introduction to cnsatm

8/14/2019 Introduction to CNSATM

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ZULFIQAR ALI MIRAN

Info: [email protected]

An Introduction to CNS/ATM


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CCOONNTTEENNTTSS

Introduction

FANS (Future Air Navigation System) CNS/ATM Concept Approval FANS-II Benefits of FANS Transition to FANS Technology Involved Application of IT in CNS/ATM Benefits of CNS/ATM

Air Traffic Management

Goals Elements of ATM Air Space Management Flight Operations Air Traffic Services Air Traffic Flow Management

Communication

Categories Key Features Air-ground communications Data Link: Definition and main objectives Controller Pilot Data Link Communications (CPDLC) Benefits of CPDLC Radio Links VDL HFDL Mode-S Communication Link ATN (Aeronautical Telecommunication Network)

Navigation

GNSS (Global Navigation Satellite System) GPS (US), GLONASS (Russia), GLONASS / GPS Comparison Augmentation Systems LAAS/GBAS


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SBAS WAAS EGNOS (Europe) MSAS

ABAS

GNSS-II (The next generation GNSS) Galileo (Europe) Geo-coordinate standard WGS84? RNP (Required Navigation Performance)

Surveillance

Automatic Dependent Surveillance ADS-Broadcast (ADS-B) ADS-Contract (ADS-C) Traffic Information Service Broadcast Airborne Collision Avoidance Systems (ACAS).

Airborne Systems

Cockpit Display of Traffic Information (CDTI) Flight Management Computer System (FMCS) Multi-Mode Receiver (MMR) ACAS (Airborne Collision Avoidance System) TCAS (Traffic Alert and Collision Avoidance System


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FANS (Future Air Navigation System)

Recognizing the increasing limitation of the then (traditional) air navigation system and theneed for improvement into it, ICAO established, in 1983, the Special Committee on FANSwith the task of studying, identifying and assessing new concepts and new technology; andmaking recommendations for the coordinated evolutionary development of air navigation.

FANS comprised of 22 members and 10 observers from ICAO member states andinternational organizations. FANS committee first met in 1984 and planned to complete thetask in five years.

FANS Special Committee concluded that the shortcomings into the then air navigationsystem were due to three factors:

i) The propagation limitations of the line-of-sight systems and/or accuracy andreliability limitations imposed by the variability of propagation characteristics of othersystems;

ii) The difficulty, caused by variety of reasons, of implementing CNS systems and ofoperating them in a consistent manner in large parts of the world; and

iii) The limitations of voice communication and the lack of digital air-ground datainterchange systems to support modern automated systems in the air and on theground.

FANS committee submitted its report in May 1988 and suggested comprehensive

Communication, Navigation and Surveillance system for Air Traffic Management based onutilizing latest technologies.

CNS/ATM Concept Approval

CNS/ATM concept was endorsed by 10th Air Navigation Conference in 1991, in Montreal,Canada and by 29th Session of ICAO Assembly in 1992.

FANS concept of CNS/ATM system involves three major functions as envisaged from itsname; Communication, Navigation and Surveillance.

FANS concept of CNS/ATM is a mix of the best use of satellite technology and the line-of-

sight systems to achieve the desired goal of organized air traffic management.

According to FANS plan Pilot-ControllerCommunication will be mainly through exchangeof data. Voice link (as being used in conventional ATC and Communication Operations) willalso be used. Medium and techniques may, however, be different for which standards wereto be worked out considering the performance of the latest technologies. Data links are toplay key role in future ATM systems for their peculiar advantages over the voice link. Datalinks will not replace at all the present voice links but provide additional means of air-ground


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and ground-to-ground communication to support the modern automated airborne andground operations.

ForNavigation, Global Navigation Satellite System (GNSS) will replace most of the presentground based Air Navigation systems such as NDB and VOR, though multi-DMEs maycontinue to function independently or to support GNSS functions.

Surveillance of areas over the oceans and long range routes for inter-continental traffic willbe made with the help of GNSS. Whereas SSR Mode-S and GNSS could both be usedindependently or simultaneously for en-route surveillance as a primary and alternate sourceof surveillance information.

FANS-II

Following the CNS/ATM concept FANS-II Special Committee was established to developinternational standards for air navigation and air traffic management.

The tasks of FANS-II were

i) To identify and make recommendations for acceptable institutional arrangements,including funding, ownership and management issues for the global future airnavigation system;

ii) To develop a global coordinated plan, with appropriate guidelines for transitionincluding the necessary recommendations to ensure the progressive and orderlyimplementation of the ICAO global future air navigation system in a timely and costbeneficial manner;

iii) To monitor the nature and direction of research and development programmes, trialsand demonstrations in CNS and ATM so as to ensure their coordinated integrationand harmonization;

iv) To develop policy guidelines for the evolution of ATM to maximize the efficient use ofairport and airspace capacity; and

v) To prepare, as required, the necessary documentation to support the expected ICAOAir Navigation Conference in 1991.

Accordingly various groups of ICAO experts were formed to produce standards andrecommended practices.

Benefits of CNS/ATM

CNS/ATM will:

Improve communications performance; Improve navigation performance; Provide visual situational awareness for the controller; Provide real-time conformance monitoring; Reduce human input errors; Reduced Separation Between Aircraft; Provide more efficient route changes;


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Have no altitude loss when crossing tracks; and Have more direct routings.

There are significant benefits to be gained from implementation of CNS/ATM. Improvementin CNS facilities will result in improved data exchange between airline operators, aircraft andair traffic service providers (ATSPs). Other benefits include global navigation and non-

precision approach capabilities through GNSS, extended surveillance with the help ofAutomatic Dependence Surveillance (ADS) method and advanced ground basedprocessing.

The new system offers improved four-dimensional navigation accuracy. Air traffic serviceproviders will benefit from improved conflict detection and resolution, automated generationand transmission of conflict-free clearances and efficient adaptation to changing trafficpatterns. ATSPs will be enabled, by the new system, to accommodate an aircrafts preferredflight profile.

An additional benefit is a level of standardization that will facilitate connectivity between airtraffic control systems. This connectivity will in turn permit access to air traffic services-

related information (e.g weather) not previously available.

Transition to CNS/ATM

In transition to CNS/ATM major elements of change are

from ground-based to satellite based systems;

from limited coverage to global coverage; and

from analog to digital (data) communication.

Transition to the new system will be one of the largest undertaking ever carried out by theaviation community. The transition will primarily affect how Civil Aviation Administrations will

provide air traffic services. There will be a great change in the pilot-controller interaction.

Though automation of ATC systems will improve performance and reduce workload,increase efficiency, remove non-essential tasks and enhance job satisfaction for ATCOs, itmust be carefully tackled. Automation is required to desist from display of too muchinformation for the controller/pilot or provision of too many options to them that could wastetheir time in assessing all computer generated possibilities. Automation in ATC require greatconfidence of controller who must trust the data that is presented. With greater level ofautomation, the more the controller relies on the system. The data links and data processingsystems, therefore, must be fail-safe and accurate. Massive failure will shake the confidenceof controller on the automated systems.

Aviation experts regard more congestion at and around airports and more delays asalternative to FANS. This is supported by the fact that predicted air travel will be more thandouble in 2005 as of the travel of year 1991. It is estimated that by 2005 approximately33,000 aircraft will be in commercial use and approximately 10 per cent of this total will beemployed in long range operations.

The Boeing Company estimates that by the year 2015, the number of departures worldwidewill jump from 15 million/day to over 30 million per day. The number of large transportcategory airplanes in service will leap from 12,600 to 26,000. World aviation community,


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therefore, had no other alternative but to prepare for the new order. These were thecircumstances for introduction of FANS plans.

