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Clarification: this question was intended to address the situation before FAR 91.225 went into effect; please answer accordingly. Feel free to also add additional content addressing the present situation now that FAR 91.225 has gone into effect.

Here are some of the airspaces where FAR 91.215 requires aircraft to have transponders--

(b) ...

(2) All aircraft. In all airspace within 30 nautical miles of an airport listed in appendix D, section 1 of this part from the surface upward to 10,000 feet MSL;

(3) Notwithstanding paragraph (b)(2) of this section, any aircraft which was not originally certificated with an engine-driven electrical system or which has not subsequently been certified with such a system installed, balloon or glider may conduct operations in the airspace within 30 nautical miles of an airport listed in appendix D, section 1 of this part provided such operations are conducted -

(i) Outside any Class A, Class B, or Class C airspace area; and

(ii) Below the altitude of the ceiling of a Class B or Class C airspace area designated for an airport or 10,000 feet MSL, whichever is lower;

Question 1: May an aircraft with no engine-driven electrical system and no transponder operate at 10,500' MSL in the airspace 10 miles west of South Valley Regional airport (U42) near Salt Lake City, where the overlying Class B shelf has a floor at 11,000', and a ceiling at 12,000' MSL? [(Link to sectional chart.)] 2

Note that KSLC is one of the airports listed in the Appendix referenced in FAR 91.215(b)(ii)-- this is a reference to the Mode C veil.

Question 2: May the same aircraft operate at 17,500' at the same location?

Question 3: (only applicable if the answers to (1) and (2) are both "yes")-- Does the "or below 10,000' MSL" clause of FAR 91.215(b)(3)(ii) have any actual practical significance of any kind? What is an example of some airspace where an aircraft with no engine-driven electrical system and no transponder may not operate, but would be able to operate if the "or below 10,000' MSL" clause were absent from FAR 91.215(b)(3)(ii)?

Note that FAR 91.215(b)(3) is simply an exemption to 91.215(b)(2), which appears to only apply up to 10,000' MSL, so it appears at first glance that the answers to the questions ought to be "yes", "yes", and "no". Is this really correct?

Question 4: What is the horizontal area affected by FAR 91.215(b)(3)(ii)? Is an aircraft without a transponder flying below 10,000' MSL supposed to stay below the altitude of the ceiling of any Class B or Class C airspace designated for an airport that happens to be within the 30-nm Mode C veil, even if the aircraft is horizontally distant from any portion of that airspace? If so, what if there is more than one than one such airport, and they have different ceilings?

Question 5: Does FAR 91.215(b)(3)(ii) have any practical significance of any kind at all? Would it ever affect where any aircraft may operate?

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  • $\begingroup$ Aren't the jets allowed to really ratchet up their speed above 10,000? Like the 250 knot limitation goes away? I don't think the FAA/ATC wants some small plane puttering along that they don't know about and having it be run over by something fast. $\endgroup$
    – CrossRoads
    Commented Jun 25, 2019 at 15:37
  • $\begingroup$ These links don't consistently display well. Have I used a format that is no longer supported? $\endgroup$ Commented Feb 10, 2023 at 19:11
  • $\begingroup$ Related: aviation.stackexchange.com/questions/74857/… $\endgroup$ Commented Feb 12, 2023 at 12:01
  • $\begingroup$ "Significance of" might better read "meaning of". Re question 3: the clause is actually " "or (below) 10,000' MSL, whichever is lower". This question really needs actual images from the sectional charts. glider and balloon tags could be added, as they rarely have transponders. $\endgroup$ Commented Feb 14, 2023 at 6:27

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The answers to Questions 1,2, and 3 are "yes", "yes", and "no". Neither FAR 91.215(b)(2) nor FAR 91.215(b)(4) have any effect above 10,000' MSL.

The "or below 10,000' MSL" clause in 91.215(b)(3)(ii) has no effect on anything at all and does not prevent an aircraft not certificated with an engine-driven electrical system from operating above Class B or Class C airspace as long as it is above 10,000' MSL.

The answer to question 4 is "no, an aircraft that is completely outside of the lateral boundaries of a given Class B or Class C airspace cannot be violating FAR 91.215(b)(3) in relation to that airspace, regardless of altitude."

All of this is clarified in this 2006 interpretation from the FAA Office of the Chief Counsel:

Section 91.215 does not prohibit gliders or sailplanes not equipped with transponders from operating above 10,000 feet MSL and thus above the ceiling of and outside Class B airspace.

and

"The practical effect of paragraph (b)(3) with respect to your question is that it allows non-equipped aircraft to enter the 30-nautical mile circles surrounding Appendix D, Section 1 airports between the surface and 10,000' MSL and to operate beneath the floors of the associated Class B airspace..."

and

In the context of your question, subparagraph (b)(4) would prohibit an unequipped glider or sailplane from operating in the ‘wedge’ of airspace that may exist directly above Class B or Class C airspace and below 10,000 feet MSL. If the ceiling of the Class B or Class C airspace is at 10,000 feet MSL, then subparagraph (b)(4) is rendered moot.

