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Non ACAS-Equipped Aircraft Operations

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Non TCAS-Equipped Aircraft Operations

Article Information
Category: Safety Alert Safety Alerts
Content source: EUROCONTROL Safety Alerts EUROCONTROL

Safety Reminder Message

Non ACAS-Equipped Aircraft Operations

Date: 21 December 2009 Safety Reminder Message.gif


This Safety Reminder Message is prompted by a recent incident involving an ACAS-equipped aircraft and a non ACAS-equipped aircraft.

Currently ACAS II shall be carried and operated in the EUR region (including FIR Canarias) by all civil fixed-wing turbine-engined aircraft having a maximum take-off mass exceeding 5700 kg or a maximum approved passenger seating configuration of more than 19. However, the provisions of Minimum Equipment List (MEL) allow ‘mandated’ aircraft to operate without ACAS II in specified circumstances (see below). In addition, it is possible to obtain temporary exemptions from ACAS II MEL requirements for certain categories of flight (see below).

Therefore, ATC may experience situations where participating traffic has serviceable, unserviceable ACAS or even is non-ACAS equipped.


Air traffic controllers are reminded that aircraft type is not necessarily a guarantee of serviceable ACAS equipment. At any one moment in time, an unspecified number of aircraft (‘mandated’ and ‘non-mandated’) will be operating in European airspace without an operational ACAS II system. This should not have an effect on the controllers as it is stated in the ICAO PANS ATM (Doc 4444) ( provisions:

“The procedures to be applied for the provision of air traffic services to aircraft equipped with ACAS shall be identical to those applicable to non-ACAS-equipped aircraft. In particular, the prevention of collisions, the establishment of appropriate separation and the information which might be provided in relation to conflicting traffic and to possible avoiding action should conform with the normal air traffic services procedures and should exclude consideration of aircraft capabilities dependent on ACAS equipment”.

Aircraft Operators - ACAS II MEL Requirements

With the exception noted below, the MEL requirement for ACAS II throughout Europe is 10 days (excluding the day of failure discovery). Operation under the terms of the EASA-OPS 1 ACAS II MEL has been agreed and accepted by the ECAC Member States. JAA TGL 26 (which is still applicable) states that ACAS II "may be inoperative provided the system is deactivated and secured, and repairs or replacements are carried out within 10 calendar days. Note: Local Authorities may impose a more restrictive rectification interval days.”

Additional MEL requirements concerning partial failures are also listed in the TGL 26.

Note: The actual MEL period applicable to an aircraft is set by the National Authority of the aircraft operator, but if longer than 10 days it would cause operational issues for flight in European airspace. In German airspace the time period during which ACAS II may be inoperative is reduced to 3 days (refer to German AIP GEN 1.5 para. 5). This applies to all aircraft. In Europe, there is no requirement to notify ATC or to make a remark in the flight plan about ACAS II being inoperative. There are different requirements outside Europe, e.g. India, where ACAS equipage needs to be stated in the flight plan. Please refer to the individual States authorities for more information.


ACAS II equipage exemptions must be requested directly from the national regulatory authorities of all countries whose airspace the flight will enter. From 1 January 2010 EUROCONTROL will no longer process any ACAS II exemption requests, including those for delivery or maintenance flights.

Exemptions for any reason must be requested directly from the regulatory authorities of all countries whose airspace the flight will enter.

Your Attention Is Required

Please note the subject and investigate the relevance in your operational environments. Share your experiences concerning the issues described.

Further Reading

  • EUROCONTROL Mode S and ACAS Programme Website - ACAS II Safety Bulletins, Equipage Requirements, FAQs etc.
  • ICAO Doc - 4444 - PANS ATM.
  • ICAO Doc - 8186 - PANS OPS.
  • ICAO Doc - 9863 - ACAS Manual.
  • JAA TGL 26


© European Organisation for Safety of Air Navigation (EUROCONTROL) December 2009. This alert is published by EUROCONTROL for information purposes. It may be copied in whole or in part, provided that EUROCONTROL is mentioned as the source and to the extent justified by the non-commercial use (not for sale). The information in this document may not be modified without prior written permission from EUROCONTROL. The use of the document is at the user’s sole risk and responsibility. EUROCONTROL expressly disclaim any and all warranties with respect to any content within the alert, express or implied.