AIRBORNE COLLISION AVOIDANCE SYSTEMS CIRCULAR 4985 INTERNATIONAL ClVlt AVIATfDH ORGANlZAf lQN MONTREAL CAMADA ApprovM by fhe Secretary General and published under his aufborify
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FOREWORD At the ICAO Communications Divisional Meeting in April 1981, there was an extensive exchange of views regarding the evolution of secondary surveillance radar SSR and airborne collision avoidance systems. A number of recommendations were issued including the following RECOMMENDATION 112 - GUIDANCE MATERIAL RELATED TO DESIGN FEATURES AND OPERATIONAL CHARACTERISTICS OF AIRBORNE COLLISION AVOIDANCE SYSTEMS That ICAO a Reaffirm the guidance material developed by the Seventh Air Navigation Conference and contained in the appendix to the report on Agenda Item 7 of Doc 9004 AN-CONFl7. b - Add the following guidance material to that contained in paragraph a above i Ground-based air traffic services will continue to be the fundamental means for assuring aircraft separation. ii Compatibility and full integration with current world-wide air traffic services can be achieved best by optimum application of SSR techniques to the problem of ground- based collision prevention and of airborne collision avoidance. iii States developing ground-based collision prevention and airborne collision avoidance systems should take account of activities under way in States and international organizations to improve the SSR system by adding discrete/selective addressing and data link capabilities. iv States developing compatible SSR improvements and airborne collision avoidance systems should take account of air traffic densities likely to be encountered during the lifetime of these systems. The use of SSR Mode S signals for air-to-air collision avoidance information exchange should be considered as a leading candidate signal format to assure the highest integrity of that communication link.
RECOMMENDATION 113 - ICAO FUTURE ACTIVITY ON SSR IMPROVEMENTS AND COLLISION AVOIDANCE SYSTEMS That a States and international organizations in a position to do so, provide ICAO with technical descriptions and other related operational and technical information covering SSR improvements to provide for improved surveillance capability, discrete addressing of aircraft arid an integral automated data communication capability. b ICAO use the material provided as the result of a above to publish an ICAO circular. c ICAO, in parallel with the above activity, establish an appropriate body to develop Standards, Recommended Practices, guidance material and procedures related to SSR enhancement and related data link and collision avoidance systems. The guidance material referenced above was contained in the report of the Seventh Air Navigation Conference 5 to 28 April 1972 as follows GUIDANCE MATERIAL RELATING TO DESIGN FEATURES AND OPERATIONAL CHARACTERISTICS OF AIRBORNE COLLISION AVOIDANCE SYSTEMS ACAS a Airborne collision avoidance systems must be fully compatible with ground ATC systems, and may need to provide for the automatic alerting of ATC units to any manoeuvres performed by aircraft as a result of ACAS operations. b The design and construction of equipments comprising an ACAS must be such that the system is capable of economic and practicable fitment, in all relevant classes of aircraft. Systems involving the use of different levels of performance characteristics to suit aircraft of different categories must be capable of compatible operation. c Avoidance manoeuvre indications given to pilots by ACAS equipment must at all times be compatible with individual aircraft performance capabilities in all relevant flight phases, and must be presented in real time. d The avoidance manoeuvre computation and selection processes inherent in the system must be capable of originating appropriate avoidance manoeuvre indications at least in the vertical plane. It is desirable that the avoidance manoeuvre indication capability also comprises the horizontal plane to increase system flexibility. e Manoeuvres initiated as a result of ACAS indications must not result in unsafe reduction of separation between affected aircraft and other "non-conflicting" aircraft operating in the same air traffic environment.