25 attenuate
ATIS abbreviation Automatic Terminal
Information Service ATM /e. ti em/ abbreviation air traf-fic management
atmosphere /tm.sf../ noun 1. a
mixture of gases in a mass surrounding the earth . The surrounding atmosphere moves with the earth. 2. a unit of meas-urement of pressure
COMMENT: The main gases found in the atmosphere are nitrogen and oxygen. The atmosphere contains less than 1% carbon dioxide and argon, and also traces of hydrogen, helium, krypton, neon, ozone and xenon.
atmospheric /tm.sfer.k/ adjec-tive referring to the atmosphere .
atmospheric density

atmospheric attenuation
/tm.sfer.k .tenjuei.(.)n/ noun
the weakening of a radio signal as it passes through the air

atmospheric pollution
/tm.sfer.k p.lu.(.)n/ noun same as air pollution . Solid particles in the air include dust, sand, volcanic ash and atmospheric pollution.

atmospheric pressure
/tm.sfer.k pre../ noun normal air pressure on the surface of the earth

atmospheric refraction
/tm.sfer.k r.frk..n/ noun
change in direction of waves due to var-iations in temperature, pressure and humidity, particularly at lower altitudes
atom /t.m/ noun the smallest amount of a substance which can take part in a chemical reaction . An atom consists of a nucleus and electrons.
atomic /.t.m.k/ adjective referring to atoms . atomic structure of matter the structure of materials and sub-stances at their smallest level
atomisation /t.ma.ze..n/, atomi-zation /t.ma.ze..(.)n/ noun the reduction of liquids to a fine spray . The fuel achieves fine atomisation under pressure.
atomise /t.ma.z/, atomize verb to
reduce liquids to a fine spray . The fuel must be atomised or vaporised to com-bine with the air to permit combustion.
ATPL abbreviation Airline Transport Pilot’s Licence
ATS abbreviation air traffic services ATSU abbreviation air traffic service unit
attach /.tt./ verb to join or fix something to something . The ice detector is attached to the fuselage.
attachment /.tt.m.nt/ noun 1.
the act of joining or fixing something to something . The attachment of winglets improved the handling characteristics of the aeroplane. 2. an accessory which can be attached . The video camera is sold with a number of attachments including a carrying strap and a battery pack.
attachment point /.tt.m.nt p..nt/ noun a place on the airframe where something such as an engine is attached by means of bolts . Additional strength is required for the power plant attachment points.
attain /.te.n/ verb to reach, to achieve something, often with difficulty . In order to attain a fuller understanding of gas turbines, it is essential to know something about basic gas laws.
attempt /.tempt/ noun a try . Any
attempt to increase range by applying more power is of little or no benefit. . verb to try . He attempted to land despite the poor visibility but then decided to divert to another airfield where he landed safely.