D

Question 1

Datum (Reference Datum)

Answer 1

An imaginary vertical plane
or line from which all measurements of arm are taken. The
datum is established by the manufacturer. Once the datum
has been selected, all moment arms and the location of CG
range are measured from this point.

Question 2

Dark adaptation

Answer 2

Physical and chemical adjustments of the

eye that make vision possible in relative darkness.

Question 3

Dead reckoning

Answer 3

Navigation of an airplane solely by means
of computations based on airspeed, course, heading, wind
direction and speed, groundspeed, and elapsed time.

Question 4

Deceleration error

Answer 4

A magnetic compass error that occurs
when the aircraft decelerates while flying on an easterly
or westerly heading, causing the compass card to rotate
toward South.

Question 5

Decision Altitude (DA)

Answer 5

A specified altitude in the precision
approach, charted in feet MSL, at which a missed approach
must be initiated if the required visual reference to continue
the approach has not been established.

Question 6

Decision Height (DH)

Answer 6

A specified altitude in the precision
approach, charted in height above threshold elevation,
at which a decision must be made either to continue the
approach or to execute a missed approach.

Question 7

Deice

Answer 7

The act of removing ice accumulation from an

aircraft structure.

Question 8

Delta

Answer 8

A Greek letter expressed by the symbol ∆ to indicate
a change of values. As an example, ∆CG indicates a change
(or movement) of the CG.

Question 9

Density altitude

Answer 9

Pressure altitude corrected for nonstandard
temperature. Density altitude is used in computing the
performance of an aircraft and its engines.

Question 10

Departure Procedure (DP)

Answer 10

Preplanned IFR ATC departure,

published for pilot use, in textual and graphic format.

Question 11

Deposition

Answer 11

The direct transformation of a gas to a solid
state, in which the liquid state is bypassed. Some sources use
sublimation to describe this process instead of deposition

Question 12

Detonation

Answer 12

The sudden release of heat energy from fuel in
an aircraft engine caused by the fuel-air mixture reaching
its critical pressure and temperature. Detonation occurs as a
violent explosion rather than a smooth burning process.

Question 13

Deviation

Answer 13

A magnetic compass error caused by local
magnetic fields within the aircraft. Deviation error is different
on each heading.

Question 14

Dew

Answer 14

Moisture that has condensed from water vapor. Usually
found on cooler objects near the ground, such as grass, as
the near-surface layer of air cools faster than the layers of
air above it.

Question 15

Dewpoint

Answer 15

The temperature at which air reaches a state where

it can hold no more water.

Question 16

DGPS

Answer 16

Differential Global Positioning System

Question 17

Differential ailerons

Answer 17

Control surface rigged such that the
aileron moving up moves a greater distance than the aileron
moving down. The up aileron produces extra parasite drag
to compensate for the additional induced drag caused by
the down aileron. This balancing of the drag forces helps
minimize adverse yaw.

Question 18

Differential Global Positioning System (DGPS)

Answer 18

. A system
that improves the accuracy of Global Navigation Satellite
Systems (GNSS) by measuring changes in variables to
provide satellite positioning corrections.

Question 19

Differential pressure

Answer 19

A difference between two pressures.
The measurement of airspeed is an example of the use of
differential pressure.

Question 20

Dihedral

Answer 20

The positive acute angle between the lateral
axis of an airplane and a line through the center of a wing
or horizontal stabilizer. Dihedral contributes to the lateral
stability of an airplane.

Question 21

Diluter-demand oxygen system

Answer 21

An oxygen system that
delivers oxygen mixed or diluted with air in order to maintain
a constant oxygen partial pressure as the altitude changes.

Question 22

Direction indication

Answer 22

The true and instantaneous reflection of
aircraft pitch-and-bank attitude by the miniature aircraft,
relative to the horizon bar of the attitude indicator

Question 23

Direct User Access Terminal System (DUATS)

Answer 23

A system
that provides current FAA weather and flight plan filing
services to certified civil pilots, via personal computer,
modem, or telephone access to the system. Pilots can request
specific types of weather briefings and other pertinent data
for planned flights.

Question 24

Directional stability

Answer 24

Stability about the vertical axis of an
aircraft, whereby an aircraft tends to return, on its own, to
flight aligned with the relative wind when disturbed from that
equilibrium state. The vertical tail is the primary contributor
to directional stability, causing an airplane in flight to align
with the relative wind.

Question 25

Distance measuring equipment (DME)

Answer 25

A pulse-type
electronic navigation system that shows the pilot, by an
instrument-panel indication, the number of nautical miles
between the aircraft and a ground station or waypoint.

Question 26

DME arc

Answer 26

A flight track that is a constant distance from the

station or waypoint.

Question 27

Doghouse

Answer 27

A turn-and-slip indicator dial mark in the shape

of a doghouse.

Question 28

Domestic Reduced Vertical Separation Minimum (DRVSM)

Answer 28

Additional flight levels between FL 290 and FL

410 to provide operational, traffic, and airspace efficiency

Question 29

Double gimbal

Answer 29

A type of mount used for the gyro in an
attitude instrument. The axes of the two gimbals are at right
angles to the spin axis of the gyro, allowing free motion in
two planes around the gyro.

Question 30

Drag

Answer 30

. The net aerodynamic force parallel to the relative
wind, usually the sum of two components: induced drag
and parasite drag.

Question 31

Drag curve

Answer 31

The curve created when plotting induced drag

and parasite drag

Question 32

Drift angle

Answer 32

Angle between heading and track

Question 33

Duplex

Answer 33

Transmitting on one frequency and receiving on a

separate frequency.

Question 34

Dutch roll

Answer 34

A combination of rolling and yawing oscillations
that normally occurs when the dihedral effects of an aircraft
are more powerful than the directional stability. Usually
dynamically stable but objectionable in an airplane because
of the oscillatory nature.

Question 35

Dynamic hydroplaning

Answer 35

A condition that exists when
landing on a surface with standing water deeper than the
tread depth of the tires. When the brakes are applied, there is
a possibility that the brake will lock up and the tire will ride
on the surface of the water, much like a water ski. When the
tires are hydroplaning, directional control and braking action
are virtually impossible. An effective anti-skid system can
minimize the effects of hydroplaning.

Question 36

Dynamic stability

Answer 36

The property of an aircraft that causes
it, when disturbed from straight-and-level flight, to develop
forces or moments that restore the original condition of
straight and level.