This document provides an overview of avionics systems. It defines avionics as electronics used in aircraft and describes some key avionics subsystems including displays, communications, flight controls, sensors, navigation, and task automation. Modern avionics play an essential role in aircraft functionality and safety by enabling minimum crew operations and automated flight. Avionics can account for a significant portion of an aircraft's total costs.

1. UNIT I INTRODUCTION TO AVIONICS
Avionics’ is a word derived from the combination of aviation and electronics. It
was first used in the USA in the early 1950s and has since gained wide scale usage
and acceptance although it must be said that it may still be necessary to explain
what it means to the lay person on occasions.
The term ‘avionic system’ or ‘avionic sub-system’ is used in this book to mean
any system in the aircraft which is dependent on electronics for its operation,
although the system may contain electro-mechanical elements. For example, a
Flyby- Wire (FBW)flight controlsystem depends onelectronic digital computers
for
its effective operation, but there are also other equally essential elements in the
system. These include solid state rate gyroscopes and accelerometers to measure
the angular and linear motion of the aircraft and air data sensors to measure the
height, airspeed and incidence. There are also the pilot’s controlstick and rudder
sensor
assemblies and electro-hydraulic servo actuators to control the angular positions
of the control surfaces.
The avionics industry is a major multi-billion dollar industry world-wide and the
avionics equipment on a modern military or civil aircraft can account for around
30% of the total cost of the aircraft. This figure for the avionics content is more
like 40% in the case of a maritime patrol/anti-submarine aircraft (or helicopter)
and
can be over 75% of the total costin the case of an airborne early warning aircraft
(AWACS).
Modern general aviation aircraft also have a significant avionics content. For
example, colour head down displays, GPS satellite navigation systems, radio
communications equipment. Avionics canaccountfor10% of their total cost. The
avionic systems are essential to enable the flight crew to carry out the aircraft
mission safely and efficiently, whether the mission is carrying passengers to their
destination in the case of a civil airliner, or, in the military case, intercepting a
hostile aircraft, attacking a ground target, reconnaissance or maritime patrol.

2. A major driver in the development and introduction of avionic systems has been
the need to meet the mission requirements with the minimum flight crew. In the
case of a modern civil airliner, this means a crew of two only, namely the First
Pilot (or Captain) and the Second Pilot. This is only made possible by reducing
the crew
workload by automating the tasks which used to be carried out by the Navigator
and Flight Engineer. The achievement of safe two crew operation has very
considerable economic benefits for the airline in a highly competitive market
with the consequent saving of crew salaries, expenses and training costs. The
reduction in weight is also significant and can be translated into more
passengers or longer range on less fuel.
This is because unnecessary weight is geared up ten to one, as will be explained
later. In the military case, a single seat fighter or strike (attack) aircraft is lighter
and costs less than an equivalent two seat version. The elimination of the second
crew member (Navigator/Observer/Radar Operator) has also significant
economic
benefits in terms of reduction in training costs. (Thecostof training and
selection of aircrew for fast jet operation is very high.)
Systems Which Interface Directly withthe Pilot
These comprise displays, communications, data entry and control and flight
control.
The DisplaySystems provide the visual interface between the pilot and the
aircraft systems and comprise head up displays (HUDs), helmet mounted
displays (HMDs) and head down displays (HDDs). Most combat aircraft are
now equipped with a HUD. A small but growing number of civil aircraft have
HUDs installed.
The HMD is also an essential system in modern combataircraft and helicopters.
The prime advantages of the HUD and HMD are that they project the display
information
into the pilot’s field of view so that the pilot can be head up and can concentrate
on the outside world.
The HUD now provides the primary display for presenting the essential flight
information to the pilot and in military aircraft has transformed weapon aiming
accuracy. The HUD can also display a forward looking infrared (FLIR) video
picture one to one with the outside world from a fixed FLIR imaging sensor
installed in
the aircraft. The infrared picture merges naturally with the visual scene enabling
operations to be carried out at night or in conditions of poorvisibility due to
haze or clouds. The HMD enables the pilot to be presented with information

