Airspace class
Encyclopedia
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.
and Air Traffic Control
(ATC). Some key concepts are:
ICAO adopted classifications:
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.
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.
has adopted a civil airspace system based on the United States National Airspace System (NAS):
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 "manoeuvring 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.
, 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.
, 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:
adopted a modified version of ICAO airspace classification on November 1, 2010. The division into classes for the airspace of Russia was introduced for the first time in the history of Russia.
The airspace above the territory of Russia is divided as follows:
Airspace controlled by Russia outside the territory of Russia has different division into classes and includes redefined Class A and Class G, but no class C airspace.
Specific boundaries of airspaces are determined by the Order of the Ministry of Transport of the Russian Federation #199 of September 15, 2010.
In addition the UK has a couple of special classes of airspace that do not fall within the ICAO classes:
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 Area
s (TRSA), which have special rules and still exist in a few places.
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 10000 feet (3,048 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
.
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.
Airspace
Airspace means the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere....
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
International Civil Aviation Organization
The International Civil Aviation Organization , pronounced , , is a specialized agency of the United Nations. It codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth...
(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 aircraftAircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
and Air Traffic Control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
(ATC). Some key concepts are:
- SeparationSeparation (air traffic control)In air traffic control, separation is the name for the concept of keeping an aircraft outside a minimum distance from another aircraft to reduce the risk of those aircraft colliding, as well as prevent accidents due to wake turbulence....
: 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 RulesInstrument flight rulesInstrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....
(IFR) or Special visual flight rulesSpecial visual flight rulesSpecial visual flight rules are a set of aviation regulations under which a pilot may operate an aircraft. It's a special case of operating under visual flight rules .- Use in different regions :...
(SVFR). All aircraft are subject to ATC clearance. All flights are separated from each other by ATC. Aircraft flying in Class A airspace are required to be IFR-equipped and have DMEDistance Measuring EquipmentDistance measuring equipment is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals....
if flying above FL240. This airspace is managed by Air Route Traffic Control Centers (ARTCCs) - Class B: Surrounds major hub airports with heavy traffic operations. This airspace is layered, generally in the form of an upside-down wedding cake, so that it surrounds all aircraft approaching or departing from the airport up to 10,000 feet MSL. Operations may be conducted under IFR, SVFR, or Visual flight rulesVisual flight rulesVisual flight rules are a set of regulations which allow a pilot to operate an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better than basic VFR weather minimums, as specified in the rules of the...
(VFR). All aircraft are required to receive an ATC clearance prior to entering Class B airspace. All flights are separated from each other by ATC. Required onboard equipment includes one VORVörIn Norse mythology, Vör is a goddess associated with wisdom. Vör is attested in the Prose Edda, written in the 13th century by Snorri Sturluson; and twice in kennings employed in skaldic poetry...
navigation unit. This airspace is managed by the approach/departure control facility linked to the airport with which the airspace is conjoined. Class B airspace is the most congested and the biggest airspace. You have to have certain specifications to be able to fly in class B airspace. These are: You must have a 2 way radio, to be able to have constant communication with ATC so you can stay updated with incoming aircraft and such. Also,you must have a mode C transponder(a mode C transponder is required in class A,B, and C airspace). This allows the ATC to see your current altitude. Class B airspace has been known as a sort of an upside down cake like airspace because of its shape (a circle).
- Class C: Operations may be conducted under IFR, SVFR, or VFR. Entering Class C airspace only requires radio contact with the controlling air traffic authority, but an ATC clearance is ultimately required. 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. This airspace is managed by the approach/departure control facility linked to the airport with which the airspace is conjoined.
- 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. The controlling authority for this airspace is the control tower for the associated airport, and radar may or may not be used.
- 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
Controlled airspace
Controlled airspace is an aviation term used to describe airspace in which ATChas the authority to control air traffic, the level of which varies with the different classes of airspace. Controlled airspace is established mainly for three different reasons:...
. Classes F and G are uncontrolled airspace
Uncontrolled airspace
Uncontrolled airspace is airspace where an Air Traffic Control service is not deemed necessary or cannot be provided for practical reasons. According to the airspace classes set by ICAO both class F and class G airspace are uncontrolled...
.
