Automatic Flight System Design Philosophy Of Airbus (Part2)

AUTOMATIC FLIGHT SYSTEM DESIGN PHILOSOPHY

FAC GENERAL

FUNCTIONS

The basic functions of the Flight Augmentation Computer (FAC) are:

- yaw damper,

- rudder trim,

- rudder travel limitation,

- flight envelope protection,

- Fault Isolation and Detection System (FIDS).

YAW DAMPER

The yaw damper has four functions and controls the rudder via yaw

damper actuators. Upon Flight Management and Guidance Computer

(FMGC), ELevator Aileron Computer (ELAC) or FAC orders, the yaw

damper provides:

- dutch roll damping,

- turn coordination in cruise,

- engine failure compensation in auto flight,

- yaw guidance order execution.

RUDDER TRIM

The rudder trim orders come from the RUDder TRIM selector, or from

the FMGC to control the rudder via the rudder trim actuator.

The rudder trim gives:

- the manual trim with RUD TRIM selector,

- auto trim on yaw axis and the generation of engine failure recovery

function when the autopilot is engaged.

RUDDER TRAVEL LIMITATION

The rudder travel limiting unit limits the deflection of the rudder according

to the aircraft speed.

The rudder travel limiting function:

- limits the deflection for structure integrity,

- prevents excessive deflections which would penalize the aircraft

performance.

Aircraft speed information is given by the Air Data/Inertial Reference

Units (ADIRUs).

FLIGHT ENVELOPE PROTECTION

For flight envelope protection, the FAC computes the various

characteristic speeds for aircraft operation, the low energy warning, the

excessive Angle-Of-Attack (AOA) and wind shear detections. The

characteristic speeds are computed using data from the ADIRU, the

Landing Gear Control Interface Unit (LGCIU), the FMGC, and the Slat

Flap Control Computer (SFCC). Then, they are displayed on the PFDs.

The alpha floor (excessive AOA) and wind shear detections are sent to

the FMGCs. The low energy warning computation is sent to the Flight

Warning Computers (FWCs) which generate an aural warning: "SPEED,

SPEED, SPEED".

FIDS

For maintenance purposes, the FIDS centralizes the failure information

from the various BITE of the AFS computers and provides an interface

between these BITEs and the Centralized Fault Display Interface Unit

(CFDIU). The FIDS function is only active in FAC 1.

CONTROLS

Each FAC receives inputs from its related P/BSW, the RUD TRIM

selector and the RUD TRIM RESET P/B. The RUD TRIM selector

deflects the rudder. The RESET P/B returns the rudder to the neutral

position.

DISPLAYS

Some of the data computed by the FAC is displayed:

- the characteristic speeds are displayed on the speed scale of the PFDs.

- the rudder trim position is displayed on the F/CTL ECAM page and on

the RUD TRIM control panel. The red WINDSHEAR indication is

displayed in the center of both PFDs.

FMGC GENERAL

CONTROLS

GENERAL

The Flight Management and Guidance Computer (FMGC) functions,

Flight Management (FM) and Flight Guidance (FG), are mainly

controlled from the Multipurpose Control and Display Units (MCDUs)

and the Flight Control Unit (FCU).

Typical actions are:

- before departure, on the MCDUs, the pilots select the flight plan

which will be followed later on by the aircraft.

- in flight, on the FCU, the pilots can engage the AP and can modify

different flight parameters leading to an immediate change in the

control of the aircraft.

MCDU

Basically, the MCDUs give the long-term interface between the crew

and the FMGCs.

The MCDUs show, for example:

- the introduction or the definition, the modification and the display

of flight plans,

- the display, the selection and the modification of the parameters

associated with the FM functions,

- the selection of specific functions.

FCU

Basically, the FCU gives the short-term interface between the crew

and the FMGCs.

For example, the FCU can be used for:

- the engagement of the AP, Flight Director (FD) and A/THR

functions,

- the selection of required guidance modes (e.g. heading hold),

- the selection of various flight parameters (e.g. heading value).

MANAGEMENT

GENERAL

The FM part mainly gives the flight plan selection with its lateral and

vertical functions. The FM part gives the navigation, performance

optimization, radio navigation tuning and information display

management. Data computed by the FM part is occasionally used by

the FG part.

FLIGHT PLAN

A flight plan contains the various elements and constraints of the route

the aircraft must fly along from take-off to landing. A flight plan can

be selected, built-up, modified and monitored through the MCDU.

LATERAL FUNCTIONS

The main lateral functions are:

- aircraft position determination,

- Inertial Reference System (IRS) alignment through the MCDU,

- automatic or manual (through MCDU) selection of VOR, DME,

ILS, ADF frequencies,

- guidance computation along the lateral flight plan.

A navigation database supplies all necessary information to build a

flight plan; however pilots can enter other data using the MCDU.

VERTICAL FUNCTIONS

The main vertical functions are:

- optimized speed computation; the resulting target speed being used

as reference for guidance functions,

- performance predictions as time, fuel, altitude, wind at various points

of the flight,

- guidance computation along the vertical flight plan.

A performance database supplies necessary data; however pilots have

to enter other data using the MCDU.

GUIDANCE

GENERAL

The FG part gives the AP, FD and A/THR functions. These functions

work according to modes generally chosen on the FCU. The normal

way to operate the aircraft is to use the management part as reference

source for the guidance part.

AP

The AP function calculates the signals for the flight controls in order

to follow the selected modes. The AP controls the pitch, roll and yaw

axis according to the selected modes. Example of AP mode: Altitude

hold.

FD

The FD displays the guidance commands on both PFDs, allowing the

pilots to fly the aircraft manually according to the FMGC demands.

Two cases have to be considered:

AP not engaged:

- the FD function displays symbols on the PFD which gives orders to

the pilot to maintain the desired parameter(s). In this case, the pilot

follows these orders by acting on the flight controls.

AP engaged:

- the FD function displays symbols on the PFDs representing the AP

orders to be monitored by the pilot.

A/THR

The A/THR function calculates the signal necessary for engine control

in order to follow a given mode.

Example of A/THR mode: Acquisition and holding of a speed or a

Mach number.

DISPLAYS

GENERAL

Various displays are used to present Flight Management and Guidance

System (FMGS) data and information. The main displays presenting

flight management and guidance information are:

- the MCDUs (display part),

- the FCU (display Part),

- the PFDs,

- the NDs,

- the ECAM/EWD and ECAM STATUS pages.

MCDU

The MCDUs display all data related to the management part. Example:

Identification of the successive waypoints of the flight plan.

FCU

The FCU is also considered as a display as it includes indication lights

and Liquid Crystal Display (LCD) windows.

The FCU includes:

- lights giving mode indications,

- LCD windows showing reference parameters.

Example: During a climb with AP, the altitude window displays the

altitude the aircraft is going to capture.

PFD

The PFDs mainly display the FD symbols and the status of guidance

functions and their modes. They also display reference parameters.

Example: The target speed value is represented by a symbol on the

speed scale of the PFD.

ND

The NDs mainly display the flight plan and various navigation data.

Example: Airports or waypoints around the present position of the

aircraft.