BIT: Built-in test. Self-testing capabilities contained within an instrument or system.
Caution Area: An area within which military training activities, though not hazardous, are of interest to
Ceiling: The height above the earths surface of the lowest layer of clouds or other obscuring
phenomena. This layer is described as broken, overcast, or obscuration and not classified as thin
Circling Approach: A maneuver initiated by the pilot to visually align the aircraft with a runway for
landing. This maneuver may be made only with ATC authorization and if the pilot has established the
required visual reference to the airport.
Class D Airspace: That airspace which surrounds tower controlled airfields and extends 4.4 nm in radius
from the center and to 2,500 ft above the airport. Radio communication with the tower is required within
this airspace. (Depicted as a segmented blue line on low altitude enroute charts)
Clearance Limit: The fix to which an aircraft is cleared when issued an ATC clearance.
Compulsory Reporting Point: A point the passage of which must be reported to ATC, unless in radar
Contact Approach: A pilot-requested approach wherein an aircraft on an IFR flight plan, operating clear
of the clouds with at least 1 sm visibility and having ATC authorization, may deviate from the prescribed
instrument approach procedure and proceed to the airport of destination by visual reference to the
Controlled Airspace: Airspace designated as Class A through Class E within which some or all aircraft
may be subject to air traffic control.
Course: A magnetic direction to fly in relation to a radio navigational facility. Note that a course is not
simply a heading. For flight inbound on a radial, the course is the reciprocal of the radial. For flight
outbound, the course and the radial are the same.