Technology Involved

Key technologies involved in CNS/ATM are:

i) Satellite Communication, Navigation and Surveillance; andii) Data Communication

Air-Ground Communication will either be through HF or VHF radio voice link. Data link willalso be established using any of the technologies such as:

communication satellite (SATCOM);

VHF Data Links (VDL);

HF Data Link; and

Mode-S Radar.

Ground-to-Ground communication may use VHF, HF, FM and other radio and telephonecircuits beside Data Communication technologies such as X.25 packet switching circuits,TDM (Time Division Multiplexing). End-to-End Transmission medium again may be differentprovided it fulfils the communication requirements. This is the area where one encountersthe fastest technological developments as compared to other CNS/ATM components.Optical Fibers and Satellite Communication mediums are replacing the microwave andconventional land lines. Data communication link between two ground ATS points maytherefore be using these technologies as a back bone to telecommunication serviceprovided by a PTSN (Public Telecom Service Network).

There is variety of communication services and technologies which may be used in variousAir Traffic Service (ATS) components. Tower control, for example, is to use multiple radio as

well as ground communication services for coordination with aircrafts, adjacent airports, ATScenters, Comm Ops, Airport Operations, Met Services, and Airline Operators etc. Same isthe case with other ATS and Communication Operation positions. All communicationfacilities (Voice as well as Data) are essentially to be integrated into a single system. Use ofIntegrated Voice and Data systems will be common in ATM components. The various typesof communication facilities in use of all elements of ATM form a network named asAeronautical Telecommunication Network abbreviated as ATN.

The ATN is the interconnection of different sub-networks, or an inter-network. Thesedifferent networks can be X.25 wide area ground networks, Ethernet local area networks,but also air-to-ground satellite link (AMSS Data-3), VHF digital link (VDL) or Mode-S.

As for Satellite Navigation Technologies are concerned United States and Russia havealready developed GPS (Global Positioning System) and GLONASS (Global NavigationSatellite System) respectively to provide navigational services through out the globe.European States are developing their own navigation satellite to cover the areas of Europe,Africa and Middle East.

Independence Surveillance (through Primary Surveillance Radar) may be continued inTerminal Areas. En-route surveillance will use either Cooperative Independence


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Surveillance systems (SSR Mode-S) or Automatic Dependence Surveillance (ADS)technologies.

Beside above various ATC systems have been developed which collect the Surveillanceinformation (data) via either of the above stated means and Fight data via ATN or variousresources, process the information and represent it into variety of forms (on variety of

displays and monitors) by using latest technologies as per user convenience and demand.

An ATC system may comprise of a single system or network of multiple ATS centers inter-connected to share and exchange surveillance and Flight data and other useful information.

In cockpit number of equipments and systems are provided to confirm CNS/ATMrequirements. Such equipments include CDTI (Cockpit Display of Traffic Information), FMCS(Flight Management Computer System), ADS-B (Automatic Dependence Surveillance-Broadcast) etc.

Application of IT in CNS/ATM:

Most of the above stated CNS systems/equipment employ computer and microprocessors(or Central Processing Systems) to perform their core and/or supportive functions. They usedifferent software packages according to nature of application and operating systems asconfirmed by the machines. They use different IT based communication techniques forinformation exchange.

For example ATC systems use computer equipments with specialized application softwareand operating systems (such as LINUX) to process surveillance and flight informationcollected via Radar, Satellite, VDL, ground-to-ground data networks. The processedinformation is then dispatched to controller working positions using servers through highspeed LAN (Local Area Network). Computers are thus involved right from the front-endprocessing (where information from external sources is received) upto the end-user (that is

controller working position) at various stages.

Broadcasting of radar information to other ATC systems uses Network Information Servers.

Surveillance systems such as SSR Mode-S also perform information processing throughhigh speed computing machines which is then routed to ATC systems via NetworkInformation Servers.

Navigation systems are also no exception as for the use of computers is concerned.

High speed processing and representation of information in Airborne Systems such asFDMS, CDTI, ADS-B, Transponders is only possible due to the fast data processing

machines.

Integrated Voice/Data systems essentially use microprocessor as the central processing unitto multiplex and distribute voice and data to various end-users.

Use of computers in Data Communication Networks as the servers is very common due todemand of high speed beside other factors.


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Information Technology deals matters concerned with computer science and technology,design, development, installation and implementation of information systems andapplications.

IT will, therefore, be the back bone of the future CNS/ATM system. IT is involved in all thethree components of CNS/ATM; that is Communication, Navigation and Surveillance. It is IT

that makes the future ATC systems and Voice/Data communication networks work efficientlyat enormously high speed. Other advantages of IT based CNS/ATM systems includeReliability, Flexibility, Multi facility Integration, Expanded Operation, User convenience,Security (of information).


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The term Air Traffic Management (ATM) covers all the functions of airspace management(including both strategic and tactical airspace management), air traffic services and air trafficflow management. The concepts, which are being developed for the CNS/ATM system, will

see the control resources more concentrated on the management of active air traffic.

Goals

Some of the important goals of the future ATM system are to:

Offer users maximum flexibility and efficiency in airspace utilization, taking intoaccount their operational and economic needs;

Provide the flexibility to cater for different levels of aircraft equipage, and allowsharing of airspace by different categories of users;

Allow for the implementation of ATM at varying levels of sophistication, to provide

services tailored to the needs of particular regions; Provide for transitions across airspace boundaries to be transparent to airspace

users ; and

Ensure that present levels of safety are maintained or improved upon, both in thefinal mature ATM system, and during the transition period.

The achievement of these goals will require co-operation between ATS, pilots and airlineoperational control, and the sharing of real-time information between them. It is importantthat, in the development of automated support for ATM functions, the human is kept in thedecision making process.

Elements of ATM

The envisaged ATM system consists of the following sub-elements:

Air Space Management (ASM) Flight Operations (ATM related aspects) Air Traffic Services (ATS) Air Traffic Flow Management (ATFM)

Air Space Management

ASM is recognized as dynamic sharing of airspace by civil and military users. The global

ATM system will not be limited only to tactical aspects of airspace use. Its main scope will betowards a strategic planning function of airspace infrastructure and flexibility of airspace use.

Strategic ASM consists two elements:

i) The determination , for any given airspace, of the ATM requirements forcommunication, navigation and surveillance; and

ii) Infrastructure planning


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Flight Operations

The ATM-related aspects of flight operations are an integral part of ATM in CNS/ATMsystems. Enhanced functional integration of ATM-related aspects of flight operations andother elements of ATM will be a key factor in the implementation of CNS/ATM systems. Forexample, automated systems on ground will assist the controller with conflict detection and

resolution based on information derived from aircraft flight management system and, atsome points, will negotiate ATC clearances with these airborne systems. Additionally, otherinformation that is now transmitted by voice will increasingly be carried out using automatictransmission of data.

The airborne part of ATM comprises three areas:

i) ATM-related functional capabilities of aircraft systems;

ii) Pilot procedures; and

iii) Integration of ATM-related aspects of flight operations into the ATM process.

The accuracy of the flight plan data used for the ground ATC system will be improved byincorporating data calculated in the flight management computer system (FMCS) for thethree or four-dimensional flight profiles. The calculation and maintenance of the flightprofiles will be shared between FMCSs and ground ATC systems through the use ofinteractive automated aids. FMCS should have the following capabilities:

To calculate the flight profile for intended flight, based on the flight plan delivered bythe airline;

To adhere to the flight profile as accepted from the ground ATC system as far as it iswithin the aircraft flight performance capability; and

To automatically notify the ground ATC system as soon as deviations from theagreed flight profile exceed the agreed limits.

