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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 '19 at 13:33
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    $\begingroup$ 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 '19 at 17:18
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    $\begingroup$ “What are the practical differences for pilots and controllers?” Yes, please help me understand why it matters... to more than one person here. $\endgroup$ – Michael Hall May 5 at 16:29
  • $\begingroup$ With some comments deleted, the two comments immediately above seem somewhat out of context-- really as of now it seems they apply more to this question aviation.stackexchange.com/questions/71406/… . $\endgroup$ – quiet flyer May 5 at 18:29
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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 '19 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 '19 at 9:44
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In brief-- E2 airspace and E4 airspace are both examples of Class E airspace that extend all the way down to the surface. A dashed magenta line that actually encircles the airport for which it is designated normally depicts E2 airspace. A dashed magenta line that does not actually encircle the airport for which it is designated normally depicts E4 airspace, which is called an "extension". Both E2 and E4 airspaces serve to bring the Class E visibility and cloud clearance requirements all the way down to the surface. But some FARs may be construed as treating E2 airspace differently than E4 airspace. See the links given at the end of this answer for more on that.

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 airspace may change to E2 or Class G airspace. If the Class D airspace changes to G, then so will any associated extensions. If the Class D airspace 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, and there is no way to tell which is the case from the sectional chart or even the Chart Supplement. The fact that very few pilots are aware of this latter point suggests that it rarely matters in actual practice.

Links to specific examples of E2 and E4 airspace on the VFR sectional charts are given in the related ASE answer In the US, how does the distinction between E2 and E3/E4 airspace affect pilots?.


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 7400.11E, effective September 14, 2020.

"E2" airspace means all the airspace descriptions that begin with "E2" on this document, found on pp E-1 through E-142. 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-157 through E-225. 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 arguably 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.

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 (and also the core "surface area" of a Class C airspace) can be designated to change to E2 airspace when the tower closes, in which case there will be no specific depiction of the E2 airspace on the VFR sectional chart.

  • 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.

Many examples can be found where the FAA is using the phrase "surface area" in a context that is clearly meant to exclude the surface-level Class E "extensions" (E3/E3a/E4 airspaces). On the other hand, air traffic controllers often use the phrase "surface area" to mean the entire column of airspace that extends up from the surface in any given location, including any surface-level Class E "extensions" that may be present. There are many cases in various FAA Orders where the word "surface area" is used in a way such that it is not clear which of these two usages is intended.

Both E2 and E4 airspace evolved from the earlier "Control Zones". To read more about this, see this related ASE answer.

Perhaps someday the notations E2, E4, etc will be inserted directly into the FARs and the AIM. That would greatly help to clarify the meaning of certain FARs.

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.

Related ASE questions and answers:

Q: In the US, how does the distinction between E2 and E3/E4 airspace affect pilots?

A: In the US, how does the distinction between E2 and E3/E4 airspace affect pilots?

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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 '19 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 '19 at 17:51
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    $\begingroup$ Class C airports also revert to Class E at night, presumably E2. $\endgroup$ – randomhead May 5 at 20:12
  • $\begingroup$ @randomhead-- yes, you are absolutely right; edited. Thanks. $\endgroup$ – quiet flyer May 6 at 2:48
  • $\begingroup$ So when I am transitioning from E2 to E4, (or vice versa) what must I do? $\endgroup$ – Michael Hall May 6 at 3:05
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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.

Source of quotes -- the FAA's "Airspace Designations and Reporting Points" document, current edition FAA Joint Order 7400.11E, effective September 14, 2020. All the entries in the relevant sections start with "E2", or "E4", as appropriate.

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  • $\begingroup$ Second try, for brevity $\endgroup$ – quiet flyer May 14 '19 at 14:29
  • $\begingroup$ This is the best answer I have seen on this fascination of yours in years! It gets my upvote. $\endgroup$ – Michael Hall May 6 at 3:07

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