Area control
Area control handles flights en route, across sectors of airspace between the terminal areas around airports. The work is done in an area control centre. A controller is responsible for the sectors they are checked out on, not for the whole centre.
A sector, not the whole map
The airspace is divided into sectors. Each has a boundary, a frequency, and the flights that are inside it. When traffic is light, a centre combines sectors and one controller works the group. When traffic grows, those sectors are split again. What is combined on a given day is that centre's operation, not a fixed map.
Some centres put high traffic and low traffic on different sectors. An overflight at high level can cross the country and never enter the sectors that handle climbs and descents near airports. Not every centre is split that way. Where a split exists, it is published.
One flight across the sector
A flight arrives as a transfer. It comes from the previous area sector, or from an approach unit if it has just departed. The controller accepts it, then keeps it separated from the other flights in the sector. The clearances are the ones that sector uses: a level, a route, a speed.
Before the flight leaves, the next sector has agreed the conditions it will accept, and the pilot is told to contact that sector. Until the next controller has the aircraft, it remains this sector's. A handoff is finished when it is accepted, not when the instruction to change frequency is spoken.
A large share of the traffic is overflying. It will not land in that country. The controller still separates it, and still hands it to the next sector. The destination does not change the task while the flight is inside the boundary.
Where there is no surveillance
Many area sectors are worked from a surveillance display. Some are not, particularly over the ocean or where there is no radar cover. There the picture is built from pilot reports of position, time, and level, and the separation is the minimum published for that airspace. The task is the same. The method is not.
The boundary with approach
Arrivals are descended and delivered to the approach unit for the destination, at a level and a point that unit can use. Departures are accepted from approach once they meet the conditions for entering the sector. That transfer is the edge of area control.
The order of aircraft onto the runway is approach's work. The runway itself is the tower's. An area controller does not issue the landing clearance, and does not control the taxiways, even when the flight they are working will land within the hour.
Busy sectors are sometimes two people
On a busy sector a centre may put two controllers on the same piece of airspace. One plans the flights and coordinates with the sectors alongside. The other talks to the aircraft. A quiet sector, or a group of sectors combined overnight, is often one person. The two-person split describes that operation. It does not describe every area position.
Military traffic in the same airspace
Where military flights use the same sky, the civil sector coordinates with the military unit. How that coordination works is set nationally. The civil controller does not become the controller of the military flight, and a military controller is not working the civil sector.
The endorsement
The endorsement covers the sectors at that centre which the controller is checked out to work. It does not cover every sector in the centre, and it does not travel to another centre. A tower and an approach unit are different ratings again.
The runway and the circuit are aerodrome control. Arrivals and departures around the airport are approach control. How the three fit together is the air traffic controller guide.