Air Traffic Services

ATS is the prime element of ATM. ATS itself is composed of several sub-elements. Theseare

i) the alerting services;

ii) flight information service (FIS); and

iii) Air Traffic Control.

The main objectives of ATC services are to prevent collisions between aircrafts and betweenaircraft and obstructions on the maneuvering area and to expedite and maintain an orderlyflow of air traffic.

The objective of FIS is to provide advice and information useful for the safe and efficientconduct of flights.


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The objective of the alerting service is to notify appropriate organizations regarding aircraftin need of search and rescue aid and assist such organizations as required.

Air Traffic Flow Management

The objective of ATFM is to ensure an optimum flow of air traffic. An ATFM therefore shouldreduce delays to aircraft both in flight and on the ground and prevent system overload.ATFM assists ATC in meeting its objectives and achieving the most efficient utilization ofavailable airspace and airport capacity. ATFM is to ensure that safety is not compromised bythe development of unacceptable levels of traffic congestion and traffic is managedefficiently without unnecessary flow of restrictions being applied.

ATM consists of a ground part and an air part, where both are needed to ensure a safe andefficient movement of aircraft during all phases of operation.


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The communication element of CNS/ATM system provides for the exchange of aeronauticaldata and messages between aeronautical users and/or automated systems. Communication

systems are used in support of navigation and surveillance functions.

Categories

There are basically two categories of aeronautical communications.

i) Safety-related communications, requiring high integrity and rapid response such as

Communications carried out among ATS units, between ATS and an aircraft forATC, flight information and alerting etc; and

Aeronautical Operational Control (AOC) communication carried out by aircraftoperators for matters related to safety, regularity and efficiency of flights.

i) Non-safety related communications such as

Aeronautical administrative communications carried out by aeronauticalpersonnel and/or organizations on administrative and private matters; and

Aeronautical passenger communications.

Key Features

Some of the key features of the new system are:

Most routine communications are to be done by data interchange;

Voice communication is mainly used in non-routine and emergency situations; and

There is emphasis on global connectivity and operation.

Air-ground communications

It is envisaged that most of the routine communications in the en-route phase of flight will bevia data interchange. The user selects a particular message from a pre-constructed set ofmessages using a screen menu, adds some specific parameters (or free text) and then

sends it. Some data transfers take place between automated airborne and ground systemswithout the need for manual intervention. Such communication arrangement betweencontroller and pilot is named as Controller-Pilot Digital Link Communication abbreviated asCPDLC.

Data Link: Definition and main objectives

Data link is a generic term for a communications technique, which enables the exchange ofdigitized information between end-users (sources and/or consumers of information). Data


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link has many different forms ( for example; Air-Ground, Air-Air, Ground-Ground ), protocols,applications ( addressable, broadcast ), and utilizes a number of communications media (such asVHF, HF, Satellite, Mode S ).

i) The main objectives of data link are to:

ii) Provide an alternative means of communication;

iii) Automate as much as possible communications tasks;

iv) Reduce both the controller and pilot workload;

v) Increase ATM efficiency, capacity, and safety;

vi) Provide additional information exchanges by utilizing airborne and ground automatedsystems capabilities; and

vii) Provide surveillance in areas that are unsuitable for radar coverage

Controller Pilot Data Link Communications (CPDLC)

Operationally, the demand for communications often exceeds the usable frequency capacityin areas of high air traffic density. The current infrastructure allows only one controller persector to interact explicitly with only one aircraft at a time, which limits the delivery ofclearances and advisories.

Controller-Pilot Data Link Communications (CPDLC), which is part of the Aeronautical DataLink system, will provide an additional digital communications channel to supplement thevoice frequencies. Multiple controllers will have the capability to send Data Link messagesfrom any given sector to any or all Data Link equipped aircraft in that sector, andtransmissions will take place simultaneously over multiple media. This represents both avast improvement over the current system capabilities and a different operational

environment. Procedures on the flight deck and in the control room will have to be adaptedto this new environment.

CPDLC allows pilots and controllers to exchange electronic messages, via a data link. Adefined set of (pre-formatted) message elements (ref. PANS-ATM, Appendix5) is used, thatcorrespond to existing phraseology employed by current ATC procedures. CPDLCmessages may consist of between one and five elements. A free text capability is alsoprovided to exchange information not conforming to defined formats. In such cases a list ofpre- formatted free text messages shall be established by the appropriate ATS authority.

Benefits of CPDLC

Potential benefits of air-ground data communication are

i) Efficient linkage between ground and airborne systems

ii) Improved handling and transfer of data

iii) Reduced channel congestion

iv) Reduced com errors


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v) Inter-operable com media

vi) Reduced workload

vii) Reduction in radio telephony workload for both pilot and controller

viii) Reduction in re-transmission caused by misunderstood messages.

ix) reduced controller stress/memory burden

x) reduced controller communication time

Radio Links

Radio links used for communication with aircraft in flight are of extreme importance to thesafety, regularity and economy of flights. As such, the necessary technical and institutionalarrangements must be in place to

i) Ensure the availability of a sufficient radio frequency spectrum for aeronauticalservices, noting present and foreseen levels of traffic;

ii) Prevent RF interference into radio frequencies, bands, services and users ofaeronautical radio systems; and

iii) Allow the provision of communication services by commercial service providers.

Transmission of air-ground messages is carried out over one of the following radio links:

i) Aeronautical Mobile Satellite Service (AMSS) a new standard introduced inCNS/ATM

ii) VHF (analog) traditional communication link

iii) HF (analog) - traditional communication link

iv) VHF digital link (VDL) a new standard introduced in CNS/ATM

v) SSR Mode-S data link a new standard introduced in CNS/ATM

vi) HF data link a new standard introduced in CNS/ATM

AMSS, VDL, SSR Mode S and HF data links use different data transmission techniques butas same individual networks, they all use the same network access protocol in accordancewith ISO OSI reference model. This provides for their interconnection to other ground-basednetworks so that the aircraft end of any of these data links can be connected to any ground

based system by adopting common interface services and protocols also based on ISO OSIreference model.

VHF digital link (VDL)

The VHF digital link (VDL) is a constituent mobile sub-network of the aeronauticaltelecommunication network (ATN), operating in the aeronautical mobile VHF frequencyband. In addition, the VDL may provide non-ATN functions, such as, for instance, digitized


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voice. The very high frequency (VHF) digital link (VDL) Standards and RecommendedPractices (SARPs) apply to aeronautical VHF digital communications systems operatingwithin the aeronautical telecommunication network (ATN).

The characteristics and specifications of VDL are provided in ICAO annexure 10 Vol-III(Part-I).

So far four modes of VDL have been developed, comparison of which is given below.

Comparison of VHF Data Link options

Candidate Systems

RequiredCapability

VDL Mode 2(CSMA)

VDL Mode 3(TDMA)

VDL Mode 4(STDMA)

Global Standard All technologies are proposed as global standards by ICAO.Operation fromblock to block

No Air-to-Aircapability, groundinfrastructurerequired(see Note 1).

No, ground masterstations required soit does not coverremote areas. AllTDMA systems needa common time base(see Note 1).

Yes, can be usedanywhere(see Note 1).

High availability No, unpredictabledelay (see Note 5)

Yes Yes

High integrity Integrity achieved through proper Implementation.

