2) Flap Control Unit (FCU) 3) Proximity Sensor Electronics Unit (PSEU) 4) Thermal Anti-Ice (TAI) Idle Relay 5) Channel Select Relay 6) Air/Ground Relay 7) Three Ground Safety Relays
 (c)  Idle speed is selected when the idle select circuit in the EEC is grounded or opened. The channel select relay will ground the idle select circuit when energized, which puts the engine to minimum idle. With the channel select relay relaxed, the idle select circuit is open, which puts the engine to approach idle. 1) When the airplane is on the ground, the PSEU relaxes a
 ground safety relay and the air/ground relay which lets the EEC/TMC discretes card supply 28 volts dc to the channel select relay. The PSEU also energizes two other ground safety relays which, in turn, energize the channel relay. With the channel select relay energized, the idle control circuit in the EEC is grounded and the engine is commanded to minimum idle.
 2)  When the airplane is in the air, the PSEU energizes a ground safety relay and the air ground relay. The PSEU also relaxes two other ground safety relays. This lets the FCU and NACELLE ANTI-ICE switch control the channel select relay and EEC/TMC discrete card. a) With the NACELLE ANTI-ICE switch in the OFF position
 and the flaps are not in the landing position, the channel select relay is energized and the engine goes to minimum idle.
 b)  When the flaps are moved to the landing position or the NACELLE ANTI-ICE switch is set to the ON position, energy in the channel select relay is removed which lets the engine go to approach idle.
 (8)  
Supplemental Control Unit (SCU)

 (a)  
If the EEC does not get power from the EEC alternator (N2 transducer), the SCU uses 28 volts dc power from the airframe and is an alternate power source to the EEC.

 (b)  
The SCU also supplies an automatic sequence of an engine start, when selected. The SCU monitors critical engine parameters and takes the necessary action when engine start anomalies are found. For more data on the autostart system, refer to AMM 80-11-00, Starting - Description and Operation.

 B.  
Control

 (1)  
The EEC controls engine thrust in relation to the thrust lever position. A thrust lever angle transducer sends two proportional signals to the EEC. At the full forward thrust lever position, the EEC commands the engine to full takeoff power.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
(2)  
The control mode of the EEC can be manually set from the flight compartment. The ELEC ENG CONTROL module, found on the pilot's overhead panel (P5), contains a two-position pushbutton switch for each engine. With the switch set to ALTN, the EEC changes to the alternate N1 control mode and ENG (1, 2, 3, or 4) EEC MODE is shown on the main EICAS screen as an advisory message and can show on the auxiliary EICAS status page as a status message. With the switch released to NORM, the EEC will change to the normal EPR control mode if there are no EEC or sensor faults which prevent EPR control.

 (3)  
The channel in control will change between A and B each time the FUEL CONTROL switch is put to the CUTOFF position and N2 rotor speed is less than 20%. If one channel is cannot fully control the engine, the other channel will stay in control.

 (4)  
Four FUEL CONTROL switches, one for each engine, are installed on the control stand below the forward thrust levers. The FUEL CONTROL switch, when put to the RUN position, commands the fuel condition control motor actuator (Ref 76-11-00/001) to open the fuel shutoff valve in the FMU. When the switch is put to the CUTOFF position, it commands the fuel condition control motor actuator to close the fuel shutoff valve.

 (5)  
The SCU controls fuel flow to the engine if the AUTOSTART switch(es), installed on the pilot's overhead panel (P5), is put to the ON position and one of the listed conditions occurs:

 (a)  
N2 less than idle rpm

 (b)  
Starter assisted in-flight start

 (c)  
Windmill in-flight start

 (d)  
Ground start

 (6)  
For ground test purposes, power can be supplied to the EEC without engine operation. Four POWER switches, one for each engine, are installed on the pilot's overhead maintenance panel (P461) EEC MAINT module. Ground test power is supplied to the EEC when the POWER switch is moved from NORM to TEST. With the POWER switch in TEST position, EEC (1, 2, 3, or 4) GND PWR status message can show on the auxiliary EICAS.
　
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