DA [ICAO] -- DYNAMIC RESTRICTION
DA [ICAO]- (See ICAO Term DECISION ALTITUDE/DECISION
HEIGHT.)
DAIR- (See DIRECT ALTITUDE AND IDENTITY READOUT.)
DANGER AREA [ICAO]- An airspace of defined dimensions
within which activities dangerous to the flight
of aircraft may exist at specified times.
Note: The term "Danger Area" is not
used in reference to areas within the United
States or any of its possessions or territories.
DATA BLOCK- (See ALPHANUMERIC DISPLAY.)
DEAD RECKONING- Dead reckoning, as applied to
flying, is the navigation of an airplane solely
by means of computations based on airspeed, course,
heading, wind direction, and speed, groundspeed,
and elapsed time.
DECISION ALTITUDE/DECISION HEIGHT [ICAO]- A specified
altitude or height (A/H) in the precision approach
at which a missed approach must be initiated if
the required visual reference to continue the
approach has not been established.
Note 1: Decision altitude [DA] is referenced
to mean sea level [MSL] and decision height
[DH] is referenced to the threshold elevation.
Note 2: The required visual reference means
that section of the visual aids or of the approach
area which should have been in view for sufficient
time for the pilot to have made an assessment
of the aircraft position and rate of change
of position, in relation to the desired flight
path.
DECISION HEIGHT- With respect to the operation
of aircraft, means the height at which a decision
must be made during an ILS, MLS, or PAR instrument
approach to either continue the approach or to
execute a missed approach.
(See ICAO term DECISION ALTITUDE/DECISION HEIGHT.)
DECODER- The device used to decipher signals received
from ATCRBS transponders to effect their display
as select codes.
(See CODES.)
(See RADAR.)
DEFENSE VISUAL FLIGHT RULES- Rules applicable
to flights within an ADIZ conducted under the
visual flight rules in FAR Part 91.
(See AIR DEFENSE IDENTIFICATION ZONE.)
(Refer to FAR Part 91.)
(Refer to FAR Part 99.)
DELAY INDEFINITE (REASON IF KNOWN) EXPECT FURTHER
CLEARANCE (TIME)- Used by ATC to inform a pilot
when an accurate estimate of the delay time and
the reason for the delay cannot immediately be
determined; e.g., a disabled aircraft on the runway,
terminal or center area saturation, weather below
landing minimums, etc.
(See EXPECT FURTHER CLEARANCE (TIME).)
DELAY TIME- The amount of time that the arrival
must lose to cross the meter fix at the assigned
meter fix time. This is the difference between
ACLT and VTA.
DEPARTURE CENTER- The ARTCC having jurisdiction
for the airspace that generates a flight to the
impacted airport.
DEPARTURE CONTROL- A function of an approach control
facility providing air traffic control service
for departing IFR and, under certain conditions,
VFR aircraft.
(See APPROACH CONTROL FACILITY.)
(Refer to AIM.)
DEPARTURE SEQUENCING PROGRAM- A program designed
to assist in achieving a specified interval over
a common point for departures.
DEPARTURE TIME- The time an aircraft becomes airborne.
DESCENT SPEED ADJUSTMENTS- Speed deceleration
calculations made to determine an accurate VTA.
These calculations start at the transition point
and use arrival speed segments to the vertex.
DESIRED COURSE-
a. True- A predetermined desired course direction
to be followed (measured in degrees from true
north).
b. Magnetic- A predetermined desired course
direction to be followed (measured in degrees
from local magnetic north).
DESIRED TRACK- 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]- 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.
DEVIATIONS-
a. A departure from a current clearance, such
as an off course maneuver to avoid weather or
turbulence.
b. Where specifically authorized in the FAR's
and requested by the pilot, ATC may permit pilots
to deviate from certain regulations.
(Refer to AIM.)
DF- (See DIRECTION FINDER.)
DF APPROACH PROCEDURE- Used under emergency conditions
where another instrument approach procedure cannot
be executed. DF guidance for an instrument approach
is given by ATC facilities with DF capability.
(See DF GUIDANCE.)
