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flight level[′flīt ‚lev·əl]
A surface of constant atmospheric pressure which is related to the standard pressure datum.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
flight level (FL)
A surface of constant atmospheric pressure that is related to a specific pressure datum, 1013.2 hectopascals (29.92 in. of mercury), and is separated from other such surfaces by specific pressure intervals. Each flight level is stated in three digits that represent hundreds of feet. For example, flight level 270 represents a pressure altitude of 27,000 ft with the altimeter set at 1013.2 hectopascals (29.92 in. of mercury). Consecutive flight levels are separated by a pressure interval corresponding to at least 500 ft (150 m) in the standard atmosphere. This does not preclude reporting intermediate levels in increments of 100 ft (30 m). See level (i).
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved