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Several FARs use the phrase "within the lateral boundaries of" (x airspace). What does the FAA interpret this phrase to mean? Specifically, what is the vertical extent of the airspace encompassed by this phrase?

The common-sense interpretation of this phrase would appear to include any airspace whose latitude-longitude coordinates fall within the boundaries of said airspace, regardless of altitude, from the earth's surface all the way to outer space, or at least to the upper limit of the airspace which the FAA has any regulatory authority over.

Otherwise, it would seem to serve just as well to dispense with the "within the lateral boundaries" phrase and simply say "within" (x airspace).

Is there any evidence that the FAA interprets "within the lateral boundaries of" differently than the meaning noted above?

The answer to this question affects the interpretations of certain FARs, describing, among other things, airspace where ADS-B-out is required, airspace where 3 miles visibility is required to enter a traffic pattern under Visual Flight Rules with no special VFR clearance, airspace within which aerobatic flight is prohibited, airspace where prior authorization is required to operate unmanned free balloons, and airspace in which an ultralight aircraft may not be flown without prior authorization from ATC.

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  • $\begingroup$ I believe the upper limit of the FAA's regulatory authority is FL600, not "all the way to outer space" $\endgroup$ – abelenky Feb 28 at 21:13
  • $\begingroup$ @abelenky-- noted-- question modified. $\endgroup$ – quiet flyer Feb 28 at 21:15
  • $\begingroup$ Pertains to several answers to this question-- aviation.stackexchange.com/questions/74808/… $\endgroup$ – quiet flyer Feb 28 at 22:44
  • $\begingroup$ @abelenky Class A ends at FL600; above that is class E up to the limits of national airspace, which is currently undefined. Various treaties set it no higher than the Karman Line. $\endgroup$ – StephenS Mar 30 at 17:13
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The FAA normally interprets the phrase "within the lateral boundaries of" (x airspace) to mean any airspace whose lat-lon coordinates fall within said boundaries, regardless of altitude, from the earth's surface all the way to outer space, or at least to the upper limits of the airspace which the FAA has any regulatory authority over.

Pilots would be wise to follow this common-sense understanding of the meaning of "within the lateral boundaries of".

However, the FAA is not a monolithic entity, nor is it immune to making the occasional blunder. On a few occasions, some subset of the FAA has adopted a very different understanding of the meaning of "within the lateral boundaries of".

For example, in the text of a spectacularly misguided Final Rule published on page 51966 of the October 5, 1993 edition of the Federal Register, the FAA implied that the phrase "within the lateral boundaries of the surface areas of ... Class E airspace designated for an airport" would not encompass any Class E airspace higher than the floor of the 700' or 1200' AGL "transition area" that invariably overlies a Class-E-to-surface airspace.

To correct this imaginary problem, the FAA changed the wording of FAR 91.157 from the existing wording

91.157 Special VFR weather minimums Except as provided in appendix D, section 3 of this part, the following special weather minimums and requirements apply to operations conducted to or from an airport in controlled airspace: (a) Operations may be conducted only under an ATC clearance-- (1) Within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport; and ...

To the new wording

91.157 Special VFR weather minimums ( a ) Except as provided in appendix D, section 3, of this part, special VFR operations may be conducted under the weather minimums and requirements of this section, instead of those contained in 91.155, below 10,000' feet MSL within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport. (b) Special VFR operations may only be conducted--(1) With an ATC clearance...

However, the FAA failed to also change the similar wording of FARs 45.22(a)(3)(ii), 91.155(d), 91.303(c), 91.309(a)(4), 93.152, 101.33(a), 103.17, 107.41, 135.205(b), and 137.43(a), thus implying that none of these FARs should be understood to apply to any Class E airspace above 700' AGL in most cases, or above 1200' AGL in the remaining cases.

This blunder has never been officially corrected-- the text published in the October 5, 1993 edition of the Federal Register has never been officially retracted.

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  • $\begingroup$ Also, I have links to discussion forums where pilots report being given a similar answer-- that the phrase doesn't encompass any airspace above the base of the overlying E5 transition layer at 700' or 1200' AGL-- when they queried FAA officials about the meaning of FAR 103.17. Obviously not the mainstream interpretation-- otherwise most of the FARs listed above would make no sense at all-- consider especially 107.41-- $\endgroup$ – quiet flyer Feb 28 at 22:49
  • $\begingroup$ future edit - last sentence of first paragraph could be changed to end "or above 1200 feet in most remaining cases." $\endgroup$ – quiet flyer Mar 30 at 1:24
  • $\begingroup$ This answer would be improved by giving specific examples to support the first paragraph; some may be found in letters of interpretation. $\endgroup$ – quiet flyer Mar 30 at 12:38
  • $\begingroup$ This answer could be improved by phrasing third paragraph in a way that uses a word stronger than "implied" or else gives the full text to clearly show that this is clearly what they meant. $\endgroup$ – quiet flyer Mar 30 at 12:42
  • $\begingroup$ This answer would be improved by giving at least one other example, to support the use of the phrase ". On a few occasions". These answers could be simply cases where FSDO staffers presented such interpretations. $\endgroup$ – quiet flyer Mar 30 at 12:46

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