What is the maximum height, in feet, that the National Airspace System (NAS) reaches within the continental United States?

The correct answer is 60,000 feet, which reflects the altitude limits set by the National Airspace System (NAS) within the continental United States. This altitude is significant because it marks the transition point where air traffic control strategies and regulations change from managing routine flights to dealing with more specialized airspace such as the upper levels used primarily by commercial airline, military, and other high-altitude operations. Understanding this threshold is crucial for pilots and air traffic controllers, as it influences flight planning, airspace classifications, and the protocols for altitudes above this point, including air traffic separation rules and the need for different certification and equipment for operations above this altitude.