What principle does self-sustainability at airports relate to?

Self-sustainability at airports primarily refers to the idea that the costs associated with operating and maintaining an airport should be covered by those who directly benefit from its services, particularly through their use of aviation. The principle encapsulated in the correct answer emphasizes an equitable approach to funding airport operations, where users of the airport's services contribute to its financial needs, while ensuring that the burden of these costs does not fall on those individuals or entities that do not use aviation services. This approach promotes fairness and encourages the development and improvement of airport infrastructure through user fees and charges.

This rationalization aids in maintaining a sustainable financial model, wherein airport operators strive to generate sufficient revenue from user fees to cover their operational costs without imposing additional financial burdens on the surrounding community or unrelated taxpayers. This principle aligns with broader economic practices that advocate for user-pay systems, ensuring that airport development and improvements are funded by those who benefit from them rather than the general population who may not have any stake in aviation activities.

The other choices address different aspects of airport funding and operations but do not directly convey the foundational element of self-sustainability as effectively as this principle does.