Which of the following is NOT one of the five types of airports in the US?

The classification of airports in the United States typically encompasses five main types: general aviation, commercial service, reliever, cargo service, and military airports. General aviation airports are used for a range of activities, including private flying, flight training, and crop dusting, making them vital for non-commercial aviation activities. Commercial service airports primarily handle airline traffic and passenger services, while cargo service airports focus on freight operations.

While the other types play significant roles in the aviation landscape, the option referring to "private charter only" does not align with the established classifications of airports. This term suggests a limitation to private charter services, which is not a formal category recognized within the framework of airport types. Such operations can occur at various types of airports, including general aviation and commercial service airports, rather than standing alone as a distinct category. Thus, the term “private charter only” is the one not included among the recognized types of airports.