Approach control

The piece of sky

The volume is published. It sits around the airport, above and outside the circuit, and inside the area sectors that carry en-route traffic. One approach unit can serve several airports. The boundary, and which airports it includes, are on the chart for that unit.

It is not the runway and it is not the taxiways. Those are aerodrome control. It is not the long flight between terminal areas. That is area control. A flight is on this frequency only while it is arriving at, or departing from, the airports that unit serves.

Arrivals

Inbound aircraft are delivered by area control, or they come from a nearby airport. The controller orders them so they reach the runway at a rate the tower can land. The usual changes are a level, a heading, or a speed. Where the unit has no surveillance, the spacing is made with time and level from the pilots' position reports.

If more aircraft are arriving than the runway can take, some are held until the sequence has room. The hold may be a published pattern, or a place the controller assigns. Holding is a way to stop the arrival rate exceeding what the airport can accept. It is not a failure of the sequence.

The aircraft is transferred to the tower for the landing, at a point agreed for that airport. The tower issues the landing clearance. Approach does not. If the aircraft goes around, it comes back to approach and is fitted into the sequence again.

Departures

A departure starts on the ground. The tower needs the climb ahead of the runway to be free before it lets the aircraft take off. At a busy airport that means approach has accepted the flight, or a standing agreement already covers it. An empty runway is not enough on its own.

Once the aircraft is airborne, approach climbs it clear of the arrivals and points it at the route. It is then transferred to area control on the conditions that sector expects: a level, a route, and a point. Until area accepts it, the departure is still an approach flight.

With the tower and with area

The runway in use belongs to the tower, and it sets the direction of the arrival sequence. When the tower changes runway, approach rebuilds that sequence. The two units also agree the gaps a departure needs, and what happens to an aircraft that has gone around.

Area control needs the other side of the same picture. Approach agrees the level and the point at which arrivals will be taken, and the level at which departures will be handed on. A transfer the next unit has not accepted is still this unit's aircraft.

Where the unit sits

The room may be in the tower building, elsewhere on the airport, or in a centre that works several airports. That is the employer's layout. It does not change the task.

The picture is usually a surveillance display. Some units still separate aircraft procedurally, from pilot reports. Those are different methods. In many states they are also different ratings, so a controller qualified on one is not automatically qualified on the other. The name on the licence is the state's.

The endorsement

The endorsement is for that approach unit. A different unit, including another airport's approach, is further training. So is a move between procedural and surveillance approach, where the state treats them as separate ratings. Neither one is a tower endorsement, and neither one is an area endorsement.

The runway and the circuit are aerodrome control. The en-route sectors are area control. How the three fit together is the air traffic controller guide.