Airspace Classification Airspace in the United States  [Figure 1-1]  is designated  as follows:  Special use airspace is the designation for airspace in which  certain activities must be confined or where limitations may  be imposed on aircraft operations that are not part of those  activities. Certain special use airspace areas can create  limitations on the mixed use of airspace. The special use  airspace depicted on instrument charts includes the area name  or number, effective altitude, time and weather conditions  of operation, the controlling agency, and the chart panel  location. On National Aeronautical Navigation Products  (AeroNav Products) en route charts, this information is  available on one of the end panels. Prohibited areas contain airspace of defined dimensions  within which the flight of aircraft is prohibited. Such areas  are established for security or other reasons associated with  the national welfare. These areas are published in the Federal  Register and are depicted on aeronautical charts. The area is  charted as a “P” followed by a number (e.g., “P-123”). Restricted areas are areas where operations are hazardous to  nonparticipating aircraft and contain airspace within which  the flight of aircraft, while not wholly prohibited, is subject  to restrictions. Activities within these areas must be confined  because of their nature, or limitations may be imposed upon  aircraft operations that are not a part of those activities, or  both. Restricted areas denote the existence of unusual, often  invisible, hazards to aircraft (e.g., artillery firing, aerial  gunnery, or guided missiles). IFR flights may be authorized  to transit the airspace and are routed accordingly. Penetration  Special Use Airspace 5. Class E. Generally, if the airspace is not Class A, B,  C, or D, and is controlled airspace, then it is Class E  airspace. Class E airspace extends upward from either  the surface or a designated altitude to the overlying  or adjacent controlled airspace. When designated as a  surface area, the airspace is configured to contain all  instrument procedures. Also in this class are federal  airways, airspace beginning at either 700 or 1,200 feet  above ground level (AGL) used to transition to and  from the terminal or en route environment, and en  route domestic and offshore airspace areas designated  below 18,000 feet MSL. Unless designated at a lower  altitude, Class E airspace begins at 14,500 MSL over  the United States, including that airspace overlying the  waters within 12 NM of the coast of the 48 contiguous  states and Alaska, up to but not including 18,000 feet  MSL, and the airspace above FL 600. 6. Class G. Airspace not designated as Class A, B, C,  D, or E. Class G airspace is essentially uncontrolled  by ATC except when associated with a temporary  control tower. 1. Class A. Generally, airspace from 18,000 feet mean  sea level (MSL) up to and including flight level (FL)  600, including the airspace overlying the waters  within 12 nautical miles (NM) of the coast of the  48 contiguous states and Alaska. Unless otherwise  authorized, all pilots must operate their aircraft under  instrument flight rules (IFR). 2. Class B. Generally, airspace from the surface to 10,000  feet MSL surrounding the nation’s busiest airports in  terms of airport operations or passenger enplanements.  The configuration of each Class B airspace area is  individually tailored, consists of a surface area and two  or more layers (some Class B airspace areas resemble  upside-down wedding cakes), and is designed to  contain all published instrument procedures once  an aircraft enters the airspace. An air traffic control  (ATC) clearance is required for all aircraft to operate  in the area, and all aircraft that are so cleared receive  separation services within the airspace. 3. Class C. Generally, airspace from the surface to 4,000  feet above the airport elevation (charted in MSL)  surrounding those airports that have an operational  control tower are serviced by a radar approach control  and have a certain number of IFR operations or  passenger enplanements. Although the configuration  of each Class C area is individually tailored, the  airspace usually consists of a surface area with a  5 NM radius, an outer circle with a 10 NM radius  that extends from 1,200 feet to 4,000 feet above the  airport elevation and an outer area. Each aircraft  must establish two-way radio communications with  the ATC facility providing air traffic services prior  to entering the airspace and thereafter maintain those  communications while within the airspace. 4. Class D. Generally, airspace from the surface to 2,500  feet above the airport elevation (charted in MSL)  surrounding those airports that have an operational  control tower. The configuration of each Class D  airspace area is individually tailored and, when  instrument procedures are published, the airspace  normally designed to contain the procedures. Arrival  extensions for instrument approach procedures (IAPs)  may be Class D or Class E airspace. Unless otherwise  authorized, each aircraft must establish two-way radio  communications with the ATC facility providing  air traffic services prior to entering the airspace and  thereafter maintain those communications while in  the airspace. 1-2