Procedural approach control is a form of non-radar air traffic control conducted from the Tower to separate arriving, departing, and overflying aircraft within a designated area around an aerodrome. Procedural approach is used in areas with little or no radar coverage, where traffic density is relatively low.
The procedural approach controller may utilise a variety of (non-radar) separation standards to achieve separation between aircraft i.e. vertical, longitudinal, lateral, geographical, or visual separation.
Without an accurate radar picture to aid situational awareness the procedural approach controller uses pilot position reports and relies heavily on visualisation to maintain a mental picture of the evolving 3D traffic scenario.
Often there is a need to deliver long and complicated departure/arrival instructions to a pilot in order to enforce a separation. For example, a complex diversionary climb instruction or a descent requirement with added terrain considerations. Resultantly, the procedural approach environment is quite susceptible to readback/hearback errors.
Procedural approach separations are generally (but not always) less expeditious than radar separations. Because of this, and the extra time taken to formulate and execute procedural separations, the capacity of a procedural approach controller (with regards to traffic levels) is less than in a radar approach environment.
In New Zealand, procedural approach is conducted from 7 regional control towers (Gisborne, Napier, New Plymouth, Nelson, Dunedin, Queenstown and Invercargill) and is a service provided concurrently by the aerodrome (Tower) controller.