What is one of the requirements for wind cones at airports?

Wind cones are essential visual aids at airports that provide pilots information about wind direction and speed. For a wind cone to function effectively, it should swing freely, which allows it to accurately display the wind’s direction. If the wind cone is hindered or restricted, it may not represent the actual wind conditions, potentially leading to unsafe decisions during flight operations.

In addition to swinging freely, proper illumination is important, particularly for visibility during low-light conditions, ensuring that pilots can see the wind direction indicator during night operations or inclement weather. This fulfills the requirement for operational standards for safety at airports.

The other options present various characteristics that may be relevant in different contexts but do not meet the essential operational requirements for wind cones specifically. For instance, while bright colors can enhance visibility, it is not a mandatory requirement that specifies only bright red. Similarly, being obscured from direct sunlight would likely impede visibility rather than enhance it, and positioning requirements can differ based on regulatory standards but aren't universally set at 100 feet from the runway. Thus, the necessity for wind cones to swing freely and be properly illuminated is integral for safety and operational effectiveness.