What does T indicate in relation to MEA change?

The designation of 'T' in relation to MEA (Minimum Enroute Altitude) change signifies that the change in altitude is indicated by a fix. This means that when pilots are navigating along an airway, specific points, or fixes, are established where the minimum enroute altitude may change. The MEA is crucial for ensuring safe vertical separation from obstacles, terrain, and other air traffic, and understanding that a fix marks the point of which a change in altitude is required helps pilots plan their ascents or descents appropriately.

In the context of IFR navigation, a fix can be a navigational aid (like a VOR or NDB) or a defined waypoint that serves as a reference point. Knowing when to change altitudes based on these fixes enhances situational awareness and flight safety.