What is Air Traffic Control (ATC)?
Air Traffic Control (ATC) is a service that ensures smooth and safe flights. The primary purpose of ATC is to prevent collisions between aircraft both in the air and on the ground. Furthermore, it provides information and assists with navigation.
ATC communicates with pilots via two-way radio connection on the designated frequency (which is different for each air traffic control unit). The other way is ACARS, which is basically a text-based radio connection. You can imagine that as some kind of messenger between pilots and ATC.
The safety of flights from take-off to landing is ensured by three centres that cooperate with each other.
A) Airport Control Service (TWR and GRD)
The airport control service operates from the airport control tower. In particular, it is responsible for safe traffic on the ground and in the airspace closest to the airport (referred to as the Control Zone – CTR), where aircraft operate immediately before landing or immediately after take-off. Furthermore, the control tower also ensures safe traffic of land vehicles on the airport grounds.
The airport control service is referred to by the abbreviation TWR (Tower) and GRD (Ground).
Small, uncontrolled airports do not have any air traffic control service – only an information service (AFIS) is provided.
B) Approach Control Service (APP)
The approach control service ensures a smooth transition between upper airspace (controlled by Area Control Service, see below) and airport airspace controlled by the Airport Control Service (see above).
The approach control service is based at the airport where a particular aircraft is to land (or depart). This airspace in the vicinity of an airport is referred to as the Terminal Control Area (TMA).
The approach control service is referred to by the abbreviation APP (Approach).
C) Area Control Service (ACC)
The area control service is responsible for controlling air traffic within a large portion of the airspace, referred to as the controlled area (CTA). The controlled area often extends over the entire territory of a country, or a substantial part of such a territory.
The area control service is referred to by the abbreviation ACC (Area Control Centre).