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The August 1992 Final Rule "Terminal Airspace Reconfiguration" (page 38963, Federal Register Volume 57 No 167, August 27 1992) (link to pdf of entire issue opening to this page) stated that the purpose of "control zones" was as follows:

A control zone ensures that aircraft arriving at an airport under IFR remain within controlled airspace when an instrument approach procedure could put that aircraft within 1000 feet of the surface. A control zone also ensures that aircraft departing an airport under IFR remain within controlled airspace between the surface and the base of adjacent controlled airspace.

The same Final Rule also makes clear (pp. 38963-38964) that surface level controlled airspace, including surface-level Class E airspace, would serve the same purpose after September 16 1993 as control zones served prior to that time.

SIT

With this in mind, why was it necessary to designate such a large area of surface-level Class E airspace at SIT/PASI airport at Sitka, Alaska? (Pictured above.) The E4 surface-level Class E "extension" is 12 miles wide, and extends to 28.3 miles northwest of the airport. (See page E-158 of the "Airspace Designations and Reporting document FAA Order 7400.11F; this airspace was last modified 11-05-2020.)

Is it really true that there are instrument procedures for this airport that could put an aircraft below 1000' AGL in all or most of this airspace? If so, which procedures are those?

Or does the FAA now designate surface-level controlled airspace based on some criteria other than the one stated above?

Wouldn't an aircraft flying over the Pacific Ocean northwest of the northwest tip of Kruzof Island, inbound for landing at SIT/PASI, flying below 1000' AGL/MSL, be in great danger of colliding with the high terrain (over 2350' MSL) near the northwest tip of Kruzof Island? Is there really any instrument procedure that could have an aircraft on approach for SIT/PASI below 1000' AGL/MSL at this location? If not, was there really any reason to extend the "extensions" much beyond the (approx) 2350' MSL terrain near the northwest tip of Kruzof Island? Based on the criteria stated above, was it really even necessary to extend it that far?

Has the E4 surface-level Class E "extension" in this area simply been sized to to completely contain some particular instrument procedure, regardless of whether or not an aircraft following that procedure might be within 1000' of the terrain (or ocean) in all parts of that "extension"?

Wouldn't much of the airspace covered by the E4 surface-level Class E "extension" extending 28.3 miles northwest of the airport be adequately be protected by a "transition area" with a Class E floor at 700' AGL, or by the existing surrounding Class E airspace floor at 1200' AGL?

This latter, more "conservative" approach would avoid imposing certain restrictions associated with surface-level controlled airspace on various aviation activities, such as the prohibition on VFR flight below a ceiling of 1000' AGL or lower without a Special VFR clearance (FAR 91.155(c)), the requirement for three miles visibility for taking off or landing (FAR 91.155(d)) (consider seaplane operations in this context), the requirement for ½-mile daytime, 1-mile nighttime visibility for part 135 helicopter operations (FAR 135.205(b)), the prohibition on aerobatic flight (FAR 91.303(c)), the prohibition on ultralight aircraft operations without prior authorization (FAR 103.17), the prohibition on Small Unmanned Aircraft operations without prior authorization (FAR 107.41), and more.

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  • $\begingroup$ Perhaps to contain Coast Guard (and civil) Seaplane and helicopter operations within controlled airspace. Sitka is a primary Coast Guard Search and Rescue location. I wonder if the Control Zone of the 90's looked the same. Read up on the importance of Sitka as a Search and Rescue site for Alaska. Interesting. $\endgroup$
    – 757toga
    Apr 22 at 0:18
  • $\begingroup$ FR link may not open to correct page on phone apps. $\endgroup$ Apr 29 at 1:54
  • $\begingroup$ Of course, the last paragraph re-opens the whole can of worms as to whether those prohibitions really apply in the "extensions" -- see several related ASE questions and answers including aviation.stackexchange.com/q/48103/34686 and aviation.stackexchange.com/a/86990/34686 and aviation.stackexchange.com/q/74738/34686. Note also that the "extension" is not included in the authorization-required area on the LAANC map for SUAS ("drone*) operations -- faa.maps.arcgis.com/apps/webappviewer/…. $\endgroup$ Apr 29 at 13:59
  • $\begingroup$ One of these days the FAA is going to have to come out with a truly definitive answer on this, and ideally one that is consistent with the original intent of the circa-1993 rule-making documents-- $\endgroup$ Apr 29 at 15:17
  • $\begingroup$ Considering coastal Alaskan weather, and the huge size of the "extension" area of surface-level Class E airspace currently extending NW of Sitka, would love to hear from someone who actually operates VFR in this area, whether in actual practice the requirement of FAR 91.155(c) to not operate VFR (w/o Special VFR clearance) under a ceiling lower than 1000' AGL in (some forms of?) surface-level Class E airspace is treated as binding throughout the entire Class E "extension" NW of Sitka. Consider creating an answer to aviation.stackexchange.com/q/48103/34686, or drop me a message (chat?) $\endgroup$ Apr 29 at 15:45

