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Aeronautical Information Manual (AIM), page 639

5/26/16
12/10/15

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

Pilot/Controller Glossary

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
divergent. The sizes of downbursts vary from 1/2
mile or less to more than 10 miles. An intense
downburst often causes widespread damage. Damag-
ing winds, lasting 5 to 30 minutes, could reach speeds
as high as 120 knots.

DOWNWIND LEG-

(See TRAFFIC PATTERN.)

DP-
(See INSTRUMENT DEPARTURE PROCEDURE.)


PCG D-3

Page 639 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   638 -- Page 639 -- 640