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12/2/21 

Pilot/Controller Glossary 

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

 A computer

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)

 A system where digital radar and beacon 

data is presented on digital displays and the 
operational program monitors the system perfor-
mance on a real

time basis. 

DIGITIZED TARGET

 A computer

generated 

indication shown on an analog radar display resulting 
from a primary radar return or a radar beacon reply. 

DIRECT

 Straight line flight between two naviga-

tional 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

 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

 

(See DISCRETE CODE.) 

DISCRETE CODE

 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 that are not equipped with 
discrete decoding capability and for other purposes 
such as emergencies (7700), VFR aircraft (1200), etc. 

(See RADAR.) 
(Refer to AIM.) 

DISCRETE FREQUENCY

 A separate radio 

frequency for use in direct pilot-controller commu-
nications in air traffic control which reduces 
frequency congestion by controlling the number of 
aircraft operating on a particular frequency at one 
time. Discrete frequencies are normally designated 

for each control sector in en route/terminal ATC 
facilities. Discrete frequencies are listed in the Chart 
Supplement U.S. and the DOD FLIP IFR En Route 
Supplement. 

(See CONTROL SECTOR.) 

DISPLACED THRESHOLD

 A threshold that is 

located at a point on the runway other than the 
designated beginning of the runway. 

(See THRESHOLD.) 
(Refer to AIM.) 

DISTANCE MEASURING EQUIPMENT (DME)

 

Equipment (airborne and ground) used to measure, in 
nautical miles, the slant range distance of an aircraft 
from the DME navigational aid. 

(See TACAN.) 
(See VORTAC.) 

DISTRESS

 A condition of being threatened by 

serious and/or imminent danger and of requiring 
immediate assistance. 

DIVE BRAKES

 

(See SPEED BRAKES.) 

DIVERSE VECTOR AREA

 In a radar environ-

ment, that area in which a prescribed departure route 
is not required as the only suitable route to avoid 
obstacles. The area in which random radar vectors 
below the MVA/MIA, established in accordance with 
the TERPS criteria for diverse departures, obstacles 
and terrain avoidance, may be issued to departing 
aircraft. 

DIVERSION (DVRSN)

 Flights that are required to 

land at other than their original destination for 
reasons beyond the control of the pilot/company, e.g. 
periods of significant weather. 

DME

 

(See DISTANCE MEASURING EQUIPMENT.) 

DME FIX

 A geographical position determined by 

reference to a navigational aid which provides 
distance and azimuth information. It is defined by a 
specific distance in nautical miles and a radial, 
azimuth, or course (i.e., localizer) in degrees 
magnetic from that aid. 

(See DISTANCE MEASURING EQUIPMENT.) 
(See FIX.) 

DME SEPARATION

 Spacing of aircraft in terms of 

distances (nautical miles) determined by reference to 
distance measuring equipment (DME). 

(See DISTANCE MEASURING EQUIPMENT.) 

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