The aim of this paper is to give an overview of the international developments, benefits, applications and operational requirements of data link (Mode S, Satellite and VHF) communications, and to consider areas where IFATCA policy should be developed.

Air-ground data communications is expected to make significant improvements to the ATM (Air T raffic Management) system in terms of safety, efficiency and control system capacity. (Air Traffic Management includes ATC, Air Traffic flow Management and Airspace Management). These potential benefits (a comprehensive list appears in section 5) arise because certain routine tasks could be undertaken with data link which would reduce controller workload and considerably lessen congestion on voice frequencies. Aircraft tracking, trajectory predictions and short term conflict alert will all be improved.

Internationally, considerable effort is being expended in developing the required technology and procedures and therefore IFATCA policy on air-ground data communications must be similarly developed. Data links will be introduced gradually between 1995 and the beginning of the next century; until then voice communications will remain the major method of air-ground information exchange. VHF and HF are the main civil frequencies in use but there are insufficient VHF channels to meet the forecast needs of aviation in the busiest airspace. In addition, voice radio operates in a broadca st mode between a single controller and all aircraft in the airspace under his control, leading to frequency congestion and thus a decrease in system efficiency when the volume of air traffic increases. Quality and quantity of information supplied for ATM is , therefore , very likely to become constrained using current technology. The increasing use of computers, in ATM ground systems and in modern aircraft, means that, given a link between these computer systems, much information currently passed by voice could be transferred automatically by data link. This would lead to an increase in the overall system safety and traffic handling capacity.

Overview of Air/Ground Data Communications Research and Development

Data link will profoundly change both the way in which ATC tasks are accomplished by controllers and the way in which pilots will receive and respond to ATC instructions. Therefore the ultimate usefulness and success of data link will be critically dependent on the extent to which it is employed to produce a system that is fully integrated with the human operators. For ATM to achieve optimal advantages from data link, a programme of research is necessary to guide system design efforts, evaluate the benefits of data link to ATC and establish benefits to controllers.

In recent years a number of initiatives has been taken by the USA, the UK, other European States and North Atlantic service Provider States aimed at improving the capacity of the ATM system whilst maintaining safety standards. These initiatives are crucial to the need to enhance capacity, take advantage of emerging technologies and exploit the use of air-ground data link communications.

The Future Navigation Systems (FANS) Committee was established by ICAO to study, identify and assess new concepts and technology in the field of air navigation and to make recommendations for the development of international civil aviation over a period of 25 years. The final FANS Report, FANS/4, was published in 1988 as a consolidation of the FANS global CNS/ATM concept for 1995/2010. (See Annex 3).

The European Civil Aviation Conference (ECAC) Strategy for the 1990’s was adopted by the Ministers of Transport of the ECAC States in March 1992. Its implementation objectives, to be achieved through the European ATC Harmonisation and Integration Programme (EATCHIP), include making air traffic control communications more efficient. Essential in achieving this will be the extension of data exchange between air traffic control computers and between the air and ground to permit enhanced automation of ATC functions.

Eurocontrol has developed the Programme for Harmonised ATM Research in Eurocontrol (PHARE) which is investigating the longer term applications of air-ground data communications. The programme is concentrating on the interaction of aircraft 4-D navigation capability and ground based ATM computers via air-ground data links; an ATM scenario for the years 20002015 has been defined. PHARE will produce validated ATM applications for Modes S data link and these will feed into the Enhanced ATM and Mode S implementation in Europe (EASIE) programme (also managed by Eurocontrol) to provide application requirements for the European core area. (See Annex 6). Current EASIE planning proposes that aircraft operating in European areas of dense traffic will be required to carry data-link capable Mode S transponders from the beginning of 1999.

(Details of European UK and USA data Link Programme are at Annexes 5,6 and 7).

European research and development of data links includes an assessment of their capability to provide proper and timely support of ATM needs. In particular it is intended to assess the suitability of the different data link types together with their associated networks for different ATM purposes. Specific characteristics of various data links mean that they cannot be applied equally in all geographical areas as well as under all traffic conditions. Research programmes should lead to validated applications of data link.

Potential Application of Data Links

Work (such as that of EASIE) has been carried out to define those ATM events (e.g. phases of flight, ATFM) which have data link applications. High-level functional descriptions and characteristics have been deliberately defined without reference to the data link medium employed. The choice of medium need not concern IFATCA – but whatever is used will need to comply with stated functional characteristics. The user must be concerned with whether or not the end to end quality of the service he demands is available. Many other potential ATM applications have already been considered and demonstrated by researchers: weather reports, NOTAMS, ATC clearances, flight plan data, information for FMS and IRS (Inertial Reference Systems), technical assistance and information on the status of airports. (Details of UK Research Programmes are at Annex 8).

