Which of the following is required for an aircraft to use airways?

In order for an aircraft to use airways, having a valid instrument rating is crucial. This requirement ensures that the pilot is capable of flying in instrument meteorological conditions (IMC) and can navigate the aircraft using instruments rather than relying solely on visual cues. Airway systems are primarily designed for flights conducted under instrument flight rules (IFR), which necessitates pilots who are trained and certified to operate such flights safely and effectively.

The instrument rating signifies that a pilot possesses the necessary skills and knowledge to handle an aircraft's navigation and controls in conditions with less visibility, which is common when flying through airspace designated as airways. This is essential for maintaining safety and adherence to air traffic control directives, especially in crowded or complex airspace systems.