For a general discussion of airspace classes, see Airspace class.

Airspace classes A through E are controlled.

It is surrounded by a control zone of airspace class "D" which is active during the hours of operation.

In Sweden, airspace is divided into airspace class C and G only.

Airspace class (United States)

The airspace class (A, B, etc.) in which special use airspace is found still controls the requirements and procedures for flying into/through it.

ICAO classifies airspace in seven classes from airspace classes.

The chart also provides information on airspace classes, ground-based navigation aids, radio frequencies, longitude and latitude, navigation waypoints, navigation routes.

This article describes the implementation of International Civil Aviation Organization airspace classes in the United States of America.

According to the airspace classes set by ICAO both class F and class G airspace are uncontrolled.

Some airspace categories have no correlation with ICAO airspace classes but are nevertheless important in United States airspace.

Tivat Airport is assigned 4D classification by ICAO, airspace class D, and is noted for its challenging approach and landing procedures.

Class D is used for controlled zones, or above and around airspace Class C designated zones where CVFR is not necessary.

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

The airspace above the bay is frequently used for flight training due to its proximity to Oakland International Airport and other local airports, but being outside of San Francisco's airspace class.

In the USA the term control zone is no longer used and has been replaced by airspace class D. Typically it extends 5 miles in diameter with a height of 2500 ft AGL (above ground level) around small commercial airports.

The Albert ROPER (1919-10-13 The Paris Convention) implementation of International Civil Aviation Organization (ICAO) airspace classes defines Classes A through E and Class G. Class F is not used in the United States.

(AIM 3-2-2) Unlike the altitude measurements used in other airspace classes, the FLnnn flight levels used in Class A airspace are pressure altitudes referenced to a standardized altimeter setting of 29.92" Hg and thus the true altitudes depend on local atmospheric pressure variations.

An exception to this rule is class B airspace class, in which ATC separates VFR traffic from other VFR traffic and from IFR traffic, which is why in Class B Airspace lower cloud clearance is required.

In the UK, an "IMC rating" which permits flight under IFR in airspace classes B to G in instrument meteorological conditions, a non-instrument-rated pilot can also elect to fly under IFR in visual meteorological conditions outside controlled airspace.

On May 27, 2010, the FAA published its final rule mandating that by 2020 all aircraft owners will be required to have ADS-B Out capabilities when operating in any airspace that currently requires a transponder (airspace classes A, B, and C, and airspace class E at certain altitudes).