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transition level[tran′zish·ən ‚lev·əl]
The flight level below which heights are expressed in feet above mean sea level and are based on an approved station altimeter setting.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The lowest flight level available for use above the transition altitude. See also transition altitude.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved