How would I have determined that the airspace overlying and within 5 miles of Barnes County Airport is Class G?

Question

(Refer to Figure 26, area 5.) The airspace overlying and within 5 miles of Barnes County Airport is

A. Class D airspace from the surface to the floor of the overlying Class E airspace.

❌B.Class E airspace from the surface to 1,200 feet MSL.

C.Class G airspace from the surface to 700 feet AGL. (this is correct)

"The Barnes County Airport is depicted inside the magenta shading, which is controlled airspace from 700 feet AGL up to but not including 18,000 feet. Therefore, the airspace below 700 feet AGL is Class G."

Studying for my private pilot exam, airspaces on the charts are a little confusing for me right now. The Magenta shading on the legend of sectional charts is specifically what is confusing me here. Why is the answer option C instead of option B? The two magenta shaded lines on the sectional charts legends both indicate class E, but one refers to Class G and the other does not. The explanations underneath them don't really make sense to me.

Thank you in advance to all the friendly folks who help me answer this.

Answer 1

Practically speaking, Class E airspace can extend upward from any of the following three options:

• 0ft AGL. This is depicted by a dashed magenta line.
• 700ft AGL. This is depicted by a shaded magenta line.
• 1200ft AGL. This is depicted by... nothing. This is the default state of Class E airspace and so it is not specifically charted. (See note below.)

BAC is surrounded by a faded magenta line. This is the second possibility: Class E begins at 700' AGL. Therefore the airspace immediately above the surface (in fact, from the surface up to 699' AGL) must be Class G.

You know that Answer B is not correct because it says that the Class E extends up to 1200' AGL. This is not what Class E does. Wherever it starts, it extends upward from that point until it reaches a higher class of airspace, like a Bravo shelf. If there is no otherwise-charted airspace above it, it extends up to the beginning of Class A airspace at 18000' MSL. Also, Answer B says the Class E begins at the surface. That would be depicted by a dashed magenta line, as at JMS, not a faded magenta line.

The two magenta shaded lines on the sectional charts legends both indicate class E, but one refers to Class G and the other does not.

A simple faded magenta line depicts Class G from the surface to 700' AGL within the line, and Class G from the surface to 1200' AGL on the outside. If there is text "CLASS G" on the hard side of the magenta line, that means that the airspace on the hard side is Class G all the way up to 14500' MSL. See the note below, and see my answer to this question for an example. This is a very rare configuration.

In both cases, Class E airspace lies above the Class G airspace.

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A note. Very technically the actual "default" for Class E is that it only extends upward from 14500' MSL. However there are so so so many areas where it is defined as going down to 1200' AGL that the real default is that 1200. They used to chart a blue shaded line around the entirety of the USA border to signify that fact, but these days they just say on the sectional "The default is 1200' and up." There are only one or two areas of true uncontrolled-up-to-14.5 airspace left in the contiguous US.