In aviation, what does the 'T' designation on a V airway signify?

The 'T' designation on a V airway indicates a Minimum Obstruction Clearance Altitude (MOCA) for that airway segment. This designation is crucial for ensuring safe navigation by providing pilots with at least the necessary clearance above obstacles such as terrain and man-made structures. A MOCA provides a level of safety by allowing pilots to fly at this altitude without the risk of colliding with obstacles in the vicinity of the airway, thereby making it an essential parameter for air traffic safety.

The other designations do not apply in this context: Transition Level pertains to the altitude at which aircraft switch from altitude-based to flight level-based operations, Maximum Operating Ceiling refers to the highest altitude an aircraft can achieve safely under specific conditions, and Minimum Off-Route Altitude is the lowest altitude a pilot can fly while navigating off an established route, but does not specifically denote the clearance above obstacles on a V airway. Hence, the 'T' designation is specifically linked to the MOCA standard for defining safe altitudes along V airways.