Final answer:
Terminal facilities can use 3 miles separation between aircraft by utilizing radar separation within terminal radar airspace, thanks to precise radar systems and the controlled airspace environment.
Step-by-step explanation:
The kind of separation that allows terminal facilities to use 3 miles separation between aircraft is referred to as radar separation. This separation standard is typically applied in terminal radar airspace areas, which allows air traffic controllers to safely handle more aircraft in a condensed space, especially near airports where traffic volume is high. Terminal radar facilities have advanced radar systems capable of accurately determining the position of aircraft, which facilitates this reduced separation. The standard five-mile separation is reduced because the radar technology allows for precise monitoring and the controlled environment of terminal airspace permits a closer following and sequencing of aircraft.
Learn more about Radar Separation