1

FLIGHT MANAGEMENT
Flight Management Part of the FMGC

The flight management part of the FMGC (Flight Management and Guidance Computer)
performs four main functions:

 Navigation based on accurate position.

 Flight planning.

 Performance prediction and optimization.

 Management of the displays.

Accurate Position Computation

Accurate position computation is one of the essential functions of the FM part of the FMGC.
Each FMGC computes its own aircraft position (FM position) from a mixed IRS position and
a computed radio position or a GPS position. The system selects the most accurate position,
considering the estimated accuracy and the integrity of each positioning equipment.

The FMGC computes a mixed IRS position from the three IRSs (Inertial Reference Systems).
If one IRS fails, each FMGC uses only one IRS, either on-site IRS or IRS 3.

The IRS computes a hybrid position, which is a mixed IRS GPS position called GPIRS. Only
one of the three GPIRS positions is selected by the system according to its figure of merit and
priority logic. If the GPIRS data does not comply with an integrity criterion, the GPS mode is
rejected, and radio position updating is used. "GPS primary lost" is displayed on the ND
(Navigation Display) and MCDU (Multipurpose Control and Display Unit) scratchpad.

Radio Position Updating

The FMGC uses on-site navaids to compute its own radio position. The navaids, which are
automatically auto-tuned, can be:

 DME DME

 VOR DME

 DME ILS lock

 DME ILS approach selected

 2

 VOR ILS lock

 DME ILS approach selected

Each FMGC computes a vector from its mixed IRS position to the radio or GPS position.
This vector is called bias. The bias is updated continuously if the radio or GPS position is
available. If the radio or GPS position is lost, the bias is memorized and added to the mixed
IRS position to compute the FM position.

At takeoff, the FM position is updated to the runway threshold position memorized in the
database. Depending on the navigation mode used by the system (IRS GPS, IRS DME DME,
IRS VOR DME, or IRS only), the FMGC computes an estimated position error (EPE).

Estimated Position Error (EPE) and Required Navigation Performance (RNP)

The EPE is compared to the required navigation performance (RNP) defined by the
airworthiness authorities as a nominal error tolerated within a flying area (TMA) or along a
given flight plan leg.

 If the EPE is lower than RNP, accuracy is high.

 If the EPE is higher than RNP, accuracy is low.

When the accuracy switches from high to low, a message "NAV ACCUR DOWNGRAD" is
displayed on the ND and on the MCDU scratchpad.

GPS Function and Position Accuracy

When the GPS function is lost, the crew must check the position accuracy using raw data
information if available. The position accuracy cross-check using raw data information has to
be done:

 Periodically during the flight unless GPS is primary.

 Systematically when "GPS primary lost" message comes up.

 Systematically when "NAV ACCUR DOWNGRAD" message comes up.

It is important to note that high/low messages are computed on estimated data; therefore,
even if "low" is displayed, the accuracy check may still be positive.

Flight Planning

For flight planning, the pilot inserts the following data into the FMGS via the MCDU:
 3

 The lateral part of the flight plan.

 The vertical part of the flight plan, including speed, time, altitude constraints, or step
climb.

Two flight plans can be inserted in the FM:

 A primary one, used for the legs to be flown.

 A secondary one, used to prepare an alternative departure or arrival, or a diversion,

which can be activated by the pilot whenever required.

Flight Management System Databases

The flight management system (FM) uses two databases to perform its computations:

 A navigation database.

 A performance database.

Navigation Database

The navigation database (NAV database) contains all the necessary information for the lateral
flight plan, such as routes, airways, VORs, non-directional beacons, waypoints, and airports.
The navigation database is updated every 28 days, and its currency and validity are checked
on this page during the pre-flight. There is an active database and a secondary or second
database. The secondary/second database is either the previous or the next database.
Databases are loaded two at a time so that if the first one expires away from a maintenance
base, the pilot can activate the second one before departure the next day.

Warning: Never activate the second database in flight, as all current active data would be
lost.

Performance Database

The performance database (PERF database) contains the aircraft performance model and is
used to optimize the flight plan and to obtain predictions such as ETAs (Estimated Time of
Arrival), EFOB (Estimated Fuel On Board), etc.

