83 FAA Chart Users’ Guide - IFR Enroute Symbology AIRSPACE INFORMATION (Continued) Airspace - U.S. Class A High Chart Only Controlled  Airspace Class B Low Chart Only Controlled  Airspace Mode C Area Low Chart Only Controlled  Airspace Open Area (White) That airspace from 18,000’ MSL to and including FL 600,  including the airspace overflying the waters within 12 NM  of the coast of the contiguous United States and Alaska  and designated offshore areas, excluding Santa Barbara  Island, Farallon Island, the airspace south of latitude  25° 04’00” N, the Alaska peninsula west of longitude  160°00’00” W, and the airspace less than 1,500’ AGL. That airspace from 18,000’ MSL to and including FL  450, including Santa Barbara Island, Farallon Island, the  Alaska peninsula west of longitude 160°00’00” W, and  designated offshore areas. Screened Blue with a Solid Blue Outline That airspace from the surface to 10,000’ MSL (unless  otherwise designated) surrounding the nation’s busi- est airports. Each Class B airspace area is individually  tailored and consists of a surface area and two or more  layers. A Solid Blue Outline That airspace within 30 NM of the primary airports of  Class B airspace and within 10 NM of designated airports.  Mode-C transponder equipment is required. (See FAR  91.215) Example: Example: See Chart example above.