What is the primary altitude range for RNAV T routes?

The primary altitude range for RNAV T routes is appropriate because RNAV T routes specifically cater to routes in the terminal area, where aircraft typically operate below 18,000 feet MSL. These routes are designed for operations where more precise navigation capabilities can improve the efficiency of air traffic and enhance safety.

The designation of these routes ensures that aircraft can navigate effectively in dense airspace and during the approach and departure phases of flight without interference from higher altitude traffic. Using RNAV systems facilitates better routing and can optimize performance for both traffic management and fuel efficiency.

Other altitude ranges mentioned do not align with the intended use and operational environment of RNAV T routes. For instance, routes up to 10,000 feet and between 12,000 to FL180 would generally not cover the full operational scope of RNAV T routes, while altitudes above FL450 drastically exceed the typical operating environment for such routes, as they are outside the scope of normal terminal and en-route operations. Thus, recognizing the designated altitude of below 18,000 feet MSL aligns accurately with the purpose and function of RNAV T routes in air traffic control systems.