Automatic Flight FMGC

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.
ECAM
The ECAM/EWD page presents warning messages related to the function or computer failures. The ECAM STATUS page displays the landing capabilities.

Credit : Nidhi Chauhan
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