The table below provides an overview of the above classes, and the specifications for each.
| Class | Controlled Controlled airspace Controlled airspace is an aviation term used to describe airspace in which ATChas the authority to control air traffic, the level of which varies with the different classes of airspace. Controlled airspace is established mainly for three different reasons:... | IFR Instrument flight rules Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules .... | SVFR Special visual flight rules Special visual flight rules are a set of aviation regulations under which a pilot may operate an aircraft. It's a special case of operating under visual flight rules .- Use in different regions :... | VFR Visual flight rules Visual flight rules are a set of regulations which allow a pilot to operate an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better than basic VFR weather minimums, as specified in the rules of the... | ATC Clearance | Separation | Traffic Information |
|---|---|---|---|---|---|---|---|
| A | Required | Provided for all flights | N/A | ||||
| B | Required | Provided for all flights | N/A | ||||
| C | Required | Provided for all IFR/SVFR | Provided for all VFR | ||||
| D | Required | Provided for IFR/SVFR to other IFR/SVFR | Provided for all IFR and VFR | ||||
| E | Required for IFR | Provided for IFR/SVFR to other IFR/SVFR | Provided for all IFR where possible, to VFR where possible but only when requested | ||||
| F | Not Required | Provided for IFR/SVFR to other IFR/SVFR where possible | Provided where possible | ||||
| G | 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.Australia
AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
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 2500 feet (762 m) AGL (depicted in MSL on a chart). 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 8500 feet (2,590.8 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 aviationGeneral aviation
General aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...
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
Visual meteorological conditions
In aviation, visual meteorological conditions is an aviation flight category in which visual flight rules flight is permitted—that is, conditions in which pilots have sufficient visibility to fly the aircraft maintaining visual separation from terrain and other aircraft. They are the opposite of...
(VMC), IFR aircraft are not provided with full IFR services. During instrument meteorological conditions
Instrument meteorological conditions
Instrument meteorological conditions is an aviation flight category that describes weather conditions that require pilots to fly primarily by reference to instruments, and therefore under Instrument Flight Rules , rather than by outside visual references under Visual Flight Rules . Typically, this...
(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 "manoeuvring 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.
Canada
There are seven classes of airspace in Canada, and each is designated by a letter (A through G).Germany
In GermanyGermany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Classes A and B are not used at all. Class C is used for Airspace above Flight Level
Flight level
A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...
(FL) 100 (or FL 130 near the Alps
Alps
The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....
) 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 for airspace above FL 100 (or FL 130 near the AlpsAlpsThe Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....
) 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 2500 ft (762 m) AGL (around airports 1000 ft (304.8 m) or 1700 ft (518.2 m) AGL) and FL 100.
- Class F is used for IFR flight in uncontrolled airspace.
- Class G is used below 2500 ft (762 m) AGL (around airports below 1000 ft (304.8 m) AGL, then rises via a step at 1700 ft (518.2 m) to 2500 ft (762 m) AGL).
Lithuania
In LithuaniaLithuania
Lithuania , officially the Republic of Lithuania is a country in Northern Europe, the biggest of the three Baltic states. It is situated along the southeastern shore of the Baltic Sea, whereby to the west lie Sweden and Denmark...
, 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 (CTRControl zoneA control zone is an aviation term that describes a volume of controlled airspace, normally around an airport, which extends from the surface to a specified upper limit, established to protect air traffic operating to and from that airport...
); - in terminal control areas (TMATerminal Control AreaA terminal control area , also known as a terminal manoeuvring area in Europe, is an aviation term to describe a designated area of controlled airspace surrounding a major airport where there is a high volume of traffic...
); - in control area (CTAControl areaA control area is an aviation term that describes a volume of controlled airspace that exists in the vicinity of an airport. It has a specified lower level and a specified upper level. It usually is situated on top of a control zone and provides protection to aircraft climbing out from the airport...
); - in upper control area (UTA).
Russia
RussiaRussia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
adopted a modified version of ICAO airspace classification on November 1, 2010. The division into classes for the airspace of Russia was introduced for the first time in the history of Russia.
The airspace above the territory of Russia is divided as follows:
- Class A applies to airspace above and including 8100 m (the boundary between lower and upper airspace in Russia). All operations in Class A airspace must follow IFRInstrument flight rulesInstrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....
and are separated from each other by ATCAir traffic controlAir traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
. Permanent two-way radio contact with ATC is required. Permission for using airspace is required except for the special cases listed in clause 114 of the Federal rules for using Russian air space. - Class B is not used.
