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D
D 1 Total aerodynamic drag.
2 Danger area (ICAO).
3 Duration of phenomenon in seconds, eg D 60 .
4 Drift.
5 Diameter (rarely, d); for tyre [tire], at rim ledge.
6 For airspace, see *-class.
7 Departure chart.
8 Pavement bending strength for dual-wheel landing
gear.
9 Drone (UK).
10 Drone director (US modified-mission prefix).
11 Electric flux density.
12 Fuze delay time.
13 PPL Group for microlights (CAA).
14 Sport-parachuting certificate: 200 free-falls, 20
landing 15m of target.
15 Detail [maintenance check], followed by number.
16 Aircraft category: gliders and motor gliders (FAI).
17 Other meanings include Doppler, downward,
distance, day, dust, delete, designated, delay, displacement,
differential coefficient, chemical diffusion
coefficient and decision.
d 1 Distance, and spacing between structural members.
2 Differential.
3 Deci, prefix, multiply by 10 –1 (not recommended).
4 Clear distance between contact areas of landing
wheels (can include axial or transverse distance between
wheels of bogie).
5 Thickness of RAM surface-wave absorber.
6 Usually as subscript, design.
7 Diameter of fuselage, jet or propeller (alternative to
D).
8 Diode.
9 Relative density.
10 90 per cent semi-span, usually measured outboard
from root.
11 Maximum depth of wing at root [assumed to be
greatest anywhere on semi-span].
D* Also called co-ordination-perception parameter,
time-response criterion for the lateral/directional control
response, combining lateral acceleration and angle of
sideslip.
D˜ In 2-D flow, often used for section drag [per unit span,
parallel to freestream].
D¯¯1, D¯¯2 Non-dimensional drag factors.
D1 Deliverable one, the first report (Sesar).
D 3 Data download and display.
D 3 S Dynamic data-display subsystem.
D8PSK Differential-8 phase-shift keying.
D 100 Drag at 100 ft/s.
D-check Major overhaul carried out every 3–5 years.
D-class Airspace up to 2,500 ft (762 m) AGL above
airfield with operating tower; 2-way dialogue radio
required.
D-code In flight plan, have DME.
D-factor Actual, or true, altitude divided by pressure
altitude.
D-gun Detonation gun, firing suspended particles of
hard surface coating by detonation of oxy-acetylene.
D-layer Region of increasing electron and ion density in
ionosphere, existing in daytime only and merging with
bottom of E-layer.
D-licence For inspection of engines after overhaul.
D-nose Strong leading edge of aerofoil, often forming
principal structural basis of wing or helicopter rotor
blade.
D-notice Issued regularly to advise [esp. Press, broadcasters]
of changes in classification status of defence or
other sensitive subjects (UK MoD).
D-nozzle Propulsive nozzle of jet engine on centreline of
fuselage or nacelle vectoring to give lift or thrust (from
cross-section).
D-ring Steel handle with which parachutist pulls
ripcord.
D-spar D-nose.
D-tube Leading edge of lightplane or micro comprising
spar and load-bearing skin, generally simpler than
D-nose.
D-value Departure from pressure altitude.
DA 1 Drift angle.
2 Diplomatic authorization.
3 Double attack.
4 Long-range (bomber) aviation, predecessor of ADD
(USSR).
5 Delayed-action (bomb).
6 Dual-alloy (turbine disc).
7 Direct action (fuze).
8 Deck alert.
9 Decision [or density] altitude.
10 Danger area.
11 Development aircraft.
12 Design authority.
13 Duplex aluminide.
14 Air defence (F).
15 Defence advisory.
16 Drought area.
17 Direct access (telecoms).
18 Descent advisor, or advisory.
19 Display Authorization.
da Deca [US, deka], prefix, multiplied by 10, non-SI.
d α 1 Radar resolution in azimuth.
2 See δ a .
D/A Digital/analog.
DAA 1 Directorate of Air Armament (UK).
2 Digital/analog adaptor.
3 Directorate, Army Aviation [DAAvn is preferred]
(UK).
DAACM Direct airfield-attack cluster munition.
DAAIS Danger area activity information service (CAA,
UK).
DAAS Defense advanced automation system (ATC)
DAAT Digital angle-of-attack transmitter.
DAAvn Directorate of Army Aviation (UK).
DAB 1 Defense Acquisitions Board (US).
2 Digital audio broadcast[ing].
DABF Digital adaptive beam-forming; N adds network
DABM Defence against ballistic missile(s).
DABRK Daybreak.
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