The ATM system of the 21st. Century must be international in scope, with compatibility worldwide technologies. The system must evolve in order to meet the test of international acceptance and interoperability. The goals for the future system must remain to maintain and improve safety standards, increase system capacity and fully utilise capacity resources. The latter will include better accommodation of user requested flight trajectories, and avionics capabilities, increased user involvement in decision making which will include computer based air-ground negotiation of flight trajectories and information on positions and manoeuvre intentions of aircraft.

The quality of information available to the system is a primary factor in determining the overall quality of ATM. The future system will select the best sources of information and utilise this data to augment ground derived data. The system will also make extensive use of automation. For example, it is envisaged when a user determines that a FPL (flight plan) amendment is required a communication process will be established between the FMS and ground based automation to recommend a new trajectory that best meets the user’s objective and satisfies ATM constraints. Human operators will exercise management and control authority over these communications processes.

Candidate applications for early implementation (1995 or earlier) include AIS/FIS (Aeronautical/Flight Information services) information. These are non-safety critical and their implementation will permit confidence building in data links by users and the technology providers. In addition, significant Alert algorithms by automatic extraction of certain air derived parameters e.g. intention data. This could well be an early safety related application of data link.

Potential Benefits of data Links to ATM

Data links provide digital, 2-way communication between aircraft and the ATC system. The primary way in which data links can improve the safety, efficiency and control capacity of the ATM system is through their potentially positive impact on the tasks of the human operators in the system. Work on assessing tasks which may be undertaken by data links continues and much more needs to be done before an operational system can be introduced. However, some specific benefits can be positively identified now. The se can be categorised as benefits to ATCO/Pilot Workload, Safety and Capacity. Some benefits apply to more than one category.

ATC/Pilot Work Load

• Reduction in planning workload, both for the ground system and the controller, through monitoring of the FMS to ensure conformance with ground instructions;
• The automation of many routine tasks e.g. handovers;
• Greater assurance of aircraft intent. Foe example, acceleration data from the FMS will indicate change of speed intention information to the controller, adding significantly to the ability to predict the short term air situation.

Safety

• A discrete addressing capability so that an aircraft receives only those communications directed to it by the ground system;
• A subsequent reduction in congestion on voice frequencies leading to immediate access when required;
• A “Safety Net” channel for relaying ATC instructions;
• Increase in flight path monitoring by the ground system;
• Automatic error checking of uplinked and downlinked information;
• An accurate and recallable record of uplinked clearances for the pilot;
• Earlier notification of potential hazards, through provision of more accurate, more plentiful and more easily accessible data on aircraft and ground system status. (E.g. Navaids, Met);
• The downlinking of ACAS information, giving the controller advance warning of potential and actual aircraft manoeuvres;
• More accurate conflict detection – both short and medium term;
• Reduction in planning workload, both for the ground system and the controller, through monitoring of the FMS to ensure conformance with ground instructions;
• Greater assurance of aircraft intent. For example, acceleration data from the FMS will indicate change of speed intention information to the controller, adding significantly to the ability to predict the short term air situation.

Capacity

• A second channel of communication between the controller and aircraft, independent of voice. This will lead to the elimination of routine communications via RTF e.g. initial route clearances;
• The ability of the FMS to communicate directly with the ground system which greatly improves the volume and quality of aircraft system data available to the ATM system;
• ATFM capabilities enhanced due to more accurate data being available;
• A more responsive ATC service to customers;
• Increase in flight path monitoring by the ground system;
• Greater assurance of aircraft intent. For example acceleration data from the FMS will indicate change of speed intention information to the controller, adding significantly to the ability to predict the short term air situation.

Potential Disadvantages

The following are areas where there may be disadvantages in using data links; work is required to quantify any such disadvantage:

• Reduction of situational awareness for both pilots and controllers;
• Data link capacity; will there be sufficient capacity to handle all the potential ATM applications?
• Decrease in voice workload offset by an increase in data input.

Requirements for the Operational Use of Data Link

Whilst it is recognised that further R&D work is necessary, the following potential requirements for the operational use of data links are endorsed by IFATCA.

