W DOC AIRBUS | AMM A320F

BRAKES AND STEERING - BITE - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL
1. BITE and Maintenance Test
F BITE System - Specifications
Depending on the different phases of flight, the BSCU automatically triggers the tests below:
  • Power-up test,
  • Permanent test,
  • Functional test: in flight with the landing gear extended until touchdown of the main gear,
  • Tachometer test: rolling without brake application,
  • Permanent monitoring: during operation of the braking or steering system.
A. Power-up Test
The BSCU has two types of reset:
  • long reset
  • short reset
(1) Long reset
(a) The conditions for triggering a long reset are :
  • detection of energization subsequent to a 115V/400 Hz cut lasting 5 seconds or more, or switching of the A/SKID & NOSE WHEEL switch from OFF to ON
  • and aircraft condition in STOP phase.
The STOP phase corresponds to:
  • MLG shock absorbers compressed
  • engines shut down
  • wheels at stop.
(b) The operations performed during a long reset are:
  • initialization of the microprocessors and memories (Flash if necessary, RAM, EEPROM,...)
  • keeping all the BSCU outputs in the inactive state
  • running of all the self-tests
  • writing of the fault codes into the memory (if applicable)
  • unlocking of the switching logic.
(2) Short reset
(a) The conditions for triggering a short reset are :
  • detection of energization subsequent to a 115V/400 Hz cut lasting less than 5 seconds
  • or a 115V/400 Hz cut lasting more than 5 seconds out of the STOP phase
  • or switching of the A/SKID & NOSE WHEEL switch from OFF to ON out of the STOP phase
  • or an auto-reset
  • or return of the power supply monitoring to OK.
(b) The operations performed during a short reset are:
  • initializations of the microprocessors and of the memories (RAM, ...)
  • keeping all the BSCU outputs in the inactive state
  • unlocking of the switching logic.
B. Operation of the Functional Test
The functional test starts as soon as the gears are locked down.
Its purpose is to do the test of the hydraulic equipment under pressure and the electronic control components of the selected BSCU system.
It also monitors the availability of the automatic braking and of the nosewheel steering systems until the touchdown.
This is to meet the safety requirements of a CAT III B landing.
For this purpose, the BSCU sends four availability discretes to the two FMGCs.
The functional tests are performed by a single system (SYS1 or SYS2), selected by the BSCU. At each flight, the BSCU changes the system performing the tests.
The functional test has two parts, running on the active system:
  • the functional test of the braking system
  • the functional test of the nosewheel steering system.
The functional test starts as soon as the gears are locked down.
Its purpose is to do the test of the hydraulic equipment under pressure and the electronic control components of the selected BSCU system.
It also monitors the availability of the automatic braking and of the nosewheel steering systems until the touchdown.
This is to meet the safety requirements of a CAT III B landing.
For this purpose, the BSCU sends four availability discretes to the two FMGCs.
The functional tests are performed by a single system (SYS1 or SYS2), selected by the BSCU. At each flight, the BSCU changes the system performing the tests.
The functional test has three parts, running on the active system:
  • the functional test of the normal braking system
  • the functional test of the alternate braking
  • the functional test of the nosewheel steering system.
(1) Functional test of the braking system.
F Braking Functional Test - Chronogram ** ON A/C NOT FOR ALL
F Normal Braking Functional Test - Chronogram ** ON A/C NOT FOR ALL
The functional test of the braking system consists in sending successive brake application/release orders on the NORMAL system. These tests are in five successive sequences.
(2) Functional tests of the nosewheel steering
F NWS Functional Test-Chronogram ** ON A/C NOT FOR ALL
F NWS Functional Test-Chronogram ** ON A/C NOT FOR ALL
These tests are performed after the normal braking functional tests. During these tests the BSCU generates low amplitude reference angle signals and monitors the nosewheel steering response. These tests are in five successive sequences, the fifth sequence being performed cyclically until the end of the test phase (Main Landing Gear touch down).
(3) Functional test of the normal braking system.
F Normal Braking Functional Test - Chronogram ** ON A/C NOT FOR ALL
The functional test of the normal braking system consists in sending successive brake application/release orders on the NORMAL system. These tests are in five successive sequences.
(4) Functional test of the alternate braking system
F Alternate Braking Functional Test - Chronogram ** ON A/C NOT FOR ALL
The functional test of the alternate braking system consists in sending successive brake application/release orders on the ALTERNATE system. These tests are in nine successive sequences.
(5) Functional tests of the nosewheel steering
F NWS Functional Test-Chronogram ** ON A/C NOT FOR ALL
These tests are performed after the normal braking functional tests. During these tests the BSCU generates low amplitude reference angle signals and monitors the nosewheel steering response. These tests are in five successive sequences, the fifth sequence being performed cyclically until the end of the test phase (Main Landing gear touch down).
