When flying to an airport with no functioning control tower, what must the pilot ensure about the flight plan?

When flying to an airport that does not have a functioning control tower, it is important for the pilot to understand the appropriate procedures regarding the flight plan. Closing the flight plan is essential to ensure that all parties involved in the flight operation, including search and rescue services, are aware of the aircraft's status.

When a pilot chooses to close the flight plan with the originating military base or through a Flight Service Station (FSS) or Air Traffic Control (ATC) facility, it ensures that there is communication and confirmation regarding the safe arrival at the destination. This step is part of good airmanship and safety protocols since it prevents unnecessary search efforts in case communication is lost or if the pilot fails to report arrival.

The requirement to either close the flight plan through the originating base or via an FSS or ATC facility provides flexibility to the pilot while still adhering to safety regulations. Hence, either option satisfies the necessity of closing the flight plan when arriving at an uncontrolled airport, which is why the correct answer encompasses both choices.