The floor of Class B airspace at Addison Airport is how high?

• A. 3,000 feet MSL
• B. 1,500 feet MSL
• C. 5,000 feet MSL
• D. Surface

Answer: (A)

Class B is laid out in layers, each with its own base or floor measured in MSL. The floor is the lowest altitude at which that segment of Class B begins, so you only enter Class B above that altitude with ATC clearance.

At Addison Airport, the area sits on a shelf of the Dallas Class B where the base is 3,000 feet MSL. That means from 3,000 feet MSL up to the top of Class B in that sector you’re inside Class B (with the required clearance). Below that, you’re outside Class B unless you’re in the innermost core where the floor is the surface. The other options don’t fit this location: the surface applies only to the core, 1,500 feet MSL corresponds to another shelf in some areas, and 5,000 feet MSL would be a higher shelf not applicable to Addison.