Legal Briefing

Learning The Aviation Alphabet

The airspace in which we fly is divided into six general classifications, designated by the letters A, B, C, D, E, and G. There are also other airspace classifications, such as prohibited areas, restricted areas, warning areas, and military operations areas, but for the moment we'll limit ourselves to a discussion of the areas with letter designations.

It used to be that these different types of lettered airspace were identified by specific terms, such as "terminal control area" and "airport traffic area," which some people found a bit easier to remember. Several years ago, however, the names were changed to make them consistent with international terminology, which used the letters A through G. While the international system uses the letter F, there is no equivalent in the United States, so that designation is not used.

Class A, B, C, D, and E airspace all can be included under the generic term controlled airspace, which is "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 airspace is any airspace that is 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 mean sea level (msl) up to and including flight level 600 - approximately 60,000 feet msl. Operation in this airspace requires an air traffic control clearance, two-way radio communications, and a transponder with altitude encoding capability. Unless otherwise authorized, all aircraft must be operated under instrument flight rules in Class A airspace.

Class B airspace generally is depicted as an upside-down wedding cake. The FAA designates this type of airspace around airports that have a large volume of air traffic, based on IFR operations and passenger enplanements. In other words, the airspace is B for busy. Aircraft are required to have an air traffic control clearance be-fore entering Class B airspace, along with two-way radio communications capability and an operating transponder/encoder. This way, air traffic controllers can maintain aircraft separ- ation. To help keep things moving efficiently, the cloud clearance requirement for VFR operations in this airspace is relaxed to "clear of clouds."

Class C airspace typically surrounds busy airports that are somewhat less active than those surrounded by Class B airspace. Class C airspace is usually depicted as a somewhat smaller upside-down wedding cake - typically with only two tiers. A Class C airport must 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. Think of it as Class C for communications. And, you must have an operating transponder with altitude encoding.

Class D airspace surrounds airports with operational control towers that are not in Class B or C airspace. Class D airspace is generally depicted on charts as a single cylinder. You are required to have two-way radio communications capability and use it. Think of this one as Class D for dialog with controllers. An encoding transponder is not required. Many Class D airports have part-time control towers. When the tower is not in operation, the airspace is reclassified as Class E or G airspace.

Class E airspace is the controlled airspace that is left over after taking out Class A, B, C, and D airspace. You can think of this one as Class E for everything else. This airspace accommodates both IFR and VFR operations, but VFR flights are not required to have clearances or communicate with air traffic control. A transponder is not required (except for aircraft operating within the 30-nautical-mile Mode C veil around Class B airports). But if your airplane has a transponder, it must be turned on within Class E airspace.

Class G airspace is uncontrolled airspace where operations may be conducted under IFR and VFR but no communication with air traffic control is required and no separation is provided. Operations in this airspace are G for government free. It is in this airspace that the see-and-avoid responsibilities of the pilots serve to keep aircraft separated. There are no clearance requirements, and there are no transponder/ encoder requirements below 10,000 feet msl. If you're flying in Class G airspace above 10,000 feet msl, you must have a transponder/encoder, unless you are within 2,500 feet above the surface.

On every flight, you will find yourself in at least one of these types of airspace. Before you take off, it's important to know which airspace you will be passing through so that you can be properly prepared and operate within the regulations.