• Surveillance (Including SSR) Policy, Regulation, Legislation & Allocation. National IFF/SSR Committee & S&SWG Secretariat. Chairman of CAA Mode S Working Group. Spectrum & frequency management for the aeronautical frequency bands. Comms & Navaids. UK aviation representative FM study group. ICAO ACP International Telecommunications Union (ITU), IFF/SSR Frequency Approvals. Spectrum & frequency management, planning frequency bands for civil & military. Liaison with HM Government, Department of Trade & Industry, DfT, MOD & special organisations on IFF/SSR, frequency management, regulation & protection. 

    ​Spectrum Release Programme

    As part of Government plans to release a proportion of public sector spectrum by 2020 for commercial use, such as for mobile broadband, the UK Civil Aviation Authority (CAA) has been tasked with assessing the possibility of safely reducing the aviation industry’s reliance on the bandwidth reserved for air traffic control radar. A major research programme will look at the feasibility of releasing 100MHz of the 2.7GHz–2.9GHz band currently being used for civil and military primary surveillance radars. 

  • Background 

    The UK Government plans to release at least 500 MHz of public sector spectrum below 5 GHz before 2020 to meet the demand from commercial services, such as mobile communications including broadband. The Department for Culture, Media and Sport published a consultation document "Enabling UK Growth - releasing public spectrum" in which it laid down the strategy for spectrum release. The document identified the 2.7-2.9 GHz and 2.9-3.1 GHz frequency sub-bands as priorities for further investigation, which are currently occupied by Primary Surveillance Radar used to support aviation, maritime, and military security tasks.

    In 2012, the CAA provided the Department for Transport with an initial feasibility assessment of potential options for releasing spectrum in the 2.7-2.9 GHz band (S band). On the basis of this assessment, the DfT supported by CAA recommendations concluded that there was sufficient potential and benefits to proceed with a programme of research for spectrum release S band. However, it was recognised that before any spectrum release could be formally supported and delivered, there would need to be extensive development trials work carried out. This is the basis for the current feasibility phase.  

    Programme context 

    The CAA is now conducting research in support of the Government's Spectrum Release Programme to investigate possible reductions in spectrum occupancy by PSR.  As part of this activity, the CAA is evaluating viability of frequency re-planning for current PSR assets, and the viability of emerging technologies that enable CAA and aviation stakeholders to achieve the need for non-cooperative surveillance while using radio spectrum more efficiently. 

    Potential wider benefits of emerging surveillance technologies

    The CAA's aim within the programme is to assess the feasibility of replacing S-Band air traffic control radars with new independent non-cooperative surveillance systems that provide benefits such as:

    • Improved coverage and detection capability
    • Reduced operating costs
    • A more cost-effective and strategic wind turbine mitigation solution
    • Higher surveillance data update rates
    • Improved redundancy and scalability
    • Long-term spectrum-efficiency


    Regular allocations

    SSR codes can be requested for prolonged use by air traffic control services or for aircraft identification.

    We need the following information by email or post to start assessing the request:

    • Name of organisation requiring codes
    • Details of any codes already allocated to that organisation
    • Number of codes required
    • Details of preferred codes
    • Requirement for codes. For example, a Police Air Support Unit requesting a single code for discrete aircraft identification, or an ANSP requesting a set of codes for air traffic control

      • If requesting a code for discrete identification, the areas of operation of any aircraft wearing that code should be provided

      • If requesting codes for air traffic control, details of the current and future number of movements to be handled by the ANSP

    • Name and telephone contact details

    The application and assessment process can take up to four months.

    The allocation of a code or set of codes does not imply any right over its continued use and it may be necessary to withdraw or reallocate codes to effectively manage requirements.

    Temporary allocations

    SSR codes can also be requested for temporary allocation, for example for military exercises or civil aviation air shows.

    Temporary requests should be submitted at least one month before the proposed use of the temporary code using the SSR NOTAM Application Form which can be posted or faxed to us.

    There are a finite number of codes available so we cannot guarantee allocations.

