What is an airport approved by the Administrator for use by an air carrier when the regular airport is not available?

The term that accurately describes an airport approved by the Administrator for use by an air carrier when the regular airport is not available is an alternative airport. This designation allows airlines to divert to an airport that meets operational and safety standards if the planned destination is compromised due to weather, runway closures, or other reasons that render it unusable.

In aviation, alternative airports are critical for ensuring that flights can continue to operate safely and efficiently, maintaining regulatory compliance and minimizing disruptions for passengers and cargo. Understanding the role of alternative airports is essential for effective flight planning and operational decision-making.

The other terms do not appropriately fit this definition; provisional airports may imply temporary status not necessarily sanctioned by the Administrator, destination airports refer to the intended landing spot for a flight and do not account for contingency plans, and emergency landing fields typically denote locations used in unforeseen or urgent situations rather than pre-approved alternate stops for regular operations.