What altitude does Class A airspace start at?

Class A airspace begins at an altitude of 18,000 feet Mean Sea Level (MSL) and extends up to and including 60,000 feet MSL. This airspace structure is designed to accommodate high-altitude flights and ensure safe separation between aircraft operating in busy air corridors, primarily for commercial air traffic. Within Class A airspace, pilots are required to operate under Instrument Flight Rules (IFR), which necessitates obtaining an Air Traffic Control clearance prior to entry. This regulation helps manage the complexity of operations at these altitudes, where aircraft generally experience higher speeds and traffic volumes. Understanding this foundational aspect of Class A airspace is essential for both flight instruction and safe navigation for pilots.