Airbus A330/A340. Flight Crew Training Manual (2007)

FLIGHT CREW TRAINING MANUAL

SUPPLEMENTARY INFORMATION

NAVIGATION ACCURACY

04.030

JAN 09/07

GENERAL

MSN 0002-0860

The primary function of the FMS is navigation, i.e. to compute the aircraft’s
position as accurately as possible. The validity of all other functions depends on
the accuracy of the FMS position.

The accuracy of the FMS navigation determines the flight crew’s strategy for
using the AP/FD modes, in addition to the ND display.

COMPUTATION OF THE AIRCRAFT POSITION

MSN 0002-0860

WITHOUT GPS PRIMARY

PRINCIPLE

The FMS position is computed from the three IRS positions, that are combined
to provide a MIX IRS position.

The radio position is also combined, if two

DMEs, a VOR/DME or a GPS supplemental are available. The GPS
supplemental is considered to be an additional form of NAVAID, and can be
accepted, if it falls within the radio position or the MIX IRS position.

INITIALIZATION

Refer to the FCTM 02.001.

TAKEOFF

Each FMGC uses the MIX IRS position as its position, until the thrust levers are
pushed forward to TOGA.

The FMS position is then updated to the runway

threshold coordinates. The difference between the MIX IRS position and the FMS
position is referred to as the TO BIAS. The TO BIAS is added to the MIX IRS
position, for the subsequent FMS position.

FMS POSITION UPDATING AT TAKE OFF

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IRS1

MIX IRS

IRS3

IRS2

TO BIAS

RWY

FOF 04030 03793 0001

IN FLIGHT

The original TO BIAS is continuously updated with the current radio aid.

UPDATING BIAS PRINCIPLE

Updated BIAS

MIX IRS

position

TO BIAS

FMS position

radio position

Updated FMS

position

FMS position

tends to radio

position

FOF 04030 03794 0001

If the radio position is lost, the system uses the updated BIAS to determine the
FMS position from the MIX IRS position.

NAVIGATION ACCURACY

The FMS computes the Estimated Position Error (EPE). The EPE is an estimate.
To compute the EPE, the FMS considers the immediately available navigation
means in the FMS position computation and applies defined tolerances for each
of them. These tolerances assume that the navigation means are working
properly. They ignore any possible excessive IRS drift or erroneous locations of
navaids. The MCDU PROG page displays the HIGH/LOW indications, according
to the EPE. These indications reflect the probable accuracy of the FMS
navigation compared to the determined accuracy criteria.

WITH GPS PRIMARY

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NAVIGATION ACCURACY

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PRINCIPLE

The GPS interfaces directly with the IRS that outputs a GPIRS position. When a
GPIRS position is available, it overrides the RADIO position, if available.
Therefore, the FMS position tends toward the GPIRS position.

INITIALIZATION

Refer to the FCTM 02.001.

TAKEOFF

The FM position is automatically updated at the runway threshold. With FMS2,
this automatic position update is inhibited.

IN FLIGHT

The FM position tends to the GPIRS position as long as the GPS satellites are
available.

NAVIGATION ACCURACY

The GPS position is characterized by two parameters:

Integrity

Accuracy.

Integrity is a direct function of the number of satellites in view of the aircraft. If
five or more satellites are in view, several combinations of the satellite signal
may be used to process "several positions" and to carry out reasonableness
tests on the satellite signals themselves.

Accuracy functions in direct connection with the satellite constellation in view of
the aircraft. If the satellites are low on horizon, or not in appropriate positions,
accuracy will be poor. It is provided as a "figure of merit".

If the GPS position fulfils both the integrity and the accuracy criteria, GPS
PRIMARY is displayed on the MCDU PROG page and the GPS position is the
best raw data position available.

SUMMARY

FM POSITION

Flight phase

WITHOUT GPS

PRIMARY

WITH GPS PRIMARY

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NAVIGATION ACCURACY

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On groundbefore Takeoff

MIX IRS

GP IRS

Takeoff

Updated at runway threshold (shift) (*)

With RADIO

Tends toward RADIO

GP IRS

flight

WithoutRADIO

MIX IRS + BIAS

GP IRS

(

) With FMS2, the FMS position update at takeoff is inhibited, when GPS

PRIMARY is active.

USE OF FMS

MSN 0002-0860

The navigation accuracy is managed through several MCDU pages:

PROG PAGE

This page indicates the GPS PRIMARY.

