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21 Answers

Transponder requirements 91.215

Asked by: 36454 views , ,
FAA Regulations, Flight Instructor, Instrument Rating, Private Pilot

Would some settle this debate.  Is an Operable transponder with mode C required below a Class C shelf.  We all agree it's required within and above Class C, but what about class E or G airspace below the Class C shelf?

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21 Answers



  1. Brian on Feb 09, 2014

    No you do not need one under the shelf. Since you are under it, you are not in Class C airspace. There is no Mode C veil like Class B has. Hope this helps.

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  2. John D Collins on Feb 09, 2014

    Edit: After reading Kris and Mark’s comments, I agree with you Brian and the wish to retract the paragraph that follows:

    Brian, that is incorrect, a mode C transponder is absolutely required above and below the area of Class C airspace. Although there isn’t an equivalent to a Class B veil, there is an outer shelf for the Class C airspace, under which one is not “In the Class C”, and the area directly above the Class C where on is not “In the Class C”, but above it. These areas above and below the Class C require a mode C transponder based on the clear wording in the regulation.

    Here is what the regulation states in part::

    This requirement applies–
    (1) All aircraft. In Class A, Class B, and Class C airspace areas;
    (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; and
    (4) All aircraft in all airspace 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; and
    (5) All aircraft except 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—-
    (i) In all airspace of the 48 contiguous states and the District of Columbia at and above 10,000 feet MSL, excluding the airspace at and below 2,500 feet above the surface; and
    (ii) In the airspace from the surface to 10,000 feet MSL within a 10-nautical-mile radius of any airport listed in appendix D, section 2 of this part, excluding the airspace below 1,200 feet outside of the lateral boundaries of the surface area of the airspace designated for that airport.

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  3. tommytom on Feb 09, 2014

    John, I’m not meaning to argue the semantics of a word. Maybe I have something to learn here. You are right the regulation clearly states above class C and class B airspace is requiring a transponder. The topic of debate amongst my peers is in the wording “Lateral” boundaries.

    We all agree a transponder is required below a shelf in class B because one would be inside the mode C vail. Since class C contains a shelf, the shelf does not extend all the way to the ground. Below the shelf one is not in Class C airspace. Are you suggesting that below the shelf that one would be considered within the “lateral boundaries” of class C?

    Sounds like we are all split on what “lateral boundaries” mean in this reg.

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  4. Kris Kortokrax on Feb 09, 2014

    John,

    I’m guessing that you are referring to 91.215(b)(4).

    I believe that all the stated conditions must be met for a Mode C transponder to be required, i.e. one must be above the B or C and within the lateral boundaries.

    I would also say that one would be allowed to fly below the shelf of not only Class C, but also below the shelf of Class B if the Class B airport is not listed in Appendix D, Section 1.

    II don’t see any legal interpretations concerning this issue. It may take one to resolve the grammatical question.

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  5. Boiler on Feb 09, 2014

    I’ve always interpreted it as Kris does. If you think about it from the stand point of separating IFR and VFR traffic it makes sense to me that ATC would want to have an altitude readout for you if you were above the class C (I’m hypothetically imagining an F16 going vertical after takeoff) but if you’re below the class C I don’t imagine them wondering about you as much. I realize I’m oversimplifying here.

    I’m sure there are a good number of aircraft that aren’t equipped with mode C who operate to and from an airport located underneath a class C shelf. I’ve never heard of anyone being violated for such operations.

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  6. tommytom on Feb 11, 2014

    Well…… More confusing….. Check out Aim 4-1-20

    Mode C transpoder Requirements / (c) Within and above all class C airspace, up to 10,000 feet MSL. “Within the class C airspace”.

    If you think of class C airspace as Cylinders then there are 2 different size cylinders. Of course the bottom cylinders has a smaller diameter than the top. Therefore making it legal to fly under the shelf….

    Of course I would always teach a student that it’s not smart to fly under without a transponder.

    Doesn’t someone know a DE or somebody that can give a final ruling on this?

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  7. Kris Kortokrax on Feb 12, 2014

    DPEs cannot interpret regulations. Even FAA Inspectors cannot interpret regulations.

    A final ruling would need to come from the FAA’s Office of Legal Counsel.
    Even that ruling may be modified by an NTSB judge, full NTSB or a court.

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  8. Mark Kolber on Feb 12, 2014

    Actually, FAA Inspectors do interpret regulations every day. it’s just good to understand it’s not particularly binding and many times not particularly accurate. The three calls to the same FSDO and getting 3 different answers is standard fare. And if you’ve ever watched two FAA inspectors disagree on their interpretations of a rule during the enforcement process, you know it can be fun to watch.

    Back on topic, FWIW, the language of the reg appears pretty clear to me:

    ==============================
    This requirement applies –
    (1) All aircraft. In Class A, Class B, and Class C airspace areas;
    ***
    (4) All aircraft in all airspace 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; and
    ==============================

    (1) says “in” the Class C airspace.
    (4) says “above the ceiling and within the lateral boundaries”

    Below the shelf is definitely within the lateral boundaries but not above the ceiling.

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  9. tommytom on Feb 14, 2014

    In my research I’m finding that this isn’t the only time this has been debated.

