Define "Class A airspace."

Class A airspace encompasses all airspace from 18,000 feet mean sea level (MSL) up to flight level (FL) 600, which extends to approximately 60,000 feet. This classification is specifically designated for instrument flight rules (IFR) operations and is managed under strict air traffic control (ATC) procedures to ensure the safety and efficiency of air traffic flying at higher altitudes, where the majority of commercial jet traffic operates.

In this airspace, all aircraft must operate under IFR, and pilots are required to maintain communication with air traffic control. This level of regulation significantly enhances safety, as it minimizes the potential for mid-air collisions and ensures orderly flow of air traffic.

The other options do not accurately describe Class A airspace. For instance, the definition involving visual flights is more aligned with Class B, C, or D airspace where visual flight rules (VFR) can be applicable. The option suggesting airspace "up to 18,000 feet" is misleading because that altitude defines lower airspace classes rather than Class A. Lastly, airspace reserved for military operations pertains to special use airspace, which does not fall under the standard classifications of airspace like Class A, B, C