Legends

Before a pilot can enter Class C airspace he (or she) must establish two-way communication with ATC. On sectional charts, a magenta (purple) box adjacent to the airspace tells pilots when and on what frequency to contact ATC. The example is located northeast of Logan International Airport in Billings, Montana. Pilots must contact Billings Approach on 119.2 MHz when they are within 20 nautical miles of Logan International. When ATC responds to a pilot's call and establishes two-way communication by stating the aircraft's N-number, the pilot may enter Class C airspace.

In a recent change to sectional chart symbology, the ATC communication box now has a white interior, which makes it easier to see and read than the old style, where the information box was printed over the terrain shading and other topographical information. As you approach Class C airspace, remember that different approach control frequencies apply to different arrival directions. At Billings, for example, a pilot approaching from the south should contact Billings Approach on 120.5 MHz.