R **ON A/C 062-099, 106-149, 151-199, 204-299, 301-399, 401-499,
 NOTE : After you open the two FCU circuit breakers (during the FCU
____ removal procedure), you will continue to see the FCU displays for some time. This is because of the residual polarization of the liquid crystals.
 A. System Functions (Ref. Fig. 006A) The FCU ensures the interface between the crew and the three following systems:
 -AFS (Ref. NOTE)

 -
EIS LEFT

 -
EIS RIGHT
 In normal operating conditions each computation channel performs a
 specific function as follow:

 -
channel B : EIS LEFT and AFS

 -
channel C : EIS RIGHT
 In the event of a failure of one channel, there is reconfiguration on the
 remaining channel.
 The reconfiguration logic is defined in the following table:

 1EFF : ALL 1 22-81-00Page 11 1 1 Aug 01/05 1 1 1CES 1

 Changeover Figure 006 
R 1EFF : 1 1 1CES  001-049, 051-061, 101-105, 201-203,  1 111 22-81-00 Page 12 May 01/05

 Control of the FCU in Normal Operation
 Figure 006A

 -----------------------------------------------------------------------------| FAILED | FUNCTIONS | | CHANNEL -----------------------------------------------------------| | EIS LEFT and AFS | EIS RIGHT | |---------------------------------------------------------------------------| | NONE | B | C | |-----------------|--------------------------------------|------------------| | B | C | C | |-----------------|--------------------------------------|------------------| | C | B | B | -----------------------------------------------------------------------------
This logic enables the maximum availability of FCU functions.
 Each channel receives all data required to ensure the three functions.
 Reconfiguration for the activated channel therefore consists in
 connection of that channel to output interfaces via ARINC bus to the
 related control panel.

 B. Operational Interface
 (1)
 Input signals

 (a)
 Connections with the FMGCs
 Channels B and C receive from each FMGC :

 -FMGC OWN A bus
 -hardwired discretes: confirmation of AP, FD and A/THR engagements
 -a hardwired discrete: FCU validity detected by the FMGC

 (b)
 ARINC feedbacks For synchronization (Ref. para. C) and internal monitoring (Ref. para. D) purposes, the AFS, EIS CP-L and EIS CP-R output buses are looped back to the two channels.

 (2)
 Output signals

 (a)
 Discrete signals The FCU delivers control data for AP1, AP2 and A/THR engagement to each FMGC in the form of hard-wired discretes. Those data are issued directly from the engagement pushbutton switches without software processing. Each pushbutton switch contains two contacts in order to duplicate the output signals.

 (b)
 ARINC 429 bus A bus is associated with each function performed by the FCU. For segregation reasons transmission of data to the engines has required the creation of four identical outputs for the AFS. The FCU therefore delivers a total of four ARINC buses.

 Those are :
 AFS-1A  *
 AFS-1B  *
 AFS-2A  *
 AFS-2B  *

 (* :Identical content)
 C. Synchronization In order to avoid display modifications during reconfigurations, the channel non-active on a given function synchronize on the values computed by the channel active on this function. This is accomplished through wrap-around buses. The passive channel permanently acquires, on this bus, the data computed by the active channel. If the active channel is faulty, the activated channel is initialized with the data just acquired on the bus associated with the related function. There is also synchronization, with aircraft in flight, after long power cuts. In this case, the data used are those stored in the RAM (Random Access Memory) prior to power cutoff. The displays are thus maintained.
 D. System Monitoring (Ref. Fig. 005) The FCU is monitored by :
 -a watchdog which checks the correct operation of the program of each computation channel
 -the active FMGC which compares, for the channel active on the AFS function, the data received from the FCU with its transmitted data.
 In the event of a fault, the faulty channel disconnects itself (FCU HLTY/B or C discrete signal). As the remaining channels are prompted on its validity status, the reconfiguration process is engaged and a failure message is sent to the FWS.
　
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