ACAS Regulation and Procedures

ACAS Regulation and Procedures

TCAS Regulation and Procedures


Regulation and Procedures

Recent operational experience confirms the importance of Airborne Collision Avoidance System (ACAS) regulation and correct use of related procedures. ACAS procedures and pilot training guidelines are included in ICAO Doc 8168 (PANS-OPS), while those for controllers are contained in ICAO Doc 4444 (PANS-ATM). In Europe, EU-OPS contains provisions for the use of ACAS.

The European Safety Programme (ESP) requires, as a high priority, action to be taken by aviation regulatory authorities, air navigation service providers, and airspace users to confirm that these ACAS regulations and procedures are correctly implemented and applied.

Every effort must be made to ensure that the relevant operations manuals include up-to-date ACAS procedures, and that appropriate training is provided to ensure that pilots and controllers are able to apply these standard ACAS procedures consistently.

Equipage Requirements

Amendment 85 to ICAO Annex 10 volume IV, published in October 2010, introduced a provision stating that:

  • all new ACAS installations after 1 January 2014 shall be compliant with version 7.1; and
  • all ACAS units shall be compliant with version 7.1 after 1 January 2017.

On 20 December 2011, the European Commission published an Implementing Rule, subsequently amended on 16 April 2016, mandating the carriage the carriage of ACAS II version 7.1 within European Union airspace earlier than the dates stipulated in ICAO Annex 10:

  • by all aircraft with a maximum certified take-off mass exceeding 5,700 kg or authorised to carry more 19 passengers from 1 March 2012;
  • with the exception of aircraft with an individual certificate of airworthiness issued before 1 March 2012 that must be equipped as of 1 December 2015;
  • aircraft not referred above but which will be equipped on a voluntary basis with ACAS II, must be equipped with version 7.1.

For additional details read the article on SKYbrary: Regulation 1332/2011 for laying down common airspace usage requirements and operating procedures for airborne collision avoidance

ACAS Procedures Concerning Pilots


ICAO Doc 8168 (PANS-OPS), Chapter 3 contains procedures for the use of ACAS. For full information operators should refer to that document, and to the attachment, "ACAS Training Guidelines for Pilots".

Within Europe, procedures for the use of ACAS should follow the complementary instructions contained in EU-OPS and the associated JAA ACJs, relevant extracts from which appear below.

EU-OPS 1.398 - Use of Airborne Collision Avoidance System (ACAS) (See also ACJ EU-OPS 1.398)

"An operator shall establish procedures to ensure that:

(a) When ACAS is installed and serviceable, it shall be used in flight in a mode that enables Resolution Advisories (RA) to be produced unless to do so would not be appropriate for conditions existing at the time.

(b) When undue proximity to another aircraft (RA) is detected by ACAS, the commander or the pilot to whom conduct of the flight has been delegated must ensure that any corrective action indicated by the RA is initiated immediately, unless doing so would jeopardize the safety of the aeroplane.

The corrective action must:

(i) Never be in a sense opposite to that indicated by the RA.

(ii) Be in the correct sense indicated by the RA even if this is in conflict with the vertical element of an ATC instruction.

(iii) Be the minimum possible to comply with the RA indication.

(c) Prescribed ACAS ATC communications are specified.

(d) When the conflict is resolved the aeroplane is promptly returned to the terms of the ATC instructions or clearance."[1]

EU-OPS 1.420 (d) 2. - Occurrence Reporting

"Airborne Collision Avoidance System Resolution Advisory. A commander shall notify the air traffic service unit concerned and submit an ACAS report to the Authority whenever an aircraft in flight has manoeuvred in response to an ACAS Resolution Advisory. [2],

EU-OPS 1.668 - [Carriage of] Airborne Collision Avoidance System (see also IEM OPS 1.668)

"An operator shall not operate a turbine powered aeroplane having a maximum certificated take-off mass in excess of 5700 kg or a maximum approved passenger seating configuration of more than 19 unless it is equipped with an airborne collision avoidance system with a minimum performance level of at least ACAS II."[3]

ACAS Procedures Concerning Controllers

ICAO Doc 4444 (PANS-ATM), Chapter 15 contains procedures in regard to aircraft equipped with ACAS. Chapter 12 contains the relevant phraseologies. For full information refer to that document.

The following are relevant extracts from Chapter 15:

  • When a pilot reports a manoeuvre induced by an ACAS RA, the controller shall not attempt to modify the aircraft flight path until the pilot reports returning "Clear of Conflict".
  • Once an aircraft departs from its ATC clearance or instruction in compliance with an RA, or a pilot reports an RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft affected as a direct consequence of the manoeuvre induced by the RA. The controller shall resume responsibility for providing separation for all the affected aircraft when:

a) the controller acknowledges a report from the flight crew that the aircraft has resumed the current clearance; or

b) the controller acknowledges a report from the flight crew that the aircraft is resuming the current clearance and issues an alternative clearance which is acknowledged by the flight crew.

Note - The phraseology to be used by controllers and pilots is contained in Chapter 12 (of the same ICAO document).

Related Articles

Regulation 2016/583

Related Media


  1. ^ EU-OPS 1.398
  2. ^ EU-OPS 1.420
  3. ^ EU-OPS 1.668

Further Reading

Details of courses and training material available from EUROCONTROL may be found on the ACAS website


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