(See DIRECTION FINDER.)
(Refer to AIM.)
DF FIX- The geographical location of an aircraft
obtained by one or more direction finders.
(See DIRECTION FINDER.)
DF GUIDANCE- Headings provided to aircraft by
facilities equipped with direction finding equipment.
These headings, if followed, will lead the aircraft
to a predetermined point such as the DF station
or an airport. DF guidance is given to aircraft
in distress or to other aircraft which request
the service. Practice DF guidance is provided
when workload permits.
(See DIRECTION FINDER.)
(See DF FIX.)
(Refer to AIM.)
DF STEER- (See DF GUIDANCE.)
DH- (See DECISION HEIGHT.)
DH [ICAO]- (See ICAO Term DECISION ALTITUDE/DECISION
HEIGHT.)
DIRECT- 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.
DIRECT ALTITUDE AND IDENTITY READOUT- The DAIR
System is a modification to the AN/TPX-42 Interrogator
System. The Navy has two adaptations of the DAIR
System-Carrier Air Traffic Control Direct Altitude
and Identification Readout System for Aircraft
Carriers and Radar Air Traffic Control Facility
Direct Altitude and Identity Readout System for
land-based terminal operations. The DAIR detects,
tracks, and predicts secondary radar aircraft
targets. Targets are displayed by means of computer-generated
symbols and alphanumeric characters depicting
flight identification, altitude, ground speed,
and flight plan data. The DAIR System is capable
of interfacing with ARTCC's.
DIRECTION FINDER- A radio receiver equipped with
a directional sensing antenna used to take bearings
on a radio transmitter. Specialized radio direction
finders are used in aircraft as air navigation
aids. Others are ground-based, primarily to obtain
a "fix" on a pilot requesting orientation
assistance or to locate downed aircraft. A location
"fix" is established by the intersection
of two or more bearing lines plotted on a navigational
chart using either two separately located Direction
Finders to obtain a fix on an aircraft or by a
pilot plotting the bearing indications of his
DF on two separately located ground-based transmitters,
both of which can be identified on his chart.
UDF's receive signals in the ultra high frequency
radio broadcast band; VDF's in the very high frequency
band; and UVDF's in both bands. ATC provides DF
service at those air traffic control towers and
flight service stations listed in the Airport/Facility
Directory and the DOD FLIP IFR En Route Supplement.
(See DF GUIDANCE.)
(See DF FIX.)
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 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 Airport/Facility
Directory 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- 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.)
(See MICROWAVE LANDING SYSTEM.)
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 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.
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.)
(See MICROWAVE LANDING SYSTEM.)
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 Information
Publications used for flight planning, en route,
and terminal operations. FLIP is produced by the
National Imagery and Mapping Agency (NIMA) 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- 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.
Damaging winds, lasting 5 to 30 minutes, could
reach speeds as high as 120 knots.
DOWNWIND LEG- (See TRAFFIC PATTERN.)
DRAG CHUTE- A parachute device installed on certain
aircraft which is deployed on landing roll to
assist in deceleration of the aircraft.
DSP- (See DEPARTURE SEQUENCING PROGRAM.)
DT- (See DELAY TIME.)
DUE REGARD- A phase of flight wherein an aircraft
commander of a State-operated aircraft assumes
responsibility to separate his aircraft from all
other aircraft.
(See also FAA Order 7110.65, paragraph 1-2-1,
WORD MEANINGS.)
DUTY RUNWAY- (See RUNWAY IN USE/ACTIVE RUNWAY/DUTY
RUNWAY.)
DVA- (See DIVERSE VECTOR AREA.)
DVFR- (See DEFENSE VISUAL FLIGHT RULES.)
DVFR FLIGHT PLAN- A flight plan filed for a VFR
aircraft which intends to operate in airspace
within which the ready identification, location,
and control of aircraft are required in the interest
of national security.
DYNAMIC- Continuous review, evaluation, and change
to meet demands.
DYNAMIC RESTRICTIONS- Those restrictions imposed
by the local facility on an "as needed"
basis to manage unpredictable fluctuations in
traffic demands.
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