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. Individual nations also designate Special Use Airspace, which places further rules on air navigation 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). Some key concepts are:

Separation: Maintaining a specific minimum distance between an aircraft and another aircraft or terrain to avoid collisions, normally by requiring aircraft to fly at set levels or level bands, on set routes or in certain directions, or by controlling an aircraft's speed.
Clearance: Permission given by ATC for an aircraft to proceed under certain conditions contained within the clearance.
Traffic Information: Information given by ATC on the position and, if known, intentions of other aircraft likely to pose a hazard to flight.

ICAO adopted classifications

Class A: All operations must be conducted under Instrument Flight Rules (IFR) or Special visual flight rules (SVFR) and are subject to ATC clearance. All flights are separated from each other by ATC. Class A airspace starts at FL 180 (18,000 ft) to FL 600 (60,000 ft). And also must change from the local altimeter to 29.92 inHg or 1013.2 mb.
Class B: Operations may be conducted under IFR, SVFR, or Visual flight rules (VFR). All aircraft are subject to ATC clearance. All flights are separated from each other by ATC.
Class C: Operations may be conducted under IFR, SVFR, or VFR. All flights are subject to ATC clearance. Aircraft operating under IFR and SVFR are separated from each other and from flights operating under VFR. Flights operating under VFR are given traffic information in respect of other VFR flights.From the primary airport or satellite airport with an operating control tower must establish and maintain two-way radio communications with the control tower.
Class D: Operations may be conducted under IFR, SVFR, or VFR. All flights are subject to ATC clearance. Aircraft operating under IFR and SVFR are separated from each other, and are given traffic information in respect of VFR flights. Flights operating under VFR are given traffic information in respect of all other flights.
Class E: Operations may be conducted under IFR, SVFR, or VFR. Aircraft operating under IFR and SVFR are separated from each other, and are subject to ATC clearance. Flights under VFR are not subject to ATC clearance. As far as is practical, traffic information is given to all flights in respect of VFR flights.
Class F: Operations may be conducted under IFR or VFR. ATC separation will be provided, so far as practical, to aircraft operating under IFR. Traffic Information may be given as far as is practical in respect of other flights.
Class G: Operations may be conducted under IFR or VFR. ATC separation is not provided. Traffic Information may be given as far as is practical in respect of other flights.

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.

Class	Controlled	IFR	SVFR	VFR	ATC Clearence	Separation	Traffic Information
A	Controlled	Yes	Yes	No	Required	Provided for all flights	N/A
B	Controlled	Yes	Yes	Yes	Required	Provided for all flights	N/A
C	Controlled	Yes	Yes	Yes	Required	Provided for all IFR/SVFR	Provided for all VFR
D	Controlled	Yes	Yes	Yes	Required	Provided for IFR/SVFR to other IFR/SVFR	Provided for all IFR and VFR
E	Controlled	Yes	Yes	Yes	Required for IFR	Provided for IFR/SVFR to other IFR/SVFR	Provided for all IFR and VFR where possible
F	Uncontrolled	Yes	No	Yes	Not Required	Provided for IFR/SVFR to other IFR/SVFR where possible	Provided where possible
G	Uncontrolled	Yes	No	Yes	Not Required	Not provided	Provided where possible

As of 2004, ICAO is considering a proposal to reduce the number of airspace classifications to three (N, K and U), which roughly correspond to the current classes C, E and G.

Use of airspace classes

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.

United States

The U.S. adopted a slightly modified version of the ICAO system on September 16, 1993, when regions of airspace designated according to older classifications were converted wholesale. The exceptions are some Terminal Radar Service Areas (TRSA), which have special rules and still exist in a few places.

With some exceptions, Class A airspace is applied to all airspace between 18,000 feet (5,500 m) and Flight Level 600 (approximately 60,000 ft). Above FL600, the airspace reverts to Class E (Reference Order 7400.9P, Subpart E). The transition altitude (see Flight level) is also consistently 18,000 feet (5,500 m). All operations in US Class A airspace must be conducted under IFR. SVFR flight in Class A airspace is prohibited.

Class B airspace is used around major airports, in an inverted wedding cake shape that is designed to contain arriving and departing commercial air traffic operating under IFR, up to 10,000 feet (3,000 m) above MSL (12,000 feet above Denver, Colorado). And must have established 2 way radio communications with ATC.

