With the advent of increasing numbers of high-speed, high-altitude aircraft on the airways of the world, airlines, aircraft manufacturers, government agencies responsible for navigational standards and air traffic control, as well as military agencies are actively engaged in studies and action directed towards significant changes in longrange air navigation practices and procedures.

These changes have been dictated by the need to utilize to best advantage the ‘limited’ air space available on long-range air routes to each individual aircraft, because of the fantastic growth rate in numbers of aircraft operating the trunk routes of the world.

In order to limit the amount of airspace required around each individual aircraft separation standards are enforced by the various agencies responsible for control of air traffic along these major trunk air routes. These separation standards are based on longitudinal, lateral and vertical limits between adjacent aircraft. In order to ensure that operating companies and flight crews are aware of these requirements, appropriate legislation is introduced by either international or national agencies and promulgated in readily assimilable form in regulations, orders, or flight or operation manuals.