Legal Briefing

Understanding airspace

Airspace training concentrates on the six broad classifications of airspace, designated by the letters A, B, C, D, E, and G--with some emphasis on other charted classifications such as prohibited areas, restricted areas, warning areas, and military operations areas. Since September 11, 2001, however, we have seen airspace boundaries grow and shrink, and we see temporary flight restrictions (TFRs) pop up and then go away. These changes are so constant that they are nearly impossible to depict on charts, and it is not always practical to publish them in the regulations. Nonetheless, you are required to know and comply with the rules that apply in the airspace in which you are operating.

Class A, B, C, D, and E airspace is included under the generic term controlled airspace, which is that "airspace of defined dimensions within which air traffic control service is provided to IFR flights and to VFR flights in accordance with the airspace classification." Class G is that airspace not designated as Class A, B, C, D, or E and is defined as uncontrolled airspace. Class A airspace exists above most of the country, from 18,000 feet above mean sea level (msl) up to and including Flight Level 600. Aircraft in Class A must be operating under instrument flight rules, unless otherwise authorized, and are required to have an air traffic control (ATC) clearance, two-way radio communications, and a transponder/encoder.

Class B airspace is designated for large volumes of air traffic, based on IFR operations and passenger enplanements. Aircraft must have an ATC clearance, two-way radio communications, and an operating transponder/encoder before entering. This way, air traffic controllers can maintain aircraft separation.

Airports in Class C airspace have an operational control tower, a radar approach control, and a certain number of IFR operations or passenger enplanements. While you don't need an ATC clearance to enter the airspace, you are required to establish and maintain two-way radio communications and have an operating transponder/encoder. Class D airspace surrounds airports with operational control towers that are not in class B or C airspace. You are required to have operating two-way radio communications capability; a transponder/encoder is not required. When the tower is closed, the airspace becomes class E or G.

Class E airspace is the controlled airspace remaining after designating class A, B, C, and D airspace. It accommodates both IFR and VFR operations, but VFR flights are not required to have clearances or to communicate with ATC. A transponder/encoder is not required (except for aircraft certificated with an electrical system when within 30 nautical miles of a Class B primary airports), but if your aircraft has one, it must be turned on.

Class G airspace is uncontrolled airspace where operations may be conducted under IFR and VFR, but no ATC communication is required and no ATC separation is provided. You are responsible for aircraft separation by seeing and avoiding others. There are no clearance requirements. And there are no transponder/encoder requirements below 10,000 feet msl. If you're above 10,000 feet msl, you must have a transponder/encoder, unless you are less than 2,500 feet above the surface.

Restricted and prohibited areas are areas of defined dimensions that usually surround an area on the surface that is not compatible with overflights. Restricted areas usually involve such hazards to aircraft as artillery firing, aerial gunnery, or guided missiles. Prohibited areas are established for security or other reasons associated with the national welfare. No person may operate an aircraft in a restricted area contrary to the restrictions imposed or in a prohibited area without the permission of the controlling agency, which may or may not be ATC.

A warning area extends three nautical miles out from the U.S. coastline and warns pilots of potential danger in that area. Military operations areas are established to identify an area of military training activities. No regulation restricts flight in these areas, but pilots should exercise extreme caution if they choose to fly in them.

Since September 11, 2001, many notams were put into effect to notify pilots of TFRs and special security instructions in air defense identification zones (ADIZs). In these cases, the FAA has identified the need to impose temporary or special restrictions in the interest of national security. Usually, the need for these restrictions is not known in advance, or is subject to constant change, and thus the FAA cannot depict all TFR and ADIZ airspace restrictions on charts or with detail in the regulations; thus they are communicated through the FAA's notam system.

Kathy Yodice is an attorney with Yodice Associates in Washington, D.C., which provides legal counsel to AOPA and administers AOPA's legal services plan. She is an instrument-rated private pilot.

Need an airspace review? See the AOPA Air Safety Foundation's Know Before You Go online course.