In aviation, a control zone (CTR) is a volume of controlled airspace, normally around an airport, which extends from the surface to a specified upper limit, established to protect air traffic operating to and from that airport. Because CTRs are by definition controlled airspace, aircraft can only fly in them after receiving a specific clearance from air traffic control. This means that air traffic control at the airport know exactly which aircraft are in that airspace, and can take steps to ensure aircraft are aware of each other, either using separation or by passing traffic information.
In places with much traffic, a Control Area (CTA) or Terminal Control Area (TMA/TCA) is usually situated directly above and sometimes also next to or around the CTR, to guide arriving and departing traffic. However, unlike a CTR, these areas do not have their base at the surface.
A CTR requires permanent radio contact while being in it, and a clearance before entering. Certain activities such as making an approach, landing and taking off also require clearances. This implies that an aircraft flying in it must be equipped with a radio. There are procedures for radio failures.
In the USA the term control zone is no longer used[1] and has been replaced by airspace class D. Typically it extends 5 miles in diameter with a height of 2500 ft AGL (above ground level) around small commercial airports.
In the UK, control zones are normally class D airspace and usually extend from the surface to 2000 ft AGL. They can be observed to be usually rectangular, extending along the axis of the main runway, although irregular shapes may be used where more complex airspace dictates this (see Liverpool and East Midlands). A control area (CTA) is often placed between a CTR and nearby airways to give uninterrupted controlled airspace to airways arrivals and departures.
In Germany, control zones are a special type of class D airspace, called D (CTR). The main difference to the regular German class D airspace is, that within a CTR there is a minimum required cloud ceiling of 1500 ft AGL.[2]
See also
edit- Airway (aviation)
- Flight information region
- Terminal control area
- Area control center (for high-altitude traffic between airports)