Final answer:
The radar controller is responsible for separating radar arrivals unless the aircraft are under visual separation, in which case pilots maintain their own separation.
Step-by-step explanation:
The radar controller performing the approach control function is responsible for the separation of radar arrivals unless the aircraft are under visual separation. Visual separation occurs when pilots are responsible for maintaining separation from other aircraft by staying in visual contact. This happens in clear weather conditions, allowing pilots to see and avoid other aircraft, mitigating the reliance on radar for separation. In scenarios where cloud layers or poor visibility prevent visual identification, radar instruments are crucial for maintaining safe distances between arriving aircraft. The radar controller uses this equipment to ensure aircraft are appropriately spaced, navigating the complexities of poor visibility akin to probing through obscuring layers as noted in your reference. However, when aircraft can maintain visual separation, the burden of maintaining appropriate separation distances shifts from the radar controller to the pilots of those aircraft.