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We have a number of questions here about E2 vs. E4 airspace (see summary of links in this answer) but what does that mean? As far as I can see, neither the AIM nor the ATC Orders mention E2 or E4 airspace, so what are they? What are the practical differences for pilots and controllers?

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  • $\begingroup$ I suspect we'll get some additional specific guidance from FAA legal counsel on some of these issues sooner or later, perhaps sooner, as the drone age continues to advance. $\endgroup$ – quiet flyer May 12 at 13:33
  • $\begingroup$ Deleting some comments-- still want to point out that if this question really is meant to include a question about the practical effects of the E2 / E4 distinction for pilots and controllers, then it is a very broad question. Not necessarily a bad thing. $\endgroup$ – quiet flyer May 12 at 17:18
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According to this website, which directly quotes an internal memorandum of the FAA, the class E airspace can be categorized as below:

  • E1 – Class E Airspace at and above 14,500 feet MSL
  • E2 – Class E airspace areas designated as a surface area for an airport
  • E3 – Class E Airspace Areas Designated As An Extension To A Class C Surface Area
  • E4 – Class E Airspace Areas Designated as an Extension to a Class D or Class E Surface Area
  • E5 – Class E Airspace Areas Extending Upward From 700 Feet Or More Above The Surface of The Earth
  • E6 – En route Domestic Airspace Areas
  • E7 – Offshore Airspace Areas
  • E8 – Class E Airspace Areas Designated As Federal Airways

The memorandum is also available as PDF.

Apart from this reference to the FAA internal memo, I could not find any official FAA documents explaining the categories.

For pilots and controllers there seems to be not many differences, but for operators of small unmanned aircraft (i.e. drones) there are.

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  • $\begingroup$ Unfortunately the phrase "Designated as a Surface Area for an Airport" is somewhat confusing and would seem at first glance to also include E4 airspace, until we read further down the list. Also a reader not already well versed in the language at play here would tend to assume the E4 airspace does not touch the surface. To make everything more complicated still, the FAA often uses the simple term "Surface Area" even without the "designated for an airport" qualifier to mean the same thing as a "Surface Area designated for an airport", i.e. including E2 but not E4 airspace-- see for example $\endgroup$ – quiet flyer May 14 at 9:35
  • $\begingroup$ (continuing) see for example the Pilot-Controller Glossary (page S-8) (faa.gov/air_traffic/publications/media/pcg_10-12-17.pdf) , as well as this document noting an airspace change at KACV federalregister.gov/documents/2017/07/07/2017-14219/… . Still, good concise answer. $\endgroup$ – quiet flyer May 14 at 9:44
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In brief-- a dashed magenta line that actually encloses the airspace directly over the airport whose approaches are being protected normally depicts E2 airspace. A dashed magenta line that does not actually enclose the airspace directly over the airport whose approaches are being protected normally depicts E4 airspace. Both E2 and E4 airspaces are Class-E-to-surface airspace, and serve to bring the Class E visibility and cloud clearance requirements all the way down to the surface. But some FARs treat E2 airspace differently than E4 airspace. Specifically, according to the letter of the regulations, FARs 91.155c, 91.303c, 91.155c, 101.33a, and 103.17 do not apply to E4 airspace. For more on this, see What is the primary reason that the non-towered airports KACV and KTLV have E4 extensions to E2 airspace? .

Near airports with part-time control towers, airspace sometimes has a different designation at different times of day-- specifically, the designation may change when the control tower at the associated airport closes or opens. When the tower closes, Class D may change to E2 or G. If the D changes to G, then so will any associated extensions. If the D changes to E2, any associated E4 extensions may either be defined to stay E4 or to change to become part of the E2-- it varies. The fact that very few pilots are aware of this latter point suggests that it rarely matters in actual practice. None of these changes are clearly shown on the sectional charts-- for example the dashed blue lines around the Class D airspace don't change to magenta when the tower closes!


Now in more detail--

"E1", "E2", "E3", "E4", "E5", and "E6" are just shorthand for different airspace descriptions, all of which apply to Class E airspace. "E2" and "E4" and the rest cannot be found in the FAR or the AIM, but they are used in other FAA documents.

The ultimate source for these descriptions is the FAA's "Airspace Designations and Reporting Points" document, current edition FAA Joint Order 7400.11C, effective August 13 2018, downloadable here https://www.faa.gov/documentLibrary/media/Order/JO_7400.11C.pdf.

"E2" airspace means all the airspace descriptions that begin with "E2" on this document, found on pp E-1 through E-140. The heading for this section is "6002. Class E Airspace Areas Designated as Surface Areas. The Class E airspace areas listed below are designated as a surface area for an airport."

"E4" airspace means all the airspace descriptions that begin with "E4" on this document, found on pp E-156 through E-224. The heading for this section is "6004. Class E Airspace Areas Designated as an Extension to a Class D or Class E Surface Area. The Class E airspace areas listed below consist of airspace extending upward from the surface designated as an extension to a Class D or Class E surface area."

Since the FARs do not reference "E2" and "E4" directly, the phrases in the titles and descriptions above are the key to understanding which FARs apply to E2 airspace and which FARs apply to E4 airspace.