The change code is only displayed in the pre-flight and done phases when the code has been
inserted. The idle and performance factors turn blue. This allows the engineering team to
modify these factors to take engine and aircraft aging into account and to adapt fuel
predictions to actual fuel consumption.
 4

Note:

 A positive idle factor gives an earlier top of descent.

 A negative one delays the top of descent.

 The performance factor relates to a percentage, which means that the airline flight
operations have evaluated the fuel deviation from the basic performance model.
Clearing the code will lock the change.

Lateral Flight Plan

The lateral flight plan includes:

 Departure

 On route

 Arrival

 Alternate

These elements are defined by waypoints and legs. The FMGC automatically strings the legs
in sequence. When flying in navigation mode (navigation managed by the FMGC), the
aircraft is guided on a leg called the active leg, defined by a "from" and a "to" waypoint. The
"to" waypoint is depicted in white on the MCDU and on the ND as well in the top right-hand
corner.

Pre-Flight Initialization

During pre-flight, the first thing to do is to confirm the correct information on the status page.
The loaded database of FM1 and FM2 must be identical, and the stored data added by the
previous crew may be cleared as shown. We are then ready to begin programming the route
of flight, which is called initializing the flight plan.

This initialization of the flight plan is done through the INIT page A.

Inserting the Flight Plan

The pilot enters the flight plan in three ways:

1. By inserting an origin/destination pair and then manually selecting departure,

waypoints, airways, and arrival.

2. By inserting a company route name stored in the database.

 5

3. By sending a request for an active flight plan initialization (CFANS).

Once the flight plan is inserted, it can be modified by two types of revisions:

 Lateral revisions, which have an immediate effect on the active flight plan.

 Lateral revisions that lead to a temporary flight plan.

These revisions are selectable from the left keys on the MCDU.

Lateral Revision at Present Position

A lateral revision at present position (P POS) allows access to the FIX INFO page. On this
FIX INFO page, if a reference is entered, it is also shown on the associated ND. Then, a
radial or a radius can be inserted, or an ABEAM point can be selected as well. After
computation, the predictions are shown, and if now the associated key is pressed again, an
interception point will be added to the flight plan.

Direct To Function

The Direct To function is an immediate effect lateral revision that allows the aircraft to fly
from the present position directly to a waypoint, with ABEAM points displayed along the
track if ABEAM PTS is selected, or to intercept an inbound or outbound radial to/from this
waypoint.

If the waypoint does not belong to the flight plan, it has to be inserted via the scratchpad.
Waypoints that can be inserted are waypoints from the database or waypoints defined by the
crew (place bearing distance, place bearing place bearing).

Deleting and Adding Waypoints

 Deleting a waypoint in the flight plan will create a flight plan discontinuity in the
active flight plan.

 Adding a waypoint in the flight plan will create a flight plan discontinuity.

Lateral Revision at Origin

Using a lateral revision at origin, the pilot can insert or modify the takeoff runway, the SID
(Standard Instrument Departure), and the enroute transition through the departure revision.
The enroute transitions (TRANS) are the various possible trajectories defined between the
last waypoint of the SID and the first enroute waypoint.

Lateral Revision at Destination

 6

A lateral revision at destination (Line Select Key 6 Left) gives access to the arrival data. The
runway and the type of approach can be chosen, as well as the STAR (Standard Terminal
Arrival Route), the VIA, and the enroute transition (if any).

Lateral Revision at Waypoint

A lateral revision at a waypoint (e.g., at the "FROM" waypoint or P POS) allows the pilot to
select the OFFSET prompt that displays the OFFSET page, where a lateral offset to the left or
right of the active flight plan can be defined. Defaulted indications, such as the start
waypoint, are displayed and can be modified by a new selection. The offset value inserted is
in nautical miles. Once the offset has been inserted, the initial flight plan appears as a dotted
line.

Inserting Airways

A lateral revision at a waypoint allows the pilot to insert into the active flight plan up to five
segments of airways starting at the revised waypoint. The airways page is accessed by Line
Select Key 5 Right on the waypoint lateral revision page. The revision is done for each
segment by first inserting its airway identification and then inserting the next waypoint
belonging to this airway.

