Braking Functional Test - Chronogram
 Figure 002

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 NWS Functional Test-Chronogram
 Figure 003

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R **ON A/C 401-499,

R  B. Operation of the Functional Test 
R  The functional test starts as soon as the gears are locked down. 
R  Its purpose is to do the test of the hydraulic equipment under pressure 
R  and the electronic control components of the selected BSCU system. 
R  It also monitors the availability of the automatic braking and of the 
R  nosewheel steering systems until the touchdown. 
R  This is to meet the safety requirements of a CAT III B landing. 
R  For this purpose, the BSCU sends four availability discretes to the two 
R  FMGCs. 
R  The functional tests are performed by a single system (SYS1 or SYS2), 
R  selected by the BSCU. At each flight, the BSCU changes the system 
R  performing the tests. 
R  The functional test has three parts, running on the active system: 
R  - the functional test of the normal braking system 
R  - the functional test of the alternate braking 
R  - the functional test of the nosewheel steering system. 
R  (1) Functional test of the normal braking system. 
R  (Ref. Fig. 002A) 
R  The functional test of the normal braking system consists in sending 
R  successive brake application/release orders on the NORMAL system. 
R  These tests are in five successive sequences. 
R  (2) Functional test of the alternate braking system 
R  (Ref. Fig. 004) 
R  The functional test of the alternate braking system consists in 
R  sending successive brake application/release orders on the ALTERNATE 
R  system.These tests are in seven successive sequences. 
R  (3) Functional tests of the nosewheel steering 
R  (Ref. Fig. 003) 
R  These tests are performed after the normal braking functional tests. 
R  During these tests the BSCU generates low amplitude reference angle 
R  signals and monitors the nosewheel steering response. These tests are 
R  in five successive sequences, the fifth sequence being performed 
R  cyclically until the end of the test phase (Main Landing gear touch 
R  down). 
R  **ON A/C 106-149, 221-299, 401-499,
 C. BSCU Internal Monitoring Devices
 The watchdog function is achieved by the software via a cross-monitoring
 between the CPU and DSP microprocessors. 

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R
R
R
D. Dialogue with the Centralized Fault Display System (CFDS). At a line stop, the CFDS is used to check most of the aircraft systems from the cockpit. The electronic functions of the BSCU are designed as BITE systems, i.e. they are capable of a certain self-diagnosis. The CFDS includes: (Ref. Fig. 005)
 -
a Centralized Fault Display Interface Unit (CFDIU) which ensures the junction with the BITE of each system and manages the display of messages

 -
a Multipurpose Control and Display Unit (MCDU),
 The BSCU is connected to the CFDS by a bi-directional ARINC 429 link
 (type 1 system).
 The type 1 system has one ARINC 429 bus input and output that enables
 bi-directional dialog.
(Ref. Fig. 005)
 The system has the capability of memorizing data related to the faults
 detected over a maximum of 64 flights.
 The system BITE comprises non-volatile memory zones (EEPROM of BSCU).
 The EEPROM has three memory zones, each keeping specified data:

 -
the Flight zone

 -
the Ground zone

 -
the Shop zone, dedicated to shop maintenance only.
 This link is used to transmit the fault messages in two operating modes:

 -Normal mode

 -Interactive mode.
　
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