This is a summary of a fairly detailed post.
Controlled Airspace A generic term that covers the different classification of airspace (Class A, Class B, Class C, Class D, and Class E airspace) and defined dimensions within which air traffic control service is provided to IFR flights and to VFR flights in accordance with the airspace classification.
Class A airspace is that airspace from 18,000 feet MSL up to and including FL 600, including the airspace overlying the waters within 12 nautical miles (NM) of the coast of the 48 contiguous States and Alaska, except for the most of the chain of islands off Alaska and Florida and in Alaska, airspace below 1,500 feet AGL. It also includes designated offshore areas in international airspace. “High” areas are from 18,000 feet MSL to FL600 while “Control” areas are from 18,000 feet MSL to FL450.
Class B airspace is defined by FAA Order JO 7400.11A. There are 30 Class B airspaces. The tops range from 7,000′ MSL at New Orleans to 12,500′ MSL at Atlanta with most at 10,000′ MSL.
Class C airspace is also defined by FAA Order JO 7400.11A. There are 124 Class C airspaces. The airspace is defined by two rings. The inner ring is 5 nautical miles in diameter and the outer ring is 10 nm in diameter. The inner ring goes from the surface to anywhere from 3,000′ MSL to 9,400′ MSL. The outer ring has a floor from 1,300′ MSL to 7,800′ MSL. Tops are usually higher in mountainous areas. Tops of the inner and outer ring are always the same. The outer ring is often segmented with different floors in each segment. The AIM 3-2-4 says that the airspace usually consists of a 5 NM radius core surface area that extends from the surface up to 4,000 feet above the airport elevation, and a 10 NM radius shelf area that extends no lower than 1,200 feet up to 4,000 feet above the airport elevation.
AIM 3-2-4 (c) (3) Note 4. Though not requiring regulatory action, Class C airspace areas have a procedural Outer Area. Normally this area is 20 NM from the primary Class C airspace airport. Its vertical limit extends from the lower limits of radio/radar coverage up to the ceiling of the approach control’s delegated airspace, excluding the Class C airspace itself, and other airspace as appropriate. (This outer area is not charted.)
Class D airspace is also defined by FAA Order JO 7400.11A. Most Class D airspace is composed of one ring centered at the primary airport. The ring varies from 4.1 nautical miles in diameter to 6.6 nm in diameter. The airspace goes from the surface to anywhere from 2,500′ MSL to 5,400′ MSL. Some Class D airspaces have Class D extensions along an IFR approach. The airspace is usually from the surface to 2,500 feet above the airport elevation surrounding those airports that have an operational control tower. The charts depict the top in MSL.
Class E airspace is also defined by FAA Order JO 7400.11A. Generally, if the airspace is not Class A, Class B, Class C, or Class D, and it is controlled airspace, it is Class E airspace. I’ve classified the order into 9 types.
- Above 14,500’—from 14,500 feet MSL up to and up to but not including 18,000 feet MSL, including the airspace overlying the waters within 12 nautical miles (NM) of the coast of the 48 contiguous States and Alaska, except for the most of the chain of islands off Alaska and Florida and in Alaska, airspace below 1,500 feet AGL.
- Airspace above FL600
- Surface area for an airport—including Class C or D that revert to E when the tower is closed
- Extension to a Class C or D surface area
- Instrument transition—upward from 700 feet or more above the surface of the earth when designated in conjunction with an airport for which an approved instrument procedure has been prescribed
- Airways—from 1,200 feet or more above the surface up to the overlying A, B, C,or D airspace.
- Offshore—Controlled airspace beyond 12 nautical miles from the coast to provide IFR enroute ATC services. Up to but not including 18,000′ MSL.
- Federal Airways—unless otherwise specified, extend upward from 1,200 feet to, but not including, 18,000 feet MSL
- Other controlled airspace—when required to provide IFR en route air traffic control services off airways
All Class E airspace below 14,500′ MSL is charted. The floor, unless otherwise noted on the chart, is 1,200′ MSL.
Class G airspace (uncontrolled) is that portion of airspace that has not been designated as Class A, Class B, Class C, Class D, or Class E airspace. I’ve classified it into 6 “types”.
- In Alaska, airspace below 1,500 feet AGL.
- Surface area for an airport—including Class C or D that revert to G when the tower is closed
- Instrument transition—below 700 feet or more above the surface of the earth when designated in conjunction with an airport for which an approved instrument procedure has been prescribed
- Federal Airways—unless otherwise specified, below 1,200 feet
- Other uncontrolled airspace—All Class G airspace is charted. The ceiling, unless otherwise noted on the chart, is 1,200′ MSL.
Terminal Radar Service Areas are not defined in 14 CFR Part 71. Participating pilots can receive additional radar services which have been redefined as TRSA Service.
Note: FAA Order JO 7400.11A is issued periodically with a letter suffix. When this post was first written, the order was JO 7400.9, but when they reached the suffix Z, they changed the number of the order as well. The best way to find the current version is to search the FAA website for the document title, Airspace Designations and Reporting Points. At the moment they are listing all publications at this site, but the location may change.