What is the definition of Class A airspace?

The definition of Class A airspace is the region extending from 18,000 feet Mean Sea Level (MSL) up to Flight Level 600 (FL600). This airspace is highly regulated and is primarily used by commercial airliners and other aircraft operating under Instrument Flight Rules (IFR). Aircraft operating in Class A airspace must be on an active IFR flight plan and must maintain communication with Air Traffic Control (ATC) at all times.

Class A airspace encompasses a significant vertical range, ensuring that high-altitude traffic is managed safely and efficiently, thus minimizing the risk of mid-air collisions. It is important for pilots to understand that entering Class A airspace requires specific qualifications, including an instrument rating and appropriate equipment, such as a transponder for radar surveillance.

The other options provided do not accurately define Class A airspace, as they reference incorrect altitude ranges or types of airspace that do not apply to the Class A designation.