above obstruction level

above obstruction level (AOL)

above obstruction level (AOL)click for a larger image
The height of an aircraft above terrain, structures, and obstacles in the area of operation. The height is nominated for aircraft carrying out very low flying. Pilots either take into consideration heights indicated on maps and charts when calculating the height they need to fly or use terrain-following radar, so they can maintain constant height. The height above obstacles may be equal to or higher than the height above ground level (AGL). See also above ground level.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
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