Access

Multi-user access to aircraft – to allow different ATCC’s or ATM operations to obtain information. Multi-access will require different ‘levels’ of data link access i.e. the current controlling facility should have access to greater data link functionality than another facility which is obtaining only information or negotiating FPL changes in anticipation of the aircraft entering its airspace.

Data Extraction

The update rates of change of various data for different conditions will need to be specified. For example, trajectory information which will be used for separation purposes will require more regular updating than weight information. Automatic extraction of data, i.e. will data need to be constantly extracted by the ground system or could the airborne system just indicate changes?

Prioritisation

Message prioritisation, storage and recall (see ATN – Annex 2). Message critically will define the order of messages.

Security and Integrity

The ATN must ensure security and extremely high integrity of aeronautical data communications.

Timelines

The timeliness of data delivery (see ATN) and dialogue transfer rate i.e. the expected number of data transfers per aircraft per flight phase will need to be defined.

Workload

Workload impact will require assessment – as for any new system. For example, the effect of displacement of work from auditory to visual and the subsequent reaction time to messages. (Annex 8 CAER).

Situational Awareness

Reduction of situational awareness for both pilots and controllers will require assessment. Will they both have the same mental picture of the spatial situation of aircraft.

Evaluation

There will be a requirement for evaluation in a realistic operational environment. (See Annexes 5&6, the work of FAA and Eurocontrol and Annex 8 CAER)

System Interface

The system interface will need to allow the controller to do his/her work and interact effectively with all other ATM functions e.g. communications management, acknowledgement aspects, environment monitoring (currently available routes etc.) . Annex 8 CAER). The interface device will need to detect and display errors accurately and promptly. The recording/replay of information will be required and capable of presentation to the controller. HCI (Human Computer Interface) requirements resulting from increased automation, other than simple display of information. For example, how will the controller interact with trajectory prediction? (Annex 8 CAER) (ODID, NERC, FAA studies).

System Failure

The operational status of data link will need to be displayed to the controller. For example, if the aircraft is outside its effective range, some data will not be available.

Thus a method of failure detection is required together with a means of displaying this to the controller. Failure of one subnetwork of the ATN (e.g. Mode S ) should be transparent to the controller in that the messages will be automatically re-routed. However there should be some indication that a failure has occurred but that the system is still operational. System failures might lead to a sudden increase in workload if the controller is not practised at working without datalink. Error recovery i.e. the number of re-tries operationally acceptable when a transmission failure occurs will require definition. This will need to include a maximum time prior to system and/or controller/pilot notification of failure, re-try and attempted termination.

Acknowledgements

The method of making/displaying operational acknowledgements i.e. has the crew received the message correctly, as opposed to technical acknowledgements i.e. has the system received it correctly will require definition.

Mixed Traffic Environment

Controller operations in a mixed traffic environment will require assessment, i.e. handling data link equipped and non data link equipped aircraft.

Message Standardisation

The standardisation of messages and abbreviations not in a free prose format will require definition. Spoken phrases may not be the best form of visual presentation.

Adjacent Area Interfaces

Adjacent area interfaces – requirements for interfacing with variably sophisticated areas.

To conclude

The evolving use of air – ground data communications within the ATM system appears to have the potential for providing, in due course, benefits in safety and system capacity and improvement of efficiency of the system. Considerable work is being undertaken internationally in the development and use of air – ground data communications; primarily EASIE and PHARE in Europe and the work of the FAATC (FAA Technical Committee). Certain potential requirements for operational use are already being addressed e.g. the ATN infrastructure will address , integrity , security, priority, reliability and transfer delay of messages. However, IFATCA should endorse a complete preliminary list of requirements as proposed in section 6.

The evolutionary introduction of data links will gradually change both the way in which ATC tasks are accomplished by controllers and the way in which pilots will receive and respond to ATC instructions. Therefore, the ultimate success of data link will be critically dependent on the extent which it is employed to produce a system that will be fully integrated with human operators. The technology is identified – the applications must be managed.

IFATCA policy on a large number of aspects of data links will be required. It is possible to make certain Policy Statements at this stage, some of which will require further work to define exact parameters.

TYPES OF DATA LINK

There are three main types of data link to be considered :

a) VHF

The system, currently used is called Aircraft Communications Addressing and Reporting System (ACARS). Its main function is for airline operational use but trials are currently underway to test the use of the system for limited ATM functions such as the passing of departure clearances. It is unlikely, however that ACARS can be developed as an ATM tool because the system does not conform with International Standards Organisation (ISO) requirements.