Low cost Yes Yes Yes.

Robust withgracefuldegradation

No, rapid andcatastrophic failurecharacteristic undervery high trafficloads (see Note 5)

Potentially not robustdue to the selectedmodulation scheme(D8PSK)(see Note 3)

Yes (see Note 2)

Maximise spectrumefficiency

No, contentionaccess; wastesavailable spectrum(CCI values ~26-27dB)(see Notes 5 and 4)

No, voice and dataare integratedtogether, but D8PSKmodulation wastesavailable spectrum(CCI values ~26-27dB) (See note 5).

Yes, data from manyusers is efficientlymultiplexed. GFSKhas good CCI values(~10dB)

Capacity for 2020traffic and beyond

Not likely; dependsavailability ofspectrum(see Note 6)

Not likely; dependson availability ofspectrum(see Note 6)

Four 25 kHz channelsplus one or two forAOC sufficient forfully redundantsurveillance of 2020traffic volumes;capacity is approx. 15times greater than


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VDL's Mode 2 & 3(see Note 6)

Flexibility tosupport newprocedures

VDL Mode 2 notsuitable for ADS-Band ATMapplications

(see Note 5)

Flexibility may belimited(see Note 7)

Yes

Support for easytransition

Not likely, assumesavailability ofspectrum

Potential transitionproblems- analogueto digital(see Note 7)

Yes.

It is assumed that only VDL Mode 4 appears to meet all the broad requirements defined (sofar) in various operational forums. VDL Mode 4 also has several advantages over the otherdata links as listed below:

i) VDL Mode 4 can provide a CDTI and ASAS including air-air data link in remoteareas. VDL Mode 3 cannot because it requires master ground stations to operate.

ii) VDL Mode 4 supports all types of data link applications, including time-critical ones.VDL Mode 2 does not support air-air communications and cannot support time-critical applications except in very low-density areas.

iii) VDL Modes 2 and 3 have much lower capacity and require more bandwidth thanVDL Mode 4.

iv) VDL Mode 2 has poor degradation characteristics, suffering very rapid failure onoverload. VDL Mode 4 exhibits graceful degradation through functions such asslaving on time from other stations, re-use of the timeslots of distant users, etc.

v) VDL Mode 4 has an incremental growth capacity through the local addition of 25 kHzchannels for gradual increase of capacity, new services and functions. This is madeavailable through a Directory of Services, which also enables autotune functions. AllVDL Mode 4 units can exploit this additional capacity.

vi) VDL Mode 4 offers very high spectrum efficiency and an ADS-B capability with longrange, redundancy and robustness.

vii) Only VDL mode 4 offers the possibility of seamless transition.

Standards for VDL Mode4 were passed on 12th of March 2001 by ICAO, the InternationalCivil Aviation Organisation. The Council of ICAO unanimously decided to include theproposed SARPs, Standard and Recommended Practicies in Annex 10. It will be publishedin November 2001 and at the same time supporting documentation will be officiallyavailable.

Background


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HF DATA LINK SYSTEM

HFDL is capable of providing a level of performance suitable for the ATN environment. TheHFDL service allows aircraft that are equipped with an HFDL control function (HCF) and HFdata radios, or equipped with HCFs, an intermediate HF data unit, and compatible HF voiceradios, to send and receive packet data via a network of HFDL ground stations. The ability

to exchange packet data via VHF data link and SATCOM networks will, of course, continueto exist.

It is suggested that a sub-network of 15 or 16 HFDL ground stations can extend air-groundcommunications coverage beyond the coverage of VHF data link sub-networks on a world-wide basis and provide an alternate or/backup to SATCOM on routes over the Atlantic,North and South Poles, South America, Africa, the Pacific, and Asia. The actual number ofground stations needed is dependent upon several factors including system availability andcapacity desired by the users and ground station operators.

HFDL can provide very significant improvements over current HF Voice Communications interms of system availability, system capacity, ease of use, and information integrity.

Role of HFDL in CNS/ATM

As the aeronautical industry progresses with the implementation of data links both on theground and airborne sides, a need emerges for HFDL. A networked-based HFDL systemsatisfies future air traffic service (ATS) and aeronautical operational control (AOC)communication requirements in oceanic areas in a cost efficient and reliable manner.Furthermore, HFDL can provide data link service over other land areas where no currentdata link service (i.e., VHF) is currently available. In this case, HFDL providesa data link service where numerous VHF data link stations may be impractical due to cost orother factors.

Additionally, HFDL may result in a reduction in the growth of requirements for HF voiceservices, as many current voice service requirements are accommodated via HFDL.

HFDL fulfills several key roles such as it

i) provides aircraft that are not SATCOM-equipped with a long-range, cost-effectivedata link;

ii) serves as a data link for polar regions where SATCOM performance degrades andiii) acts in combination with SATCOM as very high performance system capable of

meeting future ATN availability requirements.

HFDL is seen as a tool enabling communications, navigation, and surveillance/air traffic

management (CNS/ATM) to be extended to new regions and to aircraft previously not ableto afford a long-range data link.

The HFDL system shall consist of one or more ground and aircraft station sub-systems,which implement the HFDL protocol. The HFDL system shall also include a groundmanagement sub- system.

The HFDL aircraft station sub-system and the HFDL ground station sub-system shall includethe following functions:


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i) HF transmission and reception;ii) data modulation and demodulation; andiii) HFDL protocol implementation and frequency selection.

High Frequency (HF) was developed as a low cost alternative to satellite for wide areacoverage (5000 miles/site), and first went operational in 1998 to support AOC. It is currentlyproviding complete coverage over the northern polar region, but with a message transit timeof about 80 seconds is slower than satellite. HF is included in the ICAO SARPs annexure 10vol-III (Part-I).

Mode-S data Link

Mode S is a type of secondary radar that can be used to exchange longer and more varieddata. Mode S transmissions between the station and the transponder use highlysophisticated 56 or 112 bit formats called frames that fall into 3 main categories: 56-bit

surveillance formats, 112 bit communication formats with a 56-bit data field, which are in fact" extended " surveillance formats (Uplink COMM-A's and Downlink COMM-B's) and 112 bitscommunication formats with an 80-bit data (uplink COMM-D's downlink COMM-D's).

There are two types of Mode S data link, one called "specific" and the other one"interoperable". To simplify, we can say that in the first case, the station and the transpondermore or less know what type of information is contained in the frame data field, whereas inthe second, they are completely unaware of it.

The interoperable data link was designed to allow ground-to-aircraft exchanges usingMode S as a packet switching data transmission network. The messages (packets)transmitted are then cut into pieces and distributed around the data fields in the frames,

which are sent from the station to the transponder (or vice-versa) where the data fields areextracted and reconstituted a little further on at the exit from the Mode S " world ", for routingto the addressee.

On the opposite, the specific data link is more closely linked to the Mode S system itself. Inparticular there is a highly optimized "aircraft data collection" protocol using the COMM-Bframes.

It is based on the following principle : in the transponder, there is a series of 256 buffers of56 bits each, in which information concerning the flight and aircraft status are stored andpermanently refreshed. Each buffer, identified by an order number, contains data of aprecise nature formatted according to a predetermined code.

The principle is thus to consider the transponder as a multiple mailbox in which the aircraftsystem places its flight data (without knowing whether or not anyone will pick them up)whereas on the other side, the ground station reads the data completely asynchronously.This process is thus optimized from a "time" point of view as it avoids having to initiate acommunication connection with the aircraft system possessing this information

Networking Interface:


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Mode S "basic" selective surveillance only requires the use of Mode S ground sensors andairborne Mode S transponders, but interoperable services need complementary equipmenton both sides, called respectively Ground and Airborne Data Link Processors, whichconstitute the interfaces of the Mode S sub-network.

