Which aspect is important for airlines when planning terminal facilities?

When airlines plan terminal facilities, the ability to accommodate existing and future fleets is of utmost importance. This encompasses ensuring that the terminal can handle the aircraft in operation today as well as those that may be added to the fleet in the future. Various factors come into play, such as gate availability, runway capacity, and the spatial design of the terminal, which must be flexible enough to scale with changes in fleet size and type.

Airlines must also consider the dimensions and specifications of new aircraft models, which may require different gate configurations or boarding procedures. By prioritizing a design that can adapt to these evolving fleet needs, airlines can optimize their operations and enhance customer service, ultimately leading to better efficiency and profitability.

The other options, while they might play a role in terminal planning, do not address the fundamental operational necessities that support the core function of the airline, which is to transport passengers and cargo efficiently. Modern architectural design, high-end retail shops, and proximity to international borders can enhance passenger experience and potentially increase revenue, but they are secondary to ensuring that the facility effectively supports the airline's operational requirements.