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US airspace is divided into Classes A, B, C, D, E and G. Class A needs IFR, Class B needs an ATC clearance, Classes C and D need two-way radio contact before you enter, and Class E and Class G have no entry requirement for a VFR pilot. Equipment and pilot certificate rules add to that.
Checked against: AIM Chapter 3 Section 2, paragraphs 3-2-2 through 3-2-6 (AIM dated 2/20/25); 14 CFR 91.129, 91.130 and 91.131 (eCFR text held in public/FAA-Regulations/14-CFR-Part-91.xml, reviewed 10 October 2026).
| Class | Typical vertical limits | What you must have before entering | Pilot certificate |
|---|---|---|---|
| A | 18,000 ft MSL up to and including FL 600 | Operate under IFR unless otherwise authorized | Instrument rating for IFR |
| B | Surface to 10,000 ft MSL, in layers | ATC clearance regardless of weather, operable two-way radio | At least a private pilot certificate, or a student, recreational or sport pilot who meets the 91.131 conditions |
| C | Surface to 4,000 ft above airport elevation (5 NM core, 10 NM shelf from 1,200 ft) | Two-way radio communication established before entry; transponder with altitude reporting and ADS-B Out | No specific certification required |
| D | Surface to 2,500 ft above airport elevation | Two-way radio communication established before entry | No specific certification required |
| E | Varies: surface areas, transition areas, 14,500 ft MSL up to 18,000 ft, and above FL 600 | No specific entry requirement; transponder and ADS-B Out at and above 10,000 ft MSL, excluding at and below 2,500 ft above the surface | No specific certification required |
| G | Airspace not designated as A, B, C, D or E | No ATC clearance or communication requirement | No specific certification required |
The United States uses Classes A, B, C, D, E and G. There is no Class F in the US system. Classes A through E are controlled airspace, which means ATC services are available there and VFR pilots may be subject to entry requirements. Class G is the airspace left over after A through E have been designated.
The classes are not simply a ladder of restrictiveness. Class B is the most demanding for a VFR pilot because it needs a clearance. Class A is closed to VFR altogether. Class C and D need radio contact, and Class E needs nothing from a VFR pilot except compliance with the weather minimums. Learn the entry requirement for each class and the way it is drawn on a sectional chart, and the rest follows.
Two ideas apply across the classes. First, airspace dimensions are individually tailored: the numbers in this guide are the typical or general figures that AIM gives, and a particular airport can differ, so check the chart. Second, requirements stack. Entering a Class B area means meeting the Class B rules, the Class D rules that 91.131 incorporates by reference, the transponder rules and the ADS-B Out rules.
Class A airspace is, generally, the airspace from 18,000 feet MSL up to and including FL 600, including the airspace overlying the waters within 12 nautical miles of the coast of the 48 contiguous states and Alaska, and designated international airspace beyond that within areas of domestic radio navigational signal or ATC radar coverage where domestic procedures are applied.
Unless otherwise authorized, all persons must operate their aircraft under IFR in Class A. For a VFR pilot the practical consequence is simple: you do not fly there. A plan that climbs to 18,000 feet MSL or above is a planning error unless you hold an IFR clearance.
Class A is not specifically charted. Because the lower limit is an altitude rather than a shape on the map, a pilot needs to know the number: 18,000 feet MSL, which is where the altimeter setting changes to 29.92 and altitudes become flight levels.
Class B is, generally, airspace from the surface to 10,000 feet MSL surrounding the nation's busiest airports in terms of IFR operations or passenger enplanements. The configuration of each area is individually tailored and consists of a surface area and two or more layers. Some Class B areas resemble upside-down wedding cakes. It is designed to contain all published instrument procedures once an aircraft enters the airspace.
An ATC clearance is required for all aircraft to operate in the area, regardless of weather conditions, and all aircraft that are so cleared receive separation services. The cloud clearance requirement for VFR operations is clear of clouds. Under 14 CFR 91.131, the pilot in command must receive an ATC clearance from the facility having jurisdiction before operating in the area.
The pilot certificate requirement is specific. Section 91.131(b) says no person may take off or land a civil aircraft at an airport within Class B airspace, or operate a civil aircraft within Class B airspace, unless the pilot in command holds at least a private pilot certificate, or holds a recreational or sport pilot certificate and has met the stated requirements, or is a student pilot who has met the requirements of 61.94 or 61.95. For the listed major airports, at least a private pilot certificate is required.
Equipment is the other half. Unless otherwise authorized by ATC, the aircraft needs an operable two-way radio capable of communicating with ATC on the appropriate frequencies, and the transponder and ADS-B Out rules in 91.215 and 91.225 also apply. A clearance is not a courtesy request: if the controller does not clear you into the Class B, you stay out.
Class C is, generally, airspace from the surface to 4,000 feet above the airport elevation, charted in MSL, surrounding airports that have an operational control tower, are served by a radar approach control and have a certain number of IFR operations or passenger enplanements. The airspace usually consists of a 5 nautical mile radius core surface area that extends from the surface up to 4,000 feet above the airport elevation, and a 10 nautical mile radius shelf area that extends no lower than 1,200 feet up to 4,000 feet above the airport elevation.
