DOC AIRBUS | AMM A320FFLIGHT AUGMENTATION COMPUTER (FAC) - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. General
The Flight Augmentation Computer (FAC) is a 8MCU size case. Its dimensions conform to ARINC Characteristic 600.
The FAC is of modular design.
The computer design is based on digital and analog technologies.
** ON A/C NOT FOR ALL The Flight Augmentation Computer (FAC) is a 8MCU size case. Its dimensions conform to ARINC Characteristic 600.
The FAC is of modular design.
The computer design is based on digital and analog technologies.
2. Component Location
** ON A/C NOT FOR ALL 
FAC - Component Location| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C ALL | |||||
| 1CC1 | FAC-1 | 83VU | 127 | 22-66-34 | |
| 1CC2 | FAC-2 | 84VU | 128 | 22-66-34 | |
A. Description
The computer is divided into three parts:
The interfaces between the computer and the actuators, as well as the position feedbacks, are of the analog type.
Similarly, the monitor channel receives the sensor data required to compute the control laws.
Its role is:
The computer is divided into three parts:
- Two virtually identical channels, the COMMAND channel and the MONITOR channel
- One independent channel which performs the FIDS functions.
The interfaces between the computer and the actuators, as well as the position feedbacks, are of the analog type.
Similarly, the monitor channel receives the sensor data required to compute the control laws.
Its role is:
- To consolidate the computations of the command channels
- To monitor the servo loops to be able to change over to the opposite FAC.
- The digital part is based on a 16-bit microprocessor and performs input/output system and control law computation.
- The analog part performs sensor acquisition ; only the command channel assumes power amplification for the three servo loops : yaw damper, rudder trim and rudder travel limiting.
- Input management and monitoring
- Control law computation and synchronization
- Control rudder-surface servo-loop
- Engage logic
- Output management.
(1) Input management and monitoring
This part, which is doubled, is responsible for the acquisition of the input parameters.
These take various forms:
This part, which is doubled, is responsible for the acquisition of the input parameters.
These take various forms:
- Analog AC signals from various control rudder-position sensors (inductive pick-off type)
- ARINC signals from various systems (ADIRS, LGCIU, ELAC, FMGC, SFCC) and from the opposite FAC
- Discrete signals, from engagement pushbutton switches and landing gear data
- Analog DC signals.
(2) Control law computation
The actuator position commands are computed by the CPU on the basis of the above ARINC and analog data and the embedded control laws.
A real-time monitor supervises the sequencing of the various tasks and the activation of a watchdog to protect the processing unit itself against incorrect program running.
The actuator position commands are computed by the CPU on the basis of the above ARINC and analog data and the embedded control laws.
A real-time monitor supervises the sequencing of the various tasks and the activation of a watchdog to protect the processing unit itself against incorrect program running.
(3) Control rudder-surface servo-loops
This function provides current signals for actuator control.
These signals are generated from the computed software orders and the feedback position of the sensors (LVDT and RVDT) for the three analog power loops (yaw damper, rudder trim and rudder travel limiting).
This function provides current signals for actuator control.
These signals are generated from the computed software orders and the feedback position of the sensors (LVDT and RVDT) for the three analog power loops (yaw damper, rudder trim and rudder travel limiting).
(4) Engage logic
The function consolidates the statuses of the various monitors and makes possible to pressurize the servos if all the required conditions have been met.
In the event of a fault, this engage logic can cut off the control signals to the servos.
The function consolidates the statuses of the various monitors and makes possible to pressurize the servos if all the required conditions have been met.
In the event of a fault, this engage logic can cut off the control signals to the servos.
(5) Output management
This part, which is doubled, is responsible for the generation of the output parameters.
These are of various types:
This part, which is doubled, is responsible for the generation of the output parameters.
These are of various types:
- To the monitoring channel to implement the various cross-monitors,
- To the other aircraft systems (FAC opp, FMGC own, FMGC opp, DMC 1, 2, 3, trim indicator).
- Analog outputs
- Discrete outputs
(6) Power supplies
Each channel has its own power supply which, from the 28VDC aircraft network, provides the voltages used by the channel : +5V, +15V, -15V.
Each power supply is monitored by the other channel.
Each channel has its own power supply which, from the 28VDC aircraft network, provides the voltages used by the channel : +5V, +15V, -15V.
Each power supply is monitored by the other channel.
B. Software Organization
The software is organized in:
Dissymmetric programming is incorporated between the command and monitoring channels through:
Specific monitoring functions are introduced:
The software is organized in fast or slow tasks and in background tasks which can be delayed.
We therefore have:
The software is organized in:
- Application program contained in the memory modules
- Executive program which enables the control of the CPU, ARINC inputs/outputs and safety tests etc.
Dissymmetric programming is incorporated between the command and monitoring channels through:
- Different languages (PASCAL and PL/M)
- Different algorithms.
Specific monitoring functions are introduced:
- In the hardware (watchdog)
- in the software (real-time monitor)
The software is organized in fast or slow tasks and in background tasks which can be delayed.
We therefore have:
- A fast cycle (yaw computation)
- A slow cycle (computation of other functions except weight)
- A very slow cycle (weight computation).