make high voltage output pulses. The output pulses go through the ignition lead to the igniter plug.
EFFECTIVITY BEJ ALL 74-00-00
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D633W101-BEJ Sep 05/2002
PW4000 SERIES ENGINES
777 AIRCRAFT MAINTENANCE MANUAL
IGNITION -IGNITION EXCITER
EFFECTIVITY BEJ ALL 74-00-00
Page 9
D633W101-BEJ Sep 05/2002
IGNITION -IGNITERS
The igniters fit into threaded igniter plug bosses on the diffuser case. The fan air that cools the exciter-to-igniter plug cable goes out through the heat shield. This keeps the igniter plug cool.
To remove an igniter plug, you must disconnect the heat shield halves and the exciter-to-igniter plug cable. Do not remove the igniter plug boss.
You must replace the key washer if it is worn or damaged.
EFFECTIVITY BEJ ALL 74-00-00
Page 10
D633W101-BEJ Sep 05/2002
PW4000 SERIES ENGINES
777 AIRCRAFT MAINTENANCE MANUAL
IGNITION -IGNITERS
EFFECTIVITY BEJ ALL 74-00-00
Page 11
D633W101-BEJ Sep 05/2002
IGNITION -FUNCTIONAL DESCRIPTION
The EEC uses 28v dc and 115v ac to control and supply power to the ignition system.
Power Sources
The normal supply of power to energize the ignition exciters is 115v ac from the left and right main ac buses. The 115v ac standby bus is the alternate power supply to energize the ignition units.
Relays in the P110 left power management panel automatically select the supply for the ignition units.
Control
When the fuel control switch is in the RUN position, the ignition/ fire detection relay and the generator control/ignition relay send power to the EEC.
The EEC uses airplane and engine conditions to control power to the ignition exciters. Each channel of the EEC can control power to one or two ignition exciters. Each ignition exciter can get power through one of two EEC switches. Channel A of the EEC commands one switch and channel B commands the other switch.
The EEC monitors the position of each switch. A failure of one switch causes the EEC channel in command to operate the switch in the other EEC channel.
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