Vertical Flight Plan

The vertical flight plan is automatically initialized when the aircraft is airborne. The flight
plan contains a predicted profile of the aircraft, starting with the T/O (takeoff) phase and
going through the CLB (climb) phase, CRZ (cruise) phase, DES (descent) phase, APP
(approach) phase, and possibly GA (go-around) phase. For each phase, the system predicts
the flight level, altitude, and time constraints at each waypoint, along with the fuel at that
point. These predictions are based on the flight characteristics (weight, flight level, and CI)
and the performance database. The flight plan can be modified in flight to change the phase
or insert or remove constraints.

Vertical Revisions

To adjust the vertical profile, vertical revisions are used to change altitude, speed, or time
constraints.

 Speed Revision: Insert the speed in Mach or knots.

 Altitude Revision: The altitude is in feet.

 7

 Time Revision: The time constraint is in hh

. If the pilot wants to compute an approach time over a fix, the time constraint should
be inserted in the flight plan.

Altitude Constraints

 Hard Constraint: This type of constraint is defined by a level or altitude that the
aircraft has to reach or maintain over a specific fix.

 Soft Constraint: A soft constraint is a suggested constraint, but the aircraft will
prefer optimizing the vertical profile if possible.

 Window Constraint: The window constraint defines a band of altitudes between two
hard constraints or between a soft and a hard constraint.

The altitude constraints in the vertical flight plan are shown on the ND and can be modified
by the crew. When a constraint is not respected, it is displayed in amber.

Speed Constraints

Speed constraints are automatically taken into account in the vertical profile to determine the
aircraft's trajectory.

If the speed constraint is not respected, the FMCG will automatically adjust the trajectory to
meet the speed constraint. If it is impossible to respect the speed constraint, the FMCG will
show an amber indication.

Performance Prediction

The FMGC computes and displays predictions based on the vertical and lateral flight plan
and the data inserted in the INIT pages, such as wind, cost index, cruise FL (Flight Level),
and fuel.

The predictions are:

 Time predictions (ETA).

 Fuel predictions (FOB or fuel on board).

 Vertical predictions (FL, altitude).

The performance predictions are shown on the PROG page and the F-PLN page.

Cost Index and Performance Factors

 8

The Cost Index (CI) is a number inserted by the crew or automatically sent to the FMGC. It is
a compromise between time and fuel consumption. The lower the cost index, the more the
flight is optimized for fuel consumption. The higher the cost index, the more the flight is
optimized for time.

The performance factors (PF) are set by the airline to optimize the vertical profile according
to the actual performance of the aircraft.

Flight Management System Procedures

The Flight Management System (FMS) procedures provide the flight crew with operational
guidelines for the operation of the FMGC and its interfaces.

Pre-Flight Procedure

The pre-flight procedure starts with the aircraft initialization, which includes:

1. Alignment of the IRS.

2. Navigation database validation.

3. Route of flight initialization.

4. Flight plan initialization.

5. Performance initialization.

6. Secondary flight plan initialization.

7. Weight and balance data entry.

Takeoff Procedure

After completing the pre-flight procedure, the takeoff procedure includes:

1. Checking the FM position and the takeoff runway position.

2. Setting the T/O speeds.

3. Initializing the flight mode.

4. Activating the lateral and vertical navigation modes.

5. Engaging the autopilot.

Enroute Procedure

Once airborne, the enroute procedure includes:

 9

1. Monitoring the aircraft's position.

2. Adjusting the flight plan as needed.

3. Monitoring the performance predictions.

4. Revising the flight plan for changes in the route or altitude.

Descent Procedure

During the descent phase, the procedure includes:

1. Monitoring the descent profile.

2. Adjusting the speed and altitude constraints as needed.

3. Revising the approach procedure.

4. Engaging the approach mode.

Approach and Landing Procedure

The approach and landing procedure includes:

1. Confirming the approach and landing runway.

2. Setting the landing configuration.

3. Monitoring the approach profile.

4. Engaging the landing mode.

5. Conducting the final approach and landing.

Go-Around Procedure

In case of a go-around, the procedure includes:

