Aviation Theory

pages: 1: Airspace types, Class A | 2: Class B to E | 3: Special Airspace Use

CLASS B AIRSPACE

At some of the busiest airports, Class B airspace has been established to separate all arriving and departing traffic. There is no standard shape of Class B airspace since it is designed to facilitate traffic separation at a particular terminal and changes due to differences in approach and departure routes. Pilot participation is mandatory, and an ATC clearance must be received before you enter a Class B area. Some of the Class B airspace areas have VFR corridors to allow pilots of VFR aircraft to pass through them without contacting ATC.

To operate under VFR in Class B airspace, your aircraft must have a two-way radio, and either a Mode S or a 4096-code transponder with Mode C automatic altitude reporting. For IFR operations, you must also have a VOR receiver. In addition, to take off or land at certain large airports listed in Appendix D of FAR 91, you must hold at least a private pilot certificate. With certain exceptions, a transponder with altitude reporting capability is required anytime you are operating within 30 nautical miles of the primary airport from the surface upward to 10,000 feet MSL.

CLASS C AIRSPACE

Class C airspace areas are designated at certain airports where ATC is equipped to provide radar service for all aircraft. Normally, Class C airspace designations consist of two circular areas which extend outward from the primary airport and are referred to as the inner circle and outer circle. The inner circle has a radius of 5 nm and the radius and starts at the ground level. The outer circle is 10 nm and normally starts at 1,200' AGL. The upper limit of the Class C airspace is 4,000 AGL (Above Ground Level). There is also an outer area which extends 10 nm beyond the outer circle. The outer area extends from the lower limit of radar/radio coverage up to the ceiling of approach control's airspace, but excludes the Class C airspace itself. Pilot participation with ATC for flights within the outer area is strongly encouraged. Before operating within the inner or outer circles, you must establish two-way communications with the ATC facility controlling the area and maintain radio contact at all times. If you depart a satellite airport located within Class C airspace, you must establish two-way communications with ATC as soon as practicable.

All aircraft operating in Class C airspace, and in all airspace above the ceiling and within the lateral boundaries extending upward to 10,000 feet MSL, must be equipped with an operable transponder with Mode C. Aircraft operating in the airspace beneath Class C airspace will not be required to have a transponder with Mode C. Most of the airports where Class C airspace areas have been designated were once terminal radar service areas, or TRSAs. Within a TRSA, radar service provides separation between all IFR aircraft and participating VFR aircraft. Participation is not mandatory if your are operating under VFR.

CLASS D AIRSPACE

Class D airspace areas are designated at airports with operating control towers and which are not associated with Class B or C airspace. Before you enter Class D airspace you must establish and maintain two-way radio communications with the control tower. When departing the primary airport within Class D airspace, you also must establish and maintain communications with the tower. It is important to note that airspace at an airport with a part-time control tower is classified as a Class D airspace only when the control tower is in operation.

At some locations, there may be a satellite airport within the same Class D airspace designated for the primary airport. If the satellite airport also has a control tower, similar radio communications requirements with that tower prevail for arrivals and departures. If the satellite airport is a nontower field, arriving aircraft must establish contact with the primary airport's control tower. Departures from a nontower satellite must establish communication with the ATC facility (tower) having jurisdiction over Class D airspace as soon as practicable after departing. To the maximum extent practical and consistent with safety, satellite airports have been excluded from Class D airspace. For example, a satellite airport without an operating control tower might have airspace carved out of the Class D airspace, or it could be placed under a shelf of the Class D airspace.

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DIMENSIONS OF CLASS D AIRSPACE

Normally, the ceiling of Class D airspace areas are specified at 2,500 feet above the surface of the airport converted to mean sea level, and rounded to the nearest 100-foot increment. The ceiling may be raised or lowered as appropriate for local conditions. Some airports with a limited volume of nonturbine-powered aircraft may have a lower vertical limit. The ceiling of Class D airspace is shown in hundreds of feet MSL on sectional charts. Lateral dimensions of Class D airspace is depicted as blue dashed lines on sectional charts and is based on the instrument procedures for which the controlled airspace is established. Because of this, the lateral dimensions may be irregular as opposed to circular in many cases. Arrival extensions will either be charted on the sectional as part of the basic surface area or as a separate area indicated with a dashed magenta line. ATC communications are not required within the magenta lines which is Class E airspace.

CLASS E AIRSPACE

Several types of airspace may be designated as Class E. One Class E designation consists of the airspace over the 48 contiguous states, District of Columbia, and that area of Alaska east of 160° west longitude. This Class E designation begins at 14,500 feet MSL, but does not include the airspace within 1,500 feet of the surface, or restricted and prohibited areas. It extends up to, but not including, 18,000 feet MSL.

Another Class E designation includes domestic airspace areas which extend upwards from 1,200 feet or more above the surface when designated in conjunction with an airway or route. Class E designations for airways or routes coincide with the lateral dimensions of the Federal airway and extend upward from 1,200 feet or higher unless otherwise specified.

Another Class E designation includes domestic airspace areas which extend upward from 700 feet or more above the surface. These areas are designated at non-tower airports which have an approved instrument approach procedure. At part-time tower locations when the tower is closed, the surface area is designated as Class E airspace if a weather observer is available at the airport. When no weather reporting is available, the Class E airspace begins at 700 feet AGL, and the surface area up to 700 feet reverts to Class G. These airspace designations are being incorporated into the Airport/Facility Directory, a government publication which lists airport information as well as some navigational data. The lateral dimensions of Class E airspace designated for airports are depicted on sectional charts with a segmented magenta line. The magenta line denotes controlled airspace extending upward from the surface to the overlying or adjacent controlled airspace and the vertical limit is not depicted. Communication with air traffic control is not required within airspace encompassed by the magenta lines (Class E airspace).

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... page 3: Special Airspace Use