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Controlled airspace is an aviation term used to describe airspace in which traffic levels are such that it has been determined that air traffic control (ATC) must provide some form of separation between aircraft. It is the opposite of uncontrolled airspace.
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 (significantly the U. S.) 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 A to G. Controlled airspace covers classes A to E, in order of decreasing ATC regulation of flights. Flight under Instrument Flight Rules (IFR) is allowed in all airspace, controlled or uncontrolled; flight under Visual Flight Rules (VFR) is permitted in all airspace except A. Pilots of aircraft need to obtain an Air Traffic Control clearance before they enter airspace of classes A, B, C or D. If if flying under IFR they also need to obtain a clearance to fly in class E airspace.
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[edit] Class A Airspace
Class A airspace is defined as all airspace between 18,000 ft MSL and 60,000 ft MSL. Commercial flights spend the majority of their flight time in Class A airspace. In order to enter Class A airspace, an aircraft must be operating under IFR, obtain a clearance from and remain in communications with air traffic control, and carry and operating transponder. Aircraft within this airspace are separated from one another by ATC.
[edit] Class B Airspace
Class B airspace surrounds the world's busiest airports. It resembles an inverted wedding cake in structure, with a small layer near the bottom, and larger layers near the top. This allows commercial flights to remain in Class B airspace for their takeoff, climbout, approach and landing while allowing other aircraft to access smaller airports nearby without entering Class B airspace. A typical Class B airspace extends up to 10,000 ft AGL with a maximum radius of 25 miles. In order to operate within Class B airspace, an aircraft must obtain a clearance from and remain in contact with air traffic control, and carry an operating transponder. ATC is responsible for separating all aircraft from one another.
[edit] Class C Airspace
Class C airspace surrounds large airports which are not busy enough to warrant Class B airspace. Class C airspace also resembles an inverted wedding cake, typically with only two tiers. The first tier typically extends for a 5 nautical mile radius, while the second extends for 10 nautical miles. In order to enter Class C airspace, an aircraft must establish and maintain communications with air traffic control, and carry an operating transponder. Traffic separation is only provided for flights under instrument flight rules or special VFR (SVFR).
[edit] Class D Airspace
Class D airspace surrounds smaller airports which are busy enough to warrant a control tower. Class D airspace is generally cylindrical in shape with a radius of 4 nautical miles. To enter Class D airspace an aircraft must establish and maintain communications with ATC. Traffic separation is only provided for IFR and SVFR flights.
[edit] Class E Airspace
Class E airspace covers everywhere between 14,500 ft MSL and 18,000 ft MSL, as well as above 60,000 ft MSL. It also includes a large amount of airspace below 14,500 ft, where indicated on aeronautical charts. Class E airspace allows ATC to control IFR flights in areas away from airports, and in approaches to Class C and Class D airports. For VFR aircraft, there are no entry or communications requirements for Class E airspace. ATC only provides separation for IFR and SVFR flights.
[edit] Uncontrolled Airspace
All airspace outside of controlled airspace is uncontrolled airspace.
[edit] References
- Federal Aviation Regulations (14CFR
- Part 71 - Airspace
- Parts 91.127-91.135 - Operating in Class E,D,C,B,A Airspace
- Gleim, I. N., Pilot Handbook, Gleim Publications, 2000
