T routes are used by aircraft operating at what altitude?

T routes, or terminal routes, are specifically designed for aircraft operating below 18,000 feet Mean Sea Level (MSL). These routes are utilized to facilitate efficient navigation in controlled airspace, particularly in busy terminal areas where traffic management is crucial. They provide predefined paths that help guide aircraft to and from airports, ensuring organized and safe travel while minimizing the complexity for pilots navigating in the vicinity of high-density air traffic.

The altitudinal limitation of T routes being below 18,000 feet MSL is important because this altitude marks the transition from the terminal airspace to the en route airspace system, where different routing and navigation procedures come into play. Consequently, the use of T routes is primarily focused on enhancing the safety and efficiency of low-altitude operations, rather than en route navigation at higher altitudes.