ABSTRACT
Th roughout most parts of the world, aviation as an industry is expanding. Th ough air traffi c demands are notoriously diffi cult to predict, being vulnerable to powerful and unforeseeable extraneous infl uences beyond the aviation community, all current forecasts concur about substantial future increases in aircraft numbers. As a consequence, air-traffi c control must seek to accommodate increasing demands for its services. Even the most effi cient current air-traffi c control systems cannot remain as they are, because they were never designed to handle the quantities of air traffi c now expected in the longer term, and they could not readily be adapted to cope with such increases in traffi c volume. Th e combined sequential processes of devising, proving, and introducing major changes in an air-traffi c control system may take many years to implement, but to make no changes is not a practical option. Hence, air-traffi c control must evolve (Wise, Hopkin, & Smith, 1991).