1. Engaging the go-around mode.

2. Climbing to the missed approach altitude.

3. Reconfiguring the aircraft for the missed approach.

4. Revising the flight plan for a second approach.

Missed Approach Procedure

The missed approach procedure is activated if the landing cannot be completed. It includes:

1. Climbing to the missed approach altitude.

 10

2. Flying the missed approach procedure as published.

3. Revising the flight plan for a second approach or diversion.

Conclusion

The Flight Management System (FMS) is a sophisticated system that automates many aspects
of flight planning and navigation, allowing for efficient and accurate management of the
aircraft's flight path. Understanding the FMS procedures is crucial for flight crew members to
ensure the safe and efficient operation of the aircraft.
 11

RULES REGARDING THE FLIGHT

MANAGEMENT NAVIGATION
FM Navigation and Flight Planning Rules

Rule 1: Cross-Check FM Navigation Accuracy

 Importance: FM position accuracy is crucial for the proper functioning and validity
of all FMS functions.

 Cross-Check Timing:

o Periodically, except when GPS is primary.

o Whenever the messages "GPS primary lost" or "NAV ACCUR

DOWNGRAD" appear on the ND.

o Whenever there is doubt about the validity of the FM position.

 Principle: Compare the bearing and distance computed by the FM to a beacon with
the bearing and distance provided by raw data.

Rule 2: Ensure Proper Sequencing of the Flight Plan

 Navigation Mode: A "to" waypoint is sequenced when it is overflown.

 Heading Mode: If the cross-track is large, the flight plan sequencing does not occur,
disrupting FM predictions.

 Principle: In heading mode, monitor the "to" waypoint and clear any undesired "to"
waypoints.

Rule 3: Keep a Flight Plan Discontinuity Only When Desired

 Example: When radar vectoring is expected, a flight plan discontinuity may be

intentionally maintained.

Rule 4: Anticipate Your Actions on the MCDU

 Principle: Fly ahead of the aircraft by inputting known useful information into the
MCDU as soon as time allows.

 Examples:

o Input ATIS information while on the ground.

 12

o Enter an alternative clearance or a circling approach when planning.

Rules Regarding Predictions

Rule 1: Understanding Predictions

 Principle: The FMS assumes that the aircraft flies along the flight plan in managed
navigation and managed climb or descent modes.

 Exception: If selected heading, track, open climb, or vertical speed modes are used,
the FMS assumes an immediate return toward the flight plan, with a corresponding
realistic trajectory.

 Note: V/DEV on the PROG page follows the same assumption.

Rule 2: Use of Vertical Deviation (V/DEV)

 Function: Vertical deviation is provided in descent as a round symbol (yoyo) and

along a V/DEV scale in approach mode, where one dot represents 100 feet.

 Purpose: It indicates the vertical deviation between the current altitude and the
computed descent or approach path.

Rules Regarding Guidance

Rule 1: Managed Modes Availability

 Function: The managed modes of the FG guide the aircraft along the FMS lateral and
vertical flight plan.

 Speed Target:

o Managed: Computed by the FMS.

o Selected: Chosen by the pilot on the FCU.

 Climb and Descent Modes: These modes correspond to a managed trajectory and
cannot be engaged in heading or track mode.

Rule 2: Re-Engagement of NAV Mode

 Arming NAV Mode: NAV mode may be armed at any time when heading or track
mode is used for flight plan interception.

 Interception:

o Can only occur if the track crosses the active leg before the "to" waypoint.
 13

o NAV mode engages as soon as the aircraft is less than one nautical mile from
the interception point.

 Note: If the track line does not cross the active leg, the interception will not occur.

Rules Regarding Displays

Rule 1: ND Display Mode Selection

 Usage: The ND Arc and Rose navigation modes may be used without any restriction
if GPS is primary or FM navigation accuracy check is positive.

 If FM Accuracy is Negative: Raw data must be displayed on the ND.

Rule 2: FMS Monitoring in Managed Modes

 Navigation Mode:

o Monitor the PFD/FMA for mode status (armed or engaged).

o Monitor the ND for the expected trajectory and cross-track.

 Climb or Descent Modes:

o Monitor target altitude and target speed.

o Monitor V/DEV in descent and the location of pseudo waypoints on the ND.

