9/5/24 

Pilot/Controller Glossary 

without an operating airport traffic control tower, a CTAF may also be designated for the purpose of carrying 

out advisory practices for operations in and through areas with a high volume of VFR traffic. 
DESIRED COURSE

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a. 

True

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 A predetermined desired course direction to be followed (measured in degrees from true north). 

b. 

Magnetic

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A predetermined desired course direction to be followed (measured in degrees from local 

magnetic north). 
DESIRED TRACK

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 The planned or intended track between two waypoints. It is measured in degrees from either 

magnetic or true north. The instantaneous angle may change from point to point along the great circle track 

between waypoints. 
DETRESFA (DISTRESS PHASE) [ICAO]

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 The code word used to designate an emergency phase wherein there 

is reasonable certainty that an aircraft and its occupants are threatened by grave and imminent danger or require 

immediate assistance. 
DEVIATION

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a. 

A departure from a current clearance, such as an off course maneuver to avoid weather or turbulence. 

b. 

Where specifically authorized in the CFRs and requested by the pilot, ATC may permit pilots to deviate 

from certain regulations. 
DH

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(See DECISION HEIGHT.) 

DH [ICAO]

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(See ICAO Term DECISION ALTITUDE/ DECISION HEIGHT.) 

DIGITAL-AUTOMATIC TERMINAL INFORMATION SERVICE (D-ATIS)

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 The service provides text 

messages to aircraft, airlines, and other users outside the standard reception range of conventional ATIS via 

landline and data link communications to the cockpit. Also, the service provides a computer

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synthesized voice 

message that can be transmitted to all aircraft within range of existing transmitters. The Terminal Data Link 

System (TDLS) D-ATIS application uses weather inputs from local automated weather sources or manually 

entered meteorological data together with preprogrammed menus to provide standard information to users. 

Airports with D-ATIS capability are listed in the Chart Supplement U.S. 
DIGITAL TARGET

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 A computer

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generated symbol representing an aircraft’s position, based on a primary 

return or radar beacon reply, shown on a digital display. 
DIGITAL TERMINAL AUTOMATION SYSTEM (DTAS)

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 A system where digital radar and beacon data is 

presented on digital displays and the operational program monitors the system performance on a real

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time basis. 

DIGITIZED TARGET

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 A computer

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generated indication shown on an analog radar display resulting from a 

primary radar return or a radar beacon reply. 

DIRECT

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Straight line flight between two navigational aids, fixes, points, or any combination thereof. When 

used by pilots in describing off-airway routes, points defining direct route segments become compulsory 

reporting points unless the aircraft is under radar contact. 
DIRECTLY BEHIND

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 An aircraft is considered to be operating directly behind when it is following the actual 

flight path of the lead aircraft over the surface of the earth except when applying wake turbulence separation 

criteria. 
DISCRETE BEACON CODE

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(See DISCRETE CODE.) 

DISCRETE CODE

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 As used in the Air Traffic Control Radar Beacon System (ATCRBS), any one of the 4096 

selectable Mode 3/A aircraft transponder codes except those ending in zero zero; e.g., discrete codes: 0010, 1201, 

2317, 7777; nondiscrete codes: 0100, 1200, 7700. Nondiscrete codes are normally reserved for radar facilities 

PCG D

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