The interoperable services will enable the integration of Mode S sub-networks in the

Aeronautical Telecommunication Network (A.T.N.).

ATN (Aeronautical Telecommunication Network)

The communication service, which allows ground, air-ground and avionics data sub-networks to inter-operate for the specified aeronautical applications, is AeronauticalTelecommunication Network (ATN). All the above mentioned data links are ATN-compatibleand therefore constitute ATN sub-networks.

In ATN environment, sub-networks are connected to other sub-networks through ATNrouters, which select the best route for transmission of each data message. As such, the

choice of the air-ground data link is often transparent to the end-user.


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NNAAVVIIGGAATTIIOONN

Navigation systems are the basis for an aircraft's ability to get from one place to another andknow where it is and what course to follow. It's more than just maps. The closest thing

today's automobiles come to an aviation navigation system is the "navigation center" someautomobiles come with. These computers establish an automobile's position via satellite andplace the position on a moving map. Intelligence programmed into the system allows thedriver to navigate to destination by executing instructions provided by the system.

Historically, aircraft navigated by means of a set of ground-based stations called beacons,each broadcasting on its own frequencies. Aircraft systems could tune into the frequenciesof two of these beacons and fly between them (from one beacon to the next). Knowingwhere the aircraft is between two of these beacons, allows the aircraft to know where it is ina global sense. Since the 1980s, aircraft systems have evolved towards the use of satellitenavigation. Navigation satellites or Global Navigation Satellite System as named by ICAOSARPs are alternative to NDB, VOR and ILS provided they meet the required standard. The

satellites systems developed so far in this regard are said to have been successful asreplacement to traditional en-route navigation aids like NDB and VOR. Accuracy, reliabilityand other parameters of the new satellites systems are being improved by using varioustechniques, some of which are stated below, to meet the required specifications for use aslanding aids in place of ILS.

GNSS (Global Navigation Satellite System)

The major technological change in navigation will be the progressive adoption of GlobalNavigation Satellite Systems (GNSS). These systems will provide for worldwide positionalcoverage, and will eventually be used for non-precision and precision approaches, in

addition to en-route navigation. Currently, GNSS requires augmentation systems to monitorsignal reliability and enhance accuracy to make them suitable for civilian use. Theseaugmentation systems are currently being developed.

The GNSS will consist of a number of elements. These will include

i) the navigation satellites; andii) the ground-based monitoring stations.

The above elements, together with communication satellites, will form an AugmentationSystem. Ground-based differential stations with a datalink will be used at specific locationsto augment the system locally. The aircraft will select which elements of the system are to

be used depending on the operations to be undertaken.

Navigation satellite is being used today for en-route navigation, but it also assists in landingan aircraft only in good weather conditions, so called non-precision approaches andlandings. For landings in poor weather conditions, so called precision approach navigationand landing, the current Instrument Landing System (ILS) or, in certain locations, MicrowaveLanding System (MLS) will be in use for some time. Eventually, however, navigation satellitesystems will be used even in adverse weather conditions.


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It is expressed that GNSS will provide a high integrity, highly accurate navigation service,suitable for navigation, at least for en-route applications.

Benefits of GNSS

Benefits of GNSS are

i) Improved four dimentional navigational accuracy

ii) High integrity, high accuracy, world wide navigation service

iii) Cost savings as compared to ground based navigation aids

iv) Improved air transport services using non-precision approaches and precisionlanding operations

Global Navigation Satellites Systems:

GPS

The Global Positioning System [GPS] was developed by the United States Department ofDefense for position fix coordination of the inertial navigation systems [INS] on board militaryaircraft and cruise missiles, and has since become freely available - as a valuablesupplementary navigation aid - to civilian aircraft of all types and all nations - with thecompliments of U.S. Department of Defense.

GPS or the NAVigation Satellite Timing And Ranging [NAVSTAR] system consists of aminimum 24 satellites [ of which usually three are operating spares] orbiting Earth at analtitude of 20,000 km with each unit taking about 12 hours to complete one orbit. TheNAVSTAR orbits are arranged in six planes with 3 to 4 satellites in each plane. This

configuration ensures that a minimum of four satellites would be in view from most locationson Earth at any time.

NAVSTARs continuously transmit information on very low power at two UHF L bandfrequencies, a coarse acquisition ranging code [the C/A code] on 1575.42 MHz and anencrypted precise positioning service code [the P code] on 1227.6 MHz. The C/A code isfreely available to all while the additional P code is only available to authorised users. TheC/A code is designed to provide a position fixing accuracy within 300 metres 99% of thetime and within 100 metres 95% of the time but probably better than 30 metre accuracy isachievable most of the time.

At present GPS is far more accurate than NDB/ADF or VOR and certainly more accurate

than necessary for VFR flight, as being said.

The Federal Aviation Administration (FAA) is working on two GPS-based systems that couldenable this sort of antihijacking capability: the Wide Area Augmentation System (WAAS) thatwill enable aircraft to reach the so-called Category 1 decision point in an approach to anairport, and the Local Area Augmentation System (LAAS) that would enable aircraft to reachthe ground in zero visibility, known as a Category 3B landing.


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Although both systems still await final certification, testing, and installation at U.S. airports,commercial airliners and military aircraft have already demonstrated fully automaticinstrument approach and landing under Category 3B conditions.

GLONASS

Glonass is a Soviet space-based navigation system comparable to the American GPSsystem. The operational system contains 21 satellites in 3 orbital planes, with 3 on-orbitspares. Glonass provides 100 meters accuracy with its C/A (deliberately degraded) signalsand 10-20 meter accuracy with its P (military) signals.

GLONASS / GPS Comparison

GLONASS GPS

Nominal # of s/v 24 24

Launch vehicle Proton K/DM-2 Delta 2-7925

# of spacecrafts / launch 3 (occasionally 2) 1

Launch site Baikonur Cosmodrome, KazakstanCape Canaveral,USA

# of orbital planes 3 6

Orbital inclination 64.8 55

Orbit altitude 19,130 km 20,180 km

Period of revolution 11h15m40s 11h58m00s

Ephemeris representationposition, velocity and acceleration inearth-centered, earth-fixed coords.

Kepler parameters

Datum PZ-90 WGS-84

Time reference UTC (Russia) UTC(NO)

Length 152 bits 120 bits

Duration 12m30s 2m30s

day of validity week of validity

channel number S/C identifier

eccentricity eccentricity

inclination inclination

equator time almanac time

validity of almanac health

equatorial longitude right ascension

- RA rate of change

period of revolutionsq. root ofsemimajor axis

Almanac

Content

argument of perigeeargument ofperigee


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- mean anomaly

luni-solar term -

time offset time offset

- frequency offset

Signalling FDMA CDMAL1 1602.0 - 1614.94 MHz (*) 1575.42 MHzCarrier

frequency L2 7/9 L1 60/77 L1

Type of PRN code ML GOLD

C/A 511 1023# of codeelements P 5110000 2.351014

C/A 0.511 Mbit/s 1.023 Mbit/sCode rate

P 5.11 Mbit/s 10.23 Mbit/s

Crosscorrelation interference -48 dB -21.6 dB

Rate 50 bit/s 50 bit/s

Modulation BPSK Manchester BPSK NRZ

Total length 2m30s 12m30sNavigationmessage

Subframelength

30s 6s

(*) Is planned be shifted, first to 1602.0 - 1609.31 Mhz (finished by 2005) and then to1598.06 - 1605.38 MHz beyond 2005.

