In the US, can the same airspace simultaneously be E2 and E4?

Consider the case of KSTC -- St. Cloud Regional Airport, MN.

On page E-178 of the FAA's "Airspace Designations and Reporting Points" document, also known as "Joint Order 7400.11C", https://www.faa.gov/documentLibrary/media/Order/JO_7400.11C.pdf, we find the definition of the E4 airspace at KSTC. This definition clearly corresponds to the airspace that lies within the dashed magenta border but outside the dashed blue circle. No note is given to indicate that the effective hours are less than 24/7.

On page D-41 of the same document we find the definition of the Class D airspace at KSTC-- this is clearly the airspace in the dashed blue circle, up to 3500' MSL, and there is a note to see the Airport/ Facilities Directory for the effective hours of operation.

On page E-54 of the same document we find the definition of the E2 airspace at KSTC-- this is clearly written to include all the airspace in the dashed blue circle (but with no altitude ceiling) AND all the airspace within the dashed magenta line. Again there is a note to see the Airport/ Facilities Directory for the effective hours of operation.

Here is the actual description of the E2 airspace from page E-54 of JO 7400.11C:

"AGL MN E2 St. Cloud, MN

Within a 4.1-mile radius of St. Cloud Regional Airport and within 2.4 miles each side of the St. Cloud VOR/DME 143° radial, extending from the 4.1-mile radius to 7.2 miles southeast airport. This Class E airspace area is effective during the specific dates and times established by a Notice to Airmen. The effective date and time will thereafter be continuously published in the Airport/Facility Directory.''"

In most cases of airports with part-time control towers where we have a dashed magenta E4 "extensions" like this, IF when the tower closes the Class D airspace reverts to E2 rather than G (which is also possible), one of the following two situations will apply:

1) The part-time E2 airspace is defined to ONLY include the airspace in the dashed blue circle, while the E4 airspace is implied to be in effect 24/7. This is the norm-- it is by far the most common situation, nation-wide.


2) The part-time E2 airspace is defined to also include the airspace in the dashed magenta borders, but there is also a note in the E4 airspace definition to see the A/FD for the effective hours of operation of the E4 airspace, presumably implying that when the E2 description is active, then the E4 description is not. This situation is much less common over the nation as a whole, but for some reason it is fairly common in the northeastern US. Example: KLNS, and about a dozen other airports.

But neither of these descriptions apply the airspace at KSTC.

Three other airports with airspace definitions set up just like KSTC are KRST, KILN, and KRAP.

At these 4 airports,

1) Is the lack of reference in JO 7400.11C to limited effective hours of the E4 airspace simply an oversight? I.e. a mistake?


2) In such a case is it always simply assumed that the "lower" airspace class (E4) simply is superseded by the "higher" airspace class (E2) -- similar to what is presumably considered to happen when E2, E4, or any other kind of Class E airspace, which usually has no specific defined upper limit, hits the floor of the Class A airspace high above? If this is the case, then why at KLNS and about a dozen other airports where the E2 is configured like at KSTC, do we find (in JO 7400.11C) that a note to see the A/FD for the effective hours is included in the description of the E4 airspace, as well as the descriptions of the E2 airspace and the D airspace? If this note is not really needed -- if the E4 effective hours are automatically limited simply by virtue of the fact that the E4 airspace is superseded by the E2 airspace whenever the E2 airspace is effective-- then why include this note in the E4 airspace descriptions for KLNS and other airports? At the very least we have an inconsistency here.


3) Is the airspace in question considered to both E2 AND E4 airspace during the hours that E2 airspace is in effect (i.e. when the tower is closed)? I know of no specific FAR whose meaning would be confused or obscured if this were considered to be true.

Many FARs appear to apply specifically to E2 airspace-- relating to SVFR operation, aerobatic flight, ultralight flight, recreational and non-recreational sUAS operation (commercial and hobbyist "drones", model airplanes, etc), and even unmanned free balloon flight-- for more see this related question -- but the interpretation of those FARs would not necessarily be confused if the airspace were also considered to be E4 airspace at the same time.

Naturally, the Class E visibility and cloud clearance requirements for VFR flight apply to both E2 and E4 airspace, so there is no problem there.

Question A: Which of the three possibilities listed above is the most accurate description of the situation at KSTC, KRST, KILN, and KRAP, and why? Or is it simply ambiguous as to which is the case?

(It's not clear that the answer to question A would make any operational difference at these 4 airports. However it could have some bearing on the interpretation of the airspace designations at some other airports.)

Question B: Also, more generally, in the US, would it ever be permissible for the same airspace to simultaneously be considered to be E2 airspace and E4 airspace?

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Federico
    May 13 '19 at 6:28

Since I worked the airspace around KRAP, I'll cover that scenario for you. The tower at KRAP closes at 10 PM local, and the airspace at the field reverts to E2. The TRACON at KRCA closes at the same time, so Denver Center (that would've been me) gets the airspace after hours.

We treat all Class E airspace near an airport the same, so the closest of your answers for the first question would be 3.

There's confusion, however, as to whether a Special VFR can enter those extended areas when requesting entry/exit/transiting the surface area. My answer is YES, because that airspace will be protected. I will not authorize any IFR or other SVFR operation in that area, if I have given you a clearance. To do so would be an error on my part. This does not keep me from holding aircraft near the field (at HELTA)if necessary, but they will be clear of your aircraft by altitude restriction. Remember, this is the Center environment. A terminal environment may have additional restrictions placed on them, simply because they work many aircraft in a small and congested area.

As far as your second question goes, NO, the designations for individual areas within the same class would not change, but I'll still protect those areas for your flight.

  • $\begingroup$ Thanks for the answer. FYI, a few months ago I sat on on a zoom conference where several high-level FAA staffers offered conflicting opinions on whether or not the language in the FARs describing where sVFR operations may be authorized, and where VFR flight without a sVFR authorization is prohibited under certain conditions (e.g. below a 1000' ceiling), did or did not apply to "extensions", i.e. E4 airspace. $\endgroup$ Aug 5 at 4:10
  • 1
    $\begingroup$ (ctd) One of them said something to the effect of "pilot checkrides have been failed because of the ongoing confusion over this issue; it's been unclear ever since the 1993 "alphabet" airspace re-organization". $\endgroup$ Aug 5 at 4:10
  • 1
    $\begingroup$ yes, I do understand that. And one could possibly argue that if the FAA intended the conversion to Class-E surface areas, some of which were "extensions" and others of which actually contained the airports whose approaches they were protecting, to cause significant changes in the application of certain FARs, then that SHOULD have been addressed in the various NPRMs etc accompanying the rule-making process around the conversion to the "alphabet" airspace classes. But the rule-making process was rather complex, with several different rounds of NPRMs, (ctd) $\endgroup$ Aug 25 at 16:03
  • 1
    $\begingroup$ (ctd) so it's not really a decisive argument. The second half of this answer aviation.stackexchange.com/a/75022/34686 goes through several issuances from the FAA that indicate that surface-level Class E "extensions" should be treated differently from surface-level Class E airspaces that are not "extensions", in relation to the application of several different FARs. $\endgroup$ Aug 25 at 16:05
  • 1
    $\begingroup$ (Ctd) By the way, in relation to aviation.stackexchange.com/a/75022/34686, that answer is long overdue for a revision. Among other things, I intend to remove some of the content near the end, starting with "The present question goes on to ask: And which is the better interpretation of the language of the Federal Aviation Regulations...?" Basically I think the language in the FARs and supporting documents is just too poorly-written and ambiguous to decisively support one interpretation over the other-- and should be fixed. $\endgroup$ Aug 25 at 16:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.