Airspace class (United States)

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This article describes the implementation of ICAO airspace classes in the United States of America. For a general discussion of airspace classes, see Airspace class.

The United States implementation of ICAO airspace classes defines Classes A through E and Class G. Class F is not used in the United States. The other U.S. implementations are described below. The United States also defines categories of airspace that may overlap with classes of airspace. Classes of airspace are mutually exclusive. Thus, airspace can be Class E and Restricted at the same time, but it cannot be both Class E and Class B at the same location and at the same time.

Note: All airspace classes except Class G require ATC clearance for IFR operations.

Contents

[edit] Airspace classes

[edit] Class A

Class A airspace extends from 18,000 feet MSL to FL600 (approximately 60,000 feet MSL) throughout the United States.

All flight operations in Class A airspace must be under ATC control and must follow Instrument Flight Rules (IFR). Pilots operating in Class A airspace must be instrument rated. Aircraft entering Class A airspace must obtain ATC clearance prior to entry.

Since Class A airspace is restricted to instrument flight only, there are no minimum visibility requirements.

[edit] Class B

Class B airspace is defined around key airport traffic areas. The exact shape of the airspace varies from one Class B area to another, but in most cases it has the shape of an inverted wedding cake, with a series of circular “shelves” of airspace of several thousand feet in thickness centered on a specific airport. Each shelf is larger than the one beneath it. Class B airspace normally begins at the surface in the immediate area of the airport, and successive shelves of greater and greater radius begin at higher and higher altitudes at greater distances from the airport. Many Class B airspaces diverge from this model to accommodate traffic patterns or local topological or other features. The upper limit of Class B airspace is normally 10,000 feet MSL.

VFR aircraft entering Class B airspace must obtain ATC clearance prior to entry and must be prepared for denial of clearance. VFR flights may proceed under their own navigation after obtaining clearance but must obey any explicit instructions given by ATC. Some Class B airspaces include special transition routes for VFR flight that require communication with ATC but may not require an explicit clearance. Other Class B airspaces include VFR corridors through which VFR flights may pass without clearance (and without technically entering the Class B airspace).

VFR flights operating in Class B airspace must have three nautical miles of visibility and must remain clear of clouds (no minimum distance).

Pilots operating in Class B airspace must have a private pilot's certificate, or a student certificate with a special endorsement. Some Class B airspaces prohibit student pilots.

Some Class B airspaces prohibit Special VFR flights.

[edit] Class C

Class C airspace is defined around airports of moderate importance and is structured in much the same way as Class B airspace.

VFR aircraft entering Class C airspace must establish radio communication with ATC prior to entry, but need not obtain an explicit clearance. VFR flights in Class C airspace must have three miles of visbility, and fly an altitude at least 500 feet below, 1000 feet above, and 2000 feet laterally from clouds.

Pilots operating in Class C airspace must have at least a student pilot's certificate.

[edit] Class D

Class D airspace is circular in form and extends to a variable height above and to a variable radius around towered airports not otherwise in Class C or Class B airspace. Class D airspace may revert to Class E at some airports when they are not towered (if 24-hour tower services are not available), or under other special conditions.

All other requirements and characteristics are the same as those of Class C airspace.

[edit] Class E

Class E airspace originally extended from 14,500 feet MSL to 18,000 feet MSL (the lower limit of Class A airspace), with only occasional exceptions beginning at lower altitudes. Today, the exception has become the rule, and most Class E airspace begins at either 700 or 1200 feet AGL and extends to 18,000 feet MSL. The floor of Class E airspace starts at the surface in some areas, particularly at untowered airports that are not assigned Class D, C, or B airspace. Most airspace in the United States is Class E. The airspace above FL600 is also Class E.

No ATC clearance or radio communication is required for VFR flight in Class E airspace. VFR visibility requirements are as they are for Class C and Class D airspaces, except that the visibility requirement is extended to five miles above 10,000 feet MSL, and the cloud clearance requirement above 10,000 feet MSL is extended to 1000 feet below, 1000 feet above, and one mile laterally.

Pilots operating in Class E airspace must have at least a student certificate.

[edit] Class G

Class G airspace includes all airspace not otherwise classified below flight level 600. There are no entry or clearance requirements for Class G airspace, even for IFR operations. Class G airspace is typically the airspace very near the ground, beneath Class E airspace.

Pilots operating in Class G airspace must have at least a student certificate.

Radio communication is not required in Class G airspace, even for IFR operations.