3. while looking in any direction, as opposed to the limited forward field of view
of the HUD. An
essential element in the overall HMD system is the Helmet Tracker system to
derive the direction of the pilot’s sight line relative to the aircraft axes.
This enables the pilot to designate a target to the aircraft’s missiles. It also
enables the pilot to be cued to look in the direction of a threat(s) detected by the
aircraft’s Defensive Aids system. The HMD can also form part of an indirect
viewing system by driving a gimballed infrared imaging sensor to follow the
pilot’s line of sight.
Image intensification devices can also be integrated into the HMD. These
provide a complementary night vision capability enabling the aircraft (or
helicopter) to operate at night or in poorvisibility.
Colour head down displays have revolutionised the civil flight-deck with
multifunction displays eliminating the inflexible and cluttered characteristics of
1970s generation flight-decks with their numerous dial type instrument displays
dedicated to displaying one specific quantity only.
The multi-function colour displays provide the primary flight displays (PFDs)
of height, airspeed, Mach number, vertical speed, artificial horizon, pitch angle,
bank angle and heading, and velocity vector. They provide the navigation
displays, or horizontal situation indicator (HSI) displays, which show the
aircraft position and track relative to the destination or waypoints together with
the navigational information and distance and time to go. The weather radar
display can also be superimposed on the HSI display. Engine data are presented
on multi-function colour displays so that the health of the engines can easily be
monitored and divergences from the norm highlighted. The aircraft systems, for
example, electrical power supply system, hydraulic power supply system, cabin
pressurisation system and fuel management system, can be shown in easy to
understand line diagram format on the multi-function displays. The multi-
function displays can also be reconfigured in
the event of a failure in a particular display.

4. The CommunicationsSystems play a vital role; the need for reliable two way
communication between the ground bases and the aircraft or between aircraft is
self evident and is essential for air traffic control. A radio transmitter and
receiver equipment was in fact the first avionic system to be installed in an
aircraft and goes
back as far as 1909 (Marconi Company).The communications radio suite on
modern aircraft is a very comprehensive one and covers several operating
frequency bands.
Long range communication is provided by high frequency (HF) radios operating
in the band 2–30 MHz. Near to medium range communication is provided in
civil aircraft by very high frequency (VHF) radios operating in the band 30–100
MHz, and in military aircraft by ultra high frequency (UHF) radio operating in
the band
250–400 MHz. (VHF and UHF are line of sight propagation systems.)
Equipment is usually at duplex level of redundancy; the VHF radios are
generally at triplex level on a modern airliner. Satellite communications
(SATCOM) systems are also installed in many modern aircraft and these are
able to provide very reliable world
wide communication.
The Data Entry and Control Systems are essential for the crew to interact with
the avionic systems. Such systems range from keyboards and touch panels to
the use of direct voice input (DVI) control, exploiting speechrecognition
technology, and voice warning systems exploiting speech synthesisers.

5. The FlightControl Systems exploit electronic system technology in two areas,
namely auto-stabilisation (or stability augmentation) systems and FBW flight
control systems. Most swept wing jet aircraft exhibit a lightly damped short
period oscillatory motion about the yaw and roll axes at certain height and
speed conditions,
known as ‘Dutch roll’, and require at least a yaw auto-stabiliser system to damp
and suppress this motion; a roll auto-stabiliser system may also be required. The
short period motion about the pitch axis can also be insufficiently damped and a
pitch auto-stabiliser system is necessary. Most combat aircraft and many civil
aircraft in fact require three axis auto-stabilisation systems to achieve acceptable
control and
handling characteristics across the flight envelope.
FBW flight control enables a lighter, higher performance aircraft to be produced
compared with an equivalent conventional design by allowing the aircraft to be
designed with a reduced or even negative natural aerodynamic stability. It does
this by providing continuous automatic stabilisation of the aircraft by computer
control of
the control surfaces from appropriate motion sensors. The system can be
designed to give the pilot a manoeuvre command control which provides
excellent control and handling characteristics across the flight envelope. ‘Care
free manoeuvring’ characteristics can also be achieved by automatically
limiting the pilot’s commands according to the aircraft’s state. A very high
integrity, failure survival system is of courseessential for FBW flight control.
Airbus A380 flight deck
Aircraft State Sensor Systems
These comprise the air data systems and the inertial sensorsystems.

