A landing zone for a helicopter should have a clear zone diameter that is how big?

The correct choice indicates that a landing zone for a helicopter should have a clear zone diameter of 100 feet (30 m). This size ensures that there is sufficient space around the helicopter for safe landing and takeoff operations.

A clear zone of this size helps to accommodate the rotor wash, which can produce powerful winds and debris. Ensuring a larger diameter helps protect the helicopter from potential obstacles and provides a safety buffer for personnel on the ground. Specifically, the 100-foot diameter allows for adequate clearance not just directly under the helicopter, but also along the sides, helping to mitigate risks associated with flying debris and ensuring a smoother landing process.

A smaller diameter would not provide the same level of safety and could potentially lead to dangerous situations, particularly in less-than-ideal landing conditions. Therefore, the requirement for a 100-foot clear zone is a critical standard in aviation safety protocols related to helicopter operations.