Class A airspace, also known as Alpha airspace, is defined as the airspace from 18,000 to 60,000 feet. This includes the airspace above the 48 contiguous United States and Alaska. It also includes the airspace above the waters within 12 miles of the U.S. Flying in Class A airspace requires that you be on an instrument flight rules (IFR) flight plan.
Class B airspace, also known as Bravo airspace, is defined as the airspace from the surface up to 10,000 feet above sea level. This airspace surrounds the very busiest airports in the U.S., such as Boston Logan, Los Angeles LAX, or Dallas DFW. There are 12 Class B airports in the U.S. To fly into Class B airspace, you must have an altitude encoding transponder and have received an air traffic control (ATC) clearance into the Class B airspace.
Class C airspace, also known as Charlie airspace, surrounds some of the large airports that have a control tower and radar approach control. This airspace is from the surface up to 4,000 feet above the airport. Airports such as Charlotte or Albany, New York, are a couple of examples of Charlie airspace. To fly into Class C airspace, you must have an altitude-encoding transponder and have established two-way communications with ATC controlling the Class C.
Class D airspace, also known as Delta airspace, is the airspace from the surface up to 2,500 feet above the airport. Class D airspace surrounds an airport that has a control tower that is not Class B or C. These airports are usually for general aviation aircraft. To fly into the Class D airspace, you must establish two-way communications with the control tower. A transponder is not required.
Class E airspace, also known as Echo airspace, is any other airspace that is controlled. Communications are not required with ATC or anyone else.
Class G airspace, also known as Golf airspace, is the airspace that is uncontrolled. An example of Class G airspace would be the airspace in an open area of the country not near any city or town, such as in the sparsely populated areas of Montana. It also includes those areas under an altitude of 700 or 1,200 feet above the surface as defined on the aeronautical charts by shading of magenta or blue. Communications with ATC or anyone else are not required.