C. BSCU Internal Monitoring Devices
The watchdog function is achieved by the software via a cross-monitoring between the CPU and DSP microprocessors.
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:
F CFDIU/BSCU Interface
  • 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.
F CFDIU/BSCU Interface
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.
(1) Operation in the Normal mode
F Fault Message - Text Transmission to the CFDS (Label 356) from the BSCU
During a flight, as soon as a fault is detected by the BSCU BITE, it is sent to the CFDIU.
These faults are sent in plain English in accordance with the ISO 5 encoding, through the ARINC 429 link, under the label 356.
(2) Transmission in the Interactive mode
F BSCU - Main Menu ** ON A/C NOT FOR ALL
The Interactive mode corresponds to a maintenance phase on the ground.
In this mode, the computer displays a menu on the screen. The selection of the menu items is made with keys placed at level of the lines displayed on the side of the screen. The procedure is conversational. This means that the operator can call certain sub-functions of the menu (for example: self test, reminder of the last faults) and receive this information in plain language in return.
The main menu is used to access following items:
  • LAST LEG REPORT
  • PREVIOUS LEGS REPORT
  • LRU IDENTIFICATION
  • GROUND SCANNING
  • TROUBLE SHOOT DATA
  • CLASS 3 FAULTS
  • SYSTEM TESTS
  • PIN-PROG SELECTION
  • GROUND REPORT
  • SPECIFIC DATA
(a) LAST LEG REPORT
F BSCU - LAST LEG REPORT ** ON A/C NOT FOR ALL
This item presents the internal and external Class 1 fault messages detected by the braking system, that appeared during the last flight
A prompt character ">" to the right of the class number indicates the presence of Trouble Shooting Data (TSD) pages associated to this fault, these pages can be accessed by pushing the line key adjacent to the prompt.
(b) PREVIOUS LEGS REPORT
F BSCU - PREVIOUS LEGS REPORT ** ON A/C NOT FOR ALL
This item presents the internal and external Class 1 fault messages that appeared during the 64 previous flights (fault history).
This is the "sum" of the LAST LEG REPORT items over several flights.
A prompt character ">" to the right of the class number indicates the presence of TSD pages associated to this fault, these pages can be accessed by pushing the line key adjacent to the prompt.
(c) LRU IDENTIFICATION
F BSCU - LRU IDENTIFICATION ** ON A/C NOT FOR ALL
This item presents:
  • the part number of the BSCU
  • the serial number of the BSCU
  • the wheel diameter and type of brake installed on A/C.
  • the A/BRK TYPE 1 or TYPE 2
(d) GROUND SCANNING
F BSCU - GROUND SCANNING ** ON A/C NOT FOR ALL
This item presents the internal and external faults (Class1 and Class 3) present at the time of the request. A maximum of 30 faults can be displayed. The faults are not recorded in the BSCU EEPROM.
A prompt character ">" to the right of the class number indicates the presence of TSD pages associated to these faults, these pages can be accessed by pushing the line key adjacent to the prompt.
(e) TROUBLE SHOOTING DATA
F BSCU - TROUBLE SHOOTING DATA ** ON A/C NOT FOR ALL
This item presents complementary information concerning the faults. ("Snapshot" of the system environment at the time of the fault).
F Trouble Shooting Data - Internal Fault Detail ** ON A/C NOT FOR ALL
F Trouble Shooting Data - External Fault Detail ** ON A/C NOT FOR ALL
(f) CLASS 3 FAULTS
F BSCU - CLASS 3 FAULTS ** ON A/C NOT FOR ALL
This item presents the Class 3 messages that appeared during the 64 previous flights.
Class 3: faults having no consequence on the aircraft safety and availability.
(g) SYSTEM TEST
F BSCU - SYSTEM TEST ** ON A/C NOT FOR ALL
This function is to be activated after any maintenance action on the aircraft. Its purpose is to check correct operation of the BSCU and its peripherals.
Two types of tests are proposed:
  • LRU WIRING & BSCU TEST: this test launches the continuity electrical monitoring and permanent monitoring functions
  • NORMAL BRAKING TEST: this test launches the continuity electrical monitoring, the permanent monitoring and the functional braking tests on the NORMAL system.
Once the test has been selected, the BSCU indicates the conditions required to launch the test. Once these conditions have been met, you can launch the test by pushing the line key adjacent to the START TEST indication.
During the test, the IN PROGRESS indication is displayed.
After the test, several response indications can be displayed:
  • NO FAULT DETECTED: test OK
  • Fault detected : test not OK, gives the Class 1 and Class 3 fault messages detected
  • TEST NOT PERFORMED: at least one of the conditions required is not fulfilled
  • TEST TIME OUT.
