You have checked the Bravo shelf and know your hypothetical aircraft is below it. Then your instructor asks a second question: what airspace are you actually in? Answering “outside Class B” leaves that question open. Work downward through the chart until you can name the layer containing the aircraft.
This exercise uses invented terrain and boundaries. Keep a side-view sketch beside the sectional so you can separate the shelf above you from the airspace nearer the ground.
Find the next floor below the shelf
Class E is controlled airspace, while Class G is the airspace not designated A, B, C, D or E. Class G is therefore not simply everything outside the prominent airport boundaries. See FAA AIM 3-2-6 and AIM 3-3-1.
For a first practice problem, choose a location where the chart establishes a Class E transition floor at 700 feet AGL. The AIM identifies magenta shading with that transition floor and blue shading with a 1,200-foot AGL transition floor. Class E can also begin at the surface; do not apply the transition-area interpretation to every magenta boundary.
Before doing arithmetic, write the floor you actually found. Use the sectional chart guide to review the distinction between shading and dashed lines. If you cannot explain which side of a boundary your chosen point occupies, resolve that before choosing an altitude.
Put every layer on one altitude scale
Assume flat terrain at 800 feet MSL, a Class E floor at 700 feet AGL, and an overlying Class B shelf beginning at 3,000 feet MSL. Assume no other designation changes these layers.
The Class E floor in this invented example is 800 + 700 = 1,500 feet MSL. Now place three aircraft on your sketch:
- At 1,300 feet MSL, the aircraft is 500 feet AGL and below the Class E floor: Class G under our assumptions.
- At 1,800 feet MSL, it is above the Class E floor and below the Bravo shelf: Class E.
- At 3,200 feet MSL, it is within the hypothetical Bravo shelf's vertical limits.
Label the terrain, the Class E floor and the Class B floor separately. The MSL vs AGL article provides another exercise if the conversion is the difficult step.
Change the terrain before changing the aircraft
Keep the aircraft at 1,800 feet MSL, but move the hypothetical terrain up to 1,300 feet MSL. If the same 700-foot AGL Class E floor applies, that floor is now 2,000 feet MSL. Under the same simplified assumptions, the aircraft is below it.
Draw both situations side by side. This is a useful way to test whether you treated an AGL floor as a fixed MSL altitude. For an actual location, use the applicable chart and designations rather than extending this flat-terrain exercise across an entire route.
Try it in AirspaceLab
Open the airspace probe, inspect a shelf and record its floor. Then use a current sectional to investigate the airspace below it. A missing rendered volume alone is not evidence that the space is Class G.
Finish by writing two answers: the classification at your chosen altitude, and the information you used to establish it. Next, consult the VFR weather minimums guide for the appropriate conditions. Bring any disagreement between your chart reading and the visualization to your instructor.
Sources checked: November 14, 2026. All terrain elevations and boundaries in the worked exercise are hypothetical; the simulator is a study aid.