What is the altitude range for Class A airspace?

Class A airspace is defined as the airspace from 18,000 feet mean sea level (MSL) up to and including Flight Level 600. This airspace is exclusively reserved for high-altitude flight, and its purpose is to ensure the safety and efficiency of high-altitude air traffic.

Aircraft operating in Class A airspace must be on an instrument flight plan and under air traffic control (ATC) surveillance at all times. This altitude range includes a portion of the airspace where weather and atmospheric conditions can significantly affect flight operations, thereby necessitating stringent regulatory measures to maintain safety.

The other altitude ranges listed do not correspond to Class A airspace. For example, the range from the surface to 10,000 feet MSL pertains to Class B, C, or D airspace depending on the geographic area and is generally tailored to accommodate departing and arriving traffic in busy terminal areas. Similarly, the 12,000 to 18,000 feet range does not exist as a distinct classification of airspace, and the range from 2,500 feet AGL to 10,000 feet MSL typically describes various lower classes of airspace like Class E or Class G. Therefore, recognizing the correct parameters of Class A