Canadian airspace is divided into seven classifications. Each is identified by a single letter – A, B, C, D, E, F, G – and all follow a structure established in 1990 by the International Civil Aviation Organization (ICAO). The classes are defined by their dimensions, their respective flight rules, and by the interactions between aircraft and air traffic control (ATC) within them.
Class A airspace is High Level Airspace. It is divided into Southern Domestic Airspace (SDA) and Northern Domestic Airspace (NDA). NDA is further subdivided into a Northern Control Area (NCA) and an Arctic Control Area (ACA). In the SDA, Class A starts at 18,000 ft ASL (also called Flight Level 180, or FL180) and extends up to 60,000 ft (FL600). In the NCA, Class A begins at FL230 while in the ACA it begins at FL270. The airspace between FL180 and the beginning of Class A in the NDA is designated as Class G airspace.
The dimensions of Class B are from 12,500 ft ASL up to, but not including, 18,000 ft ASL. It is comprised of designated airways and any other control areas that may extend upward to the upper limit of the class. Control Zones, which are established around airports where there are operating control towers, and Terminal Control Areas within which Control Zones are located, may be classified as Class B airspace.
Terminal Control Areas, and their associated Control Zones, may also be classified as Class C airspace. Class C is, in fact, usually a Control Zone surrounding a large airport. Such Control Zones can have a radius of 3 to 10 nautical miles, and a height of 3,000 ft AGL. When the ATC unit within Class C is not in operation, Class C airspace converts to Class E.
Class D airspace, like Class C, is usually a Control Zone, though located around a smaller airport. It typically has a 5 nautical mile radius, with a height of 3,000 ft AGL. Just like Class C, when ATC in Class D is not in operation, the airspace becomes Class E.
Class E airspace is used for Low Level Airways, Control Area Extensions (CAE), and Control Zones for aerodromes with very little traffic. A CAE surrounds and overlies an associated Control Zone, is usually circular with a defined radius, and extends up to 18,000 ft ASL. Class E may be so designated where an operational need exists that doesn’t meet the requirements for Classes A, B, C, or D.
Class F airspace contains activities that, owing to their nature, must be confined to that airspace. Limitations may be imposed on aircraft that are not part of those activities. The restrictions may be temporary or permanent, and may be classified as advisory or restricted. Examples of the types of activities that may be taking place in Class F include: aerobatics, hang gliding, military operations, parachuting, soaring, and training.
Any airspace that is not designated as A, B, C, D, E, or F, is Class G airspace. Classes A through E are controlled, though in Class E there are no special requirements for VFR traffic, except that VFR minima must be maintained as is applicable to controlled airspace. Class F can be controlled or uncontrolled. Class G is always uncontrolled.
To enter Class A, B, or C – and when specified for Class D and E – an aircraft needs a functional Mode C transponder. A clearance to enter from ATC is required for Classes A, B, C, while contact must be established with ATC prior to entering Class D.
Any aircraft may fly in Class E and G airspace. Flight in Class F Advisory airspace is permitted; however, flight in Class F Restricted is not allowed, unless authorization has been granted by the agency that has jurisdiction over the airspace.
Flights in Class A must be conducted under Instrument Flight Rules (IFR). Classes B, C, D, E and G permit operations for aircraft operating under IFR, as well as Visual Flight Rules (VFR). ATC provides separation to all aircraft in Class A and B. In Class C, separation is provided between IFR traffic and other IFR and VFR flights. Also, in Class C, ATC can provide to radar-identified flights operating under VFR, traffic information and conflict resolution in respect of other VFR flights. In Classes D and E, separation is only provided to IFR traffic. ATC does not exercise control over air traffic in Class G, but it can provide flight information and alerting services.