Devenition And Abreviation Aeronautical Telecommunication (Alphabet D)

Data link communications. A form of communication intended for the exchange of messages via a data link. 

Dangerous goods. Articles or substances which are capable of posing a risk to health, safety, property or the environment and which are shown in the list of dangerous goods in the Technical Instructions or which are classified according to those Instructions. 

Dangerous goods accident. An occurrence associated with and related to the transport of dangerous goods by air which results in fatal or serious injury to a person or Danger area. An airspace of defined dimensions within which activities dangerous to the flight of aircraft may exist at specified times. 

Database. One or more files of data so structured that appropriate applications may draw from the files and update them. Data integrity. The probability that data has not been altered or destroyed. 

Data product. Data set or data set series that conforms to a data product specification. 

Data product specification. Detailed description of a data set or data set series together with additional information that will enable it to be created, supplied to and used by another party. 

Data quality. A degree or level of confidence that the data provided meets the requirements of the data user in terms of accuracy, resolution and integrity. 

Data set. Identifiable collection of data. Data set series. Collection of data sets sharing the same product specification. 

Date of manufacture. The date of issue of the document attesting that the individual aircraft or engine as appropriate conforms to the requirements of the type or the date of an analogous document. 

Datum. Any quantity or set of quantities that may serve as a reference or basis for the calculation of other quantities. 

Decision altitude (DA) or decision height (DH). A specified altitude or height in the precision approach or approach with vertical guidance at which a missed approach must be initiated if the required visual reference to continue the approach has not been established.

Declared capacity. A measure of the ability of the ATC system or any of its subsystems or operating positions to provide service to aircraft during normal activities. It is expressed as the number of aircraft entering a specified portion of airspace in a given period of time, taking due account of weather, ATC unit configuration, staff and equipment available, and any other factors that may affect the workload of the controller responsible for the airspace.
 

Declared distances.
a) Take-off run available (TORA). The length of runway declared available and suitable for 

    the ground run of an aeroplane taking off.
b) Take-off distance available (TODA). The length of the take-off run available plus the length 

    of the clearway, if provided. 

c) Accelerate-stop distance available (ASDA). The length of the take-off run available plus the 

    length of the stopway, if provided. 

d) Landing distance available (LDA). The length of runway which is declared available and 

    suitable for the ground run of an aeroplane landing.
 

Declared distances - heliports.
a) Take-off distance available (TODAH). The length of the final approach and take-off area plus

    the length of helicopter clearway (if provided) declared available and suitable for helicopters

    to complete the take-off. 

b) Rejected take-off distance available (RTODAH). The length of the final approach and take-off 

    area declared available and suitable for performance class 1 helicopters to complete a 

    rejected take-off. 

c) Landing distance available (LDAH). The length of the final approach and take-off area plus 

    any additional area declared available and suitable for helicopters to complete the landing 

    manoeuvre from a defined height. 

Defined point before landing. The point, within the approach and landing phase, after which the helicopter’s ability to continue the flight safely, with one engine inoperative, is not assured and a forced landing may be required.  

Degree Celsius (°C). The special name for the unit kelvin for use in stating values of Celsius temperature. 

De-icing/anti-icing facility. A facility where frost, ice or snow is removed (de-icing) from the aeroplane to provide clean surfaces, and/or where clean surfaces of the aeroplane receive protection (anti-icing) against the formation of frost or ice and accumulation of snow or slush for a limited period of time. 

De-icing/anti-icing pad. An area comprising an inner area for the parking of an aeroplane to receive de-icing/anti-icing treatment and an outer area for the manoeuvring of two or more mobile de-icing/anti-icing equipment. 

Dependent parallel approaches. Simultaneous approaches to parallel or near-parallel instrument runways where radar separation minima between aircraft on adjacent extended runway centre lines are prescribed. 

Derivative version. An aircraft gas turbine engine of the same generic family as an originally type-certificated engine and having features which retain the basic core engine and combustor design of the original model and for which other factors, as judged by the certificating authority, have not changed. 

Derived version of an aeroplane. An aeroplane which, from the point of view of airworthiness, is similar to the noise certificated prototype but incorporates changes in type design which may affect its noise characteristics adversely.
 

Derived version of a helicopter. A helicopter which, from the point of view of airworthiness, is similar to the noise certificated prototype but incorporates changes in type design which may affect its noise characteristics adversely. 

Designated Government Check Pilot (DGCP). A person who is the holder of a delegation of authority issued by the Director, authorizing the conduct of certain types of flight checks. 

Design landing mass. The maximum mass of the aircraft at which, for structural design purposes, it is assumed that it will be planned to land. 

Design take-off mass. The maximum mass at which the aircraft, for structural design purposes, is assumed to be planned to be at the start of the take-off run. 

Design taxiing mass. The maximum mass of the aircraft at which structural provision is made for load liable to occur during use of the aircraft on the ground prior to the start of take-off. 

Destination alternate. An alternate aerodrome to which an aircraft may proceed should it become either impossible or inadvisable to land at the aerodrome of intended landing. 

DETRESFA. The code word used to designate a distress phase. 

Direction finding - Homing. The procedure of using the direction-finding equipment of one radio station with the emission of another radio station, where at least one of the stations is mobile, and whereby the mobile station proceeds continuously towards the other station. 

Director or DGCA. The Director of the Directorate General of Civil Aviation, or any person authorized to act on his behalf. 

Digital Elevation Model (DEM). The representation of terrain surface by continuous elevation values at all intersections of a defined grid, referenced to common datum. 

Direct transit arrangements. Special arrangements approved by the public authorities concerned by which traffic which is pausing briefly in its passage through the major property damage. 

Dangerous goods incident. An occurrence, other than a dangerous goods accident, associated with and related to the transport of dangerous goods by air, not necessarily occurring on board an aircraft, which results in injury to a person, property damage, fire, breakage, spillage, leakage of fluid or radiation or other evidence that the integrity of the packaging has not been maintained. Any occurrence relating to the transport of dangerous goods which seriously jeopardizes the aircraft or its occupants is also deemed to constitute a dangerous goods incident. 

Distress phase. A situation wherein there is a reasonable certainty that an aircraft and its occupants are threatened by grave and imminent danger and require immediate assistance. 

Ditching. The forced landing of an aircraft on water. 

Displaced threshold. A threshold not located at the extremity of a runway. 

Doppler shift. The frequency shift observed at a receiver due to any relative motion between transmitter and receiver.
 

Double channel simplex. Simplex using two frequency channels, one in each direction. 

Downstream clearance. A clearance issued to an aircraft by an air traffic control unit that is not the current controlling authority of that aircraft. 

Dual instruction time. Flight time during which a person is receiving flight instruction from a properly authorized pilot on board the aircraft. 

Duplex. A method in which telecommunication between two stations can take place in both directions simultaneously.  

D-METAR. The symbol used to designate data link aviation weather report service.