| Section A | A index | 341-349 of 917 terms |
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aircraft-to-satellite data relay—(Abbreviated ASDAR.) A communication method where data are sent from an aircraft to a satellite that relays the data to another location. This method extends line-of-sight communications.
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aircraft turbulence—Irregular motion of an aircraft in flight, especially when characterized by rapid up-and-down motion, caused by a rapid variation of atmospheric wind velocities. This can occur in cloudy areas (particularly towering cumulus and lenticular clouds) and in clear air. Turbulence is the leading cause of nonfatal passenger and flight attendant injuries. The U.S. Federal Aviation Administration (FAA) classifies aircraft turbulence as follows: | Light: Causes slight, erratic changes in altitude and/or attitude, and rhythmic bumpiness as occupants feel a slight strain against seat belts. |
| Moderate: Similar to light, but of greater intensity, with rapid bumps or jolts, and occupants feel a slight strain against seat belts. |
| Severe: Turbulence that causes large, abrupt changes in altitude and attitude, and large variations in airspeed, with the aircraft temporarily out of control. Occupants are forced violently against their seat belts and objects are tossed about, with food service and walking impossible. |
| Extreme: The aircraft is tossed about so violently that it is practically impossible to control, and structural damage may occur. |
See also clear air turbulence.
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aircraft weather reconnaissance—(Or weather reconnaissance,) The making of detailed weather observations or investigations from aircraft in flight. The aircraft may either fly regularly scheduled flights along a fixed route (usually over areas not covered by land or ship stations), or it may fly a special mission to survey a particular weather phenomenon such as a thunderstorm or tropical cyclone. The RECCO code is used to report weather reconnaissance data.
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AIREP—Abbreviation for air report. AIREP is also the name of the code used to transmit the air report information.
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airfield color code—A code used to summarize, by category, actual or forecast ceiling and visibility conditions at an airfield. Each ceiling and visibility category is assigned a specific color.
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airglow—(Also called light-of-the-night-sky, night-sky light, night-sky luminescence, permanent aurora.) The quasi-steady radiant emission from the upper atmosphere over middle and low latitudes, to be distinguished from the sporadic emission of auroras that occur over high latitudes. Airglow is a photochemical luminescence (or chemiluminescence) arising from chemical reactions in the upper atmosphere. Many of these reactions leave molecules and atoms in excited states from which they can radiate at certain well-defined wavelengths. Emissions from molecular oxygen O2, atomic oxygen O, sodium Na, and the hydroxyl radical OH are especially prominent, and measurements of airglow intensity by spectrometric techniques have provided a great deal of information about upper-atmospheric dynamics and chemistry.
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