A320 Auto Flight System Overview

A320 Auto Flight System

• The A320 Auto flight system allows for fully automatic flight management, with pilots able to manually override at any time.
• Proper use of automation improves safety, crew comfort, and reduces workload.
• The Flight Management Guidance System (FMGS) uses two identical Flight Management Guidance Computers (FMGCs) which operate synchronously.
• FMGS inputs include data from ADIRS, GPS, and radio navigation systems (providing aircraft position).
• The system uses Flight Control Unit (FCU), EFIS displays, Flight Director (FD) switches, thrust levers, and Multipurpose Control and Display Units (MCDUs) for controls and indicators.
• Two MCDUs and two-channel Flight Control Unit (FCU) allow pilot inputs to the FMGS.
• "Managed" guidance (MCDU inputs) supports long-term flight operations (thrust, pitch, and lateral).
• "Selected" guidance (FCU inputs) handles short-term changes and does not alter the flight plan's thrust, lateral, or vertical data.
• FMGS signals manage autopilots, auto-thrust, flight director, and EFIS displays.
• FMGS automatically tunes navigation radios based on the plane's position.
• FMGS has three components: flight management, flight guidance, and flight augmentation.
• Flight management determines position, manages navigation along the flight plan, optimizes performance (cost, speed, and altitudes), makes predictions (waypoints, altitudes, speeds, fuel, destinations, alternates), and manages data on the EFIS system.
• Flight guidance handles autopilot commands, auto-thrust commands, and flight director commands (for pitch, roll, and yaw).
• Flight augmentation (via the Flight Augmentation Computer (FAC)) calculates flight envelope limits (VLS, VMO, VFE).
• FAC manages maneuvering speeds (VA), low-energy warnings, windshear detection and alerts, angle-of-attack protection (alpha-Floor protection).
• FAC additionally handles yaw damping, rudder trim, rudder limiting, and turn coordination.
• FMGCs synchronize to compare data, with one able to fail, while the other maintains normal operation.
• Inputs to MCDU 1 are connected to FMGC 1, then synchronized with FMGC 2, and vice-versa for MCDU 2.
• FCU inputs are sent to both FMGCs.
• One FMGC acts as a master, while the other acts as a backup, with the active FMGC based on many factors including the specific autopilot in use. For example, in Dual channel mode AP 1 remains the master.
• All pilots using MCDU for autopilot management (long-term actions) and FCU for autopilot changes (short term actions).

Autopilot & Flight Director Engage/Disengage

• Both Flight Director (FD) are typically ON during flight, and an autopilot is selected after takeoff.
• Autopilot 1 is usually selected when the Captain is flying and autopilot 2 when the First Officer is.
• Only one autopilot can be active at a time (except for Dual channel Autoland approaches).
• CAT IIIB approach uses Alert Height rather than Decision Height.
• A CAT 3 Dual system is fail-operational, enabling automatic approach and landing.
• A CAT 3 Single system is Fail-Passive; pilot manually completes the landing after a failure.
• Pilots use instinctive disconnect pushbuttons (on sidesticks and thrust levers) for immediate manual control if malfunction occurs.
• Disconnecting an AP produces an aural warning, flash warning lights, and an AP OFF message on the ECAM.
• Instinctive disconnects are self-clearing and do not cause persistent warnings.
• Non-instinctive disconnects (e.g., failure) show up as ECAM actions needing clearing.
• Dual approach disconnection downgrades the approach capability (e.g., to a Category 1 approach.)
• FDs present guidance for monitoring AP operations or hand-flying.
• Switching FDs ON/OFF activates/deactivates guidance lines/indicators on the Primary Flight Display (PFDs).
• FDs should be switched on or off together.
• FDs have horizontal (pitch) and vertical (roll) command bars.
• During takeoff and landing roll-out, a yaw bar is used rather than roll guidance.
• The HDG-V/S/TRK-FPA pushbutton on the FCU switches the flight guidance mode from standard to Flight Path Director/Vector.
• If a go-around is initiated during TRK/FPA, the PFD returns to the standard FD command bars.
• The only FMA display visible when both FDs and APs are off is the A/THR mode.
• Following an instinctive disconnect, all alerts automatically clear.

Flight Control Unit (FCU)

• The FCU is a device in the center of the glare shield containing 4 knobs and associated windows.
• The 4 knobs are the SPD/MACH, HDG/TRK, ALTITUDE, and V/S-FPA selectors.
• Pulling out a FCU knob engages "selected" mode for a short-term target value; pushing it engages a "managed" mode allowing the FMGS to control the target.
• The Speed/Mach selector sets a target speed for autopilot or auto-thrust; pulled out the selected speed is used as a pitch/thrust command by autopilot/auto-thrust. Pushed in, allows the FMGS to handle the speed.
• The HDG/TRK selector controls headings/tracks; selected, adjusts heading; pushed in, FMGS handles flight guidance.
• The altitude selector handles altitude operations; selected mode controls altitude operations; pushed in, the FMGS controls altitude operations.
• The V/S-FPA selector controls vertical speed or flight path angle; pulled out, adjusts vertical rate/angles; pushed in, the FMGS controls vertical rate and angles.
• Pushbuttons are available on the FCU for LOC, AP, A/THR, APPR and EXPED.

Flight Mode Annunciator (FMA)

• The FMA is located on top of each PFD, and provides information for armed and active flight modes, as well as FD, AP, and A/THR conditions.
• 5 columns on the FMA; leftmost for autothrust, second for vertical, third for lateral, fourth for approach capability, fifth for autopilot/FD/auto-thrust status.
• Engaged modes show in green; armed modes in different colours (blue "selected" or magenta "managed").
• Special messages in the lowest row with highest priority for control and next for systems.
• A temporary white box highlights mode changes.

Auto-Thrust (A/THR) System

• A/THR controls are located on the Autothrust pushbutton, and thrust levers.
• A/THR function is initiated when thrust levers are moved to the CLB position after takeoff.
• A/THR is not available with TOGA or Flex thrust settings.
• A/THR can maintain speeds or thrust levels.
• Thrust levers have 3 detents with specific thrust values (CLB, FLX/MCT, TOGA).
• A/THR's availability is determined by the Thrust leaver position (idle or above).
• The A/THR will set power as needed between idle and climb.
• Pilots can override A/THR with thrust lever movement.
• A/THR turns to SPEED mode when in vertical modes (ALT, V/S, FPA, GS); Target speeds are managed by FMGS/selected mode.
• A/THR disconnects when thrust levers reach IDLE.
• A/THR can be manually disconnected using instinctive disconnection technique, or by pushing the A/THR pushbutton on the FCU—the latter isn't recommended.
• Re-engage A/THR by moving thrust levers to CLB and pressing A/THR.

Explore the intricacies of the A320 Auto Flight System, focusing on the Flight Management Guidance System (FMGS) and its components. This quiz covers automation benefits, inputs, and operational controls that enhance flight safety and efficiency. Test your knowledge on managed and selected guidance functionalities within the system.