Class A airspace starts at 18,000 feet MSL and goes up to 60,000 feet MSL. Who flies here? Commercial and business jets with pressurized cabins or a supplemental oxygen source. The air is thinner. If you’ve flown cross-country in a commercial jet you’ve traveled in Class A airspace.
The “B” in Class B can be remembered as “big airports.” These include the major airports at major cities: New York, Chicago, Atlanta, Denver, Salt Lake City, San Francisco, etc. You’re not even going to want to fly in to these airports for awhile, so it’s a good thing that the sport-pilot certificate doesn’t allow it until you’re received additional training and an endorsement.
In other guides on this site, you’ll see that you can actually fly under, over, and near airspace around these big airports. Around many Class B airports are smaller airports that you might be able to land at if you obey the rules.
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Class B airspace, if seen from the side, looks like an upside-down multilayer cake. The controlled airspace expands as it goes up so that IFR aircraft can descend at an angle toward the airport. You can refer to the Aeronautical Information Manual and sectional charts for more specifics on Class B airspace.
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