Air traffic control
Air traffic control (ATC) involves communication with aircraft to help maintain separation – that is, they ensure that aircraft are sufficiently far enough apart horizontally or vertically for no risk of collision. Controllers may co-ordinate position reports provided by pilots, or in high traffic areas (such as the United States) they may use radar to see aircraft positions.
There are generally four different types of ATC:
- center controllers, who control aircraft en route between airports
- control towers (including tower, ground control, clearance delivery, and other services), which control aircraft within a small distance (typically 10–15 km horizontal, and 1,000 m vertical) of an airport.
- oceanic controllers, who control aircraft over international waters between continents, generally without radar service.
- terminal controllers, who control aircraft in a wider area (typically 50–80 km) around busy airports.
ATC is especially important for aircraft flying under instrument flight rules (IFR), when they may be in weather conditions that do not allow the pilots to see other aircraft. However, in very high-traffic areas, especially near major airports, aircraft flying under visual flight rules (VFR) are also required to follow instructions from ATC.
In addition to separation from other aircraft, ATC may provide weather advisories, terrain separation, navigation assistance, and other services to pilots, depending on their workload.
ATC do not control all flights. The majority of VFR (Visual Flight Rules) flights in North America are not required to contact ATC (unless they are passing through a busy terminal area or using a major airport), and in many areas, such as northern Canada and low altitude in northern Scotland, Air traffic control services are not available even for IFR flights at lower altitudes.