Augmentation Systems

There are three types of augmentation systems as mentioned below.

i) Ground based augmentation systemsii) Satellite based augmentation systemsiii) Aircraft based augmentation systems

Ground based augmentation systems:

LAAS/GBAS

Local Area Augmentation System (LAAS) is the ICAO definition ground based augmentationfor Satellite Navigation; whereas Ground Based Augmentation System or GBAS is the

European application of LAAS. It was estimated that LAAS could be operational byDecember 2003 including CAT 1 approaches. This schedule has now been delayed foranother year.

Satellite Based Augmentation Systems or SBAS:

Satellite Based Augmentation System or SBAS is a generic term for GPS and GLONASSwhich use geostationary satellites to broadcast information to users over a large


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geographical service. A number of such systems are being developed to fulfill requirementof various countries and regions. Some of such systems are listed below.

i) WAASii) EGNOSiii) MSAS

WAAS

In order to improve the accuracy and integrity of the Global Positioning System (GPS), toenable it to be used for precision approach and landing operations, the United States isdeveloping a system called the Wide Area Augmentation System (WAAS).

WAAS consists of two basic elements. The first is a network of differential ground-stationsthat receive the GPS signals and calculate differential correction signals. 35 ground stationsare required to cover the USA. These differential corrections are then transmitted to thesecond element of the system, which are WAAS transponders on a number of Inmarsatgeostationary communications satellites. The differential signals are then transmitted from

the communication satellites to the aircraft. In addition, the communication satellites alsotransmit integrity information about the performance of the GPS satellites and a signalsimilar to a GPS satellite.

This GPS type signal is used for navigation and gives the appearance of an additional GPSsatellite being present.

This situation highlights the importance of the GNSS receiver in the aircraft being able todetect faulty satellites and discard them from the position calculation. The FAA claim thatGPS receivers have always detected the failure of a GPS satellite and that an undetectedfailure has never occurred. The use of WAAS considerably enhances this situation, as itprovides a means to independently detect faulty satellite signals and pass this integrity

information back to aircraft receivers.

The FAA commissioned the Wide Area Augmentation System (WAAS) at 12:01AM on July10, 2003.

EGNOS

EGNOS is Europes GNSS-1 which involves signal relay transponders carried ongeostationary satellites, and a network of ground stations. Together they are to provide aregional augmentation service for GPS and GLONASS signals over Europe and cover allthe countries belonging to the European region. This augmentation is called an overlay,and the European programme is known as the European Geostationary Navigation OverlayService, or EGNOS.

MSAS

Japan is implementing the Multi Satellite-based Augmentation System (MSAS JapaneseDefinition) that will provide correction to GPS only.

Aircraft-Based Augmentation System or ABAS:


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Aircraft-based augmentation system (ABAS-ICAO definition) augments and/or integrates theinformation obtained from the GNSS elements with other information available on board theaircraft. The aim is to enhance the overall performance of the GPS equipment on board interms of integrity, continuity, availability and accuracy.

GNSS-II (The next generation GNSS)

Civilian navigation overlay systems are the first step. Not only Europe proposes to advancethe civilian use of satellite navigation, moving from the current GPS and GLONASS systemsto a next-generation system that meets the needs of the most demanding civil users, asclaimed by the developers. Development work on a so-called non-military GNSS has startedin Europe, with operational hardware already in orbit.

Research has already started in Europe on developing technologies for a second generationof satellite navigation systems, which includes satellites, user and ground equipment, theperformance of which would meet civilian user requirements.

This new technology would ,for example, lead to a sufficiently accurate, redundant andindependent system for use as the sole means of positioning, timing and navigation,including the most demanding applications. Such a future system is known as GNSS-2 orthe Second Generation Global Navigation Satellite System.

The studies will examine a variety of operational scenarios that could meet, at the very least,existing civilian operational requirements. Aviation users, for example, are looking forGNSS-2 to be accurate and reliable enough to allow its use as a sole means of navigationfor the Category 3B precision approach which allows landings in conditions of almost zerovisibility.

Galileo

An all-European satellite navigation constellation took a step closer at the start of May 1999when government ministers of ESA countries gave a financial commitment to setting upGalileo, a second-generation global navigation satellite system (GNSS-2).

Galileo will be a global navigation satellite system under civil control. It will consist of 21 ormore satellites, depending on the level of international co-operation, the associated groundinfrastructure and regional / local augmentations. GalileoSat is the complementarydevelopment initiative of the ESA for the space and the associated ground controlsegments.

Galileo will be used in all modes of transportation for navigation, traffic and fleet

management, tracking, surveillance and emergency systems. As such, Galileo will be a keyelement of the future inter-mode traffic management system. Moreover it has many non-transport applications. The system will involve a space segment of around at least 21medium earth orbit (MEO) satellites, plus three geostationary earth orbit (GEO) satellitesand will cost Euro 2.2 2.95 billion to develop. (There are system proposals for up to 40MEO satellites).

Taking the current planning, Galileo will be fully operable in 2008 at the latest, with the startof signal transmission in 2005.


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Galileo and GPS will be interoperable and compatible. International Partners will be involvedactively in the Galileo programme.

Geo-coordinate standard

In February 1994 the ICAO Council adopted Amendment 35 to Annex 11 (Air TrafficServices) and Amendment 28 to Annex 15 (Aeronautical Information Services) to theConvention on International Civil Aviation which mandated the use of WGS 84 as thecommon geodetic reference system for civil aviation with an applicability from 1 January1998.

In March 1997 the ICAO Council adopted Amendment 29 to Annex 15 (AeronauticalInformation Services) to the convention on International Civil Aviation, which mandated theuse of the vertical component of WGS 84 with selective applicability from 5 November 1998.

What is WGS84?

The World Geodetic System 1984 (WGS84) is the geodetic reference system used by GPS.WGS84 was developed for the United States Defense Mapping Agency (DMA), now calledNIMA (National Imagery and Mapping and Agency). The origin of the WGS84 framework isalso the earths centre of mass.

WGS 84 provides the basic reference frame (coordinate system), geometric figure for theearth (ellipsoid), earth gravitational model, and means to relate positions on variousgeodetic datums and systems for various operations and applications.

It should be noted that all GPS receivers compute and store coordinates in terms of

WGS84, then transform to other datums when information is displayed. Many GPS usersmay have noted that although the local datum is selected for display, WGS84 values aredownloaded via their data cable to a computer.

WGS84 is also the default datum for many GIS software packages with data either beingstored in or transformed via WGS84.

RNP (Required Navigation Performance)

ICAO has endorsed the concept of Required Navigation Performance (RNP), in which aspecific navigation performance is defined, but no specific navigation equipment is required.For en-route purposes currently four RNP "Types" have been defined (RNP1, RNP4/5,RNP12.6/10, RNP20), where the type number indicates the containment value in miles.RNP conceived by FANS committee defines navigation performance accuracy required foroperation within a defined airspace.

Under this concept aircraft will be certified or approved as meeting a certain RNP type.There will no longer be a requirement for the carriage of specified navigation equipment; norwill the navigation equipment used to achieve the performance criteria necessarily be the


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same for all aircraft. Air traffic service providers will designate certain routes or airspace asspecific RNP routes or airspace. This will indicate to the users that State approval isrequired for the operator to flight plan and fly within the designated route or airspace.


