Airspace in a fish tank

Visualize your A, B, Cs in 3D

March 9, 2026 By Sarah Deener

If your introduction to airspace is drilling cloud clearance flash cards and mnemonics about 152s and F–111s, you may be missing an understanding of how all these pieces fit together in three-dimensional space.

Controlled airspace centered around an airport is relatively straightforward: a Class D cylinder, the upside-down wedding cake of Class B, and the hat-shaped C. But all that space in between can be difficult to visualize, so AOPA Air Safety Institute eFIRC Program Manager Mary Kuehn, a CFII, encourages students to think of airspace as a fish tank.

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Illustration by Charles Floyd

Class E (water)

All those spaces in between—the water—are Class E. Below 10,000 feet, remember those 500-1,000-2,000 cloud clearances and 3 miles visibility. From 10,000 feet to 17,999, remember 5 statute miles and 1,000 below, 1,000 above, and 1 statute mile horizontal—and you’ll need a Mode C transponder up here.

Class C (upside-down tophat)

Establish two-way radio communications before entering this house with the same equipment requirements as Class B. To fly VFR, maintain visibility of 3 statute miles and stay 500 feet below, 1,000 feet above, and 2,000 feet from clouds horizontally.

Class D (cylinder)

You’ll need two-way radio communications before entering here, too—with the same visibility and cloud clearance requirements as Class C.

Class A (lid)

Starting at 18,000 feet, this airspace is out of reach for the small-fish trainers of general aviation. Up here, all flights are under instrument flight rules and altimeters are set to a standard 29.92 inches mercury.

Class B (upside-down wedding cake)

You’ll need an ATC clearance to enter this fish house—which means you’ll need a two-way radio, too. Consider the Mode C transponder requirement a fishfinder for ATC. To operate VFR here, you’ll need 3 statute miles visibility and to remain clear of clouds.

Class G (gravel)

Think of the uncontrolled airspace close to the surface as the gravel. Class G usually extends from the surface to 700 or 1,200 feet agl in the Eastern United States, or 14,500 feet msl in much of the West. Visibility and cloud clearance requirements have lots of asterisks—above 10,000 feet msl, they’re the same as Class E, but below that altitude there are different requirements for day and night, helicopters and airplanes, above or below 1,200 feet agl. Spend some time with FAR 91.155(a) through (e) to better understand scenarios that might affect you.

*Class B, C, and D all extend down to the surface

Spot it on a sectional

Class B airspace is outlined in solid blue on sectional charts; Class C is shown in magenta. Class D airspace is dashed blue lines, and Class E to the surface is shown by a dashed magenta line. Class E begins at 1,200 feet agl unless otherwise marked; look for a magenta gradient (vignette) surrounding areas with Class E beginning at 700 feet agl. Blue vignette designates the transition from a Class E floor of 1,200 feet agl to 14,500 feet msl. (The lighter side of each gradient faces the lower-altitude floor.) Class A airspace is not depicted on sectional charts.