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The LDA/DME RWY 11 approach puts you darned close to 1000 AGL over those mountains if you come in from HEXAB on the localizer - and that assumes you fly it perfectly. The course reversal for that approach is basically smack on top of that 2250 peak.

The airfield itself is basically at sea level (26' MSL), and is on the ocean, so I'd expect there's also some gnarly local air currents fairly regularly, especially for approaches that try to come in between the islands. That's all pretty rugged terrain over there, and it's got a reputation for having a lot of microclimates.

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  • $\begingroup$ Good info there, but it still seems that the outer 4 or 5 miles of the area is un-necessary because at that point the plane would be over the ocean-- $\endgroup$ Apr 22 at 11:41
  • $\begingroup$ @quietflyer I expect this is much more about inbound traffic than outbound, and because of the large difference in elevation, they might want to make sure folks are coming in high enough before vectoring them for the localizer? I'm not sure what kind of traffic they're dealing with normally. It looks like a seasonal airport, so it's probably a feast-or-famine thing $\endgroup$ Apr 22 at 13:23
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As another answer has noted, the surface-level Class E "extension" to the northwest of SIT/PASI is indeed intended to protect the LDA/DME RWY 11 approach.

In the July 20 2021 edition of the "Airspace Designations and Reporting Points" document, FAA Order 7400.11E, the E4 surface-level Class E "extension" does not exist yet (it would be on page E-160 if it did), and the E2 surface-level Class E airspace only extends 11.1 miles northwest of the airport, extending 3 miles to either side of the 313° radial.

Presumably the LDA/DME RWY 11 approach did not yet exist yet at this time, at least in its present form.

The large E4 surface-level Class E "extension" spanning from 4 miles north and 8 miles south of the 315° bearing from the airport, extending to 28.3 miles northwest of the airport, was introduced in a Notice of Proposed Rule-Making published May 7 2020, and a Final Rule published July 31 2020, effective November 5 2020. These rule-making documents do not state what new approach procedure(s), if any, required the protection of this airspace all the way down to the surface.

The NPRM does contain the following text (italics and bolding added):

This action also proposes to establish a Class E airspace area, designated as an extension to a Class D or Class E surface area, at the airport. The area would be northwest of the airport and is designed to contain IFR aircraft descending below 1,000 feet above the surface.

It does appear that the outer 5 miles of this area would have been adequately served by a Class E "transition area" with a floor at 700' AGL, or even by the existing 1200' AGL Class E floor, because aircraft in the outer 5 miles of this area are over the ocean, not over high terrain.

The subsequent revocation of this large surface-level Class E "extension" has been proposed in a NPRM published February 7, 2022. This NPRM contains the following text (italics and bolding added):

The Class E surface airspace area northwest of the airport requires modification to properly contain IFR aircraft descending below 1,000 feet above the surface of the earth. The LDA/DME RWY 11 approach procedure turn area currently extends 28.3 miles to the northwest, but the area should be reduced due to the proposed elimination of the LDA/DME RWY 11 approach procedure turn.

According to this NPRM, the surface-level Class E airspace northwest of the airport will be reduced to an E2 airspace area spanning 1.2 miles each side of the 314° bearing from the airport extending 6 miles northwest of the airport, and an E2 airspace area spanning 1.1 miles each side of the 320° bearing from the airport extending 5.2 miles northwest of the airport. The E4 "extension" will be entirely removed.

Links:

May 7 2020 NPRM proposing the large E4 "extension" to the northwest of SIT/PASI: Link to text of docket, link to PDF of entire Federal Register issue opening to relevant page

July 31 2020 Final Rule establishing the large E4 "extension" to the northwest of SIT/PASI: Link to text of docket, link to PDF of entire Federal Register issue opening to relevant page

February 7 2022 NPRM proposing elimination of the large E4 "extension" to the northwest of SIT/PASI: Link to text of docket, link to PDF of entire Federal Register issue opening to relevant page

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