AUTOMATIC FLIGHT SYSTEM DESIGN PHILOSOPHY
GENERAL
The Automatic Flight System (AFS) calculates orders to automatically
control the flight controls and the engines. It computes orders and sends
them to the Electrical Flight Control System (EFCS) and to the Full
Authority Digital Engine Control (FADEC) to control flying surfaces
and engines. When the AFS is not active, the above-mentioned
components are controlled by the same systems but orders are generated
by specific devices: side sticks and thrust levers.
NAVIGATION
A fundamental function of the AFS is to calculate the aircraft position.
To compute the aircraft position, the system uses several aircraft sensors,
which give useful information for this purpose.
FLIGHT PLAN
The AFS has several flight plans predetermined by the airline in its
memory. A flight plan describes a complete flight from departure to
arrival; it gives vertical information and all intermediate waypoints. The
plan can be displayed on the EFIS or on the Multipurpose Control &
Display Units (MCDU).
OPERATION
There are several ways to use the AFS but the normal and recommended
one is to use it to follow the flight plan automatically. Knowing the
position of the aircraft and the flight plan chosen by the pilot, the system
is able to compute the orders sent to the flying surfaces and the engines
so that the aircraft follows the flight plan. The pilot has an important
monitoring role.
NOTE: During AFS operation, side sticks and thrust levers do not move
automatically.
FLY BY WIRE
If the pilot moves the side stick when the AFS is active, it disengages
the autopilot. Back to manual flight, when the sidestick is released, the
EFCS maintains the actual aircraft attitude.
SYSTEM DESIGN
To meet the necessary reliability, the AFS is built around 4 computers.
There are two interchangeable Flight Management and Guidance
Computers (FMGCs) and two interchangeable Flight Augmentation
Computers (FACs). It is a FAIL OPERATIVE system. Each FMGC and
FAC has a command part and a monitor part to be FAIL PASSIVE.
GENERAL
The Automatic Flight System (AFS) gives pilots functions that reduce
their workload and improve safety and regularity of the flight. The AFS
is designed around:
- 2 Flight Management and Guidance Computers (FMGCs),
- 2 Flight Augmentation Computers (FACs),
- 2 Multipurpose Control and Display Units (MCDUs),
- 1 Flight Control Unit (FCU).
CONTROLS
The FCU and the MCDUs let the pilots control the functions of the
FMGCs. The FAC engagement P/BSWs and the RUDder TRIM control
panel are connected to the FACs. The MCDUs are used for long-term
control of the aircraft and do the interface between the crew and the
FMGC allowing the management of the flight. The FCU is used for
short-term control of the aircraft and is the interface required for
transmission of engine data from the FMGC to the Full Authority Digital
Engine Control (FADEC).
FMGC
There are two interchangeable FMGCs. Each FMGC is made of two
parts: the Flight Management (FM) part and the Flight Guidance (FG)
part. The FM part gives the functions related to flight plan definition,
revision and monitoring and the FG part gives the functions related to
the aircraft control.
FAC
There are two interchangeable FACs. The basic functions of the FACs
are the rudder control and the flight envelope protection.
NOTE: The FAC includes an interface between the AFS and the
Centralized Fault Display System (CFDS) called Fault Isolation
and Detection System (FIDS).
OTHER SYSTEMS
The AFS is connected to the majority of the aircraft systems.
Examples of AFS data exchanges:
- reception of the aircraft altitude and attitude from the Air Data/Inertial
Reference System (ADIRS),
- transmission of autopilot orders to the ELevator and Aileron Computers
(ELACs).
COMPONENT LOCATION
The AFS computers are located in the aft avionics rack (80VU).
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