Data received from geographically dispersed radars, either primary (2D) or secondary (3D), are the only input information which qualify modern civil air traffic control (ATC) systems to automatically update central tracks of each surveilled aircraft. In this sense, it is envisaged that the introduction and operation of automatic dependent surveillance (ADS), will have a considerable impact on future ATC performance and procedures. The ADS is a function whereby the aircraft flight management computer (FMC) automatically transmits to ground facilities, via a VHF, Mode S or satellite data link, navigational and meteorological data derived from on-board avionics equipment, including aircraft identification and three-dimensional position and speed. In oceanic and large continental areas with limited surveillance availability, the ADS function will be the only reliable means of supporting an automated tactical tracking function. Reformulated radar data fusion methods, extended to the multisensor and ADS case, are presented. The problem of optimally combining the information coming from the ADS-equipped aircraft and from en-route and/or approach radars is addressed, and a practical open-loop mode of operation of the ADS function, both in situations with and without radar coverage, is proposed.
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