I. Definitions
arriving and departing aircraft throughout 24 hours or a specified portion thereof:
Data link-automatic terminal information service (D-ATIS). The provision of ATIS via data link.
Voice-automatic terminal information service (Voice-ATIS). The provision of ATIS by means of continuous and repetitive voice broadcasts.

Base turn. A turn executed by the aircraft during the initial approach between the end of the outbound track and the beginning of the intermediate or final approach track. The tracks are not reciprocal.
Note.— Base turns may be designated as being made either in level flight or while descending, according to the circumstances of each individual procedure.

Blind transmission. A transmission from one station to another station in circumstances where two-way communication cannot be established but where it is believed that the called station is able to receive the transmission.
Broadcast. A transmission of information relating to air navigation that is not addressed to a specific station or stations.
Ceiling. The height above the ground or water of the base of the lowest layer of cloud below 6 000 m (20 000 ft) covering more than half the sky.
Clearance limit. The point to which an aircraft is granted an air traffic control clearance.
Code (SSR). The number assigned to a particular multiple pulse reply signal transmitted by a transponder in Mode A or Mode C.
Computer. A device which performs sequences of arithmetical and logical steps upon data without human intervention.
Note.— When the word “computer” is used in this document it may denote a computer complex, which includes one or more computers and peripheral equipment.

Control area. A controlled airspace extending upwards from a specified limit above the earth.
Controlled aerodrome. An aerodrome at which air traffic control service is provided to aerodrome traffic.
Note.— The term “controlled aerodrome” indicates that air traffic control service is provided to aerodrome traffic but does not necessarily imply that a control zone exists.
Controlled airspace. An airspace of defined dimensions within which air traffic control service is provided in accordance with the airspace classification.
Note.— Controlled airspace is a generic term which covers ATS airspace Classes A, B, C, D and E as described in Annex 11, 2.6.
Controlled flight. Any flight which is subject to an air traffic control clearance.
Controller-pilot data link communications (CPDLC). A means of communication between controller and pilot, using data link for ATC communications.
Control zone. A controlled airspace extending upwards from the surface of the earth to a specified upper limit.
Cruise climb. An aeroplane cruising technique resulting in a net increase in altitude as the aeroplane mass decreases.
Cruising level. A level maintained during a significant portion of a flight.
Current flight plan. The flight plan, including changes, if any, brought about by subsequent clearances.
Note.— When the word “message” is used as a suffix to this term, it denotes the content and format of the current flight plan data sent from one unit to another.
Data convention. An agreed set of rules governing the manner or sequence in which a set of data may be combined into a meaningful communication.
Data processing. A systematic sequence of operations performed on data.
Note.— Examples of operations are the merging, sorting, computing or any other transformation or rearrangement with the object of extracting or revising information, or of altering the representation of information.
Decision altitude (DA) or decision height (DH). A specified altitude or height in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established.
　
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