Aviation Communications Glossary

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ACARS - Aircraft Communications Addressing and Reporting System. Introduced by ARINC in 1978, ACARS is an air/ground, character-oriented digital data link system. ACARS was initially used by the airlines to automatically record and report basic aircraft movement messages. In 1989, its use was expanded to include air traffic service communications. It currently uses 3 radio frequency paths for delivery: VHF, HF, and SATCOM. ARINC’s ACARS service is branded as GLOBALink.

ADS - Automatic Dependent Surveillance. A data link method of automatically transmitting an aircraft’s position, altitude, air speed, and other data. The aircraft acquires position information through a navigation receiver from a global navigation satellite system such as GPS and then uses a transponder to transmit that information along with other data from the flight monitoring system to air traffic control and other aircraft.

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AOC - Aeronautical Operational Control. The applications for communications between an aircraft and its operating agency or service partners.

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ATIS - Automatic Terminal Information Service. A prerecorded announcement about current airport operations that is broadcasted over a VHF voice frequency. The aircraft flight crew listens to the ATIS broadcast to find out about weather conditions, communications equipment information, active runways, and other routine information before departing from or arriving at an airport. See also D-ATIS.

CAA - Civil Aviation Authority. The national body that has regulatory oversight of aviation within a country. For example, the Federal Aviation Administration (FAA) in the United States.

CNS/ATM - Communications, Navigation, Surveillance/Air Traffic Management. CNS/ATM is the collective term for the set of solutions for modernizing outdated processes and procedures that were identified from the FANS evaluations and recommendations. The solutions include the use of digital data link for Communications, a global navigation satellite system for Navigation, and automatic position reporting for Surveillance.

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CPDLC - Controller-Pilot Data Link Communications. Direct communications between air traffic control and an aircraft pilot via data link text messages viewed on a display in the cockpit. In contrast to voice communications, CPDLC allows for reliable and efficient communications over oceanic regions.

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D-ATIS - Digital Automatic Terminal Information Service. A data link service that provides automated delivery of ATIS information such as destination weather and terminal conditions. With Digital ATIS, information is delivered to the cockpit via data link instead of through VHF voice, allowing the flight crew to recall and review the information when needed.

DCL - Departure Clearance. The exchange of departure information between the pilot and air traffic control authorizing an aircraft to begin takeoff. Known as Pre-Departure Clearance in the United States.

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FANS - Future Air Navigation System. The result of an International Civil Aviation Organization (ICAO) initiative begun in 1983 to evaluate air traffic management systems and procedures and make modernization recommendations, the FANS concept became the plan for revamping air navigation processes for the 21st century, primarily through a shift to using satellite technology instead of depending on ground-based technology.

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FL – Flight Level. Airspace at a particular altitude in thousands of feet—for example, 29,000 feet is FL290.

GLOBALink - ARINC’s branding for our Aircraft Communications Addressing and Report System (ACARS). GLOBALink supports airline data link communications worldwide through VHF, VDL Mode 2, and HF ground stations, as well as satellite services over Inmarsat and Iridium.

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GPS - Global Positioning System. A global navigation satellite system used by persons or equipment with GPS receivers to determine accurate location and time. In aviation, GPS has enabled the use of more-efficient air routes, such as with RVSM.

HF - High Frequency. Radio frequencies between 3 and 30 MHz. ARINC’s HF service is branded as GLOBALink/HF.

HFDL - High Frequency Data Link. HFDL is a segment of ACARS used to exchange airline operational control and air traffic services messages between aircraft end systems and corresponding ground-based HFDL ground stations. Using the unique propagation characteristics of high-frequency radio waves, the ground stations provide data link communications to properly equipped aircraft operating anywhere in the world. To use the service, an aircraft only needs a communications management unit and an HFDL data radio. HFDL is the only data link technology that provides coverage in the polar regions.

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Iridium - The Iridium satellite constellation consists of a system of 66 active communication satellites with spares in orbit and on the ground. It allows worldwide voice and data communications including the poles, oceans, and airways. ARINC’s Iridium service is branded as GLOBALink/Iridium.

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OOOI - Out, Off, On, In. The collective term for the four phases of an aircraft’s flight: Out (leaving the gate), Off (takeoff), On (touchdown), and In (arriving at the gate). ACARS messages are sent at the start of each of those phases, providing the aircraft movement information and other data to operations center computers.

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PDC - Predeparture Clearance. See DCL.

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RGS - Remote Ground Station. Unit that provides the aircraft with access to the air/ground network.

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RVSM - Reduced Vertical Separation Minimum. The concept of reducing the vertical distance maintained by aircraft in flight from the original 2,000-foot separation to 1,000 feet in flight levels between 29,000 and 41,000 feet—or FL290 to FL410. A 2,000-foot separation had been the standard since the beginning of jet age flight. The separation reduction was made possible by the more-accurate equipment on board modern aircraft; however an aircraft and its equipment must be certified as RVSM-compliant in order to fly in RVSM airspace. After evaluation studies in the 1980s, RVSM was implemented in various parts of the world beginning with the North Atlantic airspace in 1997.

SATCOM - Satellite Communications. ARINC’s SATCOM service is branded as GLOBALink/Satellite.

TCAS - Traffic Alert and Collision Avoidance System. System onboard an aircraft that alerts the pilot of a potential mid-air collision with another aircraft, providing that both aircraft are equipped with the appropriate position-interrogating transponders.

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TDWR– Terminal Doppler Weather Radar. TDWR provides information on windshear, microburst, and gust front activity in the vicinity of the airport.

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TWIP - Terminal Weather Information for Pilots. TWIP is an FAA service, available only in the U.S., which uses ACARS to send airport weather advisories such as windshear, microburst, and precipitation information to an aircraft cockpit display. Because TWIP obtains information from Terminal Doppler Weather Radar (TDWR), airports need to be equipped with TDWR to provide the TWIP service.

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VDL Mode 2 - VHF Digital Link Mode 2. VDL Mode 2 was developed in the early 2000s to provide a much-needed increase in capacity for aeronautical operational control messages. It improves on VHF ACARS data link by providing 10 times the bandwidth. VDL Mode 2 is the enabling technology for Controller-Pilot Data Link Communications and the future free flight environment. ARINC’s VDL Mode 2 service is branded as GLOBALink/VDLM2.

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VHF - Very High Frequency. Radio frequencies between 30 and 300 MHz. ARINC’s VHF service is branded as GLOBALink/VHF.

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