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CFR 91.157 says that special VFR operations may be conducted below 10,000 ft MSL "within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport". Does the "controlled airspace designated to the surface" refer to only the center cylinder of the class B or C upside down wedding cake? Or is the language saying referring to all class B and C airspace in addition to the airspace between the surface and class B and C shelves? Thank you

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First question: yes. The controlled airspace designated to the surface for an airport is the center core of class B and C airspace, class D airspace, and class E airspace all the way to the surface (innermost heavy blue, innermost heavy magenta, dashed blue, and dashed magenta lines on the VFR charts.) This airspace, as well as any airspace directly above this airspace, is eligible for SVFR authorization, up to 10,000 ft MSL. The other shelves are excluded from SVFR authorization - the normal airspace rules apply to those regions. Moreover, if the center core extends above 10,000 ft MSL, that part of the center core that is above 10,000 ft MSL is also excluded.

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    $\begingroup$ There is a ruling from the Office of the Chief Counsel that addressed this; this answer would benefit from citing that. Here it is: faa.gov/sites/faa.gov/files/faa_migrate/interps/2006/… . Note that it reverses an earlier ruling that said airspace in the "shelves" was considered to be "within the lateral boundaries" of controlled airspace designated to the surface. $\endgroup$ Apr 12, 2023 at 22:52
  • $\begingroup$ Actually though this answer could use some clarification. Because the outer shelves are also depicted as heavy blue and heavy magenta lines on the VFR charts! $\endgroup$ Apr 12, 2023 at 22:56
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    $\begingroup$ Just noticed something here-- note that the way the FAR is written, any airspace "within the lateral boundaries" of the controlled-to-surface portion (i.e. the inner core) of the Class B or C is eligible for Special VFR up to 10,000' MSL. It makes no difference how high the actual ceiling of the Class B or C is. If the ceiling is say 5000' MSL, or if the ceiling is 15,000' MSL, either way, makes no difference, all airspace above that inner surface footprint all the way up to 10,000' MSL would be eligible for SVFR. This answer implies otherwise. $\endgroup$ Apr 13, 2023 at 2:02
  • $\begingroup$ The point becomes especially relevant in the case of Class D airspace, where the ceiling of the airspace is typically relatively low- or for surface-level Class E airspace- which is another kind of airspace where SVFR is allowed "within the lateral boundaries of"- keeping in mind that you won't find a specific ceiling listed for the surface-level Class E airspace on the sectional chart. Also highly relevant to related question aviation.stackexchange.com/questions/35297… -- the airspace above surface-level Class E airspace is off-limits to ultralights with no upper boundary. $\endgroup$ Apr 13, 2023 at 2:31
  • $\begingroup$ @quietflyer if the airspace does not extend beyond 10,000 ft MSL, SVFR cannot be requested by the pilot of the airport since the airspace is not under the control of the airport. As I understand SVFR, it is requested when the pilot advises that basic VFR cannot be maintained when entering into or transitioning through the surface area (typically the inner core) of the airspace. Consequently, the implicit limit of SVFR is the uppermost limit of the airspace but never beyond 10,000 ft MSL. For more info, see JO 7110.65Z 7-5-1 $\endgroup$
    – FencerPTS
    Apr 13, 2023 at 4:10
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With respect to your question, "controlled airspace designated to the surface" applies only within the airspace contained by the "...upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport." (see 14 CFR Part 91.157 Special VFR weather minimums.)

(highlight is mine)

So, for an airport at "0" feet MSL (for example), if there is a Class B shelf, the base of which starts at 7000 feet MSL, then that shelf would be outside of the "upward extension of the lateral boundaries of the controlled airspace designated to the surface..." and Special VFR would not be authorized.

This FAA Interpretation, located by @quietflyer, may be helpful in understanding Class B and Class C surface areas and shelves.

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