An offshoot of the ACARS system called Aviation VHF Packet Communications (AVPAC) is being developed which does conform to ISO standards and this will have wider ATM applications. The ICAO Air Navigation Commission (ANC) has accepted the need to develop appropriate Standards and Recommended Practices (SARPS) for VHF data links. Meanwhile, in response to growing airline and avionics industry pressure for increased utilisation of the VHF/RTF bands for data link in support of ATC applications, RTCA (Radio Technical Assembly for Aeronautics) has established a new Special Committee to develop Minimum Aviation System Performance Specifications for VHF air-ground data links.

b) SSR Mode S

Mode S data link is viewed as the most suitable future air-ground data communication system for high traffic density airspace. Mode S , which is an extension of the Monopulse SSR system , will be installed by most western European states by the year 2000. ICAO SARPS for Mode S data link are planned to be completed by 1993. By the year 2000 many aircraft will be equipped with Mode S transponders due to legislation in the USA requiring aircraft to be fitted with ACAS (Airborne collision Avoidance systems). However, these will not necessarily have sufficient capability for data link operations. The cost of the airborne equipment is, however, initially likely to be prohibitive for general aviation aircraft and so VHF data link may prove to be a valuable sub-system, although it will not have a surveillance capability and will be limited by the shortage of VHF frequencies. Mode S is , therefore , the most developed ICAO air-ground data communications system currently planned for the future.

c) Satellite

Satellite is the preferred data link for oceanic remote regions where terrestrial line of sight systems(such as mode S and VHF) either cannot be used because of their range imitations or would be impracticable, or uneconomic, to implement. Whilst the development of satellite airground data link applications was until recently lagging behind Mode S , the ICAO adoption of the FANS “Global CNS (Communications, Navigation and Surveillance) concept” – coupled with airline and aeronautical satellite services which will be available in the mid-1990s – have resulted in proposals for (AMSS) Aeronautical Mobile Satellite Systems Implementation within similar timescales to those for Mode S data link. ICAO SARPS for the AMSS are expected to be completed for ICAO in mid 1993. A major ATM application for satellite data link , in addition to pilot/controller data communications, is the provision of Automatic dependent Surveillance (ADS) in areas beyond the range of ground based radar’s. However, in the near term, there will be no satellite coverage in polar regions because of the lack of earth orbiting (non-geostationary) aeronautical communications satellites.

The EASIE programme, detailed in Annex 4, is shortly to put out to tender a comparative study of the three forms of data link. Results should be available in mid 1993.

THE AERONAUTICAL TELECOMMUNICATIONS NETWORK (ATN) INFRASTRUCTURE

To enable more than one data link system to be used and to allow flexibility of operation within the ATM system, it has been necessary to design an infrastructure. ICAO has developed a concept known as the ATN which is a collection of sub-systems interconnected by routers which will provide a network for passing information between air-ground and ground – ground. International standards are being developed by ICAO (see Annex 4) to ensure global interoperability of Mode S, satellite and VHF within the ATN.

The ATN is based on Open Standards Interconnection (OSI) which is the ISO architecture designed to ensure a transparent and reliable exchange of data messages. The ATN can support all the potential air-ground data communications systems and will enable the route of a message and the type of air-ground data communications system to be transparent to the controller. The design of certain parts of the ATN are highly dependent on ATS data link application processes.

The ATN uses information such a transfer frequency (the expected number of data transfers per aircraft per flight phase), throughput (the amount of data going through the system) priority, transfer delay, reliability and cost parameters to determine routeing and deliver the data to the specified end-user. The minimum transfer delay is one factor which determines the applicability of a particular communications system for an ATS function. Reliability is defined as the provability that an end-user message is correctly received.

The ATN will be supported by certain sub-networks e.g. Mode S which will require access control necessary to ensure security and integrity of aeronautical data communications. Security concerns access to the ATN by authorised users, whilst integrity concerns allocation of resources (e.g. throughput) among authorised users. The ATN supports the enforcement of both security and integrity control within the internetwork route, and subnetwork access, mechanisms. The ATN must abide by the provision of Annex 10 to the Convention on International civil Aviation in assignment and use of message priorities defined in the ITU (International Telecommunications Union) Radio Regulations. These Regulations and appropriate ICAO SARPS must be considered when deciding which types of message data may be handled by individual subnetworks. Allocation of priorities provides the basis to control access to the ATN and to maintain the required quality of service for authorised users.