- Class C airspace is defined below 8100 m and allows IFR and VFRInstrument flight rulesInstrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....
operations. Both IFR and VFR operations are required to have permanent two-way radio contact with ATC. IFR flights are separated from each other and from VFR flights. VFR flights are separated from IFR flights and are provided traffic information about other VFR flights. Permission for using airspace is required. - Class D is not used.
- Class E is not used.
- Class F is not used.
- Class G airspace is defined wherever Class A and Class C airspaces are not defined. Class G airspace allows IFR and VFR operations. For altitudes less than 3000 m (9843 ft) the speed must not exceed 450 km/h (280 mph). Flights are provided with flight information service as requested. IFR flights are required to have permanent two-way radio contact with ATC. No separation is provided by ATC. Prior notification of using airspace is required.
Airspace controlled by Russia outside the territory of Russia has different division into classes and includes redefined Class A and Class G, but no class C airspace.
Specific boundaries of airspaces are determined by the Order of the Ministry of Transport of the Russian Federation #199 of September 15, 2010.
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 LondonLondonLondon is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
, Birmingham and Manchester. - The London Control Zone around HeathrowLondon Heathrow AirportLondon Heathrow Airport or Heathrow , in the London Borough of Hillingdon, is the busiest airport in the United Kingdom and the third busiest airport in the world in terms of total passenger traffic, handling more international passengers than any other airport around the globe...
and the Channel IslandsChannel IslandsThe Channel Islands are an archipelago of British Crown Dependencies in the English Channel, off the French coast of Normandy. They include two separate bailiwicks: the Bailiwick of Guernsey and the Bailiwick of Jersey...
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. (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, GlasgowGlasgow International AirportGlasgow International Airport is an international airport in Scotland, located west of Glasgow city centre, near the towns of Paisley and Renfrew in Renfrewshire...
, 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), i.e. 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. ATC units may provide an "as far as practical" form of separation between some such flights, but participation in the service is voluntary.
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 2000 ft (609.6 m) AAL (above aerodrome level). 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.
- Military Air Traffic Zones (MATZ) are zones from the surface to 3000 ft (914.4 m) AAL (above aerodrome level) set up for 5 nm around military air bases in class G airspace. Stubs, 4 nm wide and 5 nm in length, extend from the main zone, are orientated with the aerodrome's main runway, and start at 1000 ft (304.8 m) and go up to 3000 ft (914.4 m). Military aircraft treat these as if they are controlled airspace; civilian traffic are advised but not obliged to do the same.
United States
The U.S.United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
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 Area
Terminal Radar Service Area
In United States aviation, a terminal radar service area is a delimited airspace in which radar and air traffic control services are made available to pilots flying under instrument flight rules or visual flight rules for the purposes of maintaining aircraft separation.TRSAs are most often...
s (TRSA), which have special rules and still exist in a few places.
- With some exceptions, Class A airspace is applied to all airspace between 18000 feet (5,486.4 m) and Flight LevelFlight levelA Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...
600 (approximately 60,000 ft). Above FL600, the airspace reverts to Class E. The transition altitude is also consistently 18000 feet (5,486.4 m) everywhere. 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 airportAirportAn airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...
s, in an inverted wedding cake shape that is designed to contain arriving and departing commercial air traffic operating under IFR, up to 10000 feet (3,048 m) above MSLSea levelMean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
(12,000 feet MSL around Denver, ColoradoDenver, ColoradoThe City and County of Denver is the capital and the most populous city of the U.S. state of Colorado. Denver is a consolidated city-county, located in the South Platte River Valley on the western edge of the High Plains just east of the Front Range of the Rocky Mountains...
). Aircraft must have established two-way radio communications with ATC, and obtained permission to enter the airspace.
- 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.
- 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' AGLAbove ground levelIn aviation and atmospheric sciences, an altitude is said to be above ground level when it is measured with respect to the underlying ground surface. This is as opposed to above mean sea level , or in broadcast engineering, height above average terrain...
or 1,200' AGL, or a customized floor of any other altitude. Class E airspace exists above Class G surface areas from 14,500' MSLSea levelMean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
to 18,000 MSL. Federal airwaysAirway (aviation)In aviation, an airway is a designated route in the air. Airways are laid out between navigational aids such as VORs, NDBs and Intersections ....
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 (uncontrolled) airspace is mostly used for a small layer of airspace near the ground, but there are larger areas of Class G airspace in remote regions.
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 10000 feet (3,048 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
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
and/or a transponder
Transponder
In telecommunication, the term transponder has the following meanings:...
.
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.