In particular, the language of the "Airspace Designations and Reporting Points" document signals that when we come across the phrase "designated for a airport" or "designated to the surface for an airport", then if we are talking about Class E airspace, we must be talking about E2 airspace, not E3 or E4 airspace.

(E3 airspace is an "extension" like E4 airspace, but adjoins Class C rather than Class D or E2.)

We can also note the following--

  • Both E2 and E4 airspaces are normally depicted by a dashed magenta border on a sectional chart.

  • Sometimes a Class D airspace can be designated to change to E2 when the tower closes, in which case there will be no specific depiction of the E2 on the chart other than the depiction of the Class D airspace.

  • A body of E2 airspace always includes the airspace directly over the airport whose approaches are being protected.

  • A body of E4 airspace never includes the airspace directly over the airport whose approaches are being protected. Rather, the E4 airspace abuts some other airspace, such as E2 or Class D, that includes the airspace directly over the airport whose approaches are being protected. That's why E4 airspace is called an "extension".

Admittedly the terminology applied to E2 and E4 airspace in the "Airspace Designations and Reporting Points" document is rather awkward. Considering that E4 airspace also goes to the surface, it's unfortunate that someone didn't come up with a better term than "Designated as Surface Areas" or "Designated as a Surface Area for an airport" to describe the E2 airspace.

Both E2 and E4 airspace evolved from the earlier "Control Zones". To read more about this, click here to see this answer to a related question.

Perhaps someday the notations E2, E4, etc will be inserted directly into the FARs and the AIM. That would help to clarify things a great deal. Nonetheless, even with the present language, according to the letter of the regulations, FARs 91.155c, 91.303c, 91.155c, 101.33a, and 103.17 ought not apply to E4 airspace. Whether or not this distinction is always observed in actual practice is another matter-- many examples can be found where the distinction has not been observed.

For more on the practical differences between E2 and E4 airspace from the viewpoint of pilots and controllers, see the many related questions and answers on the topic that have been posted to Aviation Stack Exchange. As noted above, one question that explores the differences in some detail is What is the primary reason that the non-towered airports KACV and KTLV have E4 extensions to E2 airspace?

A note on the AIM -- the Airman's Information Manual is not a regulatory document, but ideally should shed a clear light on the meaning of the regulations. The phrases used in the AIM to refer to E2 and E4 airspace are similar to, but slightly different from, the phrases used in the "Airspace Designations and Reporting Points" document. In general the language and meaning of the AIM is congruent with the language and meaning of "Airspace Designations and Reporting Points" document as outlined in this answer, except for one specific sentence.

In a revision effective May 26, 2016, a confusing and misleading sentence was added to AIM 3-2-6: "Surface area arrival extensions become part of the surface area and are in effect during the same times as the surface area". The phrase "become part of the surface area and" ought to be excised from this sentence. The intention may be just to emphasize that the E4 airspaces extend all the way down to the surface, but considering the way that both the "Airspace Designations and Reporting Points" document and the AIM use the phrase "surface area" in association with E2 airspace but not E4 airspace, the phrase "become part of the surface area" seems to carry some implication that the E4 airspaces may actually become E2 airspace, or may function exactly like E2 airspace, whenever the adjoined E2, D, or C airspace is in effect. Neither of these statements are accurate.

This particular May 26 2016 revision to AIM 3-2-6 reflects no actual change in the relevant regulations.

See also--

Does an SVFR clearance extend to Echo surface extensions?

http://goldsealgroundschool.com/uav-library/surface-E-authorizations.pdf


Sources--

Source for FARs as they existed in January 1 1993, also listing the modifications that would become effective September 16 1993

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  • $\begingroup$ You've removed the part about the names E2 and E4 being shorthand, in essence, unofficial nicknames. Explaining just that and where the naming came from (e.g., 6002) would make for a succinct answer. $\endgroup$ – ymb1 May 12 at 17:35
  • $\begingroup$ It's still there, I just removed the word "handy". Maybe someone else can do a better job of making a truly succinct answer but the question as a whole is a broad one. Hopefully the first few paragraphs of my answer are enlightening . I encourage anyone w/ an interest to borrow freely from my answer if they want to attempt to formulate something more concise. $\endgroup$ – quiet flyer May 12 at 17:51
  • $\begingroup$ A better design for the 7400.11C document would be to use the phrase "Class E airspace designated to the surface" as an overall header for subsections titled "Class E airspace designated to the surface for an airport" (E2) and "Class E airspace designated to the surface as an extension" (E4), or something like that. But that's not what we're given in reality. $\endgroup$ – quiet flyer May 13 at 14:21
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E2 = dashed magenta border that actually surrounds the airport whose approaches are being protected = "6002. Class E Airspace Areas Designated as Surface Areas. The Class E airspace areas listed below are designated as a surface area for an airport."

E4 = dashed magenta border that does not actually surround the airport whose approaches are being protected but rather adjoins some other airspace that surrounds that airport = "6004. Class E Airspace Areas Designated as an Extension to a Class D or Class E Surface Area. The Class E airspace areas listed below consist of airspace extending upward from the surface designated as an extension to a Class D or Class E surface area.

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  • $\begingroup$ Second try, for brevity $\endgroup$ – quiet flyer May 14 at 14:29

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