6. The Air Data Systems provide accurate information on the air data
quantities,that is the altitude, calibrated airspeed, vertical speed, true airspeed,
Mach number and airstream incidence angle. This information is essential for
the control and navigation of the aircraft. The air data computing system
computes these quantities
from the outputs of very accurate sensors which measure the static pressure,
total pressure and the outside air temperature. The air-stream incidence angle is
derived from air-stream incidence sensors.
The Inertial Sensor Systems provide the information on aircraft attitude and the
direction in which it is heading which is essential information for the pilot in
executing a manoeuvre or flying in conditions of poorvisibility, flying in clouds
or at night. Accurate attitude and heading information are also required by a
number
of avionic sub-systems which are essential for the aircraft’s mission – for
example, the autopilot and the navigation system and weapon aiming in the case
of a military aircraft.
The attitude and heading information is provided by the inertial sensor
system(s). These comprise a set of gyros and accelerometers which measure the
aircraft’s angular and linear motion about the aircraft axes, together with a
computing system which derives the aircraft’s attitude and heading from the
gyro and accelerometer
outputs. Modern attitude and heading reference systems (AHRS) use a strapped
down (or bodymounted) configuration of gyros and accelerometers as opposed
to the earlier gimballed systems.
The use of very high accuracy gyros and accelerometers to measure the
aircraft’s motion enables an inertial navigation system (INS) to be mechanised
which provides very accurate attitude and heading information together with the
aircraft’s velocity and position data (ground speed, track angle and
latitude/longitude co-ordinates).
The INS in conjunction with the air data system also provides the aircraft
velocity vector information. The INS is thus a very important aircraft state
sensorsystem – it is also completely self-contained and does not require any
access to the outside world.
Navigation Systems
Accurate navigation information, that is the aircraft’s position, ground speed
and track angle (direction of motion of the aircraft relative to true North) is
clearly essential for the aircraft’s mission, whether civil or military. Navigation

7. systems can be divided into dead reckoning (DR) systems and position fixing
systems; both types are required in the aircraft.
The Dead Reckoning Navigation Systems derive the vehicle’s present position
by estimating the distance travelled from a known position from a knowledge of
the speed and direction of motion of the vehicle. They have the major
advantages of being completely self contained and independent of external
systems. The main
types of DR navigation systems used in aircraft are:
(a) Inertial navigation systems. The most accurate and widely used systems.
(b) Doppler/heading reference systems. These are widely used in helicopters.
(c) Air data/heading reference systems These systems are mainly used as a
reversionary
navigation system being of lower accuracy than (a) or (b).
A characteristic of all DR navigation systems is that the position error builds up
with time and it is, therefore, necessary to correct the DR position error and
update the system from position fixes derived from a suitable position fixing
system.
The Position Fixing Systems used are now mainly radio navigation systems
based on satellite or ground based transmitters. A suitable receiver in the
aircraft with a supporting computer is then used to derive the aircraft’s position
from the signals received from the transmitters.
The prime position fixing system is without doubt GPS (global positioning
system). This is a satellite navigation system of outstanding accuracy which has
provided a revolutionary advance in navigation capability since the system
started to come into full operation in 1989.
There are also radio navigation aids such as VOR/DME and TACAN which
provide the range and bearing (R/θ) of the aircraft from ground beacon
transmitters located to provide coverage of the main air routes.
Approachguidance to the airfield/airport in conditions of poorvisibility is
provided by the ILS (instrument landing system), or by the later MLS
(microwave landing system).
A full navigation suite on an aircraft is hence a very comprehensive one and can
include INS, GPS, VOR/DME, ILS, MLS. Many of these systems are at duplex
level and some may be at triplex level.

8. Task AutomationSystems
These comprise the systems which reduce the crew workload and enable
minimum crew operation by automating and managing as many tasks as
appropriate so that the crew role is a supervisory management one. The tasks
and roles of these are very briefly summarised below.
Navigation Management comprises the operation of all the radio navigation aid
systems and the combination of the data from all the navigation sources, suchas
GPS and the INS systems, to provide the bestpossible estimate of the aircraft
position, ground speed and track. The system then derives the steering
commands for the
autopilot so that the aircraft automatically follows the planned navigation route,
including any changes in heading as particular waypoints are reached along the
route to the destination. It should be noted that this function is carried out by the
flight management system (FMS) (if installed).
The Autopilots and Flight ManagementSystems have been grouped together.
Because of the very close degree of integration between these systems on
modern civil aircraft. It should be noted, however, that the Autopilot is a ‘stand
alone’ system and not all aircraft are equipped with an FMS.
The autopilot relieves the pilot of the need to fly the aircraft continually with the
consequent tedium and fatigue and so enables the pilot to concentrate on other
tasks associated with the mission. Apart from basic modes, suchas height hold
and heading hold, a suitably designed high integrity autopilot system can also
provide a very
precise controlof the aircraft flight path for such applications as automatic
landing in pooror even zero visibility conditions. In military applications, the
autopilot system in conjunction with a suitable guidance system can provide
automatic terrain following, or terrain avoidance. This enables the aircraft to fly
automatically at high speed at very low altitudes (100 to 200 ft) so that the
aircraft can take advantage of
terrain screening and stay below the radar horizon of enemy radars.
Sophisticated FMS have come into wide scale use on civil aircraft since the
early 1980s and have enabled two crew operation of the largest, long range civil
jet airliners.
The tasks carried out by the FMS include:
• Flight planning.
• Navigation management.
• Engine controlto maintain the planned speed or Mach number.
• Control of the aircraft flight path to follow the optimised planned route.
• Control of the vertical flight profile.

