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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.
The classifications adopted by ICAO are:
- 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 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.
- 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.
As of 2004, ICAO is considering a proposal to reduce the number of airspace classifications to three, 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 a funnel 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). Class C airspace is used around airports and military air bases 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' 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.
from JROTC.ORG
Class B Airspace
Class C Airspace
Class D Airspace
Class E Airspace
Generally, if the airspace is not Class A, Class B, Class C, or Class D, and it is controlled airspace, it is Class E airspace. Class E airspace extends upward from either the surface or a designated altitude to an overlying or adjacent controlled airspace. Unless designated at a lower altitude, Class E airspace begins at 14,500 feet MSL over the United States. Class E airspace does not include the airspace at 18,000 feet MSL and above.
Class G Airspace
All airspace not designated as Class A, Class B, Class C, Class D, or Class E airspace, is deemed to be uncontrolled airspace, and is designated as Class G airspace.
Special Use Airspace
Each sectional chart in the US. contains a listing of all the special use airspace contained within that chart. The listing also identifies the controlling agency. Special use airspace has seven categories:
Prohibited Area (P)
Prohibited airspace is a portion of airspace within which aircraft operations are explicitly prohibited. Permission to penetrate a Prohibited Area is not granted.
Restricted Area (R)
This is special use airspace with restricted access. Restricted Areas denote the existence of unusual aircraft hazards, e.g., missile and gunnery activity. Penetration of Restricted Areas may be granted at times by the controlling agency
Warning Area (W)
Warning Areas exist in airspace overlying international waters. These areas lie beyond the three-mile limit offshore. Warning areas typically contain hazards similar to those found in Restricted Areas.
Military Operations Area (MOA)
MOAs are areas of defined vertical and lateral boundaries established for military training activities. Permission is not required prior to penetrating an MOA but pilots should exercise extreme caution. Pilots should contact the nearest FAA Flight Service Station to obtain information regarding current activities in an MOA prior to departure.
Alert Area (A)
Alert Areas typically contain a high volume of pilot training or unusual type of aerial activity. Flight within Alert Areas is not restricted, but pilots should exercise extreme caution. Pilots are fully responsible for collision avoidance in Alert Areas.
Air Defense Identification Zone (ADIZ)
Air Defense Identification Zones have been established to facilitate early identification of all aircraft entering into or operating in the vicinity of the U.S. All aircraft entering domestic airspace must provide for identification prior to entry
Temporary Flight Restrictions
Temporary flight restrictions are usually issued by NOTAM to protect persons/property from a hazard associated with events on the ground - such as toxic spills., volcanic eruptions, forest fires, or any event that might attract sightseers -when low flying aircraft would magnify that hazard.
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, Cotswold and Worthing.
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 Newcastle upon Tyne.
- A few airways in less busy areas allowing mid-level military VFR flights.
Class E
Parts of the Belfast and Scottish TMAs and a small part of the Durham Tees Valley CTR.
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 IFR flight in Class G airspace is relatively common and ATC units may provide an "as far as is practical" form of separation between some such flights.
A clearance is not required for VFR flights within Class E airspace, however pilots are strongly advised to contact the appropriate ATSU.
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 Information Officer or Air/Ground radio unit on the airport before entering the zone (in the case of an uncontrolled airfield), or must obey ground signals if non-radio.[1]
Military Air Traffic Zones (MATZ) are zones from the surface to 3,000 ft (900 m) AAL set up around military air bases in class G airspace. Military aircraft treat these as if they are controlled airspace; civilian traffic is 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.
In addition, Australia has 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 provides 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 VMC, IFR aircraft are not provided with full IFR services. During IMC, or marginal VMC, VFR operations are restricted in order to facilitate full IFR service for IFR aircraft.
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
- ^ Godwin, Peter (1987-2004). The Air Pilot's Manual: Aviation Law And Meteorolgy. Cranfield, England: Air Pilot Publishing Ltd.
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