These rules provide essential guidelines for the proper operation and monitoring of the
FMGS (Flight Management and Guidance System), ensuring safe and efficient flight
management.
 14

GUIDANCE PRINCIPLES
Introduction
The Autopilot (AP), Flight Director (FD), and Auto Thrust (A/THR) are integrated within the
Flight Guidance (FG) system. They operate in various modes to guide the aircraft to
associated targets such as speed, heading, glide slope, or the FMS (Flight Management
System).

Managed and Selected Modes

 Managed Mode: FG guides the aircraft along the flight plan or a speed profile
computed by the FMGS (Flight Management Guidance System). In this mode, lateral
and vertical targets are managed automatically.

 Selected Mode: The pilot selects targets on the FCU (Flight Control Unit). FG guides
the aircraft to these manually selected targets.

Example of Managed and Selected Modes:

 Managed Lateral Mode: Navigation mode guides the aircraft along the lateral flight
plan.

 Managed Vertical Mode: Climb mode guides the aircraft along the vertical flight
plan.

 Selected Lateral Mode: Heading mode guides the aircraft to a selected heading.

 Selected Vertical Mode: Open descent mode guides the aircraft to a selected descent
path.

Interaction Between AP, FD, and A/THR

 When the AP/FD pitch or vertical mode controls a vertical trajectory, the A/THR
controls the speed or Mach.

 If both AP and FD are off, A/THR controls the speed.

Vertical Mode Control

 Vertical Trajectory Control: AP/FD controls vertical speed or flight path angle,
while A/THR controls speed.
 15

 Speed/Mach Control: AP/FD controls speed or Mach target by adjusting pitch, while
A/THR maintains a fixed thrust level.

Climb and Descent Modes

Climb Mode

 The climb mode adjusts the aircraft's pitch to climb toward a target altitude at a target
speed with a fixed thrust level controlled by A/THR.

 Altitude constraints related to waypoints are taken into account. If the lateral
navigation mode is lost, the climb mode reverts to open climb.

Descent Mode

 Descent mode guides the aircraft along the FMS-computed descent path to the FCU-
selected altitude. The descent path includes various segments from top of descent to
approach.

 The aircraft respects altitude and speed constraints when feasible. If lateral navigation
mode is lost, descent mode reverts to vertical speed or flight path angle mode.

Cruise Mode
 Upon reaching the cruise flight level, the AP/FD goes into altitude cruise mode. The
target Mach number is set as the ECON cruise Mach number.

 If the aircraft is cleared by ATC to a different level, the cruise flight level on the prog
page should be updated for flight efficiency.

Takeoff and Initial Climb

Runway Mode

 The runway mode provides lateral guidance during takeoff roll and initial climb up to
30 feet. The Speed Reference System (SRS) engages automatically at power
application.

Speed Reference System (SRS)

 16

 SRS is a vertical mode that controls the pitch to maintain speed at V2 + 10 knots
minimum or V2 in case of engine failure up to acceleration altitude. The climb mode
replaces SRS after thrust reduction and at acceleration altitude.

Precision Approaches
 Precision approaches can be flown using selected or managed modes. The FMGS
provides automatic guidance on the localizer and glide slope.

Localizer and Glide Slope Capture

 The localizer can be intercepted in heading or navigation mode. Glide slope capture
occurs after localizer capture. Lock and glide slope modes are engaged automatically
when below 400 feet.

Land Mode and Flare

 Land mode engages automatically when below 400 feet if lock and glide slope are
engaged. Flare mode engages at 30 feet if the autopilot is engaged, guiding the aircraft
on the runway centerline and providing pitch attitude for the flare.

Non-Precision Approaches
 Non-precision approaches can be flown using selected or managed modes. The use of
track/flight path angle modes is recommended.

Final Approach Mode

 Final Approach mode engages when the aircraft intercepts the descent profile and
guides the aircraft on the profile down to MDA (Minimum Descent Altitude) or MDH
(Minimum Descent Height). The mode disengages when reaching MDA minus 50
feet or 400 feet above ground level.

Failures and Reversions

 In case of ILS ground transmitter or dual receiver failures, the AP/FD reverts to
heading/vertical speed mode. The approach should be interrupted unless the runway is
in sight.