The PROG displays the estimated navigation accuracy in green. This provides
the EPE, if GPS PRIMARY LOST, or is computed by the GPS, if GPS PRIMARY
is displayed

The PROG page displays the required navigation accuracy in blue (this can be
changed). The required navigation accuracy thresholds are determined,
depending on the flight phase, or can be manually entered. These thresholds are
used to change from HIGH to LOW accuracy, or vice versa. These indications
are used when flying within RNP airspace.

SELECTED NAVAIDS PAGE

The SELECTED NAVAID page is accessible from DATA/POSITION MONITOR/
FREEZE/SEL NAVAIDS. It has a DESELECT prompt, that enables the flight crew
to prevent the FMS from using the GPS data to compute the position, in the
case of a major problem. GPS PRIMARY lost is then displayed on MCDU and
ND. The GPS can be reselected using the same page.

PREDICTIVE GPS PAGE (IRS HONEYWELL ONLY)

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NAVIGATION ACCURACY

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The PREDICTIVE GPS page is accessible from PROG page. The GPS
PRIMARY criteria depend upon the satellite constellation status (position and
number) and this is predictable. The crew can assess the GPS PRIMARY status
at destination or alternate.

ND/MCDU

A GPS PRIMARY message is displayed when GPS PRIMARY is again available.
This message is clearable. A GPS PRIMARY LOST message is displayed when
GPS PRIMARY is lost. This message is clearable on MCDU but not on ND.
When the class of navigation accuracy is downgraded from HIGH to LOW
(LOW to HIGH), a NAV ACCUR DOWNGRADE (UPGRADE) is displayed on ND
and MCDU

AIRCRAFT POSITION AWARENESS AND OPERATIONAL CONSEQUENCES

MSN 0002-0860

R (1)

NAVIGATION ACCURACY INDICATIONS

The navigation accuracy indications are available on the MCDU PROG page.
The following guidelines apply:

If GPS PRIMARY is displayed, no navigation cross-check is required

If GPS PRIMARY LOST, navigation crosscheck is required in climb, in cruise,

about every 45 minutes, before the Top Of Descent, reaching TMA and IAF
and whenever a navigation doubt occurs.

The crew will use, IRS only, LOW and NAV ACCY DNGRADED messages as

indications to trigger a navigation accuracy check.

NAVIGATION ACCURACY CROSSCHECK TECHNIQUE

R (2)

The principle consists in comparing the FMS position with the RADIO position
(aircraft real position).

NAVIGATION ACCURACY CROSS CHECK TECHNIQUE 1

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FMS
POS

FMS

BRG
DIST

RAW

FOF 04030 03798 0001

There are two possible techniques:

The flight crew inserts a radio ident in the MCDU PROG page that provides a

bearing/distance in relation to the FMS position.

They then compare these

values with the raw data received from the navaid, that indicates the real
position of the aircraft. This enables the flight crew to quantify the error .

On the ND, the flight crew compares: The position of the needle and its

associated DME distance (the real position of the aircraft) with the position of
the navaid symbol and its associated distance, indicated by the range markers
(these markers provide a bearing/distance, in relation to the FMS position).

R (3)

NAVIGATION ACCURACY CROSS CHECK TECHNIQUE 2

ABC
78 nm

ABC

ABC
78 nm

ABC

Nav accuracy

check positive

Nav accuracy

check negative

FOF 04030 00201 0001

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OPERATIONAL CONSEQUENCES

The result of the crosscheck of the navigation accuracy determines the pilot’s
strategy for using the ND display, the AP/FD modes and the EGPWS.

PNF

AP/FD mode

EGPWS

GPS

PRIMARY

Arc or Rose NAVwith

raw data when

required

Lateral and

vertical

managed

modes

Navigation

accuracy

checkpositive(

≤

nm)

Arc or Rose NAV with

raw data when

required

Lateral and

vertical

managed

modes

Cruise

Navigation

accuracy check

negative(>3 nm)

ARC or ROSE NAV

may be used with
care and with raw

data

Lateral and

vertical

managed

modes with

care with raw

data

OFF

Navigation

accuracy check

positive(

≤

1 nm)

Arc or Rose NAVwith

raw data

Lateral and

vertical

managed

modes

GPS

PRI-

MARY
LOSTOr

GPS

Ap-

proach

Navigation

accuracy check

negative(>1 nm)

ROSE VOR or ILS as

required

Lateral and

vertical

selectedmodes

OFF

(1) A GPS-defined Non-Precision Approach must be interrupted, if the GPS
PRIMARY LOST message is displayed.