There is no specific pilot certification requirement. For entry, two-way radio communication must be established with the ATC facility providing services prior to entry, and maintained while in the airspace. Section 91.130(c) says the same for arrival and through flights. Establishing communication is a precise thing: if the controller answers with your callsign, for example "standby," communication has been established and you may enter. If the controller answers without using your aircraft identification, it has not been established and you may not enter.
Equipment for Class C is a two-way radio and, unless otherwise authorized by ATC, an operable radar beacon transponder with automatic altitude reporting and operable ADS-B Out equipment. Section 91.130(d) also ties the equipment to 91.215 and 91.225.
Call early. The AIM advises initiating radio contact far enough from the boundary to preclude entering before communication is established, giving your position, altitude, code, destination and a request for Class C service. If workload prevents service, the controller will tell you to remain outside until conditions permit.
Class D generally extends upward from the surface to 2,500 feet above the airport elevation, charted in MSL, surrounding airports that have an operational control tower. Its configuration is individually tailored and, when instrument procedures are published, the airspace is normally designed to contain them.
Under 14 CFR 91.129(c), each person must establish two-way radio communications with the ATC facility providing air traffic services prior to entering the airspace and then maintain them while within it. The AIM adds that no specific pilot certification is required and that, unless otherwise authorized by ATC, an operable two-way radio is required.
The detail that catches pilots out is that Class D can be part-time. Part-time Class D times are published in the Chart Supplement, and when the tower is closed the airspace reverts to either a Class E surface area or Class G airspace, as the Chart Supplement entry states, for example "other times CLASS E". Check the effective times as part of preflight and do not assume a tower that was open yesterday is open today.
If the radio fails, 91.129(d) lets a VFR pilot operate and land if the weather is at or above basic VFR minimums and visual contact with the tower is maintained, among the stated conditions. That is a regulation to read in full, not a shortcut: the point for the test is that communication is required in the first place.
Class E is controlled airspace designated to serve a variety of terminal or en route purposes. For a VFR pilot there is no specific pilot certification requirement and no specific entry requirement for arrival or through flight. The weather minimums, which depend on altitude and class, still apply, so the practical rules are in the VFR weather minimums rather than in an entry procedure.
Class E has several shapes. It can be a surface area designated for an airport without an operating control tower, a transition area that begins at 700 feet above the surface (charted as a magenta vignette) or 1,200 feet (charted as a blue vignette), and a layer from 14,500 feet MSL up to but not including 18,000 feet MSL. The airspace above FL 600 is Class E as well. Class E below 14,500 feet MSL is charted on sectional, terminal and IFR enroute low altitude charts.
Equipment requirements in Class E are tied to altitude. Unless otherwise authorized by ATC, an operable radar beacon transponder with automatic altitude reporting and operable ADS-B Out equipment are required at and above 10,000 feet MSL within the 48 contiguous states and the District of Columbia, excluding the airspace at and below 2,500 feet above the surface.
Class G is the airspace that has not been designated as Class A, B, C, D or E. There is no ATC clearance or communication requirement for entry. That does not mean no rules: the weather minimums, right-of-way rules, aircraft equipment requirements and the 91.155 cloud clearance and visibility numbers still apply, and they differ by altitude and between day and night.
The questions you will see tend to fall into three kinds. The first asks for a number: the floor of Class A, the ceiling of Class D, the dimensions of the Class C core and shelf. The second asks what is required to enter: clearance for Class B, radio contact for Class C and D, nothing for E and G. The third gives a scenario and asks what you must do before the next waypoint.
A reliable way to answer scenario questions is to ask three things in order. What class is it? What does the entry rule for that class require before the boundary? What equipment and weather minimums apply once inside? Doing this in the same order every time turns airspace from a list of facts into a short procedure.
In the cockpit the habit that matters most is planning the entry before you arrive. Know which classes lie on your route, which are part-time, which need a transponder and ADS-B Out, and where you will make the radio call. A surprise at the boundary is a planning failure, and the fix is to read the sectional chart and the Chart Supplement before the engine start.
No. Unless otherwise authorized, all persons must operate under IFR in Class A, which generally runs from 18,000 feet MSL up to and including FL 600.
An ATC clearance from the facility having jurisdiction, regardless of weather, an operable two-way radio, the required transponder and ADS-B Out equipment, and a pilot who meets the 91.131 certificate requirements, which for the major airports means at least a private pilot certificate.
The controller must respond using your aircraft identification. A response such as "N123AB, standby" means communication is established and you may enter. A response without your identification means it is not, and you may not enter.
Part-time Class D reverts to either a Class E surface area or Class G airspace, as stated in the airport entry in the Chart Supplement, for example "other times CLASS E". Check the effective times before you fly.
Unless otherwise authorized by ATC, an operable transponder with automatic altitude reporting and ADS-B Out are required at and above 10,000 feet MSL within the 48 contiguous states and the District of Columbia, excluding the airspace at and below 2,500 feet above the surface.
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