When a control tower, located on an airport within Class D airspace, ceases operation for the day, what happens to the airspace designation?

• A. It remains Class D
• B. It reverts to Class E or a combination of Class E and G airspace during the hours the tower is not in operation
• C. It becomes Class B
• D. It becomes Class A

Answer: (B)

The key idea is that Class D exists only because a control tower is operating. Once the tower closes for the day, that surface-based control is no longer in effect, so the airspace reverts to the next lower classifications around the airport. In most cases, that means the airspace becomes Class E (which may start at 700 or 1,200 feet AGL, or at the surface if a designated Class E surface area exists) or parts of Class G up to the base of Class E. So, during hours the tower isn’t in operation, you’ll be operating in the surrounding Class E or G airspace, not in Class D. This isn’t changed to Class A or Class B by the tower’s hours; those higher classes apply only under different conditions and in different locations.