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Pilot/Controller Glossary

3/29/18

PCG D−3

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.)

DOD FLIP− Department of Defense Flight Informa-

tion Publications used for flight planning, en route,

and terminal operations. FLIP is produced by the

National Geospatial−Intelligence Agency (NGA) for

world-wide use. United States Government Flight

Information Publications (en route charts and

instrument approach procedure charts) are incorpo-

rated in DOD FLIP for use in the National Airspace

System (NAS).
DOMESTIC AIRSPACE− Airspace which overlies

the continental land mass of the United States plus

Hawaii and U.S. possessions. Domestic airspace

extends to 12 miles offshore.
DOWNBURST− A strong downdraft which induces

an outburst of damaging winds on or near the ground.

Damaging winds, either straight or curved, are highly