Definition
Controlled airspace surrounding the nation's busiest airports, generally extending from the surface up to 10,000 feet MSL and shaped like an upside-down wedding cake of stacked layers tailored to each airport. Entry requires an ATC clearance, two-way radio communication, an operable transponder with altitude reporting, and (with limited exceptions) at least a private pilot certificate or a student pilot endorsement for that specific Class B airspace.
Plain English
The protected block of sky around the busiest airports. You cannot fly into it without first getting permission from air traffic control, and your aircraft and pilot certificate must meet specific requirements.
Context Anchor
Seen on charts, in airspace discussions, in NOTAM contractions, and during flight planning near major airports.
Derivation
The airspace classification system uses letters A through G, adopted from the international ICAO system. 'B' marks the second-most restrictive class, just below Class A (the high-altitude en route airspace).
Why Pilots Care
A pilot who enters without clearance risks collision with other aircraft and FAA enforcement action.
Intuition Check
Do not read “Class B” as meaning second-best or less important than Class A. Here, it means a specific controlled airspace area around a very busy airport, with permission required before entry.
Example Sentence 1
Before crossing the shelf into Class B airspace, the pilot waited until the controller said, 'Cessna 234, cleared into the Class Bravo.'
Example Sentence 2
During the cross-country flight the student checked the chart to confirm the CBAS boundaries around the destination airport.