What is the vertical dimension of the jet route system?

The correct answer reflects the established altitude range for jet routes, which is from 18,000 feet to flight level 450 (FL 450). This range was specifically designed to accommodate high-altitude, fast-moving aircraft that are traveling along these routes, ensuring efficient and safe navigation through controlled airspace. The lower bound, 18,000 feet, represents the beginning of the en route airspace where air traffic control services become more frequent and the route structure is geared towards jet operations. The upper bound, FL 450, provides sufficient vertical airspace for air traffic while maintaining separation from other types of traffic and ensuring that aircraft can operate safely at cruising altitudes. Understanding this vertical dimension is critical for pilots and air traffic controllers in navigating the airspace effectively.