 During approach, if GPS primary is lost, a triple click aural warning is triggered,
requiring navigation accuracy cross-check.
 17

This lesson outlines the various modes of the flight guidance system and their interactions
during different phases of flight, including takeoff, climb, cruise, descent, and approach.
 18

AUTO FLIGHT PROTECTIONS

FMGS and Pilot Assistance

One aspect of the Flight Management and Guidance System (FMGS) is the assistance it
provides to the pilot in maintaining safe flight within the flight envelope. This assistance
includes engine failure compensation, low-speed protections, and autopilot flight director
mode reversions. Below are the details of some of these protections.

Engine Failure Compensation

In case of an engine failure with autopilot engaged, the FMGC ensures automatic yaw
compensation in all modes. This is achieved through:

 The yaw damper for takeoff and go-around.

 The automatic rudder trim in all modes.

Additionally, the autopilot flight director speed reference system pitch mode automatically
adjusts the reference target guidance speed in case of an engine failure during takeoff or go-
around.

Low-Speed Protection

Low-speed protection is achieved by the following features:

 The auto thrust speed mode.

 The low energy warning.

 Alpha floor protection.

 Windshear protection.

When auto thrust is on and in speed mode, if the speed target selected by the pilot on the
Flight Control Unit (FCU) is below VLS (lowest selectable speed), the auto thrust will not
allow the speed to decrease below VLS.

If for any reason, such as turbulence or shear, the airspeed drops significantly below VLS
with auto thrust off, an oral warning ("Speed! Speed! Speed!") is triggered by the FMGC and
repeated every five seconds. This drives the pilot's attention to the speed scale, prompting
manual thrust increase to regain a positive flight path angle through pitch control.

Low Energy Warning

 19

An energy level is computed by the FMGC, taking into account the horizontal deceleration
rate and the current flight path angle. This triggers the low energy warning, which is activated
during the deceleration phase between 100 feet and 2000 feet radio altimeter and in
configurations 2, 3, or full, just before alpha floor detection. However, the low energy
warning is inhibited in the following cases:

 GPWS (Ground Proximity Warning System) alert.

 Alternate or direct law.

 Failure of both radio altimeters.

Alpha Floor Protection

If the airspeed continues to drop below the low energy warning and the angle of attack
increases above a given threshold, the alpha floor function of the auto thrust is triggered. This
also inhibits the low energy warning, and the auto thrust commands full thrust (TOGA
thrust).

The angle of attack threshold triggering the alpha floor protection is processed by the FMGC
based on aircraft parameters such as configuration and deceleration rate. When alpha floor is
triggered, auto thrust is turned on if it was previously off, indicated by a white "A/THR" on
the Flight Mode Annunciator (FMA). "Alpha Floor" in green is displayed as the auto thrust
mode.

The alpha floor function is available from liftoff down to 100 feet radio altimeter. However,
alpha floor protection is lost in the following situations:

 Combinations of failures.

 One thrust lever instinctive disconnect push button is pressed for more than 15
seconds.

 Engine out with slats/flaps extended.

 In alternate or direct law.

When exiting the alpha floor conditions, the auto thrust mode reverts to TOGA lock mode,
which indicates that TOGA thrust is locked regardless of thrust lever position. To regain
thrust control, the pilot must switch off the auto thrust, allowing for manual control. The auto
thrust may be re-engaged when convenient.

Windshear Protection
 20

If the aircraft encounters windshear conditions detected by the FMGC, a red "Windshear"
message is triggered for a minimum of 15 seconds on both Primary Flight Displays (PFDs),
accompanied by an oral warning ("Windshear! Windshear! Windshear!"). This reactive
windshear warning is available from three seconds after liftoff up to 1300 feet during takeoff
and from 1300 feet down to 50 feet during landing, with at least CONF 1 selected.

The FMGC provides the following protections against windshear:

 At takeoff and go-around, the autopilot flight director speed reference system vertical
mode commands a pitch ensuring a minimum positive rate of climb despite a potential
speed drop.

 During approach, with the ground speed mini function, the managed speed target is
automatically adjusted with wind variations to ensure that the aircraft's ground speed
does not drop below a minimum value.

