Controlled airspace

Not to be confused with area control center.

Controlled airspace is airspace of defined dimensions within which air traffic control (ATC) services are provided.^[1][2] The level of control varies with different classes of airspace. Controlled airspace usually imposes higher weather minimums than are applicable in uncontrolled airspace.^[3] It is the opposite of uncontrolled airspace.

Schematic representation of the main controlled airspace types and the air traffic control offices that respectively provide control service inside these airspaces. "TMA" is an abbreviation for Terminal Manoeuvring Area ("Terminal Control Area" outside Europe)

Controlled airspace is established mainly for three different reasons:

• high-volume air traffic areas, e.g. near airports^{[citation needed]}
• Instrument flight rules traffic under ATC guidance^{[citation needed]}
• security, e.g. within an air defense identification zone^{[citation needed]}

Controlled airspace usually exists in the immediate vicinity of busier airports, where aircraft used in commercial air transport flights are climbing out from or making an approach to the airport, or at higher levels where air transport flights would tend to cruise. Some countries also provide controlled airspace almost generally, however in most countries it is common to provide uncontrolled airspace in areas where significant air transport or military activity is not expected.^{[citation needed]}

The International Civil Aviation Organization divides airspace into seven classes, from A to G, in order of decreasing ATC regulation of flights. Classes A to E are controlled airspace. Flight under instrument flight rules (IFR) is allowed in all controlled airspace. Some countries also permit IFR in uncontrolled airspace). Flight under visual flight rules (VFR) is permitted in all airspace except class A.^[4]

Types

Control Zone (CTR)

A control zone 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.

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^[5] 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.^[6]

Control area (CTA)

A control area is a section of controlled airspace that extends upwards from a specified limit above the earth, which must be above 200m (700ft),^[7] and are established in areas where the density of traffic is high. The upper limit of a control area is either when an air traffic control service will not be provided above, or there is another control area above.^[8]

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.^[9]

A terminal control area (TMA) is a control area established surrounding one or major airports at the confluence of airways. It typically sits above each individual airport's CTR.^[10]

See also

• Airspace class
• Prohibited airspace
• Restricted airspace
• Special use airspace
• Terminal control area