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In aerial navigation, declination is called variation. See variation.
decoder (radar). The device used to decipher signals received from air traffic radar beacon transponders
and display them as select codes.
decompose. To separate into basic components, or elements. When electric current passes through water (a
chemical compound), the water decomposes into its two chemical elements, hydrogen and oxygen.
decontamination. The process of removing contamination from a body or a mechanism. Radiological
decontamination is the process of removing or neutralizing radioactive contaminants from a person or a
structure.
decouple. To disconnect two components that are joined together, or to isolate one electrical circuit from
another.
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dedicated computer. A small digital computer, often built into an instrument or control device, that
contains a built-in program to perform a specific function. A digital autopilot is a dedicated computer to
control an aircraft. It does not perform any other function.
de-energize. To disconnect an object from its source of power.
deep cycling (nickel-cadmium battery servicing). A maintenance procedure used with nickel-cadmium
batteries to equalize all the cells. The battery is completely discharged, all of the cells are shorted, and the
battery is allowed to stand in its shorted condition for a specified period of time. Then, the battery is
recharged to 140% of its ampere hour capacity.
deep discharge (batteries). A maintenance procedure for discharging a battery that removes all the
electrical energy from the battery before it is recharged.
When a battery is deep discharged, it is discharged at a specified rate until its voltage is down to a
certain value, and then all the terminals of all the cells are connected with shorting straps and left shorted
for a specified period of time.
Deep discharging puts all the cells in a battery in the same condition, ready to receive a new
charge.
deepening (meteorology). A decrease in the central pressure of a pressure system. This term is usually
applied to a low rather than to a high, but technically it is acceptable in either case.
deep-vacuum pump. A vacuum pump capable of removing almost all the air from an air conditioning
system. A deep-vacuum pump can reduce the pressure inside the system to a few microns.
defect. A flaw, damage, or imperfection in a component or a piece of material that requires a repair or
replacement of the part.
defective. Faulty, or not operating as it should.
deflation (pneumatic component procedure). The release of air from a pneumatic component.
deflator cap. A cap for a tire, strut, or accumulator air valve that, when screwed onto the valve, depresses
the valve stem and allows the air to safely escape through a hole in the side of the cap.
deflecting-beam torque wrench (precision hand tool).
A calibrated wrench which indicates the amount of torque being applied to a nut or bolt. This is
done by measuring the amount the beam of the wrench deflects when the torque is being applied.
According to Hooke’s law of elasticity, the beam will deflect the same amount each time a given
amount of torque is applied by the wrench.
The indication of the amount of torque is read by the position of a pointer attached to the drive of
the wrench, over a fixed scale fastened to the beam of the wrench.
defense visual flight rules. See DVFR.
degauss. To demagnetize an object, or to neutralize a magnetic field. Magnetic recording tape is erased by
degaussing it.
degeneration (negative electrical feedback). Feedback of an electrical signal from the circuit output to the
circuit input, with a phase opposite the phase of the signal on the input. Degeneration stabilizes the output
of a circuit, decreases circuit distortion, and improves the frequency response of the circuit.
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degreaser. A chemical solution used to remove oil and grease from a part. Stoddard solvent and naphtha
are two popular degreasers used in aircraft maintenance shops.
dehumidify. To decrease the amount of moisture (water vapor) in the air. Dehumidifying is often done by
installing a small cooling system in the room to cause moisture to condense on its coils. Water vapor is
removed from the air and changed into liquid water.
dehydrator. A material that removes some of the moisture from the air inside a component. Some
dehydrators use silica gel to absorb the moisture. The silica gel crystals may be colored with an indicator
dye that changes its color from blue to pink when the crystals absorb moisture.
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航空术语词典Dictionary of Aeronautical Terms 上(121)
