A320 Auto Flight System Overview

A320 Auto Flight System

• The A320 Auto Flight System allows fully automated flight management, but pilots can manually override at any time.
• Effective use of automated functions enhances safety, and reduces crew workload.
• The Flight Management Guidance System (FMGS) utilizes 2 identical Flight Management Guidance Computers (FMGCs).
• FMGCs synchronize operations, and provide core computing for FMGS. A single FMGC or the FMGS might be referenced at different points.
• Position data inputs to the FMGS include ADIRS, GPS, and radio navigation data.
• The FMGS processes this information to construct the lateral and vertical flight profiles.

FMGS Controls and Indicators

• The Flight Control Unit (FCU) is a primary control for the system.
• EFIS displays present flight data and status.
• Two FD (Flight Director) pushbuttons aid in control through the EFIS panel.
• Thrust levers and Multipurpose Control and Display Units (MCDUs) aid in system input.
• Two MCDUs and two-channel FCU allow pilot input to FMGS.

FMGS Modes: Managed and Selected

• "Managed" guidance is used for long-term flight operations, with the FMGS managing thrust, pitch and lateral guidance. Inputs are placed on the MCDU.
• "Selected" guidance is for short-term adjustments, with the pilot inputting directly to the FCU. Information regarding thrust, lateral, and vertical data is not included with selected input.

FMGS Signals and Components

• FMGS sends signals to autopilots, autothrust, and flight directors, and updates EFIS displays.
• The FMGS automatically tunes navigation radios to maintain accurate aircraft position.
• FMGS functions are organized into three sections: flight management, flight guidance, and flight augmentation.

FMGS System Details

• Flight Management: Determines position, manages navigation along flight plans, optimizes flight performance (cost, speed, altitude), produces predictions at waypoints, and manages displays.
• Flight Guidance: Provides commands for the autopilot (pitch, roll, yaw for selected guidance), commands for adjusting thrust (climb, cruise, descent, and approach), and commands for displaying the Flight Director.
• Flight Augmentation: The Flight Augmentation Computer (FAC) manages flight envelope calculations (minimum selectable speed (VLS), maximum speeds (VMO or VFE), maneuvering speed (VA), windshear warning, and angle of attack protection. This section also addresses yaw damping, rudder trim, rudder limiting, and turn coordination.

FMGC Synchronization and Operation

• FMGCs synchronize by comparing data for similar outputs.
• A single FMGC can fail without interrupting the normal operation of the other.
• Inputs from MCDU 1 are synchronized with FMGC 1, and vice versa for MCDU 2 and FMGC 2.
• FCU inputs are directed to both FMGCs.
• One FMGC acts as the master, with status determined by factors like AP 1 or AP 2 engagement (or dual channel AP).

Autopilot and Flight Director Engagement/Disengagement

• Normally, both FDs are active during the flight, and an AP is selected after takeoff.
• AP engagement occurs above 100 ft AGL, after at least 5 seconds of flight, and remains active until autoland rollout.
• Usually, AP 1 is engaged when the Captain is PF, and AP 2 is engaged when the First Officer is PF.
• Only one AP may engage at a time, except during a dual-autopilot Autoland approach (in this case, the FMA will indicate which AP is engaged/active).
• A CAT III dual approach is a Fail Operational system where, in case of in-flight failure, the remaining parts of the system will guide the aircraft to a safe landing. CAT III Single is Fail Passive. Fail-passive means the pilot would need to takeover, if a failure occurs.
• The instinctive disconnect pushbutton (on each sidestick) can manually disconnect the AP or thrust when it is engaged.
• Instinctive disconnect results in self-clearing logic cancelling all alerts. Other disconnects are handled by ECAM systems—by pilot intervention or automated actions.
• If the disconnect occurs during a dual approach, the approach capability will downgrade.
• FDs assist in flight guidance with visual commands displayed against the PFD to help align with autopilot performance or hand flying the aircraft.
• Both FDs are normally ON, and engaging them together is recommended. Operation with only one FD is not standard practice.