(h) PIN PROG SELECTION
F BSCU - PIN PROGRAMMING SELECTION ** ON A/C NOT FOR ALL
This function is to be performed after removal/installation of the BSCU.
It is used to adapt the BSCU pin programming to the aircraft pin programming (strap connection).
At the end of the Menu mode, the system must be set to OFF then to ON to be correctly reset.
Moreover, the pin programming selection must also be performed on the second BSCU system.
The various configurations available depend on the parameters below:
. aircraft type
. brake type
. wheel type (different diameters)
. deceleration rate in special automatic braking mode.
(i) GROUND REPORT
F BSCU - GROUND REPORT ** ON A/C NOT FOR ALL
This item presents the internal faults (Class1 and Class 3) that have been stored in the GROUND section of the EEPROM (i.e. faults that appeared when aircraft was on ground).
A prompt character ">" to the right of the class number indicates the presence of TSD pages associated to these faults, these pages can be accessed by pushing the line key adjacent to the prompt.
(j) SPECIFIC DATA
F BSCU - SPECIFIC DATA ** ON A/C NOT FOR ALL
This item has a front page showing four selections:
  • SERVOVALVE DATA
  • PIN PROGRAMMING DATA
  • STEERING DATA
  • SYSTEM DATA
1 SERVOVALVE DATA
This page shows the drifts in the characteristics of each Normal brake servovalve. The drift values are in psi.
2 PIN PROGRAMMING DATA
This page shows:
  • the type of brake and diameter of the wheels installed on aircraft
  • the type of automatic braking, type 1 corresponding to the standard configuration
  • the status of the fans option, installed or not installed.
3 STEERING DATA This page gives following information:
  • STRSELV: control of the nosewheel steering solenoid valve, OPEN or CLOSED,
  • ISTRSV: nosewheel steering servovalve current in mA,
  • ANGCSG: nose wheel controlled angle, in degrees,
  • RVDTCOM: RVDT angle (Command channel), in degrees,
  • RVDTMON: RVDT angle (Monitor channel), in degrees,
  • LVDT: LVDT displacement, in mm,
  • SPOTCAP: CAPT steering handwheel angle, in degrees,
  • SPOTFO: F/O steering handwheel angle, in degrees,
  • NWSON or NWSOF: NWS status
The line key adjacent to the REFRESH indication is used to refresh the NWS parameter values, as required.
4 SYSTEM DATA
F Specific Data - Detail ** ON A/C NOT FOR ALL
This function displays on three pages data related to the BSCU environment:
  • date, UTC
  • braking system,
  • aircraft identification
  • BSCU status and configurations
  • braking commands
  • servovalve currents and voltages
  • brake pressures
  • brake temperatures
  • wheel speed and wheel ref speed
  • nose wheel steering status
  • L/G status
  • hydraulic status (Green and Yellow)
The line key adjacent to the REFRESH indication is used to refresh the various parameter values.
(3) Transmission in the Interactive mode
F BSCU - Main Menu ** ON A/C NOT FOR ALL
The Interactive mode corresponds to a maintenance phase on the ground.
In this mode, the computer displays a menu on the screen. The selection of the menu items is made with keys placed at level of the lines displayed on the side of the screen. The procedure is conversational. This means that the operator can call certain sub-functions of the menu (for example: self test, reminder of the last faults) and receive this information in plain language in return.
The main menu is used to access following items:
  • LAST LEG REPORT
  • PREVIOUS LEGS REPORT
  • LRU IDENTIFICATION
  • GROUND SCANNING
  • TROUBLE SHOOT DATA
  • CLASS 3 FAULTS
  • SYSTEM TESTS
  • GROUND REPORT
  • SPECIFIC DATA
(a) LAST LEG REPORT
F BSCU - LAST LEG REPORT ** ON A/C NOT FOR ALL
This item presents the internal and external Class 1 fault messages detected by the braking system, that appeared during the last flight
A prompt character ">" to the right of the class number indicates the presence of Trouble Shooting Data (TSD) pages associated to this fault, these pages can be accessed by pushing the line key adjacent to the prompt.
(b) PREVIOUS LEGS REPORT
F BSCU - PREVIOUS LEGS REPORT ** ON A/C NOT FOR ALL
This item presents the internal and external Class 1 fault messages that appeared during the 64 previous flights (fault history).
This is the "sum" of the LAST LEG REPORT items over several flights.
A prompt character ">" to the right of the class number indicates the presence of TSD pages associated to this fault, these pages can be accessed by pushing the line key adjacent to the prompt.
(c) LRU IDENTIFICATION
F BSCU - LRU IDENTIFICATION ** ON A/C NOT FOR ALL
This item presents:
  • the part number of the BSCU
  • the serial number of the BSCU
  • the wheel diameter and type of brake installed on A/C.
