5.1 Class A, B, and C Airspace

ACS Area of Operation I, Task E (PA.I.E.K1–K4) treats the National Airspace System as a go/no-go legal system, not a coloring-book exercise. You must know which class you are in, what the weather and equipment rules are, and whether you need a clearance or only two-way communications. Class A, B, and C are the three most restrictive controlled classes. They share transponder and ADS-B Out requirements. They do not share the same entry rule. That entry-rule split — clearance versus communications — is one of the highest-yield PAR traps in this chapter.

Controlled airspace is Class A, B, C, D, and E. Class G is uncontrolled. “Controlled” means ATC has the authority to separate IFR traffic there. It does not automatically mean a VFR private pilot must talk to anyone. Class E is controlled and usually has no VFR communications requirement. Class B is controlled and you may not enter without a clearance. Memorize the class, then apply the matching 14 CFR section: 91.135 (A), 91.131 (B), 91.130 (C), 91.129 (D), 91.127 (E airports), 91.126 (G airports).

Class A — 18,000 MSL through FL 600, IFR only

AIM 3-2-2 and 14 CFR 71.33 define Class A as the airspace of the 48 contiguous States (and specified coastal waters) from 18,000 feet MSL to and including FL 600. Alaska has a parallel designation with a low-altitude exclusion. The airspace above FL 600 is Class E, not Class A.

91.135 is blunt. Except for a written ATC authorization, every person operating in Class A must conduct the operation under instrument flight rules. You need an ATC clearance received prior to entering, a two-way radio on the assigned frequency, continuous two-way communications, an operable transponder with Mode C (91.215), and ADS-B Out (91.225). VFR weather minimums in the 91.155 table read “Not Applicable” because basic VFR is not a Class A option. A private pilot without an instrument rating is not planning a legal VFR hop at FL 210.

Climbing into Class A also changes how you set the altimeter. 91.121 requires 29.92 inHg (1013.2 hPa) at or above 18,000 feet MSL so every airplane in that stratum is on the same pressure setting. That is why Class A altitudes are flight levels.

Class B — clearance required, individually tailored

AIM 3-2-3: Class B generally surrounds the nation’s busiest airports from the surface to 10,000 feet MSL, though the actual ceiling is individually tailored. The shape is the familiar upside-down wedding cake: a surface area plus two or more shelves designed to contain published instrument procedures. Solid blue lines on the sectional and a Terminal Area Chart depict the shelves. Each shelf is labeled in hundreds of feet MSL (for example 80/30 means the shelf exists from 3,000 to 8,000 MSL).

91.131(a)(1) is the sentence PAR writes items around: the operator must receive an ATC clearance from the facility having jurisdiction before operating in that Class B area. Two-way radio contact is necessary equipment (91.131(c)(2)), but contact is not the clearance. The words you need sound like “cleared into the Los Angeles Class Bravo” or an equivalent explicit clearance. “Radar contact,” “squawk 4521,” or “ident” is not a Class B clearance. If you hear only those phrases, stay outside the blue line and ask.

VFR weather in Class B is the easiest number in 91.155 and the easiest to mix up with C and D: 3 statute miles and clear of clouds. There is no 500-below / 1,000-above / 2,000-horizontal requirement inside Class B. The trade is density: ATC is providing sequencing and separation, so the cloud-clearance rule relaxes to “just don’t hit the cloud.”

Equipment, unless ATC authorizes otherwise: operable two-way radio; Mode C transponder (91.215); ADS-B Out after January 1, 2020 (91.225); and, for IFR, an operable VOR, TACAN, or suitable RNAV system. Student solo is not a free pass. 91.131(b) and 61.95 require ground and flight training in that specific Class B area, a logbook endorsement dated within the 90-day period before the flight, and an endorsement that names that area. A separate 61.95(b) endorsement is required to solo to, from, or at a specific airport inside Class B. 91.131(b)(2) still bars student, sport, and recreational pilots from taking off or landing at the primary airports listed in part 91 appendix D section 4 (the usual list includes ATL, BOS, ORD, DFW, LAX, MIA, EWR, JFK, LGA, DCA, SFO, and Joint Base Andrews). Those airports require at least a private pilot certificate.

Speed inside Class B below 10,000 MSL is the general 250 KIAS cap in 91.117(a), unless ATC authorizes otherwise. The 200 KIAS cap in 91.117(c) applies in the airspace underlying Class B or in a designated VFR corridor through Class B — not to the interior of the Bravo itself.

Class C — communications, not a clearance

AIM 3-2-4: a typical Class C is a 5 NM core from the surface to 4,000 feet above airport elevation (charted in MSL) and a 10 NM shelf from no lower than 1,200 feet AGL up to that same 4,000-foot AGL ceiling. Each area is tailored; read the numbers printed on the magenta rings. Solid magenta lines depict Class C on the sectional.

91.130 does not require a “cleared into Class C” phrase. It requires you to establish two-way radio communications with the ATC facility providing services prior to entering, then maintain those communications. AIM 3-2-4 draws the bright line PAR tests:

• If the controller answers with your callsign — including “[callsign] standby” — communications are established and you may enter unless you are also told to remain outside.
• If the controller answers without your callsign — “Aircraft calling Tampa approach, standby” — communications are not established. Stay out.
• If the controller uses your callsign and says remain outside the Class Charlie, communications exist but the stay-out instruction controls.

Equipment: two-way radio, Mode C, and ADS-B Out unless ATC authorizes otherwise. No special pilot certificate is required. VFR weather is 3 statute miles and 500 feet below, 1,000 feet above, 2,000 feet horizontal (91.155). Speed: unless ATC authorizes or requires otherwise, no more than 200 KIAS at or below 2,500 feet AGL within 4 NM of the primary Class C airport (91.117(b)). The same 200-knot bubble applies at a Class D primary. It does not apply inside Class B.

An uncharted outer area typically extends about 20 NM from the primary airport. Class C services are available there once you are talking and in radar contact; participation in the outer area is voluntary. Do not confuse the outer area with the Mode C veil.

Mode C veil — 30 NM, not the Bravo itself

91.215(b)(2) and 91.225(d)(2) create a cylinder within 30 nautical miles of each airport listed in part 91 appendix D section 1 (generally the primary Class B airports) from the surface to 10,000 feet MSL. Inside that veil you need an operable transponder with Mode C and ADS-B Out even if you never cross a Class B line — for example, remaining under a 3,000-foot shelf. Aircraft never certificated with an engine-driven electrical system (and balloons and gliders) have a narrow exception: stay outside A/B/C and below the Bravo or Charlie ceiling or 10,000 MSL, whichever is lower. The veil is equipment airspace. It is not a clearance requirement and it is not Class B.

PAR scenario: you are VFR into a Class C primary. Approach answers, “Aircraft calling, standby.” You are two miles from the 10 NM shelf. Do not enter. Communications are not established. If the next transmission is “Cessna 345AB, standby,” communications now exist and you may continue unless you are told to remain outside. Crossing the magenta line on the first transmission would be a 91.130 bust, not a paperwork nicety.