    Transponder Carriage Requirements are published in UK AIP -  GEN 1.5 - Aircraft Instruments, Equipment and Flight Documents. 

    General Mode S enquiries can be submitted to mode.s@caa.co.uk

    24-bit Aircraft Addresses

    The provision of Air Traffic Services (ATS) in an SSR Mode S environment relies on a unique ICAO 24-bit Aircraft Address (24-bit AA) for selective interrogation of individual aircraft.  The 24-bit AA is also an essential element of the airborne collision and avoidance system, ACAS II. 

    Civil Aircraft

    An ICAO 24-bit aircraft address is automatically allocated to every UK registered aircraft as part of the process to register the aircraft regardless of whether the individual aircraft is fitted with a Mode S transponder.  Applicants will be advised of their allocated aircraft address in accordance with the Aircraft Registration service standards, following receipt of the application to register their aircraft.  For details of how to  register an aircraft please refer to the Register an Aircraft page of the Aircraft Registration section of the CAA website.

    Automatic allocation of ICAO 24-bit aircraft addresses simplifies administration and saves the operator from having to make separate applications to the Applications & Approvals Department solely for the assignment of addresses. 

    All aircraft currently registered that have not previously requested the issue of an address have now had an address assigned to them.  Details of allocated addresses are available via the G-INFO UK Register database.

    If an operator needs an ICAO 24-bit aircraft address for a civil aircraft in the UK that is not required to be UK registered (such as Annex II gliders operated through the British Gliding Association scheme) please contact the Aircraft Registration Section for further details and include details of the aircraft concerned using the details below:

    020 7453 6666 - tel
    020 7453 6670 - fax          

    State Aircraft/Other Uses

    The CAA is responsible for the policy and overall management of 24-bit AAs and also deals with all other requests for 24-bit AAs, such as:

    • Assignment to State aircraft
    • SSR interrogator site monitors (Far Field Monitors and Ground-based transponders)
    • Multilateration systems (airfield and off-shore)
    • Satellite Communications Base Stations (Inmarsat)
    • Test & Development (T&D)

    All requests for 24-bit AAs in the UK that are NOT for civil aircraft should be addressed to:

    020 7453 6536 - tel
    020 7453 6565 - fax

    24-bit AAs and Aircraft Identification Reporting

    There are strict requirements regarding what information is entered in to a transponder and broadcast as aircraft identification (Ac ID), sometimes referred to as Flight Identity (Flt ID).  The correct setting of Ac ID is essential to ensure safety and for the correlation of radar tracks with flight plan data in ATM and Airport operator ground systems.  Aeronautical Information Circular AIC 101/2007 (Yellow 250) details how 24-bit AAs must be entered/hardwired into an aircraft transponder and what information and in what format must be entered as Ac ID/Flt ID in the transponder.  This information is also provided in the En Route (ENR) section, paragraph 1.6.2, of the UK Aeronautical Information Publication (AIP).

    Emergency Locator Transmitters (ELTs)

    24-bit AAs assigned to civil aircraft for use with a Mode S transponder may also be used in aircraft Emergency Locator Transmitter (ELT) systems.  Further details are available in AIC 57/2003 (Pink 55). However, it should be noted that operators who choose to use their Mode S transponder 24-bit AA as the unique identification for their ELT are still required to register it separately with the Maritime and Coastguard Agency in accordance with the AIC:

    01326 211569 - tel
    01326 319264 - fax

    CAP 761 sets out the application procedures and the basic planning principles that will be applied before approval of any new interrogator installation or changes to an existing approved interrogator installation.

    DAP 1910 - Application to Operate a Secondary Surveillance Interrogator in the United Kingdom - Ground Based Platform

    DAP 1911 - Application to Operate a Secondary Surveillance Interrogator in the United Kingdom - Maritime or Airborne Platform

    DAP 1912 - Application to Operate ACAS (TCAS) within the United Kingdom - Note: Certain types of equipment are now covered by a generic approval and an application may not be necessary; even if an approval was required previously. Check CAP 761 before submitting a new/renewal application.

    DAP 1913 - IFF/SSR Interference Reporting Form