The purpose of the different airspace rules is safety. Some areas of the US have more flights than others. Therefore, the FAA has implemented classes of airspace to reflect this activity. The level of control goes from zero in some areas to considerable control around congested, big city, airports that serve considerable airline traffic.

The US Airspace System is divided into these categories.

Airspace can be divided into Controlled, Uncontrolled, Special Use and Other. Airspace designation is determined by considering the density of aircraft, the types of operations, the level of safety required, and the national and public interest. Controlled airspace is generally where ATC service is provided. There are different requirements if the flight is operated under Instrument Flight Rules (IFR) or Visual Flight Rules (VFR). For example, a pilot flying IFR in controlled airspace will have to file an IFR flight plan and receive an ATC clearance. For VFR flight, controlled airspace means increased cloud clearance and visibility requirements.  For the VFR pilot flying in B, C, and D airspace, there are communication and/or clearance requirements.

US airspace conforms to the International Civil Aviation Organization (ICAO) system. ICAO classifies airspace by the letters A through G with A being the most restrictive and G having the least constraints. There is no Class F airspace because the US has no equivalent to ICAO Class F where ATC provides separation for IFR aircraft only as practical.

Class A

Class A airspace begins at 18,000′ MSL and extends up to and including flight level 600 (60,000′). All operations in Class A must be conducted under IFR, which means you must be instrument rated and equipped. ADS-B Out is also a requirement in Class A. Pilots must obtain an ATC clearance before entering Class A, and maintain two-way radio contact with ATC. Class A covers all of the lower 48 states and the eastern section of Alaska, but is not depicted on charts.

Class B

Located around airports where there’s a large volume of air traffic, Class B airspace, often compared to an upside down wedding cake in shape, begins at the surface and extends upward to a designated altitude typically 10,000′ MSL. When below 10,000 MSL, aircraft are permitted to fly up to 250 kts. indicated airspeed, the speed limit for operations below 10,000′ MSL.  However, aircraft operating below the overhanging layers of Class B airspace are limited to 200 kts. indicated airspeed.

Class B Airspace typically takes on the shape of an upside down wedding cake and extends to 10,000′.

Class B airports typically accommodate a high volume of airline traffic.

Before operating in Class B, you must receive authorization from ATC, maintain two-way radio communications with ATC, have an operating transponder with altitude reporting and be ADS-B Out equipped. ADS-B Out is also required above and within the lateral boundaries of Class B. Private pilots may operate at all airports within Class B, but student pilots cannot takeoff, land, or fly solo in that airspace unless they have received ground and flight instruction for the specific Class B airspace.  The student’s logbook must have been endorsed within the previous 90 days by the instructor who gave the flight instruction. Recreational and Sport pilots may fly in Class B airspace once they have received the necessary training and an instructor endorsement. At some busier Class B areas such as Chicago and Los Angeles, student pilots may not takeoff or land at the primary airport of Class B.

The minimum visibility for VFR flight in Class B is three statute miles and you must stay clear of clouds. Class B is shown on Terminal Area, Sectional, and IFR Low Altitude En Route charts. Flying within 30 nautical miles of the primary airport you must have an operating transponder and altitude reporting capability and be ADS-B Out equipped. You’ll typically see lots of airline traffic in Class B airspace, usually heaviest around pushes as an airline lands or departs many of its airplanes close together.

An example of the Chicago Class B Airspace depicted on a sectional chart and extending to 10,000′ MSL.

Class C

Class C airspace surrounds airports handling a moderate volume of air traffic and resembles a two-layer upside-down wedding cake in shape.  It typically extends to 4,000′ AGL. To operate in Class C, you’ll need to establish communications with ATC and hold at least a student pilot certificate. Note that no clearance is required to enter Class C, just establishment of communications.  This can be as simple as the controller acknowledging your call sign. A transponder with altitude reporting is required within and above Class C airspace. ADS-B Out is also required within, above and within the lateral boundaries of Class C up to 10,000′ MSL.

Class C Airspace depicted in solid magenta on a Sectional chart.

For VFR flight, a minimum visibility of three statute miles is required and you must remain 500′ below, 1,000′ above, and 2,000′ laterally away from clouds. You will find Class C airspace on Terminal Area, Sectional, and IFR Low Altitude En Route charts. It’s depicted by solid magenta circles on VFR charts. Traffic advisories are provided to all aircraft in Class C. You may not exceed 200 kts. indicated airspeed within four nautical miles of the primary airport, at or below 2,500′ AGL.