9. • Ensuring the aircraft is at the planned 3D position at the planned time slot;
often
referred to as 4D navigation. This is very important for air traffic control.
Flight envelope monitoring.
• Minimising fuel consumption.
The EngineControl and ManagementSystems carry out the task of controland
the efficient management and monitoring of the engines. The electronic
equipment involved in a modern jet engine is very considerable: it forms an
integral part of the engine and is essential for its operation. In many cases some
of the engine control
electronics is physically mounted on the engine. Many modern jet engines have
a full authority digital engine control system (FADEC). This automatically
controls the flow of fuel to the engine combustion chambers by the fuel control
unit so as to provide a closed-loop controlof engine thrust in responseto the
throttle command.
The controlsystem ensures the engine limits in terms of temperatures, engine
speeds and accelerations are not exceeded and the engine responds in an
optimum manner to the throttle command. The system has what is known as full
authority in terms of the control it can exercise on the engine and a high
integrity failure survival control system is essential. Otherwise a failure in the
system could seriously damage the engine and hazard the safety of the aircraft.
A FADEC engine control system is thus similar in many ways to a FBW flight
control system.
Other very important engine avionic systems include engine health monitoring
systems which measure, process and record a very wide range of parameters
associated with the performance and health of the engines. These give early
warning of engine performance deterioration, excessive wear, fatigue damage,
high vibration
levels, excessive temperature levels, etc.
House Keeping Management is the term used to cover the automation of the
background tasks which are essential for the aircraft’s safe and efficient
operation.
Such tasks include:
• Fuel management. This embraces fuel flow and fuel quantity measurement and
control of fuel transfer from the appropriate fuel tanks to minimise changes in
the aircraft trim.
• Electrical power supply system management.
• Hydraulic power supply system management.
• Cabin/cockpit pressurisation systems.

10. • Environmental controlsystem.
• Warning systems.
• Maintenance and monitoring systems. These comprise monitoring and
recording systems which are integrated into an on-board maintenance computer
system.
This provides the information to enable speedydiagnosis and rectification of
equipment and system failures by pin-pointing faulty units and providing all, the
information, suchas part numbers, etc., for replacement units down to module
level in some cases.
Eurofighter Typhooncockpit
Avionics Systems Integration
Introduction and Background
Major avionic systems generally comprise a number of smaller sub-systems
which are combined to form an overall system. The combination,
interconnection and control of the individual sub-systems so that the overall
system can carry out its tasks effectively is referred to as ‘systems integration’.
The number of sub-systems which need to be integrated to form a major system
can be appreciated from flight management systems.

