1. Air Ground Communication Services (AGCS):
AGCS is an Aeronautical Radio Station usually provided at small aerodromes that do not have a sufficient volume or type of traffic that would require them to provide an Air Traffic Service.
AGCS operators provide traffic and weather information to pilots operating on and in the vicinity of the aerodrome. Such traffic information is based primarily on reports made by other pilots. Information provided by an AGCS radio station operator may be used to assist a pilot in making a decision; however, the safe conduct of the flight remains the pilot's responsibility.
CAP452 Aeronautical Radio Station Operator's Guide Chapter 4 describes the AGCS.
2. Offshore Communication Service (OCS):
OCS is an Aeronautical Radio Station which provides a communication service located on offshore fixed and mobile installations. I.e. Offshore fixed and mobile platforms, Emergency Rescue and Recovery Vessels, Supply and Support vessels.
OCS involves the transmission of messages to helicopters operating in the vicinity of offshore oil rigs, platforms and vessels through the use of aeronautical radio stations.
OCS also includes Offshore Non-Directional Radio Beacons (NDBs) located on these installations.
CAP452 Aeronautical Radio Station Operator's Guide Chapter 5 describes the OCS.
3. Operational Control (OPC):
OPC is an Aeronautical Radio Station which provides a communication service which is intended to be used for the exercise of authority over the initiation, continuation, diversion or termination of a flight in the interests of safety of the aircraft and the regularity and efficiency of the flight. Such communications are usually required for the exchange of messages between aircraft and aircraft operating agencies.
These are typically established by airlines operating scheduled and charter flights for passenger and cargo transportation, airport and aerodrome operators, airport ground handling agencies, flight training organisations and organisations and individuals who either operate their own aircraft or provide maintenance facilities.
An aeronautical radio station which is licensed and established for company operational control communications (OPC) may be used only for communication with company aircraft or aircraft for which the company is the operating agency.
CAP452 Aeronautical Radio Station Operator's Guide Chapter 7 describes the OPC.
The category of OPC also includes all areas of Recreational Aviation described below
3.1 Recreational Aviation
Recreational Aviation comprises associations, clubs, societies and individuals operating gliders, hang gliders, para gliders, paramotors, microlights, parachutes, balloons, gyroplanes and simple single engine aeroplanes (SSEA).
Aeronautical radio stations, comprising fixed, mobile, portable and hand-held radio equipment, are typically established and operated by these clubs, societies and individuals to provide radio communications with aircraft for the exchange of messages related to the particular recreational aviation activity.
4. Fire Vehicle 121.6 MHz
Aeronautical radio stations, comprising mobile and portable radio equipment, are typically established and operated by an aerodrome fire service providing direct radio communications with aircraft on the ground for use during a declared emergency.
The requirements for the provision of radio equipment operating on 121.6 MHz at both EASA and National Aerodromes are contained in CAP 168 Licensing of Aerodromes Chapter 8 Rescue and Fire Fighting Service (RFFS), paragraph 23 Communications and Alerting Systems.
The frequency assignment 121.6 MHz is assigned on a non-protected basis and is shared between users so as to provide an efficient use of the aeronautical radio spectrum.
5. Data Link
Aeronautical Radio Stations for data link communications are generally established and operated as a network of stations providing a variety of data link services to aircraft over a wide geographical area. In the UK networks are operated by either ARINC Incorporated or SITA.
Data link frequency assignments are granted in accordance with an ICAO plan and are not shared with any other aeronautical radio stations providing analogue voice communications.
More information can be found in CAP 670 ATS Safety Requirements Part C, Section 1, COM 04 ATC Datalinks.