Who is responsible for assisting the pilot by ensuring the safe conduct of a flight under visual line-of-sight?

The Visual Observer (VO) plays a crucial role in ensuring the safe conduct of a flight under visual line-of-sight. The VO's primary responsibility is to assist the pilot by maintaining continuous visual contact with the aircraft while it is in operation, particularly when the pilot may become focused on the flight controls or environment. The VO looks out for obstacles, other aircraft, and any potential hazards that may affect the safety of the operation. This positioning allows the pilot to concentrate on flying the aircraft while still adhering to the requirement of maintaining visual line-of-sight as mandated by many regulatory authorities.

In the context of the other options, although a ground control operator can manage operations from the ground level and a flight instructor may provide training and guidance, their roles do not center on maintaining visual contact during flight. Similarly, a manned aircraft pilot does not have the same responsibilities when it comes to unmanned systems operations, where the VO's function is vital. Thus, the Visual Observer is essential for ensuring safety in flight operations that require a visual line of sight.