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Participation in TRSA services is completely optional. The depicted airspace is all still class E, and you can fly straight through it sans radio or transponder without violating any regulation.

Obviously, if you do talk to them, they can provide radar services, but this is no different from any other class E airspace owned by an approach facility, including (notably) the class E above and below the depicted TRSA boundaries.

So, why bother showing it at all? And even if there’s a reason to show it, what’s the point in such complex configurations that have zero impact on either pilots or ATC?

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  • $\begingroup$ Related-- aviation.stackexchange.com/q/22134/34686 (see all answers) . It seems to me that a) the reason it is complex is that the radar coverage naturally extends further at higher altitudes, and b) the reason it is depicted on the map is because it is complex. If it were simpler, like a single ring at fixed radius, it might not be depicted, seeing as it has no regulatory impact. $\endgroup$
    – quiet flyer
    Commented Apr 14, 2021 at 18:03
  • $\begingroup$ @quietflyer not all TRSAs are excessively complex, e.g. both BPT and LCH are simple concentric rings (though there are more rings than a Charlie would have). $\endgroup$
    – randomhead
    Commented Apr 14, 2021 at 19:01
  • $\begingroup$ I absolutely agree with @Pondlife's answer below. The fact that approved/positive separation from other VFR or IFR traffic is provided within the depicted TRSA airspace is an essential reason to show the boundaries. TRSA services, although not mandatory, are a great opportunity (especially during marginal VFR weather) to have an increased level of safety benefiting VFR and IFR aircraft alike. $\endgroup$
    – user22445
    Commented Apr 14, 2021 at 22:54
  • $\begingroup$ @randomhead -- re "simple concentric rings" -- I guess my concept of "not complex" would be a single ring of set radius which is the same at all TRSA airports, with coverage extending from ground level to a set AGL altitude which is the same at all TRSA airports. Similar to the old pre-1993 "Airport Traffic Area" concept which defined the airspace volume around a towered airport within which establishment of communications was required before entry-- and which in fact was not depicted on the VFR sectional charts. $\endgroup$
    – quiet flyer
    Commented Apr 15, 2021 at 15:33

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I think - and I may be wrong - that your question assumes that ATC services are the same in a TRSA and in class E in general. Or perhaps that TRSA Service and flight following give you exactly the same thing.

In fact, TRSA service is slightly different: it provides everything that Basic Radar Service does (e.g. safety alerts, sequencing), plus separation services for all participating aircraft. Usually, ATC doesn't provide any separation service to VFR traffic in class E.

The ATC Orders (JO 7110.65) sections 7-6 and 7-7 cover Basic Radar Service and Terminal Radar Service; you can read more details there. Since the ATC services available in a TRSA aren't the same as those available in general class E airspace, that seems to me like a valid reason to chart it.

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  • $\begingroup$ I wasn’t aware of VFR/VFR separation service, which isn’t available in normal class E; that explains it! $\endgroup$
    – StephenS
    Commented Apr 14, 2021 at 22:58
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    $\begingroup$ @StephenS Yes, it's an odd one. AFAIK, the only other airspace where VFR traffic is separated from all other traffic is class B. $\endgroup$
    – Pondlife
    Commented Apr 14, 2021 at 23:05
  • $\begingroup$ @Pondlife - In Class C airspace, VFR aircraft are separated from IFR aircraft (see faa.gov/documentLibrary/media/Order/7110.65Y.pdf) paragraph 7-8-3 $\endgroup$
    – user22445
    Commented Apr 14, 2021 at 23:54
  • $\begingroup$ @757toga Right, but they aren't separated from other VFR aircraft. in TRSA they are. $\endgroup$
    – Pondlife
    Commented Apr 14, 2021 at 23:56
  • $\begingroup$ @Pondlife- I agree $\endgroup$
    – user22445
    Commented Apr 14, 2021 at 23:59
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The easiest way that I was told to relate to a TRSA is to think of it as a baby Class C airspace. The TRSA is technically Class D or E airspace with almost all of the equivalent facilities and equipment of a Class C. You can receive almost all of the same ATC service of a Class C in a TRSA. But, it is not mandatory to use them.

Another way to view a TRSA is that many of them were formerly, are currently striving to be, or soon will be Class C airspace. Class C airspace. They are just currently downgraded to Class E or D.

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    $\begingroup$ Allegedly, AOPA and EAA have lobbied the FAA to not convert any more to class C due to the mode C/ADS-B/radio requirements. They’re permanently stuck in limbo. $\endgroup$
    – StephenS
    Commented Apr 14, 2021 at 22:57
  • $\begingroup$ As Pondlife's answer points out, it isn't as simple as "baby Charlie." The separation services that a participating VFR pilot receives are more than they would receive in a Charlie... but participation is not mandatory and equipment requirements are not as stringent. I wouldn't say it's "baby" or "grown up." It's just different. $\endgroup$
    – randomhead
    Commented Oct 14, 2022 at 16:14
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If you visit the Aeronautical Information Manual, section 3-5-6, it will provide the answer for you:

"TRSAs were originally established as part of the Terminal Radar Program at selected airports. TRSAs were never controlled airspace from a regulatory standpoint because the establishment of TRSAs was never subject to the rulemaking process; consequently, TRSAs are not contained in 14 CFR Part 71 nor are there any TRSA operating rules in 14 CFR Part 91. Part of the Airport Radar Service Area (ARSA) program was to eventually replace all TRSAs. However, the ARSA requirements became relatively stringent and it was subsequently decided that TRSAs would have to meet ARSA criteria before they would be converted. TRSAs do not fit into any of the U.S. airspace classes; therefore, they will continue to be non-Part 71 airspace areas where participating pilots can receive additional radar services which have been redefined as TRSA Service."

https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap3_section_5.html

You do not need to participate, but it is a service which is available to you should you choose to take advantage of it. When transitioning those areas, you are wise to take advantage of it.

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  • $\begingroup$ This is (more detail on) what I said in the first paragraph of the Q but doesn’t provide an answer to the question. $\endgroup$
    – StephenS
    Commented Apr 15, 2021 at 12:35

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