ICAO AIR-GROUND DATA COMMUNICATION DEVELOPMENTS ICAO COMMITTEES PANELS AND GROUPS SPECIAL COMMITTEE ON FUTURE AIR NAVIGATION SYSTEMS (FANS)

The FANS Committee was established by ICAO in 1983 with the task to study, identify and assess new concepts and technology in the field of air navigation, including satellite technology, and to make recommendations for the development of air navigation for international civil aviation over a period of 25 years. The final FANS Report, FANS/4, was published in 1988. It was a consolidation of the FANS global CNS/ATM concept for 1995/2010.

Upon completion of this work, the AMSSP, the ADS Study group, and subsequently the ADS Panel were established within ICAO to continue the FANS work and develop the necessary detailed specifications and procedures. In addition, a new ICAO Committee , FANS II , was established with the objective of advising on the overall monitoring and co-ordination of development in transition planning. FANS II will ensure that the implementation of the future CNS system will take place on a global basis in a cost-effective manner.

AERONAUTICAL MOBILE COMMUNICATIONS PANEL (AMCP)

The AMCP was set up in 1987 as the Aeronautical Mobile Satellite service (AMSS) panel to undertake specific studies as approved by the Air Navigation Commission (ANC). The panel is tasked with urgently developing SARPS and , where appropriate, guidance material for airground data links associated with AMSS’s. The panel has to take into consideration the requirements of ADS, other air-ground data links and ground ATM communications networks.

The AMCP is primarily concerned with standardising the satellite communications sub-system. The SARPS generated by this panel must accommodate ADS and help to ensure that ADS is compatible with other air-ground data link systems. It has also been tasked with producing SARPS for VHF data link.

AUTOMATIC DEPENDENT SURVEILLANCE PANEL (ADSP)

The ADSP is charged with the development of ATS operational procedures, applications criteria and data formats for ADS messages for ATC/cockpit interchange via various proposed airground data link systems. The panel will make proposals for related data link technical specifications.

SSR IMPROVEMENTS AND COLLISION AVOIDANCE SYSTEMS PANEL (SICASP)

SICASP was established in 1981 to develop SARPS, procedures and guidance material concerning SSR enhancement and related data link and collision avoidance systems. The panel was given the task of developing protocols to permit commonality and interoperability between Mode S and other ATS data links.

SICASP working groups have been progressing the work on matters related to the development of SARP’s, guidance material for SSR Mode S, SSR Mode S Subnetwork, ACAS and the ATN. The ATN material includes the interoperability considerations for all air-ground subnetworks.

NORTH ATLANTIC SYSTEMS PLANNING GROUP (NAT SPG)

NAT SPG is composed of Member States of ICAO which are directly involved with the provision of ATS in the North Atlantic (NAT) airspace. This group assesses the operational needs and develops co-ordinated plans to allow effective utilisation of NAT airspace over the next 25 years.

NAT SPG is concerned with future requirements for ATS systems in the North Atlantic as well as national plans for the provider states to develop and to integrate oceanic automation and ADS functions. The NAT SPG Task Force has completed a North Atlantic Implementation Document which will form the basis for the implementation of the Future Concept.

FUTURE EUROPEAN ATM SYSTEM CONCEPT (FEATS)

FEATS is the ICAO concept for providing harmonised planning throughout the European region. The concept is fully compatible in the medium and long term with adjacent regions and the rest of the world.

FEATS has 3 phases:

Phase 1 1988. Current technology enhancement and harmonisation of National ATC schemes. Includes improving radar surveillance, communications, navaids, optimisation of ATC sectorisation and a move towards area navigation.

Phase 2 1995-2010. Exploitation of advancing technology and progressive integration of national systems. Includes development of SSR Mode Sand evolution from harmonised to integrated ATC systems.

Phase 3 2005 +. Automation and full system integration.

CURRENT ICAO WORK AND SARPS

The FANS 4 Report describes the benefits that emerging technology will bring to future ATM systems and the evolutionary path to their implementation. Several phases of development are described, for example, Phase A (1990-2005) envisages the introduction of satellite systems for use in oceanic areas to support ADS, voice communication and enhanced satellite navigation. In the same timeframe ATM in high density airspace will rely on aircraft using 3-D navigation systems and air-ground data communication to enhance ATC applications such as trajectory prediction through the use of aircraft computer data transferred to the ground by air-ground data links. The ICAO FEATS concept also follows FANS/4.

In support of the FANS concept, considerable international effort is being directed towards completing ICAO SARPS for the technology envisaged in the FANS 4 Report. SICASP are drafting SARPS for the Mode S subnetwork, for approval by ICAO ANC in March 1993.

