When is a displaced threshold necessary?

A displaced threshold is necessary when an object obstructs the airspace needed for landing aircraft. This situation often arises when there is a physical obstacle, such as a building, tree, or other structure, that intrudes into the approach path of the runway. By establishing a displaced threshold, the usable runway length for landing is moved farther down the runway, allowing for safe and efficient aircraft operations while avoiding potential collisions with obstacles. This setup helps maintain adequate clearance for aircraft during the critical phase of landing, ensuring compliance with safety regulations and operational standards.

The other options do not accurately capture the primary purpose of a displaced threshold. For instance, enhancing takeoff distances and landing speeds is not the rationale behind a displaced threshold; rather, it serves to enhance safety by managing obstructions. Emergency landings might require different protocols entirely and do not inherently require a displaced threshold if no obstructions are involved.