What is the key requirement for the Nav Aid rule applied to airports with at least one operational navigational facility?

The key requirement for the Nav Aid rule applied to airports with at least one operational navigational facility is that there must be options for pilots that enhance safety and efficiency during approaches. Specifically, straight-in nonprecision approaches or either straight-in precision approaches or circling maneuvers must be available. These procedures are critical for ensuring that aircraft can navigate safely in various weather conditions and manage landing effectively.

Having both types of approaches—nonprecision and precision—provides pilots with alternatives depending on the situation, such as visibility conditions and aircraft capabilities. This requirement aligns with the need for operational flexibility and safety considerations in air traffic management. Therefore, the correct option, which encompasses both the availability of a straight-in nonprecision approach and the requirement for either a precision approach or a circling maneuver, is well-founded in ensuring that airports meet operational readiness standards.