What happens to Class D airspace when the appropriate ATC unit is not operational?

In aviation, Class D airspace is typically established around airports with an operational control tower. When the Air Traffic Control (ATC) unit that manages this Class D airspace is not operational, the Class D airspace effectively reverts to Class E airspace. Class E airspace is controlled airspace that has fewer restrictions, allowing for more flexibility in operations, particularly for VFR (Visual Flight Rules) traffic.

The transition to Class E allows aircraft to operate under visual flight rules without the usual control tower services provided by Class D airspace. This is important for the safety and efficiency of both VFR and IFR (Instrument Flight Rules) operations. When ATC is not available, pilots must rely on their navigation and communication skills while adhering to the procedures laid out for Class E airspace.

Class F airspace is not a standard classification in the United States, primarily used in certain international contexts, so it wouldn't apply in standard US airspace operations. Similarly, while restricted airspace does exist, it serves a different purpose related to safety and national security and does not automatically apply to situations where an ATC unit is inactive. Thus, the most accurate answer is that the Class D airspace becomes Class E airspace when the appropriate AT