Class B is the most restricted, class E is the least restricted. Must get ATC (Air Traffic
Control) authorization for class B, C, and D.
Class A. From 18,000 feet to 60,000 feet, all over the US.
Class B. Surrounding major airports, 0-10,000 feet. Consists of multiple layers,
like an upside-down wedding cake.
Class C. Surrounding airports with a control tower, radar, and over a specific
amount of traffic. Usually 5 NM (nautical mile) radius from 0-4,000 feet, and a 10
NM radius from 1,200-4,000 feet.
Class D. Surrounding airports with a control tower. 0-2,500 feet, no specific
radius, just shaped around flight patterns. Outside control tower hours, Class D
airspace is Class G.
Class E. Usually it starts at 1,200 feet and goes up to 18,000 feet.
Class G. Uncontrolled airspace (below class E airspace).