Class C airspace is used around airports with a moderate traffic level.

Class D is used for smaller airports that have a control tower. The U.S. uses a modified version of the ICAO class C and D airspace, where only radio contact with ATC rather than an ATC clearance is required for VFR operations.

Class E Other controlled airspace is designated as Class E - this includes a large part of the lower airspace. Class E airspace exists in many forms. It can serve as a surface-based extension to Class D airspace to accommodate IFR approach/departure procedure areas. Class E airspace can be designated to have a floor of 700' AGL (above ground level) or 1,200' AGL. Class E airspace exists above Class G surface areas from 14,500' MSL (mean sea level) to 18,000 MSL. Federal airways from 1,200 AGL to 18,000 MSL within 4 miles (6 km) of the centerline of the airway is designated Class E airspace. Airspace at any altitude over 60,000' (the ceiling of Class A airspace) is designated Class E airspace.

The U.S. does not use ICAO Class F.

Class G airspace (Uncontrolled) is mostly used for a small layer of airspace near the ground, but there are larger areas of Class G airspace in remote regions.

Canada

Canada generally follows the United States in application of airspace with some differences. For example, Canadian class "C" airspace is procedurally equivalent to United States class "B" airspace. Additionally, the term "Class F" is used for Special Use Airspace; this includes Advisory airspace and Restricted airspace.

Germany

In Germany, Classes A and B are not used at all. Class C is used for Airspace above Flight Level (FL) 100 (or FL 130 near the Alps) up to FL 660. Airspace is divided into lower airspace below FL 245 and upper airspace above FL 245.

Class A is not used.

Class B is not used.

Class C is used for controlled zones above and around airports and airspace above FL 100 (or FL 130 near the Alps) up to FL 660.

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

Class E is used for airspace between usually 2,500 ft (760 m). AGL (around airports 1,000 ft (300 m). or 1700 ft. AGL) and FL 100.

Class F is used for IFR-Flight in uncontrolled airspace.

Class G is used below 2,500 ft (760 m) AGL (around airports below 1,000 ft (300 m) AGL, then rises via a step at 1,700 ft (520 m) to 2,500 ft (760 m) AGL)

Lithuania

In Lithuania, Classes A and B are generally not used at all. Classes C and D are used in the following areas of controlled airspace of the Republic of Lithuania:

in control zones (CTR);
in terminal control areas (TMA);
in control area (CTA);
in upper control area (UTA).

Source: Airfield Guide Lithuania, 29 SEP 2005, ENR 1.1-1

United Kingdom

Class A

All airways up to FL 195 with the exception of airways lying within the Belfast CTR/TMA and the Scottish TMA.
The Terminal Control Areas (TMAs) around London and Manchester.
The London Control Zone around Heathrow and the Channel Islands Control Zone; these areas are thus off-limits to VFR flights (however Special VFR is used as a get-around for this).
The CTAs of Daventry, Clacton, Cotswold and Worthing.

Airways typically start at FL 70 and routing options become more attractive above FL 140.

Class B

No Class B in the UK

Class C

All UK airspace between FL 195 and FL 660. N.b: The Upper Flight Information Region (UIR) boundary begins at FL 245

Class D

The CTRs and CTAs around the larger airfields except London Heathrow, such as London Gatwick, Glasgow, Birmingham and Manchester.
A few airways in less busy areas allowing mid-level military VFR flights.

Class E

Parts of the Belfast and Scottish TMAs.

A clearance is not required for VFR flights within Class E airspace, however pilots are strongly advised to contact the appropriate ATSU.

Class F

"Advisory Routes" (ADRs): regularly used routes similar to airways but where traffic levels are not high enough to warrant establishment of an airway.

