Legends

On sectional and terminal area charts (shown) solid cyan (blue) lines indicate the boundaries and airspace layers of Class B airspace, which surrounds the nation's busiest airports. The configuration of each Class B area is tailored to the airport's needs and is composed of a surface area and two or more layers. A thin cyan line encircles the airport at a 30 nautical mile radius, is labeled Mode C, and indicates the area in which an altitude-reporting Mode C transponder is required for most aircraft.

Generally, Class B airspace starts at the surface and tops out at 10,000 feet with elevated "floors" outside the airspace's core. Numbers separated by a horizontal line give the floor and ceiling for that segment of Class B airspace delineated by the cyan lines. In the example, Class B extends from the surface (SFC) to 10,000 feet around Chicago O'Hare International, and just to the west, it starts at 1,900 feet and extends to 10,000 feet.

Terminal area charts provide more details of Class B airspace than sectional charts, and pilots should use TACs when flying in or under Class B. TACs are easier to read because they are devoid of the terrain information found on sectional charts. They include "flagged," often pictorial, surface features, such as the ski jump northwest of O'Hare, that pilots can recognize from the air and controllers can use to direct them. Wide, shaded cyan lines indicate suggested VFR flyways and altitudes that help VFR pilots avoid Class B layers and major controlled traffic flows.

Pilots must have an ATC clearance to fly in Class B airspace, and the appropriate contact frequency is given in a box that is usually printed outside the Mode-C veil (not shown). In addition, dashed cyan lines with four-engine aircraft or arrows superimposed on them show the Class B arrival and departure routes and give an altitude range in which the aircraft fly.