Separation of aircraft in terminal areas is made difficult by the convergence of tracks, continual changes of height, and traffic density. The application of longitudinal separation is too restrictive at busy aerodromes. Vertical separation is suited to the approach phase, but has limitations in the departure phase. The most useful form of separation is lateral, although it is often difficult to apply. The difficulties arise from organizational rather than operational causes and efforts to overcome them can be most rewarding.

Other difficulties of a terminal area arise from the conflicting patterns of adjacent aerodromes, the mixing of terminal and overflying traffic, and the mixing of departing and arriving traffic. Lateral separation can assist in all these problems.