11. It is instructive to review the development of avionic systems and their
integration into overall systems in the light of the technology available and the
circumstances prevailing at the time. The object is to put the development of
today’s advanced systems and the even more advanced systems currently under
development in perspective.
In many cases the current concepts and philosophy are not new – often the
originators of particular system developments in the pastwere far sighted in
their concepts, but, as always, were limited by the technology available at the
time.
World War 2 (WW2) resulted in a major growth in the electronic equipment
installed in aircraft and the birth of avionics, with the very rapid development of
airborne radar systems and associated displays, radar warning systems and
ECM, and more advanced autopilot systems exploiting electronics. Installation
of the electronic
equipment (or ‘black boxes’), however, was very much on an ad hoc basis due
to the very rapid developments and time scale pressures in war time. Some very
limited degree of integration between sub-systems was introduced, for example
coupling the bomb sight to the autopilot – as readers who have seen the film
‘Memphis
Belle’ may have noted. In general, however, the systems were ‘stand alone’
systems and their integration into an overall system was carried out by specific
crew members such as the navigator, bomb aimer or radar operator.
The 1950s period saw the emergence of a number of avionic sub-systems (some
of which were initiated duringWW2) which have since undergone continual
development and now form part of the avionic equipment suite of most civil and
militaryjet aircraft and helicopters. For example, auto-stabilisers (or stability
augmentation systems), ILS, VOR/DME, TACAN, Doppler, air data computers,
attitude heading reference systems, inertial navigation systems.
The first major step towards integrating avionic systems was taken in the mid-
1950s with the establishment of the ‘weapon system’ concept. These concepts
were incorporated in the 1960s generation of aircraft, some of which are still in
service.
The conceptrequires a total system approachto the task of carrying out the
mission effectively with a high probability of success. Theaircraft, weapons
and the avionic systems required by the crew to carry out the mission
effectively must thus be considered as an integrated combination. It should be
appreciated, of course, that the total system approachis applicable to any
project, military or civil. As with many methodologies, however, military
applications provided the spur and the initial funding.

12. The very widely used ‘programme evaluation review technique’, or ‘PERT’
networks, and ‘critical path analysis’, for example, were originally developed
on the POLARIS missile program.
As an example of the overall system approach, consider the requirements for a
naval strike aircraft. The aircraft must be able to operate from an aircraft carrier
in all weathers and be able to find the target and attack it with a suitable weapon
(or weapons) with a high probability of success. Operational analysis shows that
to
minimise the probability of detection and alerting the enemy’s defences, the
aircraft needs to approachthe target at high subsonic speeds (550–600 knots) at
very low level at a height of 100 ft or so above the sea so as to stay below the
radar horizon of the target as long as possible. The avionic sub-system
specifications can then be
determined from the overall system requirements with an aircraft crew
comprising pilot and observer/navigator. Hence in the above example, the
avionic equipment fit would comprise:
• Radar – target acquisition in all weather conditions.
• Doppler – accurate ((4 knots) velocity sensorfor DR navigation. (Note: IN
systems capable of accurate initial alignment at sea on a moving carrier were
still under development in the early 1960s.)
• Attitude heading reference system (or master reference gyro system – UK
terminology) – attitude and heading information for pilot’s displays, navigation
computer, weapon aiming computer, autopilot.
• Air data computer – height, calibrated airspeed, true airspeed, Mach number
information for pilot’s displays, weapon aiming, reversionary DR navigation,
autopilot.
• Radio altimeter – very low level flight profile during attack phase and all
weather operation.
• Navigation computer – essential for mission.
• Autopilot – essential for reduction of pilot work load.
• Weapon aiming computer – essential for mission.
• HUD – all the advantages of the HUD plus weapon aiming for low level
attack; for example, ‘toss’ bombing.
• Stores management system – control and release of the weapons.
• Electronic warfare (EW) systems – radar warning receivers, radar jamming
equipment. Essential for survivability in hostile environment.
Identification system (identification friend or foe – ‘IFF’)– essential to avoid
attack by friendly forces.
• Radio navigation aids – location of parent ship on return from mission.
• Communications radio suite – essential for communicating to parent ship,
cooperating aircraft, etc.

13. ]
Interconnections of avionic sub-systems by multiplexed data
bus.
A significant degree of integration was required between the avionic sub-
systems. For example, the weapon aiming system required the integration of the
HUD, weapon aiming computer, AHRS, air data computer and the radar
system.
The basic avionic systems specified for a naval strike aircraft for service
introduction in the 1960s, for example the Royal Navy Buccaneer aircraft,
would also be required in a 2010–2020 naval strike aircraft. The systems would
need to be of much higher performance, however, and there would also be
additional systems in a 2010–2020 aircraft which did not exist in the early
1960s. For example, laser gyro INS, helmet mounted displays, GPS, FLIR,
‘smart weapons’, etc., and a much greater level of systems integration would be
required. The aircraft would also be a single crew aircraft. The point being
made is the essential continuity of the role of
avionic systems and their development, although their implementation changes
as new technologies become available.
It should be stressed that although the above example is a military one, the same
principles apply to civil avionic systems in terms of their role in enabling the
mission to be carried out safely and effectively with the minimum flight crew.
Most civil avionic sub-systems have also been directly developed from military
avionic systems (e.g. air data computer, INS, GPS, etc.) and, until fairly
recently, military aircraft generally required a larger number of avionic sub-
systems with a higher degree of integration.
A major step towards facilitating the integration of avionic sub-systems in civil
aircraft was taken in the early 1950s with the adoption of ARINC specifications

