The Interface Between GNSS and Air Traffic Control

R. Farnworth. N. Makins, A. Watt, J. Storey

Abstract:	When aircraft are using GNSS as either the sole or primary means of navigation in controlled airspace there will be a requirement for Air Traffic Services (ATS) units to be aware of the system status. EURO- CONTROL is currently supporting the EGNOS pro- gramme in co-ordination with its Member States and its partners in the European Tripartite Group - ESA and the European Commission. One of the roles of EURO- CONTROL is to provide user requirements for the system. One such requirement is the interface between the EGNOS system and Air Traffic Control. Annex 1 I to the Convention on International Civil Aviation requires that ATS units be kept informed of the current operational status of non-visual navigation aids within their area of responsibility. Historically this has been a straightforward task controlled within na- tional boundaries. The system of air traffic routes cur- rently relies on ground-based navigation aids strategi- cally positioned to provide navigation services to air- craft on those routes. The impact of a failure in such a navigation aid is immediately apparent to the Air Traf- fic Controller responsible for that portion of airspace. Alternative procedures are in place to manage such outages generally relying on other available navigation aids in the local area. Such procedures are described in terms of distances and bearings from specific aids. There will inevitably be times when individual GNSS elements will not conform to their specifications. This may result in performance outages in particular areas. The most common form of outage will be the failure, or removal from service, of an individual satellite in the constellation. The orbits of GNSS satellites are accu- rately predictable so it is possible to model the effects of a known satellite outage and predict its impact on navigation performance in a particular region of air- space. There is clearly a need to pass this information to ATS units; however there are many different ways in which the data can be displayed to a controller and this requires further investigations. The presentation of in- formation is highly dependent on what the controller can do with it in order to ensure the safe flow of traftic. Pictorial representations are possible showing how footprints of downgraded service move across the air- space. This kind of representation could be useful for forward planning but it is likely to be too complex to present to controllers in real-time. It may be safer to use text messages of a more general nature. This paper describes a multi-disciplinary work pro- gramme to investigate the need for an interface between GNSS and ATS units. It involves experts in Air Traffic Management, Satellite Navigation and Real Time Simulations in EUROCONTROL, States and Industry. The work is sponsored by the EUROCONTROL Sat- ellite Navigation Applications Sub-Group and Member States contribute through the Operational and Certifi- cation Requirements Task Force. The data available from systems such as EGNOS and WAAS concerning system status information could be useful to ATS units and it is intended to establish the information that is required and the method of transfer- ring the data and displaying the system status to ATC. The work also aims to identify the ATC procedures necessary to deal with satellite navigation system fail- ures. A demonstration ATC processing and display system will be developed by EUROCONTROL at its Experimental Centre at Bretigny sur Orge, near Paris. This should lead to recommended standards for infor- mation exchange between satellite-based augmentation systems and ATS units. This paper will describe the status of the work so far and present preliminary ideas.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1173 - 1181
Cite this article:	Makins, R. Farnworth. N., Watt, A., Storey, J., "The Interface Between GNSS and Air Traffic Control," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 1173-1181.
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