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ECU - CFM Engines Figure 013
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FQI The FQI issues four buses, FQI-1A, 1B, 2A, 2B. DMC 1 acquires 1A and 2A. DMC 3 acquires 1A and 2B. DMC 2 acquires 1B and 2B. Each DMC preferably uses the FQI-1 (A or B) bus parameters. If the FQI CHANNEL SUPERIORITY signal (bit 13 of word 276) requests the switching to the FQI-2 bus, the DMCs switch to this FQI-2 bus. However the DMC keeps using a given FQI-X bus only if this bus is valid. If the two FQI-1 and 2 buses are invalid, the DMC permanently switches from one to the other until a valid one is found. Meanwhile, the fuel quantity parameters are flagged (XX) on the ECAM E/W image. TCAS (Ref. Fig. 014) Each DMC receives and processes TCAS data. The NDs indicate the position of intruders in the airspace in ROSE or ARC mode. The PFDs provide the crew with vertical speed indications to avoid these intruders. The Flight Warning Computers (FWC) ensure the monitoring and the validity of these data. If one part of the TCAS is faulty, a message is displayed on the engine page of the upper ECAM display unit.
B.
FWC Message Bus (RS 422) Inside each DMC, the principle of selection of the FWC 1 or FWC 2 message bus obeys the same rules as for the ARINC 429 bus. Each DMC preferably works with the FWC 1 RS-422 bus. In case of detected failure, it automatically switches to the FWC 2 RS-422 bus. A given FWC RS-422 bus is considered as valid if :
-each block is complete : detection of the start of block (Soh code for E/W blocks, Stx for S blocks) and of the end of block (Etb code for E/W blocks, Eot for S blocks)
-the number of characters which are received by the DMC matches the number of characters which are transmitted. This number is given in the 3-digit number which follows the end of block code (the 3 characters of the 3-digit number are included in the total number of characters which are transmitted)
-each character is valid : for the characters, a parity check is made. If a character is not valid, the block is considered as invalid if the failure is confirmed during 3 successive transmissions
-the time between two successive blocks of the same nature does not exceed 1.5 s.
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TCAS Buses Figure 014
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C. Weather Radar Buses (ARINC 453) (Ref. Fig. 015) A Weather Radar equipment which complies with ARINC 708-4 is installed. Each DMC receives from the W/R transceivers units their two data buses, D1 and D2. The DMC processes information from the operating W/R transceiver (only one at a time according to the position of the 1-2 selection switch on the W/R control unit and provided that W/R operation is enabled by the W/R request control signal). Provided that the W/R operation is requested on the W/R control unit, the ND presents a W/R image in all the ND modes except the PLAN mode. If both pilots select the PLAN mode, the DMCs send the W/R REQUEST discrete signal in the open state, which disables the W/R XCVR. This avoids useless operating hours. Data bus selection : The DMCs which operate on side 1 normally work with the DATA 1 buses (XCVR 1-1 or XCVR 2-1), which correspond to the CAPT range selection. However, the DMCs which operate on side 1 may operate with a DATA 2 bus,
i.e. using the data corresponding to the range selected by the F/O, in case of an FMGC 1 failure which leads to an automatic changeover to the FMGC 2 data in the DMC 1. In this case, the DMC 1 (or DMC 3 if the EIS DMC selector switch is set to CAPT/3) processes the DATA 2 bus from the W/R XCVR in operation. The range markers and the mode on the Captain ND are then those corresponding to the F/O selection, which is indicated on the Captain ND by an amber message : SELECT OFFSIDE RANGE & MODE. This message may disappear sooner, if the Captain selects the same range as the First Officer. The same applies for the DMCs working on side 2, which normally use the D2 buses, but which use the D1 buses in case of FMGC 2 failure.
NOTE : The W/R equipment has different buses, D1 being associated to the
____
CAPT range, and D2 to the F/O range.
NOTE : If there is a discrepancy between the range selection from the FCU
____ and the range selection sent on the corresponding W/R data bus, no W/R image is displayed and the W/R RANGE red message is displayed.
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W/R Transceiver - DMCs Interface
Figure 015
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