What do the T's represent on a low IFR chart?

The T's on a low IFR (Instrument Flight Rules) chart signify changes in altitude for Minimum En Route Altitude (MEA), Minimum Obstacle Clearance Altitude (MOCA), and Maximum Authorized Altitude (MAA). These altitudes are crucial for ensuring safe vertical separation from terrain and obstructions, as well as maintaining safe operational altitudes while navigating in IFR conditions.

The MEA ensures that aircraft have adequate clearance over obstacles and provides acceptable navigation signal coverage along the route. The MOCA relates to the minimum height that guarantees obstacle clearance but within a specific distance from the navigation aid, which is particularly relevant for pilots navigating close to terrain or obstacles. The MAA indicates the ceiling for safe flight operations within controlled airspace to avoid exceeding the designated altitude for safety and operational purposes.

Thus, the presence of T's on the chart serves as a visual reminder for pilots about these key altitude changes, aligning their navigation with safety standards and regulations during IFR operations.