Generally, that airspace from 18,000 feet MSL up to and including FL 600, including the airspace overlying the waters within 12 nautical miles off the coast of the 48 contiguous States and Alaska; and designated international airspace beyond 12 nautical miles off the coast of the 48 contiguous States and Alaska within ...

In the United States, the legal definition of "controlled" airspace officially extends up to Flight Level 600, which is approximately 60,000 feet (18,000 meters). Above this altitude, the airspace is classified as Class E, which continues upward but is largely unregulated for standard civil aviation. While there is no single, universally agreed-upon "top" of national sovereign airspace in international law, most legal experts and the FAA generally consider it to end where "outer space" begins. The most commonly cited boundary is the Kármán line at 100 kilometers (approx. 62 miles) above sea level. However, for practical aviation purposes, the FAA's primary control ends at FL600. Beyond this point, specialized high-altitude balloons and spacecraft operate, but they are not subject to the same "air traffic control" rules as commercial airliners, which typically cruise much lower at 30,000 to 42,000 feet.