• Overview

    Radio spectrum covers the part of the electromagnetic spectrum that are used for a wide range of wireless telecommunications. Aviation is a major user of radio spectrum for communications, navigation and aeronautical surveillance (e.g. radar). Radio spectrum is a finite, scarce, resource and therefore we have a responsibility to ensure that it is used safely and efficiently.

    The International Telecommunications Union

    To prevent interference between different users, the use of the radio spectrum is coordinated by an international body, the United Nation’s International Telecommunication Union (ITU) and contracting States are required to ensure compliance with these requirements, typically through national legal instruments and enforcement. The ITU maintains the Radio Regulations, which among other things define:

    • the allocation of different frequency bands to different radio services;
    • technical parameters to be observed by radio stations, especially transmitters;
    • procedures for coordination and notification of frequency assignments by States

    The process of dividing up the frequency spectrum resource is handled through the ITU World Radio Conference (WRC). A WRC is held every three to four years. It is the job of WRC to review, and, if necessary, revise the  Radio Regulations.

    Our role in spectrum

    Under agreement with Ofcom and the Ministry of Defence, we are the band manager for several sets of radio spectrum frequencies, including:

    • 117.975 – 137.000 MHz (VHF Aeronautical communications
    • 960-1164 MHz (Distance Measuring Equipment and Secondary Surveillance Radar
    • 2.7-2.9 GHz (Primary Surveillance Radar)

    As band manager, we assign frequencies for UK aeronautical use in these bands and ensure that users of this band meet the safety requirements of the aeronautical sector, including the UK’s international obligations under ICAO. We also co-ordinate use of these spectrum bands in the UK with military users as part our wider shared airspace responsibilities.

    Liaison with Eurocontrol

    In accordance with the Network Management Implementing Rule, the CAA coordinates with the Network Manager in Eurocontrol over the the management of radio frequencies within aviation frequency bands and radar transponder codes to enable ATM to function effectively. The frequencies and transponder codes are limited in availability and are planned centrally by the Network Manager.

    Examples of what we do

    700 MHz clearance and Programme Making and Special Events

    The 700 MHz band is currently used to deliver Digital Terrestrial Television (DTT) services. In addition, many wireless microphones used at events such as concerts and theatre performances ('audio Programme Making and Special Events (PMSE)' devices) also transmit in the 700 MHz band.

    The use of the 700 MHz band is changing to enable the delivery of mobile data services in this band. This aligns with a number of other countries plans that already use or plan to use the band for mobile data, allowing economies of scale in the manufacture of equipment (e.g. mobile phones) and reliability and interoperability for consumers wherever in the world you are.

    Ofcom has developed detailed access arrangements for sharing spectrum allocated to aeronautical systems with audio PMSE and a safety support case for the operation of PMSE equipment in the band, as this represents a potential change to the Radio Frequency environment in which aeronautical systems are operating.

    Joint CAA/Ofcom Communication on PMSE sharing of the 960-1164MHz band

    PMSE workshop material and stakeholder comments on draft safety support case

  • 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

    Please send this information to:

    Policy Lead CNS
    Future Safety, 2W Aviation House
    Gatwick Airport South,
    West Sussex
    H6 0YR
    SRCodeAllocations@caa.co.uk

    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 scanned, emailed or posted to us at the address above.

    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 NISC secretariat for further details and include details of the aircraft concerned using the details below

    nisc@caa.co.uk
    020 7453 6536 - tel      


    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:

    mode.s@caa.co.uk
    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 P004/2015. 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.

    • Registration or updating a registration can be completed online at: www.gov.uk/406beacon
    • There are no charges to register or update a registration for a 406 MHz beacon.

    For help with registering, the UK Beacon Registry can be contacted at:

    epirb@mcga.gov.uk  
    01326 211569 - tel

    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