Federal Aviation Regulations (FAR) 135 Oral Practice Test

Class C airspace is designed as two layers around a towered airport: a core and a surrounding shelf. The core is a 5 NM radius that extends from the surface up to 4,000 ft above the airport’s elevation. The outer shelf reaches out to a 10 NM radius and extends from roughly the floor up to the same top of 4,000 ft above the airport elevation. In practice, when the airport sits near sea level, this tops out around 4,000 ft MSL, so you commonly see it described as from the surface to about 4,000 ft with 5- and 10-mile radii. This structure means entry requires two-way radio communication with ATC and a discrete transponder code (Mode C generally, when available). The other options describe different airspace configurations: one is far taller and larger (more like Class B), another uses a very small radius not characteristic of Class C, and the last describes high-altitude airspace that isn’t Class C.