What characteristic is NOT used to define the Taxiway Design Group (TDG)?

The characteristic that is not used to define the Taxiway Design Group (TDG) is runway length. The TDG primarily focuses on aircraft characteristics that influence the design and size requirements for taxiways, ensuring that they can accommodate various types of aircraft safely and efficiently.

Key factors that are included in the TDG criteria are main gear width, as it impacts the layout of taxiways and the space needed for safe maneuvering; cockpit to main gear distance, which determines the turning radius and clearance needed for the aircraft on the taxiway; and runway and taxiway separation requirements, which help establish necessary distances to enhance safety and operational efficiency.

Runway length, while important for overall airport operations, does not directly affect the specific design and geometric criteria of taxiways, which is the focus of the TDG classification. Therefore, it is excluded from the characteristics used to define the Taxiway Design Group.