direction of a fixed point (as the observer’s heading).
BASE LEG. A flight path at right angles to the landing runway off its approach end. The base
leg normally extends from the downwind leg to the intersection of the extended runway
centerline. See Traffic Pattern.

BEARING. The horizontal direction to or from any point, usually measured clockwise from true north or magnetic north.
BLAST FENCE. A barrier used to divert or dissipate jet blast or propeller wash.
BUILDING RESTRICTION LINE (BRL). A line that identifies suitable building area
locations on the airport.

CIRCLING APPROACH. A maneuver initiated by the pilot to align the aircraft with the
runway for landing when flying a predetermined circling instrument approach under IFR.
CLASS A AIRSPACE. See Controlled Airspace.
CLASS B AIRSPACE. See Controlled Airspace.
CLASS C AIRSPACE. See Controlled Airspace.
CLASS D AIRSPACE. See Controlled Airspace.
CLASS E AIRSPACE. See Controlled Airspace.

CLASS G AIRSPACE. See Controlled Airspace.
COMPASS LOCATOR (LOM). A low power, low/medium frequency radio-beacon installed
in conjunction with the instrument landing system at one or two or the marker sites.

CONTROLLED AIRSPACE. Airspace of defined dimensions within which air traffic control services are provided to instrument flight rules (IFR) and visual flight rules (VFR) flights in accordance with the airspace classification. Controlled airspace in the United States is designated as follows.