Airspace classes

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.

On March 12, 1990, ICAO adopted the current airspace classification scheme. The classes are fundamentally defined in terms of 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:

Note: These are the ICAO definitions. Country-specific adaptations (such as "two-way communications" instead of "clearance" for Class C in the US) are discussed in the sections below.

Special Airspace: these may limit pilot operation is certain ares. Consist of Prohibited areas, Restricted areas, Warning Areas, MOAs (military operation areas), Alert areas, Controlled firing areas (CFAs) all on can be found on the flight charts.

Classes A–E are referred to as controlled airspace. Classes F and G are uncontrolled airspace.

The table below provides an overview of the above classes, and the specifications for each.

Each national aviation authority determines how it uses the ICAO classifications in its airspace design. In some countries, the rules are modified slightly to fit the airspace rules and air traffic services that existed before the ICAO standardisation.

Australia has adopted a civil airspace system based on the United States National Airspace System (NAS):

Australia used to have a non-standard class of airspace for use at the capital city general aviation airports, called a General Aviation Airport Procedures Zone (GAAP Zone). A control tower provided procedural clearances for all aircraft inside the zone. Additionally, any aircraft operating within 5 nmi (9.3 km; 5.8 mi) of the zone must obtain a clearance. VFR aircraft arrive and depart using standard arrival and departure routes, while instrument arrival and departure procedures are published for IFR operations. During visual meteorological conditions (VMC), IFR aircraft are not provided with full IFR services. During instrument meteorological conditions (IMC), or marginal VMC, VFR operations are restricted in order to facilitate full IFR service for IFR aircraft.

...
Wikipedia