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  10. William on Feb 25, 2014

    Is a transponder, mode A, required in class E and G more than 30 miles laterally from class B and C airports? Bill

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  11. tommytom on Feb 25, 2014

    Bill – I assume that your are asking if a Transponder is required beyond the Mode C Veil which is typically 30NM from a Class B airport. Answer: Depends on the Altitude. A transponder is required when at or above 10,000 MSL. So a transponder isn’t required in Class E and G airspace. ***However; Even if you were below 10,000 MSL a transponder is required above Class C and Class B airspace. In other words if you were flying outside of the Mode C Veil below 10,000 msl and above Class C or B airspace you would be required by FAR 91.215. to have a transponder.

    Thank you Bill for your question! I don’t know if you intended to ask your question to get me thinking about the transponder requirements below Class C airspace debate again. Your question has helped me to come to my own conclusion whether or not a transponder is required below Class C airspace.

    Answer to that is “YES”!

    Why: Because your question had me thinking about “aircraft not certified with an engine driven electrical system” I looked at FAR 91.215 again. So many times we look at the regulation at what applies only to us and we don’t bother looking and reading what doesn’t apply to us.

    When I read FAR 91.215 (3) is say’s that any aircraft that wasn’t originally certified with an engine driven electrical system may conduct operations in the airspace within 30 NM of an airport listed in Appendix D, Sect 1 provided such operations are conducted

    – Outside any Class A, B or C airspace area and

    -**** “Below” the altitude of the “ceiling” and “within” the lateral boundaries of a Class B or C airspace area designated for an airport “or” 10,000 msl, whichever is lower.

    If it’s OK one way then the opposite must be true. I interpret that the Reg is saying that the only time it’s “OK” to operate without a transponder below the Ceiling of Class C or B airspace is when you are operating an aircraft that was not originally certified with an engine-driven electrical system.

    This has taught me that when I struggle with the Reg’s to read the reg’s in its entirety and not skip past the parts that I think don’t apply to what I’m doing.

    Thanks again Bill!!!

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  12. tommytom on Feb 25, 2014

    What do you think about that Kris, John, Boiler and Mark?……….

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  13. tommytom on Feb 25, 2014

    By the way my tone is not meaning to be condescending but rather boastful….. : )

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  14. Mark Kolber on Feb 25, 2014

    The short answer is I think tommytom is misreading a little bit. (b)(3) is an exception to (b)(2). It authorizes certain aircraft to operate within the Mode C veil within certain limits. To read more into it than that is a mistake to begin with, especially when you start to use “reverse psychology” on the regs.

    And although I think tommytom is also misreading the “Below the altitude of the ceiling of a Class C airspace area designated for an airport” language, even if he is correct, we would only be talking about Class C airspace that is also within the Mode C veil, not Class C airspace generally.

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  15. Mark Kolber on Feb 25, 2014

    I didn’t think is was condescending at all.

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  16. tommytom on Feb 25, 2014

    You know what to say! A good pilot is always learning.

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  17. tommytom on Feb 25, 2014

    I meant “what they say”

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  18. tommytom on Feb 25, 2014

    Mark it’s clear that I misread a little bit. But if (b)(3) is an exception to (b)(2) then where in 91.215 does it state that an aircraft that is not originally certified with an engine driven electrical system has an exception to fly under a “general” class C airspace “outside” of the mode C veil?

    Are you pointing out that only when an aircraft is “within” the 30 nm veil is the only time an airplane (that is not originally certified with an engine driven electrical system) is exempt from having a transponder under class C airspace?

    Sorry I’m not meaning to argue but I just can’t sleep tonight until I ask that question.

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  19. Mark Kolber on Feb 26, 2014

    Arguments are fine. None of us have a monopoly on knowledge and disagreements can (should) be a starting point for further inquiry and positive learning experience for all involved.

    Let’s back up a minute. I think most of the confusion over the issue involves what is meant by the phrase Class C “airspace area designated for an airport.” That’s further confused by the fact that the FAA also uses the phrase “surface area designated for an airport.” Looking through the various Chief Counsel opinions on the subject, it looks like the confusion has bee in that group as well.

    Best I can do is refer to two Chief Counsel opinions from 2006.

    The Hucker opinion talks about the confusion in the context of the prohibition on aerobatic flight in certain airspace areas.

    The Knickerbocker opinion specifically discusses glider operations above Class C within the 30 NM veil and presents a couple of helpful scenarios.

    I could certainly be wrong but what I get out of these opinion letters is that when a reg refers to airspace “designated for an airport” it is referring to surface areas – airspace areas that go all the way to the ground – the inner circle of Class B and C, Class D airports and Class E to-the-ground airports.

    See what you get out of them.

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  20. tommytom on Feb 26, 2014

    Mark – Thank you for the information. I’ll dig in…

    If you haven’t guessed I’m that guy who asks lots of questions when I don’t understand something. I have been thanked for asking the questions that are on other peoples minds but too afraid to ask. (Not sure if that’s a compliment or not…)

    Let me know if I need to send a check in the mail for Ground School. Ha,ha,ha…

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  21. Gary S. on Jan 02, 2015

    On Feb. 12, 2014, Mark said, “Below the shelf is definitely within the lateral boundaries but not above the ceiling.”

    I disagree. Below the shelf of Class C is NOT within the lateral limits of Class C. Nor is it in Class C airspace. Like someone here alluded to, if it wasn’t for the Mode C veil a transponder may not even be required under a Class B (Bravo) shelf.

    So…I think we can all agree that because it is written “above Class C to 10,000′ msl…” that one must be ABOVE and not below the shelf when defining “lateral limits” and the requirement for the use of a Mode C transponder.

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