What must be ensured for simultaneous operations on parallel runways in opposite direction?

For simultaneous operations on parallel runways in opposite directions, it is essential to ensure VFR (Visual Flight Rules) conditions. VFR conditions indicate that the weather is clear enough for pilots to fly visually rather than relying solely on instruments. This requirement is crucial because it allows pilots to maintain visual separation from other aircraft, which is necessary when operating in close proximity to one another on parallel runways.

In VFR conditions, pilots can easily see and avoid other aircraft, helping to prevent potential conflicts that could arise from simultaneous operations. This visibility ensures that pilots can effectively manage their approach and departure paths, thus enhancing safety during these operations.

The other options, while relevant in different contexts, do not directly address the foundational requirement for safe simultaneous operations. For instance, one-way radio communication and traffic advisories are important for maintaining communication and situational awareness among air traffic controllers and pilots, but they do not replace the essential need for visual separation that VFR conditions provide. Ground visibility, while important, specifically refers to conditions on the ground and may not adequately address the vertical or lateral separation needed during flight operations.