# How do I find the floor of controlled airspace on sectional charts?

So, I understand finding floors and such when seeing something a fraction like 45/10 or 39/SFC, but I've been reviewing and gotten a couple of questions that look like this:

What is he floor of the controlled airspace overlying the Coeur D'Alene Airport?

The answer is "At the surface" but I can't figure out where it says that? The second question said this:

What is the floor of the controlled airspace overlying the Sandpoint Airport?

The answer is "700 feet MSL". Cant find that either.

It does not say it anywhere because the answer is not variable like class B airspace but lets dig in.

The question here is really trying to get you to identify the airspace that surround Coeur D'Alene Airport and we can see the dashed magenta line encircling it. If you take a look at the legend you will see that denotes

Class E (sfc) Airspace.

The same goes for Sandpoint Airport which is surrounded by a faded magenta line. The legend again denotes

Class E Airspace with a floor 700ft. above the surface

The controlled airspace around Sandpoint begins at 700 ft AGL. The elevation of Sandpoint Airport is 2131 ft MSL as indicated by the airport data. The floor of controlled airspace needs to be in terms of MSL which would be the airport elevation + the start of the Class E airspace or 2131 ft MSL + 700 ft AGL = 2831 ft MSL.

I don't understand why the answer would be 700 ft MSL.

• The logical explanation based on the premise and the asker accepting the above surface answer, is that they made a typo while asking here.
– user14897
Commented Jun 18, 2019 at 22:01

In the example figure 22: Coeur D'Alene Airport is the thick Magenta lined airspace. (thick Magenta according to legend = airspace with floor 700ft above surface.) Brooks airport ( dashed magenta) is "overlying" Coeur D'Alene Airport. According to the legend dashed magenta = "Class E surface airspace"

what confuses people here is that you also have the VOA (hashed blue line circle/compass rose) overlying the class e airspaces.

the correct answer is "at the surface" because dashed magenta airspace overlying Coer D'Alene is Class E surface airspace. Surface to 700 AGL

• Welcome to AviationStackExchange. As a correction, Brooks Seaplane Base (S76) airspace does not overlie COE airspace. S76 is depicted by an anchor at the very edge of the Class E to the surface airspace of COE on the shore of Coeur D'Alene Lake at the edge of the city. It does not have its own airspace per se. It is barely in Class E with its takeoff and landing run appearing to be in to be Class G up to 700 feet AGL. COE on the other hand has a Class E to the surface (the magenta segmented circle with an extension) which is then surrounded by a much larger Class E starting at 700 feet AGL. Commented Mar 2, 2021 at 19:38
• Also, what is "VOA"? Commented Mar 4, 2021 at 6:48