SICASP recognised the importance of complying with the ISO OSI communications model. The OSI model provides a structured approach to the development of standards and protocols to define a data communication system. Thus the SARPS being developed by SICASP not only apply to Mode S data link but to others such as satellite and VHF. They will also serve to ensure that the interface with ground-ground communications systems such as the Common ICAO Data Interchange Network (CIDIN) are uncomplicated.

The NAT SPG view the implementation of satellite communications as a vital step in the enhancement of ATM in the North Atlantic. NAT SPG is expecting to use the AMSS to provide ADS from 1996/97 onwards

THE USA PROGRAMME FOR IMPLEMENTATION OF DATA COMMUNICATIONS IN ATM

The USA FAA has been following a data link research programme over a 10-15 year period. Due to their requirement for Airborne Collision Avoidance Systems (ACAS), the US is more advanced than Europe with its plans for the implementation of Mode S surveillance. Mode S is a fundamental element use of ACAS which will be required to be carried by US or foreign registered aircraft operating into all the major US airports. The FAA has developed a comprehensive data link implementation programme.

This programme, mainly based on SSR Mode S, is being carried out in four steps. Step 4, in the 2000-2010 timeframe, will provide air-ground data communication support for Automated Enroute ATC (AERA) 2 and 3. The FAA states that AERA 2 will require air-ground data link to achieve their desired reduction in controller workload. Similarly their Terminal ATC Automation programme also requires air-ground data links. In the short-term, prior to the introduction of Mode s, to overcome voice congestion they are using the airline’s data link system to pass predeparture clearances to aircraft at the departure gates.
Over the last few years the FAA has also started a large development plan to introduce satellite communication into their ATM system. Initially Satellite Communications will provide enhanced communication in the Pacific Ocean but the FAA is also co-ordinating implementation in the North Atlantic through the NAT SPG.

Operational Evaluation of Initial Data Link ATC Services

(Talotta) FAA Technical Centre (FAATC) February 1990.

The above report details the results of the operational evaluation of initial data link studies carried out at the FAATC with their data link test bed. Initial data link studies have been evaluated in order to identify the service delivery methods which optimise controller acceptance, performance and workload. The FAA’s R&D programme is ensuring that data link has a positive impact on ATC.

The trials have measured the benefits of data links on VHF frequency congestion and the impact on ATC performance, effectiveness, workload and controller acceptance. The ATC services studied were altitude assignment and transfer of communications.

The controller study demonstrated the benefit that the initial group of data link services can be expected to have on relieving frequency congestion of voice RTF. The availability of these functions decreased the number of controller voice transmissions by up to 41% and total ATCO occupation time of RTF by 45%. Furthermore, as more data link equipped aircraft were introduced, there was an apparent increase in the effectiveness of the communications process as requirements for repetition of voice messages decreased.

The positive impact of data link was not achieved by any observed loss in ATC performance or controller capability. It also showed that data link transition delays failed to have a negative effect on controller activities. Based on the results of these trials it was recommended that the initial group of data link ATC services be incorporated as modifications to current en-route ATC software and hardware and that they be subjected to operational test and evaluation.

The FAA’s Air Traffic data Link Validation team will take part in the tests and evaluations. The necessary R&D will cover en-route and terminal ATC and interactions between the validation team and pilots.

The FAATC is committed to its goal of ensuring that data link will play a major role in enhancing human performance and aviation safety.

FAA Validation Flight For satellite Data Link

In March 1992, United Airlines and ARINC (Aeronautical radio Inc.) conducted a formal FAA validation flight of the world’s first application of datalink via satellite for ATC. ACARS and SATCOM systems were used for transmitting progress reports at each of 10 required navigation waypoints along their planned route. Each report was electronically acknowledge by the ARINC radio operators using the same ACARS and SATCOM systems in reverse. Conventional HF radio was used only as a back-up and for requests for change in cruise altitude. This successful validation led to United Airlines receiving approval from the FAA to begin routine use of satellite communications for position reporting over US controlled Pacific airspace on Boeing 747-400 aircraft equipped with SATCOM and ACARS.

EUROCONTROL PROGRAMME FOR ENHANCED ATM AND MODE S IMPLEMENTATION IN EUROPE (EASIE)

EASIE has been developed in close co-operation with the Eurocontrol Member states. Its aim is to bring about a significant improvement in ATM system capacity in Europe and to accommodate traffic increases forecast for the turn of the century. The programme is viewed as the basis of the advanced phase (Phase IV) of EATCHIP.

