Procedural control is a non-radar air traffic control method in the absence of radar. It is used in certain places in the world, specifically low-traffic areas and oceans, where radar coverage is either unrealistically expensive or would not be justified. It is also used as a back-up system in the case of radar failure.
Controllers provide horizontal separation based on time, the geography of predetermined routes, or aircraft position reports via ground-based navigation aids, for aircraft that are not vertically separated.
The overall gist of procedural control is that each aircraft is cleared onto a predetermined route, and no aircraft traveling on the same or intersecting routes at the same flight level should come within 10 minutes of each other.
The controller must maintain a mental picture of the locations of every aircraft under their jurisdiction based on the fight progress strips. If a conflict occurs, the controller will issue a speed, altitude, or heading change until the conflict is gone. Altitudes and routes are constantly checked against each other to find possible conflicts.
With procedural approach control, separation is maintained by allowing one aircraft to make an approach at any one time; the proceeding aircraft must either be in visual contact by the airport’s control tower, or have reported that it has landed before the next aircraft is allowed to leave their hold and commence the approach.