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Functional Levels
Often referred to as 'ECAC reference' levels. The ATC procedures and automated system functionality considered necessary to achieve the operational and implementation objectives of the ECAC En-Route Strategy for the 1990s (now superseded by EUROCONTROL ATM 2000+ Strategy). Different functional performance levels were defined corresponding to different levels of ATC complexity to support the Convergence and Implementation Plan, since replaced by the European Convergence and Implementation Plan (ECIP). These levels, shown below, are no longer used in EATM.
Required ECAC functional performance level:
-
 No specific level - flexible application of CIP objectives

-
 Basic

-
 Advanced

-
 Very advanced.

Category of ATC complexity:

-
 Very low

-Low or medium
- High
-(no complexity category defined).
Functional Requirements
Operational requirements that determine what function a system should perform.  They can usually be expressed by a verb applying to a type of data, (e.g. display aircraft position).
Future Air Navigation Systems
An acronym or term usually associated with a Special Committee established by the International Civil Aviation Organisation Council to, inter alia, study technical, operational, institutional and economic questions, including cost/benefit effects, relating to future potential air navigation systems.
G
Gain (of Antenna) A measure for the antenna of the increased radiation intensity radiated in a particular direction as compared with the radiation intensity that would have been radiated from an isotropic antenna with the same power input (expressed in dB). Gantt Chart A graphic display of schedule-related information, in which activities or other project elements are listed down the left side of the chart, dates are shown across the top, and activity duration is shown as date-place horizontal bars. (Also called 'Bar Chart'). (Source Project Management Institute (PMI) - PMBOK guide). Garbled The reply-code that is received by a particular decoder in a form other than that in which it was transmitted. Garbled Mode A The condition of the Mode A in the original format is regarded as garbled. Garbled Mode B The condition of the Mode C in the original format is regarded as garbled.

 
Garbling A term applied to the overlapping in range and/or azimuth of two or more SSR replies so that the pulse positions of one reply fall close to or overlap the pulse positions of another reply, thereby making the decoding of reply data prone to error. Gatelink A system used to communicate with aircraft whilst on an apron. The link is either physical or short range directed transmission (such as infra red). Data can be passed to FMC data bus for updating purposes. The design is based on data transfer of 100 Megabits per second. The connection can be established either through a automatic connection using infrared beams across a free air gap or through a manual connection using a ground connector. Gate-to-Gate The gate-to-gate scope is considered to start at the moment the user first interacts with ATM and ends with the switch-off of the engines, including also the processes of charging users for ATM services. The scope does not encompass ATM processes only. Gate-to-Gate Environment Data processing support during the different flight’s phases: from parking, taxiing, departure, via en-route, approach and landing, to taxiing and parking again. Gateway A system used to interconnect dissimilar networks. A gateway may contain all seven layers of the OSI reference model. General Air Traffic Encompasses all flights conducted in accordance with the rules and procedures of ICAO. General Air Traffic (GPA) Flights conducted in accordance with civil (ICAO) air traffic procedures. Note, these may include military flights for which ICAO rules satisfy their operational requirements. General Aviation Operation is an aircraft operation other than a commercial air transport operation or aerial work operation. General Communications A category of communications that includes APC, public correspondence, and other non-operational and non-administrative communications. General Topology Subnetwork General topology sub networks (e.g., WANs) we are often used to connect geographically dispersed ISs and ESs. Geocentric Relative to the earth as a centre, measured from the centre of the earth. Geodesy The science related to the determination of the size and shape of the earth (geodic) by such direct measurements as triangulation, levelling and gravimetric observations; which determines the external gravitational field of the earth and, to a limited degree, the internal structure. Geographical Association and Classification of Eve It provides trace facilities to keep track of all traffic residing in (selected) volumes of airspace. These volumes of airspace can be defined, selected and manipulated with the help of a graphical user interface (GROBI the Graphical Object Interface). Geographical Paging System Technique for deriving location from space-based assets / Système mondial de localisation.