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The region of the atmosphere above which aircraft cannot fly.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(Aeronautics) the region of the upper atmosphere above which aircraft cannot fly
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
the indefinite boundary in the upper atmosphere beyond which the air is too thin for conventional aircraft to operate.
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
Region in which functional effects of the atmosphere on man and aircraft cease to exist.
Dictionary of Military and Associated Terms. US Department of Defense 2005.
the region in the upper part of the earth’s atmosphere where the air is too thin for aircraft to operate properly.See also: Atmosphere, Aviation
-Ologies & -Isms. Copyright 2008 The Gale Group, Inc. All rights reserved.