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Circuit Mode A configuration of the communications network which gives the appearance to the application of a dedicated transmission path. Circuit Mode Channel In the AMSS the C-channel is used to provide full-duplex voice or data communications. Because any given channel can pass traffic in only one direction, C-channels are assigned in pairs, one for the uplink (ground-to-air) and one for the downlink (air-to-ground). The C-channel is capable of passing digitised voice at 9.6 kilobits per second (or less) or data at 10.5 kilobits per second (or less). C-channel also contains a sub-band data channel which is time-multiplexed with the voice. This sub-band channel operates about 200 bits per second and carries system control and signalling information as well as user data. Circular Error Probable In a circular normal distribution (the magnitudes of the two one.dimensional input errors are equal and the angle of cut is 90 degrees), circular error probable is the radius of the circle containing fifty percent of the individual measurements being made, or the radius of the circle inside of which there is a fifty percent probability of being located. Civil Aviation Authority An organisation responsible for the provision of services to aviation users within the domestic boundaries of a State as well as in any international airspace for which it has been assigned responsibility by ICAO. Civil/Military Co-ordination The communication between civil and military elements (human and/or technical) necessary to ensure safe, efficient and harmonious use of the airspace. Classification Track classification is the process that sorts the trajectory data into well defined classes. It allows to basically classify tracks between Aircraft, Non-Aircraft and Ambiguous. Classification (Input) Process that sorts the Plot, Track and Reference Trajectory data into well defined classes using clearly defined Classification criteria. Class-of-flight (MTCD) Flights are classified based on flight data (MTCD). Examples of classes-of-flight are: a) all flights with a common destination, or b) all en-route flights above FL185. Clearance See Air Traffic Control Clearance Clearance Function The formulation and transmission of a clearance by an air traffic control unit as well as the acknowledgement and acceptance of such clearance by the Aircrew. Clearance Limit The point to which an aircraft is granted an air traffic control clearance. Cleared Flight Level The flight level at or to which an aircraft is authorised to proceed under conditions specified by an ATC unit. Cleared Level The flight level that a flight should be maintaining or trying to attain.

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Cleared Level Conformance An aspect of flight conformance that expresses how well a flight is adhering to its cleared level. Quantified by calculating the cleared level deviation. Cleared Level Deviation The distance between a flight’s current flight level and its cleared level. For a flight that is in a level flight phase the cleared level deviation is used to determine when a cleared level non-conformance situation arises. Cleared Level Deviation Threshold A monitoring criteria parameter that determines whether a cleared level non-conformance exists. Cleared Level Non-Conformances A flight related situation that exists, for a flight that is in a level flight phase, whenever the flight’s cleared level deviation exceeds the cleared level deviation threshold. Client NOF Any NOF which has subscribed to the services provided by a NOTAM Processing Unit. Client Static Database Static Data prepared and produced by the ESDF and made available to the Client ATS functions. Clients Generic term used to describe both Data Providers and Users. There are no commercial connotations. Cluster The collection of Modules required by a main actor (e.g. Aircraft Operator or Sector Planner). Clutter A general term used for interfering reflections of radio energy in PSR from fixed or slow moving objects. There can be a number of different types of clutter: ground clutter (generally non-moving); weather clutter (rain, snow, etc.); sea clutter; angel clutter (slow moving flocks of birds and anomalous propagation conditions). Clutter Density The total number of unwanted Primary Radar echoes per nautical mile degree of the radar coverage area. Coach Person monitoring the trainee in order to provide advice, guidance, help and encouragement towards the final achievement of the required goals or operational functions. Coasting To allow for missed individual radar returns, radar trackers estimate the subsequent positions of an established track for a number of cycles if there is no plot before dropping the track. This is known as coasting. Cockpit A SASS-C GUI (Graphical User Interface) to facilitate the access to the data and to avoid executing programs from the command line. Cockpit / Crew Resource Management Using all available resources - information, equipment and people - to achieve safe and efficient flight operations (Lauber, 1984). Cockpit Display of Traffic Information A concept by which traffic information pertinent to a given flight would be displayed in the cockpit along with a data tag containing information relevant to the safe conduct of flight.