VFR visibility requirements in Class G airspace are one mile by day, and three miles by night, for altitudes below 10,000' MSL. Beginning at 10,000' MSL, five miles of visibility are required, day and night. Cloud clearance requirements are to maintain an altitude that is 500 feet below, 1000 feet above, and 2000 feet laterally below 10,000 feet MSL; at or above 10,000 feet MSL, they are 1000 feet below, 1000 feet above, and one mile laterally. By day at 1200 feet AGL and below, aircraft must remain clear of clouds, but there is no minimum distance.

[edit] Special use airspace

Some airspace categories have no correlation with ICAO airspace classes but are nevertheless important in United States airspace. The airspace class (A, B, etc.) in which special use airspace is found still controls the requirements and procedures for flying into/through it.

[edit] Alert and Warning areas

Alert and Warning areas contain special hazards that pilots must take into consideration when entering the areas. They do not require a special ATC clearance, but ATC can advise on the status of the area in some cases (whether or not hazardous activities are in progress, for example).

[edit] Restricted airspace

Entry into restricted areas is prohibited under certain conditions without a special clearance obtained from the controlling agency obtained directly or via ATC. Examples of restricted areas include test firing ranges and other military areas with special hazards or containing sensitive zones.

[edit] Prohibited airspace

Entry into prohibited areas is forbidden under all circumstances. Prohibited areas exist over a handful of extremely sensitive locations, such as the White House.

[edit] Military Operation Areas (MOAs)

Military Operation areas or MOAs are areas in which military activities are regularly conducted. No special clearance is required to enter MOAs, but pilots should verify with ATC or FSS that no hazardous activity is underway before entering a MOA.

[edit] VFR chart notation

Main article: Aeronautical chart conventions (United States)

Specific conventions are used to indicate airspace boundaries on VFR sectional and terminal area charts (TACs) for the United States.

[edit] Class A

Class A airspace is not shown on VFR charts, but it is assumed to extend from 18,000 feet MSL to 60,000 feet MSL everywhere.

[edit] Class B

Class B airspace is delimited by a heavy cyan border. Each distinct segment of Class B airspace contains figures indicating the upper and lower altitude limits of that segment in units of one hundred feet, shown as a fraction, e.g., 100 over 40 indicates a ceiling of 10,000 feet MSL and a floor of 4000 feet MSL (SFC indicates that the segment begins at the surface). In some areas each segment may also be assigned a letter for identification during communication with ATC.

In many cases the boundaries of Class B airspace segments are coincident with specific radials from a specific VOR station or with specific distances from such a station; these are normally marked on the chart. In other cases, the boundaries may follow natural topological features or may be defined in other ways, which may or may not be explicitly indicated on the chart.

[edit] Class C

Class C airspace is delimited by a heavy magenta border. Each distinct segment of Class C airspace contains figures indicating the upper and lower altitude limits of that segment in units of one hundred feet, shown as a fraction, e.g., 100 over 40 indicates a ceiling of 10,000 feet MSL and a floor of 4000 feet MSL. (SFC indicates that the segment begins at the surface, and T indicates that the ceiling ends where overlying Class B airspace begins.)

In many cases the boundaries of Class C airspace segments are coincident with specific radials from a specific VOR station or with specific distances from such a station; these are normally marked on the chart. In other cases, the boundaries may follow natural topological features or may be defined in other ways, which may or may not be explicitly indicated on the chart.

[edit] Class D

Class D airspace is delimited by a thin, dashed cyan line, generally in the form of a circle centered on an airport. A number enclosed in a box surrounded by a similar dashed line and usually within the Class D area gives the upper limit of the airspace (the lower limit of Class D is always the surface).

[edit] Class E

Class E airspace is delimited in different ways depending on its lower altitude limit. Airspace in this class that begins at the default altitude of 14,500 feet MSL is not delimited. Class E airspace that begins at 1200 feet AGL is delimited by a broad, shaded cyan border. Class E airspace that begins at 700 feet AGL is delimited by a broad, shaded magenta border. Airspace in Class E that begins at the surface is delimited by a thin, dashed magenta line (this type of Class E is most often seen as an extension to Class D airspace that facilitates control of IFR routes to and from an airport).

In many cases, the expanse of airspace that is Class E beginning at 1200 feet AGL is so large that only the areas that differ are marked on the chart. Thus, one may see only external borders within the chart, with the 1200-foot region extending off the chart.

When Class E airspace begins at altitudes other than 1200 feet AGL, 700 feet AGL, or 14,500 feet MSL, a delimiting border resembling links in a chain in dark cyan separates the areas, and specific altitudes are marked within them.

[edit] References

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