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:

Airspace class (United States)

The United States airspace system's classification scheme is to provide maximum pilot flexibility with acceptable levels of risk appropriate to the type of operation and traffic density within that class of airspace – in particular to provide separation and active control in areas of dense or high-speed flight operations.

The Albert ROPER (1919-10-13 The Paris Convention) implementation of International Civil Aviation Organization (ICAO) airspace classes defines classes A through G (with the exception of class F which is not used in the United States). The other U.S. implementations are described below. The United States also defines categories of airspace that may overlap with classes of airspace. Classes of airspace are mutually exclusive. Thus, airspace can be "class E" and "restricted" at the same time, but it cannot be both "class E" and "class B" at the same location and at the same time.

Note: All airspace classes except class G require air traffic control (ATC) clearance for instrument flight rules (IFR) operations.