International Civil Aviation Organization

World-wide CNS/ATM Systems

Implementation Conference

Rio de Janeiro, 11 – 15 May 1998

International Civil Aviation Organization

World-wide CNS/ATM Systems

Implementation Conference

Rio de Janeiro, 11 – 15 May 1998

WW/IMP–WP/40

11/5/98

Item 1

Agenda Item 1:	Overview of CNS/ATM systems implementation

SURVEILLANCE SYSTEMS

(Presented by the Secretariat)

Information Paper

1.	Introduction

1.1	Two main surveillance techniques are included in the CNS/ATM systems concept: independent and dependent surveillance. In independent surveillance, the aircraft position is determined by the ground system and then transmitted to the air traffic control (ATC). In dependent surveillance, the aircraft position is determined on board and then transmitted to ATC.

1.2	Independent surveillance is based on primary surveillance radar (PSR) and/or secondary surveillance radar (SSR). The automatic dependent surveillance (ADS) makes use of digital communications to downlink position information.

2.	Radars: PSR and SSR

2.1	There is no need for ICAO Standards and Recommended Practices (SARPs) for PSR considering that compatibility and performance issues applicable to most aeronautical systems are not relevant in the case of PSR. Guidance Material on testing of PSR systems is provided in the Manual on Testing of ATC Radar Systems (Doc 8071, Volume III).

2.2	SARPs for SSR are contained in Annex 10 – Aeronautical Telecommunications, Volume IV – Surveillance Radar and Collision Avoidance Systems, including the technical characteristics of the system for the ground station and the airborne equipment for SSR Mode A/C and SSR Mode S. Guidance Material on SSR systems is contained in the Manual of Secondary Surveillance Radar (SSR) Systems (Doc 9684).

2.3	Mode S air-ground data link is an inherent part of the SSR Mode S. SARPs for the SSR Mode S data link (Mode S network) are contained in Annex 10 – Aeronautical Telecommunications, Volume III – Communication Systems, Part I – Digital Data Communication systems. This data link is a means of performing an interchange of digital data through the use of SSR Mode S interrogators and transponders, in accordance with the protocols compliant to the aeronautical telecommunication network (ATN). These SARPs also define a stand alone mode of Mode S data link operation known as the Mode S specific services. Guidance Material is contained in the Manual on Mode S Specific Services (Doc 9688).

3.	ads and ads-broadcast (ads-b)

3.1	In addition to providing aircraft position and intent information in areas where radar-based surveillance is not feasible or available, ADS will find beneficial application in other areas, where it may serve as an adjunct and/or back-up for radar-based surveillance. SARPs for ADS and related procedures are being included in Annex 2 – Rules of the Air and Annex 11 – Air Traffic Services to become applicable on 5 November 1998 and related provisions are combined in the Procedures for Air Navigation Services – Rules of the Air and Air Traffic Services (PANS-RAC, Doc 4444).

3.2	ADS-B is an expansion of the ADS technique. ADS-B equipped aircraft broadcasts its position and relevant data derived from on-board equipment. Any user either airborne or ground-based, within range of this broadcast can process the information. ADS-B is currently defined only for line-of-sight operations (e.g. over VHF digital link or SSR Mode S extended squitter). SARPs for the Mode S extended squitter technique have been developed for ADS-B use in a compatible manner with current SSR transmissions. These SARPs are being included in Annex 10 – Aeronautical Telecommunications, Volume IV – Surveillance Radar and Collision Avoidance Systems to become applicable on 5 November 1998.

4.	Status

4.1	Although the use of PSR is declining, it will continue to be needed in areas where there is a mix of SSR transponder-equipped aircraft and non-SSR transponder-equipped aircraft, in order to provide compatible services to both categories.

4.2	SSR is in wide use in many parts of the world and its stand-alone applications for the provision of air traffic services has been adopted. The accuracy and over-all performance of position information (range and azimuth) is improved by the application of monopulse techniques and/or the use of large vertical aperture antennas. With Mode S, the selective address and data link capabilities will further enhance the role of SSR for surveillance purposes.

4.3	SSR Mode S stations are being implemented in several States. In other States, a two-step implementation has been preferred, which is to upgrade/renew conventional SSR stations with the monopulse technique as a first step, and to change to Mode S in a second step.

4.4	ADS is being implemented for some oceanic routes. Trials and validation of ADS-B are being conducted in a number of States.

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