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UK Civil Aviation Regulations

These are published by the CAA on our UK Regulations pages. EU Regulations and EASA Access Guides published by EASA no longer apply in the UK. Our website and publications are being reviewed to update all references. Any references to EU law and EASA Access guides should be disregarded and where applicable the equivalent UK versions referred to instead.

Definitions of the different radio equipment can be found in the form below:


Automatic Direction Finder - Determines the relative bearing from the aircraft to a ground-based transmitter.

Close ADF

Area NAV

Area Navigation (AKA: RNAV) - Navigation from point to point. The system will receive sensor inputs and compute the best track between points.

Close Area NAV

ATC Transponder

Air Traffic Control Transponder - Used on aircraft to automatically respond to ground based ATC secondary surveillance radar interrogations. It provides altitude information, and surveillance data to aid in the tracking of aircraft by air traffic controllers. Surveillance data is also used by ACAS to identify threat aircraft and co-ordinate evasive manoeuvres.

Close ATC Transponder


Distance Measuring Equipment - Used to determine the distance from a VORTAC, VORDME or localizer ground station. Accurate to within half a mile or three percent, aircraft distance to the station is typically displayed to the pilot and can be used in conjunction with other DME distances or other navigation data to determine aircraft position in RNAV systems.

Close DME


Emergency Location Transmitter - Used as an alerting and locating aid in an aircraft crash scenario.

Close ELT

Electronic Conspicuity Device

Electronic Conspicuity (EC) is an umbrella term for a range of technologies that can help airspace users to be more aware of other aircraft in the same airspace. It includes transponders and radios. At the most basic level, aircraft equipped with an EC Device effectively signal their presence to other airspace users, turning the 'see and avoid' concept into 'see, BE SEEN, and avoid.' Many EC devices also receive the signals from others. This then alerts pilots to the presence of other aircraft which may assist the pilot in being able to take avoiding action as necessary

Close Electronic Conspicuity Device


Global Positioning System - Uses radio signals transmitted by satellites to determine accurate aircraft location.

Close GPS

HF Communication

High Frequency Communication - Radio transmissions at frequencies between 2 and 30 MHz are widely used for long distance communications.

Close HF Communication


By means of a transmitter, marker beacons serve to identify a particular location in the space along an airway or on the approach to an instrument runway.

Close Marker

Radio Altimeter

Indicates the aircraft's height over water or terrain by means of radio signal.

Close Radio Altimeter

Satellite Communication

Equipment that provides telephone and data link solutions to aircraft via a communications satellite.

Close Satellite Communication


Satellite Based Augmentation System (SBAS) is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages. It augments the GPS system by using additional satellites and ground based elements. SBAS includes the European Geostationary Navigation Overlay Satellite System (EGNOSS) and the USA's Wide Areas Augmentation System (WAAS). Equipment complying with ETSOs C145 and C146 are EGNOSS and WAAS compatible.

Close SBAS


Traffic Alert and Collision Avoidance System/ Airborne Collision Avoidance System - Determines the relative altitude and proximity of surrounding aircraft and provides warning if the risk of mid-air collision is present. ACAS can issue advisories to the crew so that they may instigate evasive manoeuvres.


VHF Communication

Very High Frequency Communication - Radio transmissions at frequencies between 118MHz and 137MHz are used for short distance communications. VHF is less affected by atmospheric noise and interference from electrical equipment that lower frequencies.

Close VHF Communication

VHF Communication and Navigation

Very High Frequency Communication and Navigation - Installed onto aircraft for both communication and navigational purposes. VHF covers the radio spectrum from 30 to 300 MHz.

Close VHF Communication and Navigation

VHF Navigation

Very High Frequency Navigation - Capable of receiving and processing ILS Localizer, Glideslope, Marker Beacon and VOR (VHF Omni-directional Radio) signals.

Close VHF Navigation

Weather Radar

Capable of detecting precipitation via the reflection of microwaves.

Close Weather Radar