Automation is simply one class of resources among many available to the human operator or manager. Human-centered automation means automation designed to work cooperatively with human operators in the pursuit of stated objectives. Piloting is the use by a human operator of a vehicle to accomplish a mission. A mission consists of a number of functions, each involving from one to many tasks and subtasks, which are accomplished using a variety of human and machine resources. The modern airplane is the product of a program of research, development and refinement in detail that no other structure or mechanism has ever matched. Air traffic controllers are responsible for the safe direction and separation of air traffic. Strategic management and coordination of, and assistance to, tactical air traffic controllers is designed to maximize airspace usage while preventing overload of individual air traffic control facilities.