EASIE is aimed at extending the automation of ATC functions in order to improve controller productivity and airspace use, thereby contributing to increased system capacity, while maintaining a high level of safety. New technology, particularly the introduction of SSR Mode s and its air-ground digital data communications capability, allowing closer coupling between airborne and ground processing systems, provides the potential for greater automation.

EASIE embraces avionics systems, air-ground communications and surveillance systems, ground communications networks, the ATC data processing system and controller workstations. The three major elements of the programme comprise the Air Traffic Management System, the ATN and air-ground data links as sub-networks of the ATN. The relative contributions of Mode S, VHF and satellite data links are to be addressed by EASIE.
The programme, which commenced in 1990, is in two separate phases; the Design phase of approximately 5 years and the Implementation phase, of approximately 10 years. The objective of the Design phase is to provide an overall functional design of the system.

A fundamental premise of EASIE is that the functional design of ATM systems must be based on validated user requirements for air-ground data exchange. The development of such requirements is supported by the Programme for Harmonised ATM Research in Eurocontrol (PHARE).

PHARE has been set up to validate and demonstrate the merits and feasibility of the concept of air-ground coupling, including the development of the appropriate experimental facilities; it assume the existence of air-ground data links. It is a research and development programme comprising both the ATC and the aeronautical element.

The PHARE scenario is focusing on those functions to become operational in a phased approach in the 2000-2015 timeframe.

Control of an experimental aircraft has been achieved via Mode S data link. Eurocontrol, in collaboration with UK CAA gave a world first demonstration in October 1991. It represented an important milestone in the development of data link facilities, showing the enormous progress made in the programme and that the technology is rapidly emerging for ATM purposes. The report (Eurocontrol Mode S – A report on flight trials to demonstrate Mode S link in an ATS environment) describes the demonstration and presents details of the technical performance achieved.

The main objective was to demonstrate the capabilities of current technology, drawing attention to potential benefits of data link by demonstrating several possible applications in an ATS environment :

• Automatic delivery of aircraft avionics data to the ground system. In future operational system this information could enhance other applications e.g. accuracy of tracking and trajectory prediction;
• Remote interrogation of a ground data-base by the pilot;
• Transmission of ATC instructions and pilot acknowledgements.

The demonstration clearly showed advantages of Mode S Data Link including better computer compatibility with airborne and ground systems communicating freely without human involvement, allowing enhancements to ground radar and flight data processing systems.

The fourth phase of the EATCHIP programme will be embraced by the EATMS (European ATM System) concept. One of the three main axis of development of the concept is air/ground integration aimed at extensive co-operation in the performance of ATM functions, at the improvement of the overall system performance and increase in controller handling capacity through higher levels of automated assistance. Widespread use of data exchanges, based on the inter-operability of Mode S, satellite and VHF air/ground data links and high speed ground networks to ensure adequate transfers of data :

• ground-ground for surveillance and flight data, between ATM units and aircraft operations;
• air-ground between airborne and ground computers and between crews and ATM staff.

UK POSITION ON THE DEVELOPMENT OF DATA LINK SYSTEMS FOR ATC

The UK CAA is involved in the development of international standards mainly in ICAO and Eurocontrol Panels and Working Groups, for air-ground data links for aviation use. In addition the CAA is sponsoring practical work and studies related to the development and testing of practical data links in the Mode S and satellite areas. It is also evaluating the concept of the use of VHF data link for oceanic clearance delivery. It is the CAA’s view that any data link and associated infrastructure introduced for ATC operational use must conform to ICAO agreed standards and be consistent with the ATN concept. Furthermore, the CAA is fully committed to the use of bit orientated procedures for data link in conformance with the internationally agreed Open System Intercommunication (OSI) architecture developed by ISO.

It is recognised that the airline industry has, for its own purposes, developed a VHF data link which currently uses character oriented procedures and that this system is now in use by a number of airlines for airline operational control and administrative purposes, the airlines have stated that it is their firm intention to move to bit oriented procedures at the earliest possible time. This commitment is welcomed by the CAA and it is believed that the aviation authorities, airlines and service providers should co-operate to bring about this change at an early date. The development of ICAO SARP’s for this system is now under way. However, it is recognised that an evolutionary means will have to be found to integrate the older character oriented technology into the OSI approach and minimise the cost to the airlines. The CAA believes that every opportunity must be taken to introduce OSI based systems in an evolutionary manner. The CAA urges the airlines and other bodies to support the development, standardisation and application of common world wide VHF data links to achieve this objective as a means of evolutionary introduction of the ATN thus enabling existing systems to support evolving ICAO standards.