POSITION UPDATE

In the case of an obvious and major map shift, indicated by messages, such as
"CHECK A/C POSITION, FM1/FM2 POS MISMATCH", the aircraft position may
be updated on the MCDU PROG page. There are two possible techniques:

The recommended technique is to update the FMS over a beacon by pressing
the UPDATE prompt once estimating that the aircraft overflies the beacon using
the associated needle. The potential error induced is approximately 4 to 5 NM.
When the position update is achieved, the EPE is automatically set to a higher
value and the navigation accuracy is low.

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SUPPLEMENTARY INFORMATION

ZFW - ZFCG ENTRY ERRORS

04.040

JAN 09/07

GENERAL

MSN 0002-0860

Before engine start, the FMGC computes the aircrafts Gross Weight (GW) and
Center of Gravity (CG). After engine start, both the Flight Envelope Computer
(FE) and the Fuel Control and Monitoring Computer (FCMC) calculate the GW
and CG.

These GW and CG values provide information for:

Aircraft GW and CG displays

FM predictions and speeds

The AP/FD and flight control laws

The calculation of the VS1G

The calculation of the characteristic speeds (VLS, F, S, GD), for display on

the PFD

CG control

If a ZFW or ZFWCG is not correctly entered on the INIT B page of the MCDU,
this results in calculation errors.

TECHNICAL BACKGROUND

MSN 0002-0860

To calculate the GW and CG:

1. The pilot enters the ZFW and ZFWCG on the INIT B page of the MCDU.

2. The FCMC calculates the GW and CG by taking into account the ZFW and

ZFWCG (entered on the INIT B page of the MCDU), and the quantity of fuel
in each tank.
The GW and CG, calculated by the FCMC, are:
.

Used by the FCMC to regulate the center of gravity

Transmitted to the ECAM SD for display

Transmitted to the FE.

3. The FE transmits the GW and CG to the:

FM, for predictions and speeds

PRIM, for the computation of the VS1G and for flight control laws

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FG, for the AP/FD control laws

EIS, for the display of characteristic speeds

Note:

The FE computes a backup:
-- GW, with aerodynamic data or from Fuel Used (FU) data
-- CG, with aerodynamic data, and the THS position.
If FCMC data are available, the GW and CG FCMC computed are
used.
If FCMC data are not available, the GW and CG FE computed are
used.
However, if the FCMC-computed CG, and the FE-computed CG
differs more than a specified threshold, the PRIM uses 30% CG for
flight control laws.

. The FE uses VS1G from the PRIM to compute characteristic speeds

(VLS , F, S, GD).

These speeds are displayed on PFD.

. For the calculation of ValphaPROT, ValphaMAX, and VSW, the PRIM

uses AOA data only.

4. The FE-computed CG is used to trigger the Excess AFT CG warnings of the

FWC. This works independently from the FCMC.

GW AND CG COMPUTATION AND USE

GW and CG
computation

CG control

Fuel sensors

FCMC

ECAM SD

Vs1g computation
Flight control laws

PRIM

Predictions
Speeds

AP control laws

Characteristic
speeds on PFD

EIS

FWC

EXCESS
AFT CG
WARNING

Back up
CG and GW
FE computed

OVHT

CLR

D/R

PROG

PERF

INIT

DATA

F−PLN

FUEL

SEC

MCDC
MENU

PRED

F−PLN

RAD
NAV

AIR

PORT

ZFW

ZFWCG

FOF 04040 03731 0001

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ZFW - ZFCG ENTRY ERRORS

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ENTRY ERROR AND OPERATIONAL CONSEQUENCES

MSN 0002-0860

The following summarizes the impact of erroneous ZFW or ZFWCG entries on
the INIT B page of the MCDU:

ERRONEOUS ZFWCG ENTRY

If the ZFWCG entry is not correct, the FCMC-computed CG will not be correct,
and:

An erroneous CG appears on both the SD page of the ECAM, and on the

FUEL PRED page of the MCDU.

Affects CG regulation.

However, the EXCESS AFT CG warning remains reliable.

Slightly affects FM predictions.

Impacts the VLS and VAPP speeds, that appear on the PERF APPR page of

the MCDU (A340-500/600 only).

The pitch trim setting may not be correct at takeoff.

The PRIM operates with a CG of 30% in flight.

However, this will have a very small effect on aircraft handling.

Slightly affects AP/FD control laws.

Impacts the VLS that appears on the PFD (A340-500/600 only).