  • the A/BRK TYPE 1 or TYPE 2
(d) GROUND SCANNING
F BSCU - GROUND SCANNING ** ON A/C NOT FOR ALL
This item presents the internal and external faults (Class1 and Class 3) present at the time of the request. A maximum of 30 faults can be displayed. The faults are not recorded in the BSCU EEPROM.
A prompt character ">" to the right of the class number indicates the presence of TSD pages associated to these faults, these pages can be accessed by pushing the line key adjacent to the prompt.
(e) TROUBLE SHOOTING DATA
F BSCU - TROUBLE SHOOTING DATA ** ON A/C NOT FOR ALL
This item presents complementary information concerning the faults. ("Snapshot" of the system environment at the time of the fault).
F Trouble Shooting Data - Internal Fault Detail ** ON A/C NOT FOR ALL
F Trouble Shooting Data - External Fault Detail ** ON A/C NOT FOR ALL
(f) CLASS 3 FAULTS
F BSCU - CLASS 3 FAULTS ** ON A/C NOT FOR ALL
This item presents the Class 3 messages that appeared during the 64 previous flights.
Class 3: faults having no consequence on the aircraft safety and availability.
(g) SYSTEM TEST
F BSCU - SYSTEM TEST ** ON A/C NOT FOR ALL
This function is to be activated after any maintenance action on the aircraft. Its purpose is to check correct operation of the BSCU and its peripherals.
Two types of tests are proposed:
  • LRU WIRING & BSCU TEST: this test launches the continuity electrical monitoring and permanent monitoring functions
  • NORMAL BRAKING TEST: this test launches the continuity electrical monitoring, the permanent monitoring and the functional braking tests on the NORMAL system.
Once the test has been selected, the BSCU indicates the conditions required to launch the test. Once these conditions have been met, you can launch the test by pushing the line key adjacent to the START TEST indication.
During the test, the IN PROGRESS indication is displayed.
After the test, several response indications can be displayed:
  • NO FAULT DETECTED: test OK
  • Fault detected : test not OK, gives the Class 1 and Class 3 fault messages detected
  • TEST NOT PERFORMED: at least one of the conditions required is not fulfilled
  • TEST TIME OUT.
(h) GROUND REPORT
F BSCU - GROUND REPORT ** ON A/C NOT FOR ALL
This item presents the internal faults (Class1 and Class 3) that have been stored in the GROUND section of the EEPROM (i.e. faults that appeared when aircraft was on ground).
A prompt character ">" to the right of the class number indicates the presence of TSD pages associated to these faults, these pages can be accessed by pushing the line key adjacent to the prompt.
(i) SPECIFIC DATA
F BSCU - SPECIFIC DATA ** ON A/C NOT FOR ALL
This item has a front page showing four selections:
  • SERVOVALVE DATA
  • PIN PROGRAMMING DATA
  • STEERING DATA
  • SYSTEM DATA
1 SERVOVALVE DATA
This page shows the drifts in the characteristics of each Normal brake servovalve. The drift values are in psi.
2 PIN PROGRAMMING DATA
This page shows:
  • the type of brake and diameter of the wheels installed on aircraft
  • the type of automatic braking, type 1 corresponding to the standard configuration
  • the status of the fans option, installed or not installed.
3 STEERING DATA This page gives following information:
  • STRSELV: control of the nosewheel steering solenoid valve, OPEN or CLOSED,
  • ISTRSV: nosewheel steering servovalve current in mA,
  • ANGCSG: nose wheel controlled angle, in degrees,
  • RVDTCOM: RVDT angle (Command channel), in degrees,
  • RVDTMON: RVDT angle (Monitor channel), in degrees,
  • LVDT: LVDT displacement, in mm,
  • SPOTCAP: CAPT steering handwheel angle, in degrees,
  • SPOTFO: F/O steering handwheel angle, in degrees,
  • NWSON or NWSOF: NWS status
The line key adjacent to the REFRESH indication is used to refresh the NWS parameter values, as required.
4 SYSTEM DATA
F Specific Data - Detail ** ON A/C NOT FOR ALL
This function displays on three pages data related to the BSCU environment:
  • date, UTC
  • braking system,
  • aircraft identification
  • BSCU status and configurations
  • braking commands
  • servovalve currents and voltages
  • brake pressures
  • brake temperatures
  • wheel speed and wheel ref speed
  • nose wheel steering status
  • L/G status
  • hydraulic status (Green and Yellow)
The line key adjacent to the REFRESH indication is used to refresh the various parameter values.
[Rev.10 from 2021] 2026.04.01 00:50:07 UTC
"Aviabrain" 2025