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temperature stabilizes at -67°F (-55°C), and it remains at this temperature until it reaches an altitude of
about 82,000 feet.
atmospheric electricity. Static electricity that exists between clouds and between clouds and the surface of
the earth.
atmospheric noise (radio reception). Noise produced in radio equipment by electricity in the atmosphere.
atmospheric pressure. The pressure exerted by the atmosphere because of the attraction of gravity exerted
on the air directly above the measuring instrument.
Under standard conditions, at sea level, the atmospheric pressure is 14.69 pounds per square inch,
29.92 inches of mercury, 1013.2 millibars and 1.01325 newtons per square meter. This is called one
atmosphere of pressure (one atm).
Atmospheric pressure is also called barometric pressure.
atmospherics (radio reception). A form of static in radio reception caused by atmospheric electrical
phenomena such as electrical storms.
atom. The smallest particle of a chemical element that can exist, either alone or in combination with other
atoms.
An atom is made up of a nucleus, which contains protons and neutrons and electrons, which spin
around the nucleus. In a balanced atom, there are as many electrons spinning around the nucleus as there
are protons in the nucleus.
atomic fission. The reaction that causes the nucleus of a heavy atom such as uranium to split and form the
nucleus of a lighter atom. When the nucleus splits, a tremendous amount of energy, usually in the form of
heat and light, is released.
atomic fusion. The reaction that causes two light atomic nuclei to combine to form a heavier nucleus.
When the nuclei combine, a tremendous amount of energy, usually in the form of heat and light, is
released.
atomic number. The number of protons in the nucleus of an atom of the element. The atomic number of an
element determines the position of the element in the periodic table of elements.
atomic weight. The weight of an atom of a chemical element. It is approximately equal to the number of
protons and neutrons in the nucleus of the atom.
atomization. The process of breaking a liquid into tiny droplets or a fine spray. Atomized liquids vaporize
easily.
atomize. To break up a liquid into a very fine spray of tiny droplets. A paint spray gun atomizes the liquid
finishing material and then blows the atomized liquid onto the surface being painted.
atomizer. A device that breaks a liquid into a fine spray to aid in its vaporization.
ATR racking system. A system of standardized mounting racks for electronic equipment installed in an
aircraft.
ATS route (ICAO). A specified route designed for channeling the flow of traffic as necessary for the
provision of air traffic services.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 51
attenuate. To weaken, or lessen the intensity, of an action. The volume control of a radio attenuates the
sound allowed to come from the speaker. The amount of attenuation can be expressed as a ratio of the
strength of the output signal to the strength of the input signal.
attenuation (radar meteorology). Any process which reduces power density in radar signals.
Precipitation attenuation reduces the power density because of absorption or reflection of energy
by precipitation.
Range attenuation is the reduction in radar power density because of distance from the antenna.
Range attenuation occurs in the outgoing beam at a rate that is proportional to 1/range2. The return signal is
also attenuated at the same rate.
attenuator (electrical equipment). A network of resistors used to decrease the amplitude of an electrical
signal without causing any phase shift or frequency distortion.
attitude (aircraft flight condition). The relationship between the axes of an aircraft and a fixed reference.
The earth’s horizon is often used as this reference.
attitude indicator (aircraft flight instrument). A gyroscopic flight instrument that gives the pilot an
indication of the attitude of the aircraft relative to its pitch and roll axes.
The attitude indicator in an autopilot is in the sensing system that detects deviation from a
level-flight attitude.
attraction. A force which acts between particles of matter to try to draw them together.
audio-frequency amplifier (electronic component). An electronic amplifier capable of amplifying
alternating current whose frequency is in the range that can be heard by the human ear.
audio-frequency oscillator (electronic component). An electronic circuit that produces an alternating
current whose frequency is in the audio-frequency range.
audio-frequency vibrations. Vibrations at a frequency which produce sound that can be heard by the
　
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