above obstruction level

above obstruction level (AOL)

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.