Class G

All remaining airspace, comprising by far the largest part of the airspace below FL 195. The UK is unusual in that it has not adopted a widespread class E system of airways for most airspace lower than FL 70. Therefore for light aircraft, IFR flight in Class G airspace is relatively common. Use of a radio or transponder is not required, even in IMC.^[1]

ATC units may provide an "as far as practical" form of separation between some such flights, but participation in the service is voluntary. ^[2]

In addition the UK has a couple of special classes of airspace that do not fall within the ICAO classes:

Aerodrome Traffic Zones (ATZ) are zones around an airport with a radius of 2 nm or 2.5 nm, extending from the surface to 2,000 ft (600 m) AAL. Aircraft within an ATZ must obey the instructions of the tower controller (if present), or must make radio contact with the Aerodrome Flight Information Service unit or Air/Ground Communication Service unit for the aerodrome before entering the zone (in the case of an uncontrolled airfield), or must obey ground signals if non-radio.^[3]

Military Air Traffic Zones (MATZ) are zones from the surface to 3,000 ft (900 m) AAL (above aerodrome level) set up for 5nm around military air bases in class G airspace. Stub's, 4nm wide and 5 nm in length, extend from the main zone, orientated with the aerodrome's main runway start at 1,000 ft (300 m) and go up to 3,000 ft (900 m). Military aircraft treat these as if they are controlled airspace; civilian traffic are advised but not obliged to do the same.

Australia

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

Class A is used above FL 180 along the populated coastal areas, and above FL 245 elsewhere.
Class B is not used.
Class C is used in a 360° funnel shape in the Terminal Control Zones of the major international airports, extending up to the base of the Class A, generally at FL 180 over these airports. It also overlays Class D airspace at smaller airports.
Class D is used for the Terminal Control Zones of medium sized airports, extending from the surface up to 4,500 feet (1,370 m). Above this, Class C airspace is used, although generally only in a sector, and not 360° around the airport.
Class E is used along the populated coastal areas, from 8,500 feet (2,590 m) to the base of the overlying Class A or Class C airspace.
Class F is not used.
Class G is used wherever other classes are not - almost always from the surface to the base of the overlying Class A, C, D or E airspace.

Transition from GAAP to Class D

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 nm 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.

As of the 3rd of June 2010, all GAAP aerodromes were changed to Class D aerodromes, and the previous Class D procedures were changed. The new Class D procedures are similar to the FAA Class D procedures. VFR Aircraft are no longer required to enter the airspace via set inbound/outbound points, however can be directed there by ATC. VFR and IFR aircraft now require taxi clearance in the "movement area" of the aerodrome, but can still taxi within set apron areas without a clearance. IFR aircraft now receive slot times and the visibility requirements of Special VFR are reduced from 3000m Visibility to 1600m.

Airspace classes and VFR

Authorities use the ICAO definitions to derive additional rules for VFR cloud clearance, visibility, and equipment requirements.

For example, consider Class E airspace. An aircraft operating under VFR may not be in communication with ATC, so it is imperative that its pilot be able to see and avoid other aircraft (and vice versa). That includes IFR flights emerging from a cloud, so the VFR flight must keep a designated distance from the edges of clouds above, below, and laterally, and must maintain at least a designated visibility, to give the two aircraft time to observe and avoid each other. The low-level speed limit of 250 knots does not apply above 10,000 feet (3,000 m), so the visibility requirements are higher.

On the other hand, in Class B airspace, separation is provided by ATC to all flights. Now the VFR flight only needs to see where it is going, so visibility requirements are reduced and there is no designated minimum distance from clouds.

Similar considerations determine whether a VFR flight must use a two-way radio and/or a transponder.

Special use airspace

Each national authority designates areas of special use airspace (SUA), primarily for reasons of national security. This is not a separate classification from the ATC-based classes; each piece of SUA is contained in one or more zones of letter-classed airspace.

SUAs range in restrictiveness, from areas where flight is always prohibited except to authorized aircraft, to areas that are not charted but are used by military for potentially hazardous operations (in this case, the onus is on the military personnel to avoid conflict). Refer to the external links for more specific details.

References

^ http://www.caa.co.uk/docs/64/200890108ATSAirspaceClassificationV3.pdf
^ http://www.airspacesafety.com/content/ATSOCAS.asp
^ Godwin, Peter (1987–2004). The Air Pilot's Manual: Aviation Law And Meteorolgy. Cranfield, England: Air Pilot Publishing Ltd.{{cite book}}: CS1 maint: date format (link)

External links

[1] ttp://www.caa.co.uk/docs/64/200890108ATSAirspaceClassificationV3.pdf

[2] ttp://www.airspacesafety.com/content/ATSOCAS.asp

[3] Godwin, Peter (1987–2004). The Air Pilot's Manual: Aviation Law And Meteorolgy. Cranfield, England: Air Pilot Publishing Ltd.{{cite book}}: CS1 maint: date format (link)

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