Types of Controlled Airspace. Depending on location, controlled airspace may start as low as the ground or as high as 14,500 feet in the United States. With each airspace having varying requirements for pilots and weather, it's important to be aware of classes you might potentially encounter on and flight.

In the United States and many other regions, controlled airspace typically extends from the surface or a designated floor up to Flight Level 600 (60,000 feet). The most restrictive category, Class A airspace, begins at 18,000 feet Mean Sea Level (MSL) and continues up to FL600. Above this altitude, the airspace is generally classified as Class E (controlled) or Class G (uncontrolled) depending on the country's specific regulations, but most commercial and civil air traffic control services do not extend beyond this "ceiling." Internationally, while there is no universal treaty defining the vertical end of sovereign airspace, many nations recognize the Kármán Line (100 km or approximately 62 miles) as the legal boundary between a nation's atmosphere and outer space. For practical aviation, however, the "controlled" environment where pilots must follow active Air Traffic Control (ATC) instructions ends far lower, at the aforementioned 60,000-foot mark, where the air becomes too thin for most conventional wings to maintain stable aerodynamic flight.