Which of the following airspace classifications normally requires a clearance before entering?

Class A airspace extends from 18,000 feet mean sea level (MSL) up to and including FL 600. Operating in this airspace requires pilots to follow strict regulations, including the necessity of obtaining an air traffic control (ATC) clearance before entry. This is primarily due to the high density of traffic and the presence of high-performance aircraft, which demands a higher level of oversight and coordination from ATC. Pilots operating in Class A airspace must also operate under instrument flight rules (IFR), ensuring that all users are compliant with established procedures for safety.

In contrast, the other airspace classifications have different requirements. Class E and Class G airspace do not typically require a clearance to enter, allowing for more flexibility and freedom for pilots, especially during VFR (Visual Flight Rules) operations. Class F airspace is a special type of airspace that may have some limitations or specific regulations, but it is not universally recognized across all regions like Class A. Thus, it doesn’t have the same clearance requirement as Class A.