What is ACAS ?
The Airborne Collision Avoidance System II (ACAS II) was introduced in order to reduce the risk of mid-air collisions or near mid-air collisions between aircraft. It serves as a last-resortsafety net irrespective of any separation standards. ACAS II is an aircraft system based on Secondary Surveillance Radar (SSR) transponder signals.ACAS II interrogates the Mode C and Mode S transponders of nearby aircraft (‘intruders’) and from the replies tracks their altitude and range and issues alerts to the pilots, as appropriate. Non-transponding aircraft are not detected.
Types of ACAS
- ACAS I Gives Traffic Advisories (TAs) but does not recommend any manoeuvres.
- ACAS II Gives Traffic Advisories (TAs) and Resolution Advisories (RAs) in the vertical sense (direction)
- ACAS III Gives TAs and RAs in vertical and/or horizontal directions
How does it works ?
You are flying into the EU? As of 01/12/2015 your aircraft needs to be equipped with the latest airborne collision avoidance system.
Subject matter and scope This Regulation lays down common airspace usage requirements and operating procedures for airborne collision avoidance to be fulfilled by:
(a) operators of aircraft referred to under Article 4(1)(b) and (c) of Regulation (EC) No 216/2008 undertaking flights into, within or out of the Union; and
(b) operators of aircraft referred to under Article 4(1)(d) of Regulation (EC) No 216/2008 undertaking flights within the airspace above the territory to which the Treaty applies as well as in any other airspace where Member States apply Regulation (EC) No 551/2004 of the European Parliament and of the Council
Definitions For the purposes of this Regulation the following definitions shall apply:
(1) ‘airborne collision avoidance system (ACAS)’ means an aircraft system based on secondary surveillance radar (SSR) transponder signals which operates independently of ground-based equipment to provide advice to the pilot on potential conflicting aircraft that are equipped with SSR transponders;
2)‘airborne collision avoidance system II (ACAS II)’ means an airborne collision avoidance system which provides vertical resolution advisories in addition to traffic advisories;
(3) ‘resolution advisory (RA) indication’ means an indication given to the flight crew recommending a manoeuvre intended to provide separation from all threats or a manoeuvre restriction intended to maintain existing separation;
(4) ‘traffic advisory (TA) indication’ means an indication given to the flight crew that the proximity of another aircraft is a potential threat.
Airborne collision avoidance system (ACAS)
1. The aeroplanes referred to in Section I of the Annex to this Regulation shall be equipped with and operated in accordance with the rules and procedures as specified in the Annex.
2. Member States shall ensure that operation of aeroplanes referred to in Article 1(2)(a) of Regulation (EC) No 216/2008 comply with the rules and procedures specified in the Annex in accordance with the conditions set out in that Article.
Special provisions applying to operators subject to Council Regulation (EEC) No 3922/91 (1)
1. By derogation from provisions OPS 1.668 and OPS 1.398 of Annex III to Regulation (EEC) No 3922/91, Article 3 and the Annex to this Regulation shall apply for operators of aeroplanes referred to in Article 1(a).
2. Any other obligation imposed on air operators by Regulation (EEC) No 3922/91 as regards the approval, installation or operation of equipment shall continue to apply to ACAS II.
Entry into force and application
1. This Regulation shall enter into force on the 20th day following its publication in the Official Journal of the European Union.
2. Articles 3 and 4 shall apply as of 1 March 2012.
3. By way of derogation from paragraph 2, in the case of aircraft with an individual certificate of airworthiness issued before 1 March 2012, the provisions of Article 3 and 4 shall apply as of 1 December 2015.
Original document : Download
source : EASA (European Aviation Safety Agency)
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