14. for avionic systems and equipment. ARINC is a non-profit-making organisation
inthe USA which is run by the civil airlines with industry and establishment
representation,
which defines systems and equipment specifications in terms of functional
requirements, performance and accuracy, input and output interfaces,
environmental requirements and physical dimensions and electrical interfaces.
For example, air data computers, attitude heading reference systems, INS,
communication
radio equipment, data bus systems, etc. Equipment made to an ARINC
specification by one manufacturer should thus be completely interchangeable
with equipment made by another manufacturer to the same ARINC
specification. The electronic implementation of the two systems can be totally
different provided they conform
to the ARINC specification in terms of form–fit–function. For example, the
LRUs (line replaceable units) must conform to the ARINC specifications
dimensionally with the specified rack fixing arrangements, connectors and the
pin allocations in the connectors. The systems must also meet the ARINC
performance and accuracy
specifications and the environmental requirements in terms of temperature
range, acceleration, shock and vibration and EMC. The use of avionic
equipment qualified to ARINC specifications thus ensures a competitive
situation enabling procurement to be made from manufacturers on a worldwide
basis.
Flight Management Systems
8.3.1 Introduction
The FMS has become one of the key avionics systems because of the major reduction in pilot work load which
is achieved by its use.In the case of military aircraft, they have enabled single crew operation of advanced strike
aircraft.
Flight management systems started to come into use in the mid 1980s and are now in very wide scale use,
ranging from relatively basic systems in commuter type aircraft to ‘all-singing, all-dancing’ systems in long
range wide body jet airliners.
They have enabled two crew operation of the largest civil airliners and are generally a dual FMS installation
because of their importance.
Quantifiable economic benefits – provision of automatic navigation and flight path guidance to optimise the
aircraft’s performance and hence minimise flight costs.
• Air traffic – growth of air traffic density and consequently more stringent ATC requirements, particularly the
importance of 4D navigation.
• Accurate navigation sources – availability of accurate navigation sources.For example, INS /IRS, GPS, VOR,
DME and ILS / MLS.
• Computing power – availability of very powerful, reliable, affordable computers.
• Data bus systems – ability to interconnect the various sub-systems.
The FMS carries out the following tasks:
1. Flight guidance and lateral and vertical control of the aircraft flight path.
2. Monitoring the aircraft flight envelope and computing the optimum speed for
each phase of the flight and ensuring safe margins are maintained with respect

15. to the minimum and maximum speeds overthe flight envelope.
3. Automatic control of the engine thrust to control the aircraft speed. In addition the FMS plays a major role in
the flight planning task, provides a computerised flight planning aid to the pilot and enables major revisions to
the flight plan to be made in flight, if necessary,to cope with changes in circumstances.
Two independent Flight Management Systems; FMS-1 on the Captain’s side and FMS-2 on the First Officer’s
side carry out the flight management function.
The cockpit interfaces to the flight crew provided by each FMS comprise a Navigation Display (ND), a Primary
Flight Display (PFD), a Multi-Function Display (MFD), a Keyboard and Cursor Control Unit (KCCU) and an
Electronic Flight Instrument System (EFIS) Control Panel (EFIS CP).
The Multi-Function Display (MFD) displays textual data; over 50 FMS pages provide information on the flight
plan, aircraft position and flight performance. The MFD is interactive; the flight crew can navigate through the
pages and can consult, enter or modify the data via the Keyboard and Cursor Control Unit (KCCU).
The Keyboard and Cursor Control Unit (KCCU) enables the flight crew to navigate through the FMS pages on
the MFD and enter and modify data on the MFD, as mentioned above, and can also perform some flight plan
revisions on the lateral Navigation Display (ND).
The EFIS Control Panel (EFIS CP) provides the means for the flight crew to control the graphical and textual
FMS data that appear on the ND and PFD.
There are three Flight Management Computers; FMC-A, FMC-B and FMC-C to carry out the functional
computations, which can be reconfigured to maintain the systemoperation in the event of failures.
There are three different FMS operating modes; Dual Mode, Independent Mode and Single Mode dependant on
the systemstatus.
FMS architecture