Transponder code function

Aircraft are identified by Secondary Surveillance Radar (SSR) using transponder codes comprised of four digits (0-7). These codes are assigned following the International Civil Aviation Organisation's (ICAO) Originating Region Code Assignment Method (ORCAM). ORCAM is based on the strategic allocation of sets of codes to individual States and on the alternate use of transit and local definitions of codes per participating area (PA). This allows the same codes to be used for transit in one PA and for local purposes in adjacent PAs. Together they cover the entire ICAO EUR Region.

However, this structure fails to provide sufficient SSR codes for today’s demand (due to increased levels of traffic and also changes in traffic flows). Besides, the current structure has difficulties coping with Functional Airspace Blocks (FABs) and direct routes.

At EUROCONTROL, in our capacity as Network Manager (NM), we provides efficient SSR code allocation to cope with increasing air traffic and changes in traffic flows, mitigating the limitations of the existing ICAO Originating Region Code Assignment Method (ORCAM).

As part of our transponder code function (TCF), we, as NM, manage transponder codes and provide associated services in accordance with the Single European Sky (SES) regulatory framework, international obligations and high-level agreements between ICAO, the European Union and EUROCONTROL. It is a specific service carried out on behalf of ICAO.

Our work is driven and supported by the aircraft identification (ACID) and the Network Management function implementing rules, as well as by ICAO and EU agreements for non-EU States.

We also provide ORCAM support to all ICAO EUR Region States on behalf of the ICAO EUR/NAT Paris Office, as agreed under the Memorandum of Cooperation between EUROCONTROL and ICAO. We maintain the SSR Code Allocation List for the ICAO EUR Region (CAL) documents on behalf of the EUR/NAT office as an attachment to EUR Doc 023. The document contains the agreed allocation of SSR codes to States and air traffic system (ATS) units.