What Class Airspace Surrounds TRI Cities?

Question

I'm planning out a "fly the Appalachian Trail" route, and as the AT comes out of the Great Smokey Mountains and heads for its crossing of the Nolichucky river, it puts anyone flying along it extremely close to KTRI which looks like this on a sectional:

What does the grey-outlined airspace from 3,500/4,000/5,100 to 10,000 ft around the airport signify?

If I look VERY closely I can see the Class D (D = Dashed) outline... but Class D airports don't have radar airspace...

It looks like Class C, but it's the wrong color (grey, instead of 'cranberry') and Class C don't have dashed outlines for their local control jurisdiction...

Since the route is meant to be flown VFR, it's important for me to know if I need clearance or just radio contact to traverse the airspace.

Answer 1

The Grey outlined area surrounding TRI-Cities airport is a "Terminal Radar Service Area" (TRSA).

See this information from the Aeronautical Information Manual (AIM) paragraph 3-5-6, and this information, also from the AIM, paragraph 4-1-18 b, regarding TRSA airspace.

(note the bottom left corner from the sectional chart legend excerpt below)

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Answer 2

The airspace at Tri-Cities Airport is Class D when the tower is open and surface-level Class E when the tower is closed. The shape of this airspace is a simple circle, 4.3 miles in radius. There is also a small surface-level Class E "extension" (depicted by a dashed magenta line) extending to the northeast, which is in effect 24/7. The descriptions can be found on pages D-112, E-110, and E-206 of the Airspace Designations and Reporting Points document (FAA Order 7400.11F).

The grey line, and the elevation figures, denote the boundaries of a "Terminal Radar Service Area". This is noted on the Sectional Chart Legend
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and also on page 19 of the Aeronautical Chart User's Guide.

This information (as well as the actual schedule of the operating hours of the tower/ effective hours of the Class D airspace) is also available in the current (24Mar2002) Chart Supplement which was accessed via the FAA Digital Products Search Page.

The resource mentioned in another answer gives some good information on the practical significance of a TRSA to VFR pilots, and on why some TRSAs still exist at all rather than being converted to ARSAs (now Class C airspace) as was the FAA's intention at one time.

Here's a bit of closing trivia-- when TRSAs were first introduced, they were charted with solid magenta lines. I've seen examples of this on sectional charts from 6-9-83 and 11-19-87. ARSAs ("Area Radar Service Areas", now Class C airspace areas) were introduced later, and were originally charted with wide segmented blue lines (e.g. sectional charts from 11-21-85 and 11-20-86). Then ARSAs were changed to wide segmented magenta lines (e.g. sectional charts from 11-19-87 and 8-20-92). Then TRSAs were changed to solid grey-black lines (e.g. charts from 4-30-92 to present). And then ARSAs (now Class C airspace) were changed to solid magenta lines (e.g. charts from 11-12-92 to present). So TRSAs have been charted in two different ways, and ARSAs (now Class C airspace areas) have been charted in three different ways, and the current charting method for Class C airspace areas (formerly ARSAs) was once used for TRSAs!