Class A Airspace — The Flight Levels
Class A airspace extends from 18,000 feet MSL (FL180) up to and including 60,000 feet MSL (FL600) across the entire contiguous United States, including the waters within 12 nautical miles of the coast.
All operations in Class A must be conducted under Instrument Flight Rules (IFR). There are no VFR operations permitted. You must have an IFR-capable aircraft, an instrument rating, an ATC clearance, and a functioning transponder with Mode C (altitude reporting) and ADS-B Out.
Altimeters are set to 29.92 inHg above 18,000 feet, and altitudes are expressed as flight levels (FL180, FL250, etc.). This standardization ensures vertical separation between aircraft.
Class B Airspace — Major Airports
Class B airspace surrounds the nation's busiest airports — approximately 37 airports including those serving major metropolitan areas. The shape resembles an inverted wedding cake, with multiple layers expanding outward at higher altitudes. Typical dimensions extend from the surface to 10,000 feet MSL, with a lateral radius of about 30 nautical miles.
Entry requirements:You must receive explicit ATC clearance ("Cleared into the Class Bravo") before entering. A student pilot can enter Class B with specific CFI endorsements and restrictions (some Class B airports are prohibited for student pilots — see 14 CFR 91.131).
Equipment: Two-way radio, transponder with Mode C, ADS-B Out. For IFR operations, an IFR-certified GPS or VOR receiver.
VFR weather minimums: 3 statute miles visibility and clear of clouds. This is less restrictive than other controlled airspace because ATC provides separation services.
Speed limit: 250 knots indicated airspeed (KIAS) below 10,000 feet MSL. Additionally, 200 KIAS at or below 2,500 feet AGL within 4 NM of the primary airport.
Class C Airspace — Medium Airports
Class C airspace surrounds airports with an operational control tower, radar approach control, and a certain level of IFR or passenger operations. There are roughly 120 Class C airports in the US.
The typical shape has two layers: an inner circle from the surface to 4,000 feet AGL with a 5 NM radius, and an outer shelf from 1,200 feet AGL to 4,000 feet AGL with a 10 NM radius. An outer area extends to 20 NM where participation is recommended but not required.
Entry requirements:Establish two-way radio communication with ATC before entering. You do not need explicit clearance — hearing ATC say your callsign establishes communication (e.g., "N12345, standby" is sufficient).
Equipment: Two-way radio, transponder with Mode C, ADS-B Out.
VFR weather minimums: 3 statute miles visibility, 500 feet below clouds, 1,000 feet above clouds, 2,000 feet horizontally from clouds.
Speed limit: 200 KIAS at or below 2,500 feet AGL within 4 NM of the primary airport. The general 250 KIAS below 10,000 feet also applies.
Class D Airspace — Towered Airports
Class D airspace surrounds airports with an operational control tower that do not have radar approach control service. It typically extends from the surface to 2,500 feet AGL with a radius of approximately 4-5 nautical miles (exact dimensions are depicted on sectional charts).
Entry requirements: Establish two-way radio communication with the tower before entering, same as Class C. No explicit clearance needed — contact and acknowledgment is sufficient.
Equipment: Two-way radio is required. A transponder with Mode C and ADS-B Out are required if the Class D airspace lies within a Mode C veil (30 NM radius of a Class B airport).
VFR weather minimums: 3 statute miles visibility, 500 feet below, 1,000 feet above, 2,000 feet horizontally from clouds.
When the tower closes: Class D airspace reverts to Class E or Class G (as published). Check your sectional chart and Chart Supplement for tower operating hours.
Class E and Class G Airspace
Class E (controlled) is the most common airspace in the US. It exists everywhere that is designated as controlled airspace but is not Class A, B, C, or D. Most IFR enroute operations below 18,000 feet occur in Class E.
Class E has several common configurations: it typically begins at 1,200 feet AGL across most of the US, but in many areas starts at 700 feet AGL (shown by a magenta fade on sectional charts) to protect instrument approach procedures. Surface-based Class E (shown by a dashed magenta line) exists at airports without towers that have instrument approaches.
Class E VFR weather minimums: Below 10,000 feet MSL — 3 statute miles visibility, 500 below/1,000 above/2,000 horizontal from clouds. At or above 10,000 feet MSL — 5 statute miles visibility, 1,000 below/1,000 above/1 statute mile horizontal from clouds.
Class G (uncontrolled) exists from the surface up to the base of overlying Class E airspace. In most of the US, this means Class G extends from the surface to 1,200 feet AGL (or 700 feet AGL near airports with instrument approaches).
Class G has the least restrictive VFR weather minimums: during the day, below 1,200 feet AGL, you need only 1 statute mile visibility and clear of clouds. Night operations require 3 statute miles visibility and standard cloud clearance. No ATC communication is required, and transponders are not mandatory outside Mode C veil areas.
Special Use Airspace and TFRs
Prohibited Areas (P): Flight is completely prohibited at all times (e.g., P-56 over the White House and Capitol). No exceptions without specific authorization.
Restricted Areas (R):Operations are restricted during published times due to hazards like artillery firing, aerial gunnery, or missile testing. When not active ("cold "), you may fly through. Contact the controlling agency or FSS to determine status.
Military Operations Areas (MOAs): Designated for military training. VFR traffic may transit MOAs without permission, but exercise extreme caution. IFR traffic will be rerouted or cleared through by ATC. Check NOTAM and schedule status before entering.
Alert Areas (A): Indicate high-volume pilot training or unusual aerial activity. No ATC authorization required, but vigilance is essential.
Warning Areas (W): Similar to restricted areas but located over international waters (beyond 3 NM from the coast). The FAA cannot restrict flight here under domestic law but warns of potential hazards.
Temporary Flight Restrictions (TFRs): Issued via NOTAMs to restrict flight around events (presidential movements, major sporting events, disasters, space launches). TFRs define specific geographic boundaries, altitudes, and time windows. Violating a TFR can result in certificate action, interception, and in post-9/11 security TFRs, potentially lethal force. Always check TFRs during preflight briefing.