When should a rotating beacon be observed during daylight?

The correct answer is based on specific regulations and visibility requirements for aircraft operations. A rotating beacon is typically used at airports to indicate their location during poor visibility conditions. Specifically, the regulations state that a rotating beacon should be observed when visibility is less than 3 statute miles and the ceiling is below 1,000 feet. This is because beacons serve as an important visual aid for pilots navigating in low visibility scenarios, helping to ensure safe approaches and landings.

In contrast, during optimal weather conditions, such as when visibility is good, a rotating beacon would not necessarily be required to be illuminated for navigation. Therefore, other options that suggest observing the beacon under conditions of good visibility or within controlled airspace do not align with the specific requirements established for the use of the rotating beacon.