the Aviation Dictionary

decision height (DH) (USA) . deicer tubes
position and rate of change of position, in relation to
the desired flight path.
decision height (DH) (USA) - With respect to the
operation of aircraft, means the height at which a
decision must be made, during an ILS or PAR
instrunlent approach, to either continue the approach or
to execute a missed approach.
NOTE: Jeppesen approach charts use the abbreviation
DA(H). The decision altitude "DA" is referenced to
mean sea level (MSL) and the parenthetical decision
height (DH) is referenced to the TDZE or threshold
elevation. A DA(H) of 1,440 Tt.. (200 ft.) is a Decision
Altitude of 1,440 ft. and a Decision Height of 200 ft.
decision-making process - Intolves an evaluation of
risk elements to achieve an accurate perception of the
flight situation. The risk elements include the pilot, the
aircraft, the environment, the operation, and the
situation.
declination - The angular difference between magnetic
north and true north caused by the magnetic north pole
not being located at the same place as the true north
pole. In navigation for aircraft this is called variation.
decoder - The device used to decipher signals received
from ATCRBS transponders to effect their display as
select codes.
decomposing - The process of a material being broken
down into its basic elements. Example: water breaking
down into oxygen and hydrogen by the process of
electrolysis.
decontamination - The removal or neutral~zation of
undesired material from an area, a piece of equipment,
a building, or a person.
decouple - To release or disconnect a unit.
dedicated computer -A
one function.
computer that is used only for
deductible - The amount that the policyholder is
responsible for in the event of a claim.
de-energize - To turn off a piece of electrical
equipment.
deep cycling - A treatment of nickel cadmium batteries
in which the battery is completely discharged, the cells
shorted out and allowed to "rest." The battery is then
recharged to 140% of its ampere-hour capacity.
deep discharge - The procedure of removing all
electrical energy from a battery. After discharging a
battery down to a low level, the cells are shorted out
with shorting clips until all cells are completely
discharged. This allows all cells to be recharged from
the same starting condition.
deepening - A decrease in the central pressure of a
pressure system; usually applied to a low rather than to
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a high, atthough technically, it is acceptable in either
sense.
defect - Any imperfection, fault, flaw, or blemish that
may require repair or replacement of a part.
defective - Faulty. Not operating normally.
defense mechanisms - Subconscious ego-protecting
reactions to unpleasant situations.
defense visual flight rules (DVFR) - Rules applicable
to flights within an ADIZ conducted under the visual
flight rules in FAR 91.
deferred item - An item on a Minimum Equipment List
(MEL) that can be inoperative under- specified
conditions. When an item is deferred, it is often
accompanied by some sort of flight limitation.
deflate - To decrease the amount of air or gas held by an
object.
deflecting-beam torque wrench - A hand-operated
torque wrench in which the amount of torque applied to
a bolt is indicated by the amount the beam is bent. The
indication is read against a fixed scale on the handle of
the wrench.
deflection - The movement of an electron beam up and
down or sideways in response to an electric or
magnetic field in a cathode-ray tube.
degauss - To remove magnetism or magnetic field from
an object or piece of equipment.
degeneration - Feedback of a portion of the output of a
circuit to the input in such a direction that it reduces the
magnitude of the input; also called negative feedback.
Degeneration reduces distortion, increases stability,
and improves frequency response.
degreaser - A solvent used for removing oil or grease
from a part.
dehumidify - To reduce the amount of water vapor in
the air.
dehydrator - A piece of equipment or substance used to
remove water vapor from the air. Silica gel is often
used to absorb water within a closed space.
dehydrator plug - A plastic plug with threads screwed
Into a spark plug opening of an aircraft engine cylinder.
These plugs are filled with silica-gel and an indicator to
remove moisture from the air inside the cylinder and
indicate the condition of preservation of the cylinder.
deicer - A system or substance that removes ice from an
aircraft structure.
deicer boots - Inflatable rubber boots attached to the
leading edge of an airfoil. They can be sequentially
inflated and deflated to break away ice that has formed
over their surface.
deicer tubes -The inflatable tubes in the deicer boot.