Airspace class

The world's navigable airspace is divided into three-dimensional segments, each of which is assigned to a specific class. Most nations adhere to the classification specified by the International Civil Aviation Organization (ICAO) and described below, though they might use only some of the classes defined below, and significantly alter the exact rules and requirements. Similarly, individual nations may also designate Special Use Airspace with further rules for reasons of national security or safety.

ICAO definitions

On March 12, 1990, ICAO adopted the current airspace classification scheme. The classes are fundamentally defined in terms of flight rules and interactions between aircraft and Air Traffic Control (ATC). Generally speaking, the ICAO airspaces allocate the responsibility for avoiding other aircraft, namely either to ATC (if separation is provided) or to the aircraft commander (if not).

Some key concepts are: