Pilot/Controller Glossary 

4/20/23 

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

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 A separate radio frequency for use in direct pilot-controller communications 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

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 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)

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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

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 A condition of being threatened by serious and/or imminent danger and of requiring immediate 

assistance. 
DIVE BRAKES

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(See SPEED BRAKES.) 

DIVERSE VECTOR AREA

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 In a radar environment, 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)

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 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

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(See DISTANCE MEASURING EQUIPMENT.) 

DME FIX

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 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

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 Spacing of aircraft in terms of distances (nautical miles) determined by reference to 

distance measuring equipment (DME). 

(See DISTANCE MEASURING EQUIPMENT.) 

DoD FLIP

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 Department of Defense Flight Information Publications used for flight planning, en route, and 

terminal operations. FLIP is produced by the National Geospatial

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Intelligence Agency (NGA) for world-wide 

use. United States Government Flight Information Publications (en route charts and instrument approach 

procedure charts) are incorporated in DoD FLIP for use in the National Airspace System (NAS). 
DOMESTIC AIRSPACE

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 Airspace which overlies the continental land mass of the United States plus Hawaii 

and U.S. possessions. Domestic airspace extends to 12 miles offshore. 
DOMESTIC NOTICE

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 A special notice or notice containing graphics or plain language text pertaining to almost 

every aspect of aviation, such as military training areas, large scale sporting events, air show information, Special 

PCG D

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