However, ValphaPROT, ValphaMAX, VSW are not affected, because they are
calculated on the basis of aerodynamic data.

ERRONEOUS ZFW ENTRY

If the ZFW entry is not correct, the FCMC-computed GW and, to a lesser
degree, the CG will not be correct, and:

Erroneous GW and CG appear on both the ECAM and on the FUEL PRED

page of the MCDU.

Slightly affects CG regulation, because the aft CG target depends on the

weight.

However the EXCESS AFT CG warning remains reliable.

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May affect the SRS guidance mode (If VLS is greater than the V2 that is

entered on the PERF TO page of the MCDU).

Affects FM predictions and speeds.

Slightly affects FG and the PRIM control laws

Affects the characteristic speeds that appear on the PFD.

However, ValphaPROT, ValphaMAX, VSW are not affected, because they are
calculated on the basis of aerodynamic data.

ERRONEOUS FUEL ON BOARD (FOB) ENTRY

If the FOB entry is not correct, the GW and will not be correct until the engines
are started, and all of the above-mentioned consequences apply.

When the

engines are started, fuel figures are updated and applicable data is also updated
accordingly.

OPERATIONAL RECOMMENDATIONS

MSN 0002-0860

It is possible to limit the number of ZFW or ZFWCG entry errors by applying the
following recommendations:

If the flight crew performs a manual refuelling, the flight crew should carefully

check the CG calculation, because the load and trim sheet CG is calculated
on the basis of the standard distribution of fuel.

Both flight crewmembers should crosscheck ZFW and ZFWCG entries.

The CG on the load and trim sheet should be compared with the CG on the

ECAM.

If the flight crew detects a GW error in flight (e.g. a characteristic speeds error),
then a GW update can be made via the FUEL PRED page of the MCDU.

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CENTRE OF GRAVITY

04.050

JAN 09/07

PREFACE

MSN 0002-0860

The Center of Gravity (CG) is the point at which weight is applied. The CG is
expressed as a percentage of the Mean Aerodynamic Chord (MAC). It must
remain within a range determined by the CG’s impact on the aircraft:

Performance

Structure

Handling characteristics (when in direct law).

These factors define the range that the CG must remain within. This range is
referred to as the CG envelope.

MSN 0002-0860

MECHANICAL ASSUMPTIONS

For pitch control, there are three forces that must be considered when airborne:

The weight applied on the CG

The lift applied on the Center of Pressure (CP)

The downward force created by the Trimmable Horizontal Stabilizer (THS).

FORCES APPLIED ON FLYING AIRCRAFT

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LIFT

WEIGHT

THS

Nose up

counter moment

Nose down
moment

FOF 04050 03769 0001

Because the first two forces are not applied at the same point, they create a
pitching moment, that must be counteracted by the THS setting.

INFLUENCE OF THE CENTER OF GRAVITY ON THE AIRCRAFT PERFORMANCE

MSN 0002-0860

The position of the CG has a significant impact on performance, because it
determines the balance of the longitudinal forces.

When the CG moves forward, the nose down moment increases. The THS
produces a greater downward force to counteract this moment. As a result, lift
must increase, in order to balance both the weight and the THS downward force.
Therefore, a forward CG will result in a greater stall speed value. On A330/A340,
the stall speed increases by 1.5 knots, when the CG varies from 26% to full
forward CG.

INFLUENCE OF THE CG POSITION

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CENTRE OF GRAVITY

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LIFT

WEIGHT

THS

FOF 04050 03770 0001

IMPACT ON TAKEOFF PERFORMANCE

TAKEOFF SPEED AND ASSOCIATED DISTANCES

The aircraft operating speeds are referenced to the stall speed, e.g. V2>1.13
VS1g.

If the CG moves forward

VS1g increases

V2 increases

TOD increases (or

the runway-limited TOW decreases).

ROTATION MANEUVER

An aft CG gives the aircraft a nose up attitude, that helps the rotation. A forward
CG results in a nose heavy situation, and a difficult rotation. It is "heavier",
therefore longer, at forward CG.

CLIMB GRADIENT

As mentioned above, a forward CG is counteracted by a greater THS downward
force. This creates drag, that, in addition to the drag caused by the lift increase,
degrades aircraft performance, for example, the climb gradient.

For example:

A340Performance decrement with CG full forward, in comparison
with CG 26%Conf. 3, Packs On, ISA, Zp=0

CG 26 %

CG full forward

TOD

3165 m

3241 m

76 m

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Airbus A330/A340. Flight Crew Training Manual (2007) - page 23