UK PROGRAMME OF R&D FOR CIVIL AVIATION OPERATIONS AND THE NATIONAL AIR TRAFFIC SERVICES

The following are current UK R&D programmes concerning the development of data links :

A. The Development and Demonstration of the Data Exchange Capability of SSR Mode S Air-Ground Data Link

A UK Mode S trials facility has been completed enabling both the surveillance and data link capabilities to be evaluated and demonstrated. A simple communications network and demonstration facilities have been established and potential ATC application types demonstrated using the full range of Mode S signals -in-space. This R&D project has enabled the CAA to make a significant contribution to the development of Draft ICAO Mode S Subnetwork SARPS.

Much of this work will be co-ordinated with EASIE. Maintenance of the developed trials facility is being continued in support at other R&D projects, especially Computer assistance En-Route (CAER).
In the future the trials facility will be enhanced in compliance with the proposed ICAO Mode S subnetwork SARPS.

B. Development and Demonstration of Satellite Communications for ATC in Oceanic Airspace

The development of the Aeronautical mobile satellite service (AMSS) is being progressed within the airline and communication service provider community. It is anticipated that AMSS will also provide important voice and data communications services for ATC use initially in oceanic airspace. ADS of aircraft flying over the North Atlantic is likely to be the most important initial application of the AMSS for ATM purposes.

The objective of this project is to develop and demonstrate the capability of satellite data links to provide an ATC air-ground communications system for use in NAT airspace. Results of this will be shared with the FAA.

Following a study contract which was placed with industry to develop a specification for an airborne ADS unit for use in trials , an industry contract has been placed for the supply of this unit. It is being installed in a British Airways 747-400 together with a satellite communications terminal as part of the collaborative ADS trials programme which has been set up by industry, airlines and satellite services providers.

The results will be fed into ICAO and industry groups. The work is due to be completed in 1995.

C. To Investigate and Evaluate the Communications Infrastructure to Support GroundGround and Air -Ground ATC Data Communications

Within ICAO, SARPS are being developed to define an OSI-based data communications architecture for ATC data communications. This will be known as the ATN and will support airground and ground-ground data communications. The key element is the Internetwork Router which interconnects ground and airborne subnetworks. The objective is to develop a communications infrastructure based on the OSI model, within which air-ground and ground-ground data communications systems can interoperate. This work will feed into the ICAO ATN SARPS and the EASIE ATN.

D. Mode S

the UK Mode S development programme is at the forefront of the European EASIE design phase. The objective is to complete Mode S development to meet essential future ATC surveillance and communications needs.
Current UK work includes :

a) Maintaining the current Mode s systems,

b) Mode S ground system specification,

c) Mode S data link interface development,

d) Evaluation of ACAS.

From 1992 specifications for each of the components of the Mode S ground system will be completed.

E) Computer assistance En-Route – CAER

Progressive introduction of computer assistance to augment the ATC task is seen as one of the prime ways of increasing controller productivity and thus enhancing system capacity in the longer term.

The overall objective is to undertake a phased R&D programme aimed at the provision of computer assistance and exploitation of data links in the future ATM systems.

The objectives are to:

• Develop computer assistance tools for tactical traffic management with a 20 minute “lookahead” time (trajectory prediction, deviation monitor, conflict probe and planning aids) and investigate the value of the various tools in enhancing the ATC process;
• Investigate the progressive exploitation of data link as part of the advanced ATM task;
• To undertake air-ground integration experiments, based on the EFMS (enhanced FMS) equipped BAC 111. The EFMS will provide , via data link, the up and downlinking of flight plan and other data in order to define 4-D trajectories.

This programme is the major element of UK’s contribution to the Eurocontrol co-ordinated PHARE programme.

In the longer term the CAER programme will be looking at all aspects of the controller task with a view to assessing the requirement for future computer assistance – utilising a mutually agreed aircraft trajectory via data links, computer derived trajectories and the automatic monitoring of agreed trajectories. Flight trajectories will be transmitted by data link and agreed at all stages with the ground system. EFMS work at the Royal Aircraft establishment in Bedford, England, will bring about the capability of sophisticated 4-D navigation, downlinking of a 4-D trajectory and maintaining it within pre-defined limits.