Just a little confused on a reg. 91.215 (b) (4) makes mention of having to have mode C above the ceiling and within the lateral boundaries of class B or C. Do they mean if you're above AND within the lateral limits, or are they mutually exclusive? Curious if you really need a mode C to underfly a class C shelf. Didn't think so but I find the wording a little confusing.
Transponder under class C
- Thread starter JordanD
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rframe
pǝʇɹǝʌuı
I interpret lateral boundaries as meaning altitude doesn't matter, if there's a class C line you cannot cross it without a transponder. From a practical point of view I think that makes sense. If I dont have a transponder how does ATC know I'm below the shelf? They dont so they'd have to separate their traffic from me as if we were a the same altitude. At least that's what I think.
Right, that was my thought, but the interpretation seems a little grey to me. Big surprise!
ozziecat35
4 out of 5 great lakes prefer Michigan.
That was one of my dpe's "gotchas" during my Commercial ride...I said yes you needed a transponder, she said no...but agreed that it would be safer.
Hammertime
Well-Known Member
What be this interpretation you refer to?
I agree with rframe's answer. Both safety and a careful reading of the reg seem to imply that you need Mode C below the shelf.
"91.215 ATC transponder and altitude reporting equipment and use.
...
(b) All airspace. Unless otherwise authorized or directed by ATC, no person may operate an aircraft in the airspace described in paragraphs (b)(1) through (b)(5) of this section, unless that aircraft is equipped with an operable coded radar beacon transponder...
(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..."
My interpretation is that the "airspace area" listed in b(1) refers to within, and "within the lateral boundaries" listed in b(4) would imply above and below
Hammertime
Well-Known Member
Hmmm. It would be interesting to get some input from a fed. Given that the AIM is advisory, and 4-1-20 begins with a statement along the lines of "refer to 91.215 for a more specific description of these general guidelines," I'm not entirely convinced. While the wording in the reg is vague, to me a correct parsing of the sentence would imply below as well as above. Plus, there's the obvious commonsense fact that an approach controller would flip his lid if you were wandering around 6 or 7 miles out at 1000' AGL with no Mode C. As far as the AIM goes, well it wouldn't be the first time the FAA has published a handbook or manual that's downright wrong... When they rewrote the Instrument Flying Handbook 2-3 years back, it was a disaster.
JustinS
Well-Known Member
Considering how widely it is taught and practiced for so long, it would seem the AIM is correct on this issue. The AIM may not be regulatory, but it gives us guidelines for how to operate within the confines of the FARs.
I'm still doing some research on this issue. Through lots of googling though, it is widely taught "in and above" for Class C airspace. From reading the regulation itself though, it does leave the question. Just by going off the AIM I would say you don't need it below, and I think that would hold a lot of water when going up against the FAA if they tried to violate you.
Why? The wording is clear. You just read the bold and ignored the underline I've conveniently added.
PS The AIM is regulatory if it refers to interpretation of regulatory material. Otherwise it's advisory.
Hammertime
Well-Known Member
Why? The wording is clear. You just read the bold and ignored the underline I've conveniently added.
PS The AIM is regulatory if it refers to interpretation of regulatory material. Otherwise it's advisory.
Uh, the discussion was never about the airspace above the Class C. It was about whether the "within the lateral boundaries" line referred to the airspace BELOW the shelf.
BTW, thanks JustinS for pointing me to the AIM. It certainly appears clear there.
I understand the question, that's why I underlined the words "airspace above the ceiling." The regulation clearly reads above and within. The AIM clarifies. What I don't understand is the confusion here.
Perhaps it would be more helpful to explain why I say the regulation is clear. Here:
b(4) All aircraft in all airspace above the ceiling and within the lateral boundaries.
The conjunction 'and' is where the regulation becomes clear. If the conjunction used was 'or' then it could be argued that the reference is both to above and below. Then again the regulation would be redundant if that wording were chosen. In other words, if the intent was for the meaning to be above and below the regulation would need only to read "All aircraft within the lateral boundaries of..."
The long and short of it is the regulation is saying above the ceiling AND within the lateral boundaries.
b(4) All aircraft in all airspace above the ceiling and within the lateral boundaries.
The conjunction 'and' is where the regulation becomes clear. If the conjunction used was 'or' then it could be argued that the reference is both to above and below. Then again the regulation would be redundant if that wording were chosen. In other words, if the intent was for the meaning to be above and below the regulation would need only to read "All aircraft within the lateral boundaries of..."
The long and short of it is the regulation is saying above the ceiling AND within the lateral boundaries.
Agreed. The Regulation's use of the word "AND" means that BOTH of the conditions listed must be met therefore and airplane must be "Above" AND "Within the lateral boundaries."
Beyond BELOW the airspace but within the lateral boundaries is the same as being above the airspace but beyond the lateral boundaries. In both of these situations, you lose one of the two requirements that are needed to be required to operate a Mode C Transponder.
The same applies to Class Bravo airspace protruding beyond the 30 NM Mode C Veil (Atlanta for example). You need it above and in, but not below (again, if you are below the bravo airspace but OUTSIDE of the mode C veil.
KSCessnaDriver
Well-Known Member
Unless you have an aircraft that was built without an electrical system. Then the mode C veils mean nothing, just stay below the bravo.