Control area (aviation)

In aviation, a control area (CTA) is "a controlled airspace extending upwards from a specified limit above the earth", not less than 200m (700 feet), although the limit does not need to be established uniformly within a control area. ICAO recommends for the lower level to coincide with a VFR cruising level if the lower level limit of a control area is above 900 m (3000 feet) MSL (mean sea level), and the VFR cruising level to not have to be lowered to less than 200 m (700 feet) due to atmospheric conditions. The upper limit should be established when either air traffic control service will not be proveded above that level, or there is another (upper) control area above this control area.

Control areas are established in any areas when the density of air traffic is high:
 * An airway is a case of a "control area or portion of thereof established in the form of a corridor".
 * Terminal Control Area is "a control area normally established at the confluence of ATS routes in the vicinity of one or more major aerodromes."

A control area usually is situated on top of a control zone (CTR) and provides protection to aircraft climbing out from the airport by joining the low-level control zone to the nearest airways. In the UK, they are generally class A, D or E.

Control areas are particularly useful where there are busy airports located close together. In this case, a single CTA will sit over all of the individual airports' CTRs. In larger-scale cases, this is known as a terminal manoeuvring area (TMA, or TCA).