What is the standard altitude for Class A airspace?

In the context of aviation regulations, Class A airspace is defined as the airspace from 18,000 feet above mean sea level (MSL) up to and including flight level 600 (FL600), which is approximately 60,000 feet. This airspace is strictly for IFR (Instrument Flight Rules) operations and requires pilots to be on an air traffic control flight plan. The reasoning behind placing this airspace at such a high altitude is to ensure that aircraft operating in Class A are adequately separated from all other traffic and are maintained within a controlled environment, which is crucial for safety in busy airspace regions.

Since the question is specifically about the standard altitude for Class A airspace, identifying this range accurately as being above 18,000 feet is essential for understanding airspace classifications and associated regulations. The other altitude ranges do not meet the criteria set for Class A, as they refer to other classes of airspace with different operational rules and requirements.