Class B airspace surrounds large, busy airports.
Its shape is generally an upside-down wedding cake but it can vary quite a bit. The main idea is that there are layers that get progressively wider and have a higher floor than inner layers.
For example, in St. Louis (pictured below) the inner ring extends from the surface up to 8000 feet MSL.
The next ring out extends from 2000 feet up to 8000, so there is room to fly under it. If you look closely you will see that the floor actually starts at 1700 in some places and 2500 in other places within this ring.
Going out further the next ring has a floor at 3000 and the larger ring has a 5000 foot floor (although it starts at 3500 feet in some sections).
There are also some extensions of this airspace that stick out of the normal area with a floor of 4500 feet. These are generally for the approach and departure paths into and out of Lambert International. They are shaped differently from the rest of the airspace but they still operate as class B.
What is required to enter class B airspace?
VFR Aircraft must be “cleared into the bravo” before entering class B airspace.
When I get a clearance into bravo airspace I always read back “cleared into the bravo” in a slow, clear, enunciated way to make sure that the controller hears me correctly, and that it is picked up on the recording in case there is some claim of a misunderstanding later.
In addition, if you are within 30 miles of the center of class B airspace you need to have your transponder on and in altitude reporting mode. This is true even if you do not intend to actually enter the airspace.
What are the weather requirements in class B airspace?
In class B airspace you must remain clear of clouds. This is the least restrictive VFR requirement and allows you to get as close to the clouds as you want as long as you don’t fly into them. In class B airspace all aircraft are under positive ATC control and there is little risk of a plane appearing out of a cloud next to you. However, you should always be vigilant anyway because ATC is manned by humans who could possibly make a mistake.
The visibility must be 3 statute miles or greater.
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