At what altitude does Class A airspace start?

Class A airspace begins at 18,000 feet Mean Sea Level (MSL) and extends up to and including 60,000 feet MSL. This airspace is specifically designed for high altitude flight operations primarily involving IFR (Instrument Flight Rules) flights. The designation of 18,000 feet as the starting point for Class A airspace is crucial for ensuring safe and efficient management of aircraft operating in controlled airspace, particularly at higher altitudes where air traffic becomes denser and the complexity of operations increases.

This altitude buffer also provides a transition zone from lower classes of airspace, allowing air traffic control to ensure that all aircraft within Class A are operating under IFR and adhere to standardized separation requirements. This separation is essential for maintaining safety in the busy airspace where commercial and private aircraft frequently operate.