At which altitude does Class A airspace begin?

Class A airspace begins at 18,000 feet Mean Sea Level (MSL). This designation is crucial as it denotes the airspace where pilots must operate under Instrument Flight Rules (IFR) and where air traffic control (ATC) has a significant role in managing air traffic to ensure safety and efficiency.

Class A airspace covers all airspace from 18,000 feet MSL up to and including 60,000 feet MSL, making it uniquely structured compared to other classes of airspace, which may have variable floor heights. The requirement for IFR in this airspace helps maintain organized flight patterns and mitigates potential conflicts among numerous aircraft operating in higher altitudes, where air traffic is typically denser. Having this established altitude also simplifies navigation and enhances safety for both pilots and passengers in the national airspace system.