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I'm a bit new to airspace and I'm trying to figure out if the airspace around Gulfport-Biloxi International (KGPT) changes to class G or E when the tower closes. Looking at KGPT's airspace on a sectional, it is Class D with a note to check NOTAMs/Supplement for Class D/E (sfc) effective hrs.

GPT on sectional

I've checked the chart supplements and it says Class G when the tower is closed, but the AIM leads me to think it would be Class E at 700' MSL (with Class E extensions changing to Class G) when the tower is closed since it has ASOS. Does this sound right, or am I missing something?

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To expand a little more on what @rbp said, the VFR Sectional Note is referring to the Class D and Class E (sfc) designations. So, when referring the the Chart Supplement, which says AIRSPACE: CLASS D svc (1200-0500Z) other times CLASS G they are referring to the Class D and Class E (sfc) specifically—just as @rbp said.

Now consider what the next level of controlled airspace is when the tower is closed and the airspace over KGPT becomes Class G. It would be 700’ AGL Class E airspace. The AIM goes on to detail this (emphasis mine):

Where a Class D surface area is part-time, the airspace may revert to either a Class E surface area (see paragraph 3−2−6e1) or Class G airspace. When a part–time Class D surface area changes to Class G, the surface area becomes Class G airspace up to, but not including, the overlying controlled airspace.

Source: Aeronautical Information Manual (AIM), Change 1, May 26 2016, 3-2-5 Class D Airspace (13 MB PDF)

And goes on to explain in Note 2 of paragraph 3-2-5 (with added emphasis):

Normally, the overlying controlled airspace is the Class E transition area airspace that begins at either 700 feet AGL (charted as magenta vignette) or 1200 feet AGL (charted as blue vignette). This may be determined by consulting the applicable VFR Sectional or Terminal Area Charts.

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If the chart says its Class G when the tower is closed, they are talking about the surface area ("sfc" in the note), not the overlying airspace.

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