Summary of Requirements

ATM depends upon its surveillance infrastructure. Ensuring that the surveillance data provided depends upon a comprehensive set of requirements.Such requirements include the performance of the surveillance system itself but also upon the equipment carried on board the aircraft and ensuring interoperability between all components in the surveillance chain. Legislative requirements underpin all of the above.

The following pages expand upon the requirements that must be met for a safe and efficient surveillance infrastructure.

Performance Requirements

Surveillance data is an essential tool for the efficient execution of Air Traffic Control in a demanding environment.

Specifications with the aim of achieving the optimal use of the air traffic surveillance function and the harmonised application of separation minima have been produced. These can be found in the library section of this website.

Avionic Requirements

To conduct flights in European airspace an aircraft may be required to be equipped with a range of avionics. The airspace requirements are published in Aeronautical Information Publications supplemented by Aeronautical Information Circulars. States requirements are being supplemented by European wide legislation introduced by the European Commission. See next tab for further details.

It is important that aircraft operators are in compliance with avionic requirements including ACAS, SSR transponders, SSR Mode S transponders and, in the near future, ADS-B Extended Squitter. You may find a summary of requirements here under our Avionics requirements section.

It is the legal responsibility of an aircraft operator to ensure that the aircraft is appropriately equipped and certified in accordance with the airspace in which the flight will be conducted.

It is the legal responsibility of an aircraft operator to ensure that the aircraft is appropriately equipped and certified in accordance with the airspace in which the flight will be conducted. Please also note that in order to operate in airspace designated as Reduced Vertical Separation Minima (RVSM) that additional airframe and operational approvals may be required – please see EUR RMA for further details.


The Surveillance and Code Coordination Unit provides impartial advice and expert support to the stakeholders in areas such as the definition of strategies, the development of technical specifications, the writing of procurement documents and the development of safety cases. In this context, the Surveillance and Code Coordination Unit has provided the technical expertise to draft implementing rules (IRs) for surveillance performance and interoperability (SPI), for the use of aircraft identification (ACID) and for Mode S interrogator code allocation (MSI). Indeed, with regard to the last example, EUROCONTROL has agreed to provide the Mode S interrogator codes allocation service to the ICAO European Region and Middle Eastern Region Service Providers.

Links to European Commission Implementing Regulations can be found here.

Surveillance Performance and Interoperability Implementing Regulation

For further details please refer to the Aircraft Equipage Requirements in the European Commission IRs 1207/2011 and 1028/2014.

Aircraft Identification Implementing Regulation (ACID IR)

The legislation stemming from the ACID IR (see European Commission Regulation 1206/2011) establishes a progressive requirement to use the downlinked aircraft identification data item for unambiguous and continuous individual identification of aircraft within the EATMN airspace with the main objective being to progressively eliminate the issue of discrete Mode A code shortage within the EATMN.

This requirement will progressively extend from 9 February 2012 for a limited number of member states and in a limited proportion of their airspace representing at least 50% of the flights flying in their airspace up to 2 January 2020 for all member states in all their airspace.

The use of the aircraft identification data item will initially be limited to the aircraft being capable of down-linking that data item and provided that the flight is entirely located in an area where aircraft identification is supported. In the second phase, the Central Flow Management Unit (CFMU) will flag those aircraft coming from non-ACID areas but which land in ACID areas.

When a flight matches the above criteria, a Mode A conspicuity code (e.g. 1000) will be assigned to that aircraft, otherwise the aircraft will be assigned with a discrete Mode A code and will be identified on that basis.

The implementation of the ACID IR will progressively phase-out all classical and monopulse SSR that are not able to downlink the aircraft identification data item and that are also less efficient in terms of transponder occupancy and in terms of RF spectrum (1030-1090 MHz bands) usage.

Due to the increasing implementation of Mode A conspicuity code within the EATMN airspace, it is also likely that classical and mono-pulse SSR that are not part of the EATMN (e.g. those used for air defence or some military ATC purposes) will no longer be usable anymore and will therefore also be decommissioned.

MODE-S Interrogator Code Implementing Regulation (MSI IR)

The scope of the legislation stemming from the MSI IR (see European Commission Regulation 262/2009) is all Mode S interrogators operating within the EATMN.

The objective of the legislation is to provide a solid legal support to the coordinated process of allocation of Mode S interrogator codes within the EATMN and to alleviate the interrogator code shortage issue within the EATMN by requiring Mode S ground interrogator to support the use of II/SI code operation.

The legislation specifies:

  • The process for the coordinated allocation of interrogator code to operational Mode S interrogator,
  • The monitoring process to verify that the interrogator codes are set as the result of the coordinated allocation process and that the Mode S interrogators operating in the member states but outside the EATMN are using their reserved interrogator codes,
  • The requirements on Mode S interrogator to support the use of II/SI code operation.


A fundamental requirement for surveillance systems is global interoperability.

A surveillance system is composed of many components including avionics, ground stations and multi-sensor trackers, with interfaces to the ATM and sensor systems, etc. Therefore a systematic approach is needed to ensure that the functionality and performance delivered by each constituent part contributes effectively to the overall system requirements. Standardisation at international level is the means of achieving this, and EUROCONTROL has a principal role in this process.

Examples of existing operational and technical standards in which EUROCONTROL has taken a leading role include ICAO documentation (ASP, SASP, etc.), SPR/INTEROP and MOPS for ADS-B applications and systems by EUROCAE/RTCA, acceptable means of compliance (AMCs) or certification specifications (CS) by EASA, and the EUROCONTROL ASTERIX data format. Other pages on this website provide further details.

The Surveillance and Code Coordination Unit is ideally placed to support standardisation activities. It integrates operational matters and technical constraints, interfaces avionics and ATC systems, and provides a focal point for the views of stakeholders such as ANSPs, regulators, aircraft operators, standardisation authorities and industry; it ensures that the pieces in the “surveillance jig-saw” all fit seamlessly together.

Surveillance and Code Coordination (SCC) Unit

For further information on this subject please contact us.