The answer to question 5 therefore appears to be "regardless of the actual wording, FAR 91.215(b)(3)(ii) should simply be interpreted as an indication that 91.215(b)(3) does not give relief from 91.215(b)(4), which requires a transponder for flying "above the ceiling and within the lateral boundaries of a Class B or Class C airspace area designated for an airport upward to 10,000 feet MSL". Meaning that even aircraft not certified with engine-driven electrical systems are not exempt from the transponder requirement in the airspace directly above Class B and C ceilings, up to 10,000' MSL. In other words, there is an unstated implication that 91.215(b)(3)(ii) does not apply to any airspace that lies beyond the lateral boundaries of Class B or Class C airspace. This could have been more clearly accomplished by other means, for example by replacing the text of 91.215(b)(3)(ii) with the simple phrase "clear of the airspace described in 91.215(b)(4)".


However...

  1. It's important to note that the fundamental reason that FAR 91.215(b)(3)(ii) has no effect on anything that happens above 10,000' MSL is that 91.215(b)(3)(ii) is spelling out the terms under which certain aircraft can operate contrary to 91.215(b)(2), and 91.215(b)(2) explicitly has no effect on any airspace above 10,000' MSL.

  2. As a thought experiment, we can ask ourselves "If 91.225 had never been introduced, but 91.215(b)(2) were modified tomorrow to extend up to 15,000' MSL, then is there anything either in the literal language of 91.215(b)(3)(ii), or in the logic used in the 2006 interpretation referenced above, that would allow aircraft (not certificated with engine-driven electrical systems) lacking transponders to fly in any of the airspace below 15,000' directly above the ceiling of Class B or Class C airspace that lies within a Mode C veil?" The answer appears to be "No, all the airspace between the Class B or Class C ceiling and 15,000' MSL would be off-limits to such an aircraft in that case." The point being that since 91.215(b)(2) doesn't apply above 10,000' MSL anyway, the 2006 interpretation shouldn't be read to construe that language used in 91.215(b)(3)(ii) inherently could never affect airspace above 10,000' MSL, and there's nothing in the actual language of 91.215(b)(3)(ii) that indicates that either.

  3. In fact, by similar logic, the 2006 interpretation doesn't even unambiguously indicate that the "or (below) 10,000' MSL, whichever is lower" portion of the language of 91.215(b)(3)(ii) inherently should never be construed to apply to any airspace that does not directly overlie a Class B or Class C ceiling. After all, if the "or (below) 10,000' MSL, whichever is lower" portion of the language used in 91.215(b)(3)(ii) were construed to apply to all airspace, even airspace outside the lateral boundaries of any nearby Class B or Class C airspace, this would simply mean that pilots who are using 91.215(b)(3)(ii) as a way to operate contrary to 91.215(b)(2) would have to stay below 10,000' MSL, and 91.215(b)(2) doesn't apply above 10,000' MSL anyway, so above that altitude the point is moot.

  4. All this has unfortunate consequences for the clarity, or lack thereof, of the newer FAR 91.225, the ADS-B-out requirement, which unfortunately has incorporated language identical to that used in 91.215(b)(3)(ii).

  5. The specific issue is FAR 91.225(d)(4), which explicitly does apply to airspace above 10,000' MSL. It's unclear exactly how aircraft (not certificated with engine-driven electrical systems) operating above 10,000'MSL and 2,500' AGL without ADS-B-out can be construed to be in compliance with FAR 91.225(e)(2) in any of this airspace, and particularly in the portions that lie directly above the ceilings of Class B or Class C airspace.

  6. For more, see the related ASE question Does the FAA construe FAR 91.225 to prohibit aircraft w/o electrical systems w/o ADS-B-out from flying above 10,000' MSL unless below 2500' AGL?

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  • $\begingroup$ Related: aviation.stackexchange.com/questions/74857/… $\endgroup$ Commented Feb 12, 2023 at 12:02
  • $\begingroup$ (sorry, saw something else that had to fix, that's all for today) $\endgroup$ Commented Feb 12, 2023 at 14:15
  • $\begingroup$ RE just before the "However" section-- the statement "In other words, there is an unstated implication that 91.215(b)(3)(ii) does not apply..."-- could perhaps be better stated "...there is an unstated implication that 91.215(b)(3)(ii) does not restrict any a/c from flying in any airspace that lies beyond the lateral boundaries of Class B or Class C airspace, at least if that airspace lies below 10,000' MSL. $\endgroup$ Commented Feb 12, 2023 at 18:01
  • $\begingroup$ (ctd) ... The horizontal extent of the area that would be affected by the "or (below) 10,000 MSL, whichever is lower" portion of the language of 91.215(b)(3)(ii) is arguably a little less clear, except for the fact all of the airspace affected by 91.215(b)(2) lies below 10,000' MSL, so anything above that is a moot point anyway and can never be affected by 91.215(b)(3)(ii). Also: bullet point 3: replace "portion of the language" with "phrase in the language." $\endgroup$ Commented Feb 12, 2023 at 18:17
  • $\begingroup$ Or "should only be understood to restrict a/c from flying in airspace that lies directly above... " $\endgroup$ Commented Feb 13, 2023 at 11:53

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