Class C airspace dimensions follow a standard two-tier design centered on the primary airport: an inner core with a 5-nautical-mile radius from the surface up to 4,000 feet above airport elevation, and an outer shelf reaching from 5 to 10 nautical miles with a floor of 1,200 feet and the same 4,000-foot ceiling. An uncharted Outer Area extends the procedural footprint out to 20 nautical miles, where radar services are available but voluntary. Individual airports can deviate from the template when terrain or neighboring airspace requires it.1Federal Aviation Administration. Procedures Handling Airspace Matters – Class C Airspace Planning
Shape and Horizontal Dimensions
Picture an upside-down wedding cake with two tiers. The lower, wider tier is the inner core, a circle with a 5-nautical-mile radius measured from the airport reference point. ATC controls all traffic in that core from the ground up. The upper tier is the outer shelf, a ring extending from the 5-nautical-mile mark out to 10 nautical miles. Aircraft flying beneath the outer shelf’s floor are outside Class C airspace entirely, which is what gives the structure its layered profile.2Federal Aviation Administration. Pilot’s Handbook of Aeronautical Knowledge
The 5-and-10 radii are the standard design, not a rule. Individual Class C areas are tailored to each airport’s traffic patterns, and any departure from the template has to be justified in a staff study and approved by the FAA Service Center.1Federal Aviation Administration. Procedures Handling Airspace Matters – Class C Airspace Planning
Vertical Dimensions
The inner core starts at the surface and extends up to 4,000 feet above the airport’s field elevation. The outer shelf has a floor at 1,200 feet above the surface and shares the same 4,000-foot ceiling.1Federal Aviation Administration. Procedures Handling Airspace Matters – Class C Airspace Planning The gap beneath the outer shelf is intentional. It lets aircraft operating below 1,200 feet AGL cross the 5-to-10-mile ring without entering Class C at all.
One detail trips up newer pilots. The design criteria reference altitudes in feet above ground level, but the boundaries actually published on aeronautical charts are converted to mean sea level. An airport sitting at 500 feet MSL would have its Class C ceiling charted at 4,500 feet MSL, not “4,000 feet.”2Federal Aviation Administration. Pilot’s Handbook of Aeronautical Knowledge
Custom ceilings exist too. At some airports the 4,000-foot standard gets trimmed because the airspace would otherwise bump into an overlying Class B shelf or conflict with adjacent airspace. On charts you may see a ceiling value of “T,” which means the Class C tops out just below the floor of the Class B above it.3Federal Aviation Administration. Aeronautical Chart Users’ Guide
The Outer Area Beyond the Charted Rings
Beyond the charted 10-nautical-mile ring, Class C airports have a procedural Outer Area reaching out to 20 nautical miles. It does not appear on sectional charts, and pilot participation is voluntary. You can request termination of services at any time while inside it.4Federal Aviation Administration. AIM 3-2-4 Class C Airspace
If you participate, approach control provides full Class C-level radar services, including traffic advisories and safety alerts. Outside the Outer Area, controllers still offer basic radar services on a workload-permitting basis and can drop you when things get busy.4Federal Aviation Administration. AIM 3-2-4 Class C Airspace Contacting approach well before reaching the charted 10-mile boundary is good practice, not just a regulatory box to check.
Reading Class C Dimensions on a Sectional Chart
Class C airspace appears on VFR Sectional Charts and Terminal Area Charts as concentric circles drawn in solid magenta. The ceiling and floor altitudes for each ring are printed in solid magenta numbers with the last two zeros dropped. A label reading “40” over “SFC” means that ring goes from the surface to 4,000 feet MSL. A label reading “40” over “12” means a 1,200-foot MSL floor and a 4,000-foot MSL ceiling.3Federal Aviation Administration. Aeronautical Chart Users’ Guide
A magenta box near the airspace lists the approach control frequency for arriving VFR aircraft. That is the frequency you use to establish two-way radio contact before entering. Some Class C airports do not operate around the clock; when the tower is closed, the airspace typically reverts to a different classification, and a chart note indicates the limited hours.3Federal Aviation Administration. Aeronautical Chart Users’ Guide
Equipment Required to Enter
Two pieces of avionics are mandatory. First, an operable transponder with Mode C altitude-reporting capability, so radar displays your altitude automatically in 100-foot increments.5eCFR. 14 CFR 91.215 – ATC Transponder and Altitude Reporting Equipment and Use Second, ADS-B Out. That requirement has been in effect since January 1, 2020, and applies to all Class B and Class C airspace, plus certain other areas.6eCFR. 14 CFR 91.225 – Automatic Dependent Surveillance-Broadcast (ADS-B) Out Equipment and Use
ATC can authorize deviations from both equipment requirements on a case-by-case basis or as a continuing authorization, but the permission has to be in hand before you enter the airspace.7eCFR. 14 CFR 91.130 – Operations in Class C Airspace
Two-Way Radio Contact
Before entering Class C airspace, you must establish two-way radio communication with the ATC facility providing services, and maintain it the entire time you are inside.7eCFR. 14 CFR 91.130 – Operations in Class C Airspace
What counts as “established” matters. If the controller responds using your callsign in any way, communication is established and you may enter. That includes the controller saying your callsign followed by “standby.” A generic “aircraft calling, standby” without your specific callsign does not count. In that case you stay outside until the controller uses your callsign.8Federal Aviation Administration. Section 8. Class C Service – Terminal
Speed Limit Inside Class C
Within 4 nautical miles of the primary airport and at or below 2,500 feet AGL, the speed limit is 200 knots indicated airspeed. This applies to Class C and Class D alike and exists to reduce closing speeds in the traffic pattern area.9eCFR. 14 CFR 91.117 – Aircraft Speed ATC can authorize a higher speed if operations warrant it, but absent that authorization, 200 knots is the ceiling.
VFR Weather Minimums
Because Class C is controlled airspace, the VFR weather minimums are stricter than what you would need in uncontrolled Class G. You need at least 3 statute miles of flight visibility and must remain 500 feet below clouds, 1,000 feet above clouds, and 2,000 feet horizontally from them.10eCFR. 14 CFR 91.155 – Basic VFR Weather Minimums These are the same minimums that apply in Class D and most of Class E below 10,000 feet MSL. If conditions drop below these limits, you need an IFR clearance or you stay out.