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Of all the US airports with part-time control towers and with E4 "extensions", in which cases are the airspace definitions written so that the E4 "extensions" change to E2 and become part of a larger E2 "surface area" -- which also includes the airspace that was Class D during the daytime -- when the tower closes for the night?

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With these 21 airports, the airspace definitions are written so that the E4 "extensions" change to E2 and become part of a larger E2 "surface area" - which also includes the airspace that was Class D during the daytime -- when the tower closes for the night.

The page number references are for the FAA's "Airspace Designations and Reporting Points" document, FAA JO 7400.11C. The page numbers listed are for the E4 airspace designation, the E2 airspace designation, and Class D airspace designation.

  1. KENA or PAEN
    AAL AK Kenai, AK
    Kenai Municipal Airport
    E-158, E-7, D-5

  2. KGCK
    ACE KS Garden City, KS
    Garden City Regional Airport
    E-159, E-17, D-7

  3. KJEF
    ACE MO Jefferson City, MO
    Jefferson City Memorial Airport
    E-162, E-21, D-11

  4. KNHK
    AEA MD Patuxent River, MD.
    Patuxent River NAS (Trapnell Field)
    E-165, E-28-29, D-15

  5. KITH
    AEA NY Ithaca, NY
    Ithaca Tompkins Regional Airport, Ithaca
    E-167, E-30-31, D-19

  6. KPOU
    AEA NY Poughkeepsie, NY
    Dutchess County Airport, Poughkeepsie
    E-167, E-32, D-19-20

  7. KCXY
    AEA PA Harrisburg, Capital City Airport, PA
    Capital City Airport, Harrisburg
    E-169, E-35, D-22

  8. KLNS
    AEA PA Lancaster, PA
    Lancaster Airport
    E-170, E-35, D-23-24

  9. KRDG
    AEA PA Reading, PA
    Reading Regional/Carl A. Spaatz Field, Reading
    E-170, E-36, D-24

  10. KUNV
    AEA PA State College, PA
    University Park
    E-171, E-35, D-25

  11. KIPT
    AEA PA Williamsport, PA
    Williamsport-Lycoming County Airport
    E-171, E-37, D-24

  12. KLYH
    AEA VA Lynchburg, VA
    Lynchburg Regional-Preston Glenn Field Airport
    E-172, E-38-39, D-26

  13. KNTU
    AEA VA Oceana NAS, VA
    Oceana NAS (Apollo Soucek Field)
    E-172, E39-40, D-28

  14. KAPN
    AGL MI Alpena, MI
    Alpena County Regional Airport
    MI E-176, E-45, D-36

  15. KMKG
    AGL MI Muskegon, MI
    Muskegon County Airport
    E-177-178, E-48, D-39

  16. KRST **
    AGL MN Rochester, MN
    Rochester International Airport
    E-178, E-54, D-41

  17. KSTC **
    AGL MN St. Cloud, MN
    St. Cloud Regional Airport
    E-178, E-54-55, D-41

  18. KGFK
    AGL ND Grand Forks, ND
    Grand Forks International Airport
    E-179, E-56-57, D-42-43

  19. KILN **
    AGL OH Wilmington, OH
    Wilmington, Wilmington Air Park
    E-181, E-59, D-46

  20. KRAP **
    AGL SD Rapid City, SD
    Rapid City Regional Airport
    E-181, E-61, D-47

  21. KPRC
    AWP AZ Prescott, AZ
    Ernest A. Love Field
    E-210, E-129, D-140

** means that in these 4 cases, no limit on the effective hours is given for the E4 airspace - apparently it is simply assumed that the E4 will be superseded by the E2 whenever the E2 is in effect.

Among airports with part-time control towers and with E4 "extensions", the style of airspace designation that is much more common over the nation as a whole is for the E4 airspace to be in effect 24/7, and for only the Class D airspace to change to E2 when the tower closes for the night. Here's an example of such a designation:

KMFR
ANM OR Medford, OR
Rogue Valley International-Medford Airport
E-189, E-80-81, D-64

Note that there is no way to tell one style of designation from the other just by looking at the sectional chart or the Airport/ Facility Directory. Perhaps this may be taken as a hint that the distinction rarely matters in actual practice.

Note the uneven distribution of the airports in the list above among states and regions. For some reason, in some regions such as the northeast, the style of airspace designation that we're discussing here is actually more common than the style that we see at KMFR.

To understand why the distinction between the two styles of airspace designation might matter, at least in theory, to pilots flying at first light before the tower is open for the day, including ultralight flight, aerobatic practice, non-recreational sUAS (drone) activities, and possibly now that the FAA is implementing some new regulatory changes, recreational sUAS (e.g. RC model airplane) activities, see the first two links below. Whether this distinction has ever yet mattered in actual practice is an open question-- perhaps in actual practice the airspace in these extensions is simply treated as E4 airspace 24/7 in relation to FARs 91.303c, 103.17, and 107.41. Nonetheless, pilots of such aircraft would undoubtedly hope that this unusual style of airspace designation is avoided in the future.

It is interesting to note that on the FAA's LAANC map for authorization for sUAS (drone, model airplane) flight, these projecting E4 extensions that change to E2 when the tower is closed at the 21 airports listed above are NOT covered by the grid squares that indicate the areas where pre-authorization is required. This supports the idea that these extensions are simply treated as E4 airspace 24/7, at least in relation to FAR 107.41.

Unlike what is implied by the actual language of FAR's 91.303c and 9.155c, it seems unlikely that the distinction between the two different styles of airspace designation has ever mattered in actual practice to a pilot seeking to obtain a Special VFR clearance, or planning to fly beneath a cloud ceiling below 1000' AGL without obtaining a Special VFR clearance. See the third and fourth link below for more.

For more, see these related question or answers:

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    $\begingroup$ "Whether this distinction has ever yet mattered in actual practice is an open question-- perhaps in actual practice the airspace in these extensions is simply treated as E4 airspace 24/7 in relation to FARs 91.303c, 101.33a, 103.17, 107.41." could be the subject of another question, but I'll save it for another day. $\endgroup$ – quiet flyer May 11 at 15:49

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