Final answer:
UAS must have anti-collision lighting visible for 3 statute miles during civil twilight to maintain safety and visibility in the airspace.
Step-by-step explanation:
When operating an Unmanned Aircraft System (UAS) during civil twilight, the aircraft must be equipped with anti-collision lighting. This lighting must be visible for at least 3 statute miles and have a flash rate sufficient to avoid a collision. Anti-collision lights are required to ensure the UAS is visible to other aircraft and to prevent potential accidents in lower visibility conditions that occur during civil twilight. This is a safety measure to make the UAS more visible to others and to maintain safe operation of the aircraft within the airspace.