Flight Control Unit (FCU)

• The FCU is located centrally, and is used by the flight crew to select short-term operational adjustments.
• The FCU controls and selects target values for various guidance modes.
• The FCU uses 4 knobs for speed/mach, heading/track, altitude, and vertical speed/flight path angle.
• Pulling a knob selects a “selected” mode to guide to a specific value, while pushing a knob engages a “managed” mode, where the targets are set by the FMGS.
• "Selected" modes are short-term flight guidance; "Managed" is long term.
• The SPD/MACH knob allows speed selection; pulling it engages speed control by the autopilot or autothrust.
• Pressing the knob engages managed speed control by the FMGS .
• Selected HDG/TRK selection determines lateral route guidance.
• Pulling this knob selects a “selected” lateral mode, while pushing engages a “managed” mode.
• Pushing the HDG/TRK knob with "manage" mode engages FMGS Primary Flight Plan.
• The Altitude selector knob is used to target specific altitudes.
• The inner ring on the Altitude selector sets the target altitude value.
• The outer ring on the Altitude selector sets the increments (100 ft or 1000 ft.).
• Pulling the Altitude knob selects a vertical climb/descent to the target altitude (ignoring constraints of the vertical flight plan).
• Pushing the knob selects vertical climb/descent to the target altitude, complying with the vertical flight plan constraints.
• METRIC ALT pushbutton allows displaying altitude in meters.
• The V/S-FPA selector knob allows selecting V/S or FPA guidance.
• Positioning the V/S-FPA knob can select "selected" Vertical speed mode guidance (V/S or FPA). Pressing the knob sets vertical level.
• LOC pb arms the localizer (LOC) mode.
• APPR pb arms the approach modes selected in the FMS.
• EXPED pb accelerates the climb or descent toward the selected altitude.
• AP 1 and AP 2 pbs engage specific autopilot channels.
• A/THR pb arms the Autothrust system; armed automatically during takeoff.

Flight Mode Annunciator (FMA)

• The FMA displays flight guidance modes and states for Flight Director (FD), Autopilot (AP), and Auto Thrust (A/THR).
• The FMA displays "managed" (long-term) and "selected" (short-term) modes.
• The FMA displays include speed, heading, altitude, vertical/lateral modes, approach capability, and status of the A/THR and AP.
• Five columns on the FMA. AP/FD vertical modes, Lateral modes, Approach capability, AP/FD/A/THR status are displayed, all in sync between PFDs.
• Special messages appear in the third row, often displaying in red, amber, or blue. Flight control messages have priority.

Auto Thrust (A/THR)

• A/THR controls thrust after takeoff.
• Thrust levers are used to set the maximum thrust available (TOGA, FLX/MCT,CL), which A/THR uses.
• A/THR systems (used to maintain either speed or thrust) will control pitch or thrust depending on what is engaged.
• A/THR is unavailable during TOGA or FLX thrust settings.
• A/THR can maintain target speed or thrust.
• A/THR is active when the thrust levers are between the IDLE position and the climb detent on the thrust lever.
• Thrust level is set by the pilot during takeoff (TOGA/FLX/MCT).
• On-ground THR is manually set.
• A/THR activates/arms automatically at CL position (after takeoff).
• "LVER CLB" reminder to select CL position on the lever after takeoff.
• A/THR can be operated in THR or SPEED mode, depending on the selected flight guidance mode.
• Thrust levers can override A/THR thrust control at any time. A/THR will reactivate if the levers are returned to the climb detent.

Answers to questions from the supplement

• Which FMGC provides signals to the Autopilots? The master FMGC.
• With AP1 and AP2 engaged for a Dual Channel approach, which FMMA is the master? AP 1.
• Which device is responsible for providing the autotune function of the Navigation Radios? The FMGS.
• Pilot inputs to the FCU are considered ____________ inputs. Selected.
• Pilot inputs to the MCDU are considered ____________ inputs. Managed.
• When both FDs and all APs are off, the only FMA display that may be visible is ______________. A/THR modes.
• After an Instinctive Disconnect is used, the alerts ________________. self-clear.
• A CAT 3 Dual system is a fail ___________ automatic landing system. operational.