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SSUURRVVEEIILLLLAANNCCEE

Surveillance systems are set up for the air traffic control system to know where the aircraft isand where it is heading. Position information from the surveillance system supports many

different ATC functions. Aircraft positions are displayed for the controller as he or shewatches over the traffic to ensure that aircraft do not violate separation criteria. A number oftechniques are available to obtain surveillance data such as:

i) Independent Surveillance (IS), provided by primary radar (PR);

ii) Co-operative Independent Surveillance (CIS), provided by secondary surveillanceradar (SSR) in its monopulse (M-SSR) and Mode S forms;

iii) Automatic Dependent Surveillance (ADS)

Primary Surveillance Radar, traditionaly used for Terminal or Approach Control, provides

range and bearinginformation of the targets to Air Traffic Control centre. SecondarySurveillance Radar (Mode A/C), mainly used for En-route or Area Control, providesidentification and altitude information of an aircraft (equipped with SSR transponder) to AirTraffic Control centre. The both systems jointly provide Four Dimension information to ATC.

CNS/ATM surveillance provides for an accurate and automated surveillance system byovercoming technical limitations of the former systems. Surveillance uses SSR Mode-S(Secondary Surveillance Radar Mode-S), VHF data-link or satellite link to send surveillanceinformation. A major information source is ADS (Automatic Dependent Surveillance), whichallows implementation of the Traffic Alert and Collision Avoidance System (TCAS).

Automatic Dependent Surveillance

Automatic Dependent Surveillance is a surveillance technique, which may be used inconjunction with other surveillance techniques for delivering air derived information to users.

ADS-Broadcast (ADS-B)

The Automatic Dependent Surveillance Broadcast (ADS-B) Surveillance application allowsthe transmission of on board data to air or ground based Users via a data link (e.g. Mode Sor VHF) using a broadcast Mode. The aircraft originating the broadcast has no knowledge ofwhich systems are receiving the broadcast. Any air- or ground-based User may choose toreceive and process this information.Surveillance Data which will be transmitted by ADS-B includes the airframe identification,position, time, Figure-Of-Merit and emitter category. The addition of other potential Data(such as the ground vector, air vector, short term intent, rate of turn and aircraft type) andthe use of an event driven transmission is possible in the future.

It allows an aircraft to intermittently broadcast position data without having any knowledge ofwhat ATS Unit, if any is receiving the data. ADS-B will allow for rapid update rates with


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minimum data latency and may in some cases be used in lieu of conventional ground basedindependent surveillance systems.

ADS-Contract (ADS-C)

ICAO defines ADS-C (or ADS-A) as a surveillance application in which an aircraft

automatically transmits data derived from on-board systems, via a data link (e.g. satellite orVHF). The transmission of ADS data will be based on a contract between a ground systemand an aircraft. Various contracts are foreseen including demand, periodic and event driven.Surveillance data which can be provided using ADS-C include the basic ADS message (e.g.aircraft position, time, figure-of-merit and aircraft identification) and optional ADS information(e.g. ground vector, air vector, projected profile, meteorological information, short term intentand extended projected profile).

It allows an aircraft to send position data addressed to a specific ATS Unit at specifiedintervals, or on the occurrence of a specific event, at the request of the ATS Unit. ADS-A isnot intended to supplant radar but rather to be used in those areas where proceduralseparation is applied. It will replace manual position reporting in those areas.

Key benefits of enhanced surveillance systems are:

Enhanced flight safety Imp[roved surveillance of air traffic in non-radar areas Possible reduction of separation minima in non-radar airspace Reduced delays The accommodation of user preferred flight profiles Increased ATC capacity Efficient and economic aircraft operation

Traffic Information Service - Broadcast

TIS-B (Traffic Information Service - Broadcast) is a surveillance technique that providessurveillance information from the ground to suitably equipped air or ground-based mobilesor Objects of Interest (mobile: an aircraft in the air or on the ground, or a surface vehicleequipped to receive TIS-B)

TIS-B Objects Of Interest (OoIs) are the physical objects for which any TIS-B user mayrequire information, principally the aircraft and airport vehicles.

The broadcast traffic information (Tracks data for the Objects Of Interest) is derived fromone or more ground surveillance sources.

The related ground system originating the broadcast has no knowledge of which systemsare receiving the broadcast.

TIS-B is a supplement to ADS-B for Airborne Surveillance Applications (ASA) that:

can provide equipped users with the ability to receive the information of traffic thatcannot adequately be obtained directly via ADS-B. For example mobiles that are notADS-B equipped or the mobiles that are equipped on incompatible data links; and


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can also deliver equipped users with state information on all traffic (Full Picture)

The following are the major functional components involved by TIS-B system.

i) the ground acquisition functions of the surveillance data from the various sources

(radars, multilateration, Airport Surface Detection Equipment [ASDE] and ADS-B)involved in the detection of the TIS-B Objects Of Interest,

ii) the Surveillance Data Processing & Distribution (SDPD) that will generate thecorresponding tracks,

iii) the TIS-B management and distribution function including the selection of theappropriate role (Gap Filler/Full Picture), tracks and data items required and thedistribution (up-link) to the suitably equipped mobiles,

iv) the mobile acquisition function of the TIS-B data.

Airborne Collision Avoidance Systems (ACAS).

ACAS is designed to work both autonomously and independently of the aircraft navigationequipment and ground systems used for the provision of air traffic services.

Through antennas, ACAS interrogates the ICAO standard compliant transponders of allaircraft in the vicinity. Based upon the replies received, the system tracks the slant range,altitude (when it is included in the reply message) and bearing ofsurrounding traffic.

The main feature of ACAS is that it functions according to time criteria and not distance.From several successive replies, ACAS calculates a time to reach the CPA (Closest Point ofApproach) with the intruder, by dividing the range by the closure rate. This time value is the

main parameter for issuing alerts and the type of alert depends on its value. If the aircrafttransmit their altitude, ACAS also computes the time to reach co-altitude.

ACAS can issue two types of alert:

i) Traffic Advisories (TAs), which aim at helping the pilot in the visual search for theintruder aircraft, and by alerting him to be ready for a potential resolution advisory;

ii) Resolution Advisories (RAs), which are avoidance manoeuvres recommended tothe pilot. When the intruder aircraft is also fitted with an ACAS system, both ACASco-ordinate their RAs through the Mode S data link, in order to select complementaryresolution senses.

ACAS was officially recognized by ICAO on 11 November 1993. Its descriptive definitionappears in Annex 2; its use is regulated in PANS-OPS and PANS-RAC. In November 1995,the Standards And Recommended Practices (SARPs) for ACAS II were approved, and theyappear in Annex 10.

Types of ACAS


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i) ACAS I provides TAs (no international implementation is planned at the ICAO level);

ii) ACAS II provides TAs, and RAs in the vertical plane; and

iii) ACAS III provides TAs, and RAs in both the vertical and horizontal planes.

As far as the equipment is concerned, only TCAS complies with ICAO ACAS standards,

TCAS I for the ACAS I standards and TCAS II for the ACAS II SARPs. No ACAS IIIequipment currently exists, and none is likely to appear in the near future, because oftechnical and operational difficulties, as being said by the experts.

Benefits

The implementation of ACAS II will improve flight safety, by providing a significant reductionin the risk of mid-air, or near mid-air, collision by at least a factor 3. It can provideoperational safety benefits, particularly in the following circumstances:

i) Flight crew/Controller errorii) Airspace management constraints

iii) FR/VFR traffic mixiv) Technical on-board or ATC system failures

Required Total System Performance

The CNS/ATM based system is intended to be viewed as the total sum of individualcomponents such as airspace, flight operations, and the facilities and services provided. Theconcepts of Required Communications Performance (RCP) and Required SurveillancePerformance (RSP) are being developed and are intended to form, along with RNP, thebasis of Required Total System Performance (RTSP). This may ultimately result inquantitative measures being available for all elements of total system performance


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AAIIRRBBOORRNNEESSYYSSTTEEMMSS

Aircraft must be equipped for several functions to support implementation of CNS/ATM.