If the angle of attack gets too high and reaches the fly-by-wire angle of attack protection, the
autopilot disengages. The fly-by-wire maximum angle of attack protection assists the pilot in
best reacting to the situation.

Mode Reversions of Autopilot Flight Director and Auto Thrust

Mode reversions are automatic mode changes that allow comprehensive autoflight system
behavior when the pilot modifies a target on the FCU, experiences a loss of navigation mode,
or encounters flight envelope limit speed protection.

Mode Reversions Due to FCU Altitude Changes

When the autopilot is on and the aircraft is in climb using either open climb or climb to a
target altitude, suppose ATC requires a level-off at a lower altitude. Upon selecting the new
target altitude on the FCU, the autopilot flight director vertical mode reverts to vertical speed
with the current vertical speed value. It is then up to the pilot to decide how to regain the
desired altitude by dialing the desired vertical speed target or by pulling the altitude selector
to engage open descent or open climb.

Mode Reversion Due to Loss of Navigation Mode

When the autopilot is on and the aircraft is in climb or descent using a navigation mode,
suppose ATC requires a turn to a new heading. Upon selecting the new target heading on the
FCU, the autopilot flight director vertical mode reverts from climb or descent to open climb
 21

or vertical speed mode, respectively. The aircraft's pitch behavior remains unchanged. Note
that the loss of navigation mode may also be caused by a flight plan discontinuity.

Mode Reversion When Flight Director Orders Are Not Followed (Manual Flight)

Suppose the aircraft is manually flown with the flight director on and autopilot off, and the
flight director orders are disregarded. If the aircraft is pitched up or down contrary to the
flight director's guidance, the speed increases or decreases significantly. If the speed reaches
certain thresholds, both flight directors disengage, and the auto thrust reverts to speed mode
to regain the target speed.

This flight envelope limit speed protection ensures that at minimum or maximum speed, the
flight director bars are removed, and the auto thrust mode reverts to speed mode to recapture
the target speed, maintaining safe operation within the flight envelope.
 22

FAILURE CASES
FMGC Synchronization and Dual Mode of Operation

Both FMGCs exchange data through a cross-talk bus and are synchronized. When both
FMGCs crosstalk, they operate in dual mode. The FMGC driving the synchronization is
called the master. The master FMGC is automatically determined by the engagement status of
the autopilot flight director:

 If Autopilot 1 is on, FMGC1 is the master.

 If Autopilot 2 is on, FMGC2 is the master.

 If Autopilot 1 plus 2 and/or Flight Director 1 plus 2 are on, FMGC1 is the master.

In this scenario, FMGC1 is the master as Autopilot 1 is on. The autothrust is driven by the
master FMGC. When Flight Director 1 plus 2 are on, each FMGC drives its flight director
and FMA on its side PFD.

Independent Mode Operation

If crosstalk is lost between both FMGCs, each FMGC operates independently in what is
called independent mode. The crew is advised by a message on the scratchpad: "Independent
Operation." The independent amber light on each MCDU indicates that the on-site FM has
detected independent mode. In this mode:

 Each FMGC drives its own FG autopilot flight director.

 Each FMGC drives its own EFIS PFD ND and MCDU.

In independent mode, the crew must make the same entries on each MCDU to ensure
consistent guidance orders for both autopilot FDs and consistent information displayed on
EFIS and MCDU. When crosstalk is recovered, the FMGCs automatically revert to dual
mode.

Failure of One FMGC

Consider the failure of FMGC1, assuming no previous faults have occurred during flight. If
Autopilot 1 and Autothrust were engaged, an ECAM alert triggers "AP Off" and "Autothrust
Off," causing AP1 and Autothrust to disengage. The crew can re-engage the autopilot on the
healthy side, AP2, and re-engage Autothrust.
 23

An amber FM1 light on the MCDU indicates that the on-site FM has failed. MCDU1
becomes a copy of the other MCDU, displaying the scratchpad message "OPP FMGC in
Process." This mode is called single mode. In single mode:

 Both FMAs display "Flight Director 2," indicating that flight director bars on both
PFDs are driven by FMGC2.

 Only FMGC2 computes the position and tunes the offside nav aids.

