The airspace is divided into seven classes, A to G.

Class A airspace is one with the highest level of requirements and services provided, it’s only for IFR flights. Usually used for the highest flight levels of enroute environment.

Class B airspace is designed usually for the world biggest aerodromes.

Class C airspace is the most commonly used controlled airspace both for enroute and terminal traffic.

Class D airspace is usually designed for aerodromes and TMAs with lower traffic levels.

All the above are controlled airspace items, which means that each flight is subject to an ATC clearance. You cannot enter them unless you have flight plan active, established two-way communication, and you must be cleared to get in.

Class E airspace is something in between, although classified as controlled one, it is controlled airspace for IFR and practically uncontrolled, like Class G, for VFR traffic. So, IFR flights are subject to an ATC clearance while VFR not. The air traffic services in Class E airspace are usually provided simultaneously by two units – ATC for IFR and FIS for VFR traffic.

Class F airspace is uncontrolled one offering advisory and flight information services. Rarely used, and if so, it would be usually as a temporary measure.

Class G airspace is uncontrolled airspace where flight information service is provided. In uncontrolled airspace radar service is available, usually on pilot’s request, the service is provided in some FIRs by ATC units on workload providing basis, in others the service, which is practically an advisory one, may be provided by FIS.

In all classes of airspace alerting service is provided.

The structure of airspace varies between FIRs, some do not have Class A, and/or B airspace, in others class E doesn’t exist. (Class F is very rare because it is considered as a “temporary” one).

Each airspace is mainly made up of the following elements:

Control Area or just Area – controlled enroute airspace where the ATC service is provided by area control (call sign “RADAR” / ”CONTROL” / ”CENTER”)

CTA – control area - generally means the controlled airspace governed by area control, at some locations, are designed CTAs where the ATC service is delegated to a different unit, i.e., piece of airspace delegated from area control to approach control. (call sign according to the unit providing service – “APPROACH”, or “RADAR” / “CONTROL” / “CENTER”)

TMA – terminal control area (former name: terminal manoeuvring area) - controlled airspace designed for transition between enroute and aerodrome/terminal environment, where the ATC service is provided by approach control (call sign “APPROACH”). In areas of high traffic level, the service may be divided into “ARRIVAL”, “DEPARTURE”, “DIRECTOR”.

CTR – control zone – controlled airspace designed for aerodrome traffic, where ATC service is provided by tower control (call sign “TOWER”). At busy aerodromes the service may be divided into tower control “TOWER”, ground control “GROUND” and clearance delivery “DELIVERY”.

All the above pieces of airspace can be also referred to as:CONTROLLED AIRSPACE

MCTR, MTMA or MATZ – military CTR, TMA or ATZ

ATZ – aerodrome traffic zone – uncontrolled airspace designed for some uncontrolled aerodromes, there may be a flight director or radio operator designated, if not, pilots shall broadcast their message. (call sign “RADIO” or, while broadcasting information, call sign “TRAFFIC” is also used).

In some congested ATZ the flight information service is provided by aerodrome flight information service (AFIS), (call sign “INFORMATION”)

In uncontrolled, area type airspace, there is flight information service provided (call sign “INFORMATION”). At some locations certain services may be provided by nearby ATC units.

Below we have a general picture of an airspace structure.