Class B airspace (“Big / Busy”).

• Floor: surface (SFC).
• Ceiling: typically 10 000 ft MSL.
• Shape: inverted wedding cake — progressive tiers expanding upward and outward from the busiest airports (ATL, LAX, ORD, JFK, SFO, BOS, etc.).
• Sectional marking: solid blue lines.
• Drone rule: always needs ATC authorization (Part 107.41 / LAANC).