 ND1 displays "Set Offside Range Mode" and "Map Not Available."

MCDU Lock and Circuit Breaker Reset

If you cannot insert data into the scratchpad or change any MCDU page, the MCDU is
locked. This failure is not automatically detected. To recover the faulty MCDU, pull the
related circuit breaker, wait 10 seconds, and then push it back. The same procedure applies in
case of an MCDU failure indicated by the amber enunciator "FAIL" on the MCDU.

Navigation Backup Mode

In case of failure of both FMGCs, a navigation mode called nav backup is available to the
crew using the MCDUs and the IRS plus GPS. The nav backup mode is possible due to the
continuous downloading of the flight plan from the FMGCs to their related MCDUs.
Selecting the nav backup prompt on the MCDU menu pages activates the mode. When
activated, nav backup provides:

 Aircraft position.

 Flight Plan display on ND.

 Automatic Waypoint sequencing.

 Bearing and distance from aircraft present position to the waypoint.

 True track, time estimate, and distance between waypoints.

 Total time and distance to the destination.

 Limited direct-to function.

 APFD selected modes.

For navigation, it is recommended to use track FPA. At least one FG must be available to
engage AP and Autothrust. Time estimates on each MCDU are computed using the current
ground speed from the on-site IRS.
 24

Nav Backup Mode Limitations

Nav backup mode has several limitations:

 Navigation database and performance database are lost.

 Most predictions are unavailable.

 Nav aids auto-tuning is lost.

 Automatic landing elevation selection is not possible.

 Managed modes of APFD are not available.

 Crosstalk between MCDUs is lost, requiring the crew to make the same flight plan
modifications on both MCDUs.

Since the FMS is lost, nav aids must be manually tuned using the RMPS. Additionally, the
landing elevation must be manually adjusted, and the optional data display push buttons on
the FS control panels become inoperative. When activated, nav backup can be deactivated by
selecting the "Deselect Nav Backup" prompt on the MCDUs or automatically if an FM
source change occurs or by selecting an FM subsystem on the MCDU menu page.

Backup Flight Plan Page

The backup flight plan page is accessed by pushing the flight plan key once nav backup is
activated. This page displays, for each waypoint:

 Waypoint ident and coordinates.

 True track and distance between two consecutive waypoints.

 Time to go and time between the aircraft and the given waypoint.

 Bearing between the aircraft and the two-way point.

On line 6, data related to the destination airport, including the airport ident, coordinates,
distance to destination, and time to go, is displayed.

Direct-To Function in Nav Backup

The direct-to function in nav backup mode is called by pushing the "DIR" key while nav
backup is active and the aircraft position is valid. It allows the selection or insertion of the
desired waypoint with the same information found on the backup flight plan page.

Backup Progress Page

 25

The backup progress page is accessed by pushing the "PROG" key once nav backup is
activated. This page displays:

 The ident of the last sequenced waypoint and the altitude at which sequencing was
done.

 Bearing, distance, and time to go to a waypoint entered by the crew.

 Navigation means used by the MCDU (e.g., GPS NAV default, IRS only).

 Current aircraft position based on the navigation means in use and ground speed from
the selected IRS.

 Desired track from the backup flight plan active leg and actual track from the selected
IRS.

 Access to the on-site backup IRS page and the backup GPS page (if a GPS is
installed).

Backup IRS and GPS Pages

The backup IRS page displays the current aircraft position, true track, ground speed, true
heading, magnetic heading, wind direction and velocity, and GPIRS accuracy and position.
The GPIRS fields are dashed if GPS information is unavailable and blanked if GPS is not
fitted.

The backup GPS page displays the current GPS position, true track, UTC, ground speed,
figure of merit, altitude, mode of operation, and the number of currently tracked satellites.
Line 5 allows deselection of the GPS for nav backup, but not for regular FM navigation. Line
6 allows returning to backup progress.

Scratchpad Messages in Nav Backup Mode

Two new scratchpad messages can appear on the MCDUs in nav backup mode:

 "IRS Only Navigation" indicates that GPS is lost (not displayed if GPS is manually
deselected).

 "NAV GO" indicates that GPS is recovered (not displayed if GPS is manually
selected).