These are Airline Operational Control (AOC) datalink, Automatic Dependent Surveillance(ADS), Air Traffic Control (ATC) datalink, Global Positioning System (GPS) integration,Required Navigational Performance (RNP), and Required Time of Arrival (RTA).

Airline Operational Control Datalink

The AOC link gives airline data systems the ability to transmit new routes, position reports,and updated winds through the datalink network.

Automatic Dependant Surveillance

The ADS function reports the current flight position via satellite or VHF datalink to the air

traffic controller or to the airline. This improves the surveillance of en-route aircraft.

Air Traffic Control (ATC) Datalink

This function replaces the tactical communication between the flight crew and air trafficcontroller, allowing the flight crew to request deviations to, or replacements of, the filed flightplan. The air traffic controller also has the ability to directly request tactical changes to theaircraft flight plan.

Global Positioning System Receiver

This improvement provides a more accurate position for en-route operations and some

approach operations. The navigation system must demonstrate that it can meet the requirednavigational performance criteria.

Required Navigational Performance

RNP criteria address accuracy, integrity and availability as set forth in CNS/ATM. The actualnavigation performance is constantly monitored; if it exceeds the required navigationalperformance, the flight crew is alerted so that they can compensate for a situation in whichthey have less accurate information than the route requires.

Required Time of Arrival

This gives the flight crew the ability to assign a time constraint to a waypoint, allowing theaircraft to cross a latitude or longitude at a specified time. The cruise speed is automaticallyadjusted to achieve that time, plus or minus 30 seconds. If the RTA is not possible, the flightcrew is notified with a visual alert.

Beside above number of traditional communication and surveillance equipment such asSSR transponder are also to be carried out on board. But following are some major systemsthat will revolutionize the working of a pilot in command.


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Cockpit Display of Traffic Information (CDTI)

CDTI will provide the position (latitude, longitude, and altitude) and heading data for nearbyaircraft. These data are displayed in the cockpit to augment the "see and avoid" concept.This data link capability can be achieved by using either an ground-based CDTI or an air-to-air CDTI. The benefit of using ground-based CDTI is that VFR aircraft can be displayed. The

air-to-air application is independent from the ground system and, thereby, avoids problemswith ground system availability and capacity. The CDTI functionality is planned to bedemonstrated through two prototype implementations: helicopters servicing oil rigs in theGulf of Mexico (GOMEX ) and monitoring of aircraft in secure airspace during the AtlantaOlympics.

FMCS ( Flight Management Computer System )

The Flight Management Computer System (FMCS), in conjunction with other interfacingequipment in the aircraft, forms an integrated, full-flight regime control and informationsystem which provides automatic navigation, guidance, map display, and in-flightperformance optimization. It reduces cockpit workload by eliminating many routine tasksand computations normally performed by the flight crew. The system operates continuouslyat all times if properly initialized. It can be coupled to the autopilot, flight director, andautothrottle to provide guidance through integrated commands for controlling roll, pitch andengine thrust and provides course guidance for RNP/RNAV operations.

The major functions of the integrated FMCS are:

Storage of navigation, aerodynamic, and engine data with provisions for routineupdating of the navigation data base on a 28 day cycle

Provisions for centralized data entry for alignment of the inertial reference units

Means for entry, storage and in-flight modification of a complete flight plan from thedeparture gate to the destination runway via company routes, SIS's STAR's airways,and named or pilot-defined waypoints

Means for entry of performance optimization and reference data including grossweight, winds aloft, ISA temperature deviation, fuel reserves ,cost index, andcomputations of the optimum vertical profile utilizing this data plus the entered route

Transmission of data to generate a map of the route on the Horizontal SituationIndicator, including relative positions of pertinent points such as navaids, airports,runways, etc.

Calculation of the aircraft's position and transmission of this information for displayon the moving map and Control Display Unit (CDU)

Capability to select VOR/DME stations which can yield a more accurate estimate ofairplane position then the inertial reference sensors and tune the receiversaccordingly

Capability to blend GPS and DGPS positions which will yield the most accurateestimate of airplane position


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Capability to transmit pitch, roll, and thrust commands to the autopilot, autothrottle,and flight director to fly an optimum vertical flight profile for climb, cruise, decent andapproach while simultaneously following the lateral portion of the flight plan

Multi-Mode Receiver (MMR)

The MMR is installed in-place of the current individual ILS/VOR/MLS radios in the aircraft'savionics bay. The MMR provides aircraft operators with a modular upgrade path toadvanced navigation technology including GPS LAAS/WAAS. Currently there are over 7,000MMR's on order or delivered for air transport aircraft.

Collision Avoidance Systems:

ACAS (Airborne Collision Avoidance System), which is an ICAO (International CivilAviation Organisation) standard, is intended to improve safety by acting as a last resort toolfor preventing collisions or near collisions. By utilising SSR (Secondary Surveillance Radar)technology, the system operates independently of ground-based aids and ATC. ICAOrecommends the carriage of ACAS II all over the world (ICAO, 1997a).

Currently the TCAS (Traffic Alert and Collision Avoidance System) equipment is the onlyavailable implementation of an ACAS. The existing TCAS II version 6.04A does not complyfully with ACAS II SARPs (Standards And Recommended Practices). However, the MOPS(Minimum Operational Performance Standards) for the forthcoming version, TCAS II version7.0, will be ACAS II SARPs compliant.


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CCOONNCCLLUUSSIIOONN

In nutshell CNS/ATM involve the following main standards/systems.

Communication

Voice/Data links, Aeronautical Mobile Satellite system, Mode-S Secondary Radar,Aeronautical Telecommunication Network.

Navigation

Area Navigation/Required Navigation Performance (RNP), Global Navigation SatelliteSystem (GNSS), Microwave Landing System.

Surveillance

Automatic Dependance Surveillance (ADS), Secondary Surveillance Radar Mode A/C andMode S.

FFAANNSSIISSNNOO MMOORREEAAFFUUTTUURREEAAIIRRNNAAVVIIGGAATTIIOONNSSYYSSTTEEMM


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Books and Publications

Global Plan for CNS/ATM. National CNS/ATM Plan. Manual of ATS data link Applications by ICAO. Manual of SSR systems by ICAO. ICAO Document 9705 Global Air Traffic Safety Plan of ICAO Aeronautical Telecommunications: Annexure 10 to the Convention on International

Civil Aviation. Air Traffic Services: Annexure 11 to the Convention on International Civil Aviation. Aeronautical Information Services: Annexure 15 to the Convention on International

Civil Aviation.

Datalink Manual Manual on the implementation of HFDL A Guide to GNSS in Europe WGS 84 Implementation Manual by EUROCONTROL and IFEN Augmentation of GPS/LAAS with GLONASS by P. Misra, M. Patt and B. Burke (MIT:

Lincoln Lab)

Websites:

http://www.icao.int

http://www.eurocontrol.int

http://gps.faa.gov/index.htm

http://www.airforce.forces.ca/ http://www.gpsworld.com

http://www.navsource.com

http://www.ainonline.com/index.html

http://www.lba.de/english/trchnical/technical.htm

introduction to cnsatm

Documents