Controlled airspace is an aviation term used to describe airspace

Airspace

Airspace means the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere....

 in which ATC

Air traffic control

Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

has the authority to control air traffic, the level of which varies with the different classes of airspace. Controlled airspace is established mainly for three different reasons:

• high-volume air traffic areas, e.g. near airports
• IFR traffic under ATC guidance
• security, e.g. ADIZ

It is the opposite of uncontrolled airspace

Uncontrolled airspace

Uncontrolled airspace is airspace where an Air Traffic Control service is not deemed necessary or cannot be provided for practical reasons. According to the airspace classes set by ICAO both class F and class G airspace are uncontrolled...

.

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.

ICAO classifies airspace in seven classes from classes A to G. Controlled airspace is classes A to E, in order of decreasing ATC regulation of flights. Flight under instrument flight rules

Instrument flight rules

Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....

 (IFR) is allowed in all controlled airspace (some countries also permit IFR in uncontrolled airspace); flight under visual flight rules

Visual flight rules

Visual flight rules are a set of regulations which allow a pilot to operate an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better than basic VFR weather minimums, as specified in the rules of the...

 (VFR) is permitted in all airspace except A. Most countries use only a subset of the seven ICAO classes to classify their airspace.

See also

• Airspace class
  Airspace class
  The world's navigable airspace is divided into three-dimensional segments, each of which is assigned to a specific class. Most nations adhere to the classification specified by the International Civil Aviation Organization and described below...
  
  
• Special use airspace
  Special use airspace
  Special use airspace , is an area designated for operations of a nature such that limitations may be imposed on aircraft not participating in those operations. Often these operations are of a military nature...
  
  
• Restricted airspace
  Restricted airspace
  Restricted airspace is an area of airspace in which the local controlling authorities have determined that air traffic must be restricted for safety or security concerns...
  
  
• Prohibited airspace
  Prohibited airspace
  Prohibited airspace refers to an area of airspace within which flight of aircraft is not allowed, usually due to security concerns. It is one of many types of special use airspace designations and is depicted on aeronautical charts with the letter "P" followed by a serial number...