(b)  
The FMC transmits the following data to the AFDS CP:
 1) FMC discretes
 2) Horizontal steering
 3) Selected altitude
 4) Selected airspeed
 5) Selected mach
 6) Vertical steering rate
 7) Vertical steering

 (c)  
The data transmited and received by the FMC is low speed digital data. The FMC receives an analog discrete which defines the A/T servo Arm status.

 (25)
 Electronic Engine Control (EEC) (Fig. 16)

 (a)  The EECs control actual engine thrust by controlling the fuel flow to the engines. The EECs receive engine trim commands from the FMC's thrust management function. They use these commands along with throttle resolver angle signals to compute fuel flow commands. The throttle resolver angle signals are indirectly controlled by the FMC through the FMC's control of the A/T servo motor.

 (26)
 Air/Ground Relay (Fig. 17)

 (a)  This analog discrete sends the NAV DATA UPDATE signal for enabling the loading of navigation data. Navigation data can only be loaded into the FMC while the airplane is on the ground.

 (27)
 Instrument Source Select (ISS) (Fig. 18)

 (a)  The ISS controls the captain's and F/O's IDU NAV source selection. The possible sources for NAV data are the L-FMC, R-FMC, L-CDU, R-CDU and C-CDU. The ISS also controls the selection of the ADC source select.

 (28)
 Go Around (Fig. 19)

 (a)  
The go around switches are located on the throttle levers. These switches enable the airplane to automatically pull out of an approach flight path.

 (b)  
Following the activation of the go around switch the FMC will control airplane thrust to either an FMC referenced EPR or an engine specified maximum EPR. If the autopilot was engaged at the time the go around switch was pressed, the thrust will be controlled to a referenced EPR. If the go around is activated for a second time then the thrust will be controlled to a maximum EPR. If autopilot was not engaged at the time of activation then thrust will be controlled to the maximum EPR.

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 34-61-00
 ALL  ú ú 26 Page 19 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 (29)
 A/T Disconnect and Reset (Fig. 19)

 (a)  The A/T disconnect and reset switches are located on the throttle levers. They control the deactivation and activation of the FMC autothrottle control. Pressing the A/T disconnect and reset switch causes the CAUTION light on the glareshield to illuminate and the AUTOTHROT DISC message to appear on the AUX EICAS while the switch stays depressed. If autothrottle servo was engaged prior to pressing the switch, the autothrottle is disconnected and the message is displayed until the A/T disconnect switch is pressed a second time.

 (30)
 EICAS Control Panel/FMC Switch (Fig. 20)

 (a)  The FMC master switch controls the selection of the tuning FMC for VHF NAV radios and the data source for the FCCs. The panel also contains the heading select switch.These switches are: 1) FMC master switch (left or right) - The master FMC is
 defined as the FMC which supplies tuning commands to the VHF NAV radios, supplies source data to the FCCs and conducts the self-test when initiated by the CMC. The FMC master switch controls the FMC master switching relays which inturn controls the source data for the VHF NAV radios and FCCs.
 2)  TRUE/NORM switch - this switch controls the selection of the north reference. Selecting NORM results in a magnetic north referenced display, so long as valid magnetic heading data is available. The display automatically switches to a true north reference when magnetic data is unavailable. Selecting TRUE results in a true north referenced display regardless of the availability of magnetic heading.
 (31)
 A/T arm (Fig. 20)

 (a)  The A/T arm switch enables autothrottle mode requests from the thrust management function. The switch position must be in the ARM state for thrust management control of the selected modes. If the A/T arm switch is in the OFF postion the thrust management function will still send reference commands to the autopilot but will not send the mode requests.

 (32)
 Data Loader/Recorder (Fig. 21)

 (a)  The data loader enables the loading of FMC operational software and navigational data. It also has the capability of recording data onto a diskette. There exists a handshake method of data transfer. The data loader sends a request signal. The requested LRU responds with a load enable signal at which time the data loader transfers the required software over a high speed digital bus. The selection of the LRU to be loaded is made on the data loader selector switch located in the crews clothes closet.
　
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