Class D

Class D airspace surrounds tower-controlled airports that do not have an associated Class B or C area. You must establish two-way radio communications with ATC before operating in Class D airspace, but a clearance is not required. You must possess a minimum of a student pilot certificate.  Recreational and Sport pilots with an endorsement may also fly in Class D airspace. Class D airspace is depicted on VFR charts with a segmented blue line. Many have arrival extensions, giving the airspace the shape of a keyhole.

Class D Airspace depicted as a segmented blue line on the Sectional chart.

The vertical boundary is charted inside a blue segmented box in hundreds of feet MSL. VFR traffic advisories from ATC are provided on a workload permitting basis. Some towers operate part time, and when the tower is not in operation, Class D airspace reverts to the less restrictive Class E or G airspace. Just like Class C, you may not exceed 200 kts. indicated airspeed within four nautical miles of the primary airport, at or below 2,500′ AGL.

Class E

Class E airspace is controlled airspace that is not included in Classes A, B, C, or D.  It extends upward from the surface at some non-towered airports, or up from a floor of either 700′ or 1,200′ AGL. It extends up to, but not including, 18,000′ MSL unless there is an overlying B or C airspace. Radio contact is not required to fly VFR in Class E airspace, but ADS-B Out equipment is required in Class E above 10,000′ MSL excluding that airspace at and below 2,500′ AGL.

Class E extends up from a floor of either 700′ or 1,200′ AGL and extends up to 18,000′ MSL unless there is an overlying B or C.

Cloud clearances in Class E and below 10,000′ MSL are 500′ below, one thousand feet above and two thousand feet horizontally from clouds.  Below 10,000′ three miles visibility is required.

At and above 10,000′ MSL, and more than 1,200′ AGL, this increases to five miles visibility and cloud clearances of 1,000′ above and below and one statute mile horizontally. To takeoff, land, or enter the traffic pattern of an airport in Class E airspace, you must have a minimum ceiling of 1,000′ and a minimum visibility of three statute miles.

Class E airspace is depicted on VFR charts in various ways. Class E airspace having a floor of 700′ AGL is encompassed within a magenta vignette. The airspace outside of these magenta vignettes is assumed to be Class E with a floor of 1,200′ AGL. When Class E airspace, with a floor of 1,200′ AGL, abuts Class G airspace, it’s charted with a blue vignette. This is most common in the western states.

Inside the magenta vignette, Class E airspace begins at 700′ AGL. It’s assumed to begin at 1,200′ AGL outside of the vignette.

In cases where the floor of class E is other than 700′ or 1,200′ AGL, but less than 14,500′ MSL, it’s depicted by jagged blue lines and the floor is marked in AGL or, in some areas, MSL altitudes, most often near airways or NAVAIDs.

Some of the Class D airport extensions are also designated full-time Class E airspace.  These are depicted by magenta segmented lines. Some non-towered airports are surrounded by Class E airspace that goes all the way to the surface. These are depicted by a segmented magenta line.

Except where charted at a lower altitude, Class E airspace begins at 14,500′ MSL and extends up to, but not including, 18,000′ MSL.

Inside the blue vingette, Class E airspace begins at 1,200′ AGL. On the sharp side of the vingette, Class E does not begin until 14,500′ MSL with Class G below.

Class G

Class G airspace, also referred to as uncontrolled airspace. The rules for operating in Class G are fairly simple. You don’t have to talk to anybody or get permission to be there, but you do need certain visibility and cloud clearances for VFR operations which vary by altitude and whether it’s day or night.

Below 10,000′ MSL, visibility must be one mile. At night this goes up to three miles. At or above 10,000′ MSL, and more than 1,200′ AGL, day and night, this increases to five miles.

At 1,200′ or less above the ground, you have to stay clear of clouds. Between 1,200′ AGL and 10,000′ MSL, you must remain 500′ below, 1,000′ above and 2,000′ horizontally from clouds.

Above twelve hundred feet AGL and at or above ten thousand feet MSL you must stay 1,000′ below, 1,000′ above and one statute mile laterally from clouds.