Acas

WP-6.1– ACAS brochure ACASA/WP6.1/015

26-01-1999 Version 1.0

ACAS II Programme
NOTE

This document is designed for the training of people involved in the implementation and the use of the Airborne Collision Avoidance System (ACAS). However, it is not, per se, designed for the complete training of controllers or pilots. The principal and essential technical and operational features ofACAS are introduced. For a deeper knowledge, the reader is advised to refer to ICAO and RTCA documentation listed in the bibliography section.

John Law ACAS Programme Manager

ACAS Programme

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WP-6.1– ACAS brochure ACASA/WP6.1/015

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This brochure has been translated and adapted, in the framework of the European Project: ACASA (ACAS Analysis), from adocument produced by CENA (Centre d’ Etudes de la Navigation Aérienne - France), entitled “ Livret d’ information ACAS ” .

CENA and EUROCONTROL have contributed to the development of this document.

ACAS Programme

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TABLE OF CONTENTS

CHAPTER I : GENERAL INTRODUCTION ⇒ ⇒ ⇒ ⇒ ⇒ Historical background ACAS principles Typesof ACAS TCAS II development Towards a world-wide mandatory carriage

4 4 4 4 5 5 6 6 6 10 10 11 12 13 14 14 15 16 16 17 21

CHAPTER II : TECHNICAL DESCRIPTION OF TCAS II ⇒ System components ⇒ Cockpit presentation CHAPTER III : ACAS IN THE OPERATIONAL ENVIRONMENT ⇒ ⇒ ⇒ ⇒ Regulations Operational use Training Examples of conflicts solved by TCAS

CHAPTER IV : TARGET SURVEILLANCE ⇒ Thesurveillance function ⇒ Interference limiting CHAPTER V : THE COLLISION AVOIDANCE LOGIC ⇒ Principle ⇒ CAS functions CONCLUSION
Bibliography Abbreviations

ACAS Programme

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WP-6.1– ACAS brochure ACASA/WP6.1/015

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General introduction
Historical background
Over the years, air traffic has continued to increase. The developments of modern air traffic control systemshave made it possible to cope with this increase, whilst maintaining the necessary levels of flight safety. However, the risk of airborne collision remains. That is why, as early as the fifties, the concept and initial development of an airborne collision avoidance system, acting as a last resort, was being considered. A series of mid air collisions occurred in the United States, initiating thefurther stages of the system’ development. s • In 1956, the collision between two airliners, over the Grand Canyon, spurred both the airlines and the aviation authorities to continue the system development studies. • In 1978, the collision between a light aircraft and an airliner over San Diego led the FAA (Federal Aviation Administration) to initiate, three years later, the development of TCAS(Traffic alert and Collision Avoidance System). • Finally, in 1986, the collision between a DC-9 and a private aircraft, at Cerritos, required the FAA, based on a Congressional mandate, to issue, in 1989, new aviation legislation, which required some categories of American and foreign aircraft to be equipped with TCAS for flight operations in US airspace. In parallel to the development of TCASequipment, ICAO (International Civil Aviation Organisation) has developed, since the beginning of the eighties, standards for Airborne Collision Avoidance Systems (ACAS). The main feature of ACAS, which was first proposed by Dr John S. Morell in 1955, is that it functions according to time criteria and not distance. From several successive replies, ACAS calculates a time to reach the CPA (Closest Pointof Approach) with the intruder, by dividing the range by the closure rate. This time value is the main parameter for issuing alerts and the type of alert depends on its value. If the aircraft transmit their altitude, ACAS also computes the time to reach co-altitude. ACAS can issue two types of alert: • Traffic Advisories (TAs), which aim at helping the pilot in the visual search for the intruder...