What purpose does the centerline of the runway sheaves serve by projecting above the surface of the runway?

The centerline of the runway sheaves is designed to project above the surface of the runway primarily to protect the tapes from damage during arrestment. This elevation ensures that the tapes, which are crucial for the safe and effective operation of the system, are safeguarded from potential wear and tear that could occur if they were flush with the runway surface. When the tapes are elevated, they can move freely during the arrestment process without being ground down or cut, thereby maintaining their integrity and functionality.

In contrast, while achieving a standard setback, facilitating easier operations, and optimizing tape sweep may all be relevant considerations in runway design, they do not directly address the protective role that the sheaves' raised centerline serves for the tapes. The primary importance lies in ensuring that the tapes are preserved during their operational use, highlighting the crucial balance between safety and operational efficiency in runway design.