Class B, C and D: what you need to enter

Class B (91.131)

• An ATC clearance. You must hear "cleared into the Class Bravo airspace." Being told to "squawk" or "stand by" is not a clearance.
• A two-way radio.
• A Mode C transponder and ADS-B Out.
• At least a private pilot certificate, or a student pilot with the specific endorsements of 61.95. Student pilots can't operate at some of the busiest Class B primary airports at all.

The transponder (Mode C) and ADS-B Out requirement also applies within 30 NM of the Class B primary airport (the Mode C veil), from the surface to 10,000 ft MSL.

Class C (91.130)

• Two-way radio communication established before you enter. If the controller responds with your call sign, communication is established, even if they say "stand by." If they say "aircraft calling, stand by" without your call sign, it isn't.
• A Mode C transponder and ADS-B Out, in Class C and in the airspace above it up to 10,000 ft MSL.

Class C is usually a 5 NM core from the surface to 4,000 ft above the airport, and a 10 NM shelf from 1,200 to 4,000 ft above the airport.

Class D (91.129)

• Two-way radio communication established with the tower before you enter, the same standard as Class C.
• No transponder requirement just for being in Class D (unless something else, like a Mode C veil, requires it).

When the tower is closed, Class D usually becomes Class E or G; check the Chart Supplement.

ADS-B Out (91.225)

ADS-B Out is required in Class A, B and C; within the Mode C veil; above the ceiling of Class B or C up to 10,000 ft MSL; and in Class E at and above 10,000 ft MSL, excluding airspace at and below 2,500 ft AGL.