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3 Answers

Expired transponder check, VFR flight; combined transponder and ADS-B unit

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FAA Regulations

Greetings...

An aircraft that I rent often had its transponder and pitot-static checks expire as of 12/1; I was planning to fly the aircraft to work on some VFR maneuvers (I'm chipping away at a commercial rating mostly just to develop the stick and rudder skills) and at first I was pretty sure that I could complete the flight with the checks expired (VFR, not in any airspace that requires a transponder) but then I started looking at the regulations to see if it would be legal.  The answer that I came to was NO, but I'm curious if I've missed something obvious in parsing this out..

The aircraft has a GTX-345 in it, so it is a combined transponder and ADS-B out unit.  There would be no way to make the transponder inoperative but leave the ADS-B out piece functioning (and to be clear, I'd never choose to fly an aircraft with the transponder disabled simply because it was a few days expired -- but I'm looking for the by the book answer here)

I think that the relevant sections of the CFRs are:
  • 91.215 (ATC Transponder and Altitude reporting equipment and use)
  • 91.225 (ADS-B Out equipment and use)
  • 91.413 (ATC Transponder tests and inspections)
91.225 was an interesting one, and it's what put the kibosh on my thought that I could just disable the transponder and placard it inop.  91.225 paragraph (f) with some emphasis:
(f) Except as prohibited in paragraph (i)(2) [drones, N/A] of this section, each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times unless - [unless exceptions aren't applicable, text not included here]
So to me, this says that if you've got ADS-B out you MUST use it at all times (which was new information to me in general!  especially considering all the aircraft that have tailbeacons where the nav lights have to be on for ADS-B out to work.. I'd obviously run it anyway, but I didn't know it was required by regulation!)  That obviously rules out disabling the combined transponder/ads-b unit, since I'd then be in violation of 91.225.

91.215 and 91.413 are a little circular, but the paragraphs that grabbed me:
§ 91.413 ATC transponder tests and inspections.

(a) No persons may use an ATC transponder that is specified in 91.215(a), 121.345(c), or § 135.143(c) of this chapter unless, within the preceding 24 calendar months, the ATC transponder has been tested and inspected and found to comply with appendix F of part 43 of this chapter;
and
 
§ 91.215 ATC transponder and altitude reporting equipment and use.

(a) All airspace: U.S.-registered civil aircraft. For operations not conducted under part 121 or 135 of this chapter, ATC transponder equipment installed must meet the performance and environmental requirements of any class of TSO-C74b (Mode A) or any class of TSO-C74c (Mode A with altitude reporting capability) as appropriate, or the appropriate class of TSO-C112 (Mode S).
.....jumping to...
 
(c) Transponder-on operation. Except as provided in paragraph (e)(2) [not applicable] of this section, while in the airspace as specified in paragraph (b) of this section or in all controlled airspace, each person operating an aircraft equipped with an operable ATC transponder maintained in accordance with § 91.413 shall operate the transponder, including Mode C equipment if installed, and shall reply on the appropriate code or as assigned by ATC, unless otherwise directed by ATC when transmitting would jeopardize the safe execution of air traffic control functions.
So, to sum up what this looks like to me.. 91.225(f) tells me that I must use the unit if its installed due to ADS-B. 91.413(a) says that I CANNOT use the equipment if it hasn't had its 24 month checkup. 91.215(a) sets out the TSOs that the installed transponders must meet for all airspace, and 91.215(c) indicates that if I've got a maintained and operable transponder in the airplane I need to use it in all controlled airspace (which would include Echo).

At the end of the day, my determination was that I'd be breaking regulations to fly the aircraft unless I advised ATC ahead of time, or unless I were flying the aircraft to a facility to get the transponder checks done.  Have I interpreted things correctly, or am I missing something obvious?
 
Thanks!
 
Joe
 
 
 

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3 Answers

  1. Best Answer


    Bryan on Dec 08, 2021

    You’ve got a lot going on with that question and I think you got the right answer. 91.225(f) says if the aircraft has ADS-B installed, it has to be on…and the two exceptions are very narrow and would not apply to a VFR flight to practice maneuvers. I suppose you could uninstall the unit and get an ATC clearance to operate without ADS-B Out per 91.225(a), (b), or (d)…but that would just be silly.

    I want to point out two things though. First, you said, “I’d never choose to fly an aircraft with the transponder disabled simply because it was a few days expired.” While I can appreciate your desire to be safe, the regulations do not allow the use of a transponder that has not been inspected within the last 24 months because its signals may not be reliable. The FAA is literally saying here that they would prefer a disabled transponder to a potentially unreliable one.

    The second thing is that the two sections of 91.215 you cited don’t actually speak to your question about where can you fly without a transponder. You cited 91.215(a). That just talks about the performance and environmental requirements of different transponder modes. You also mentioned 91.215(c). That just says if you’re using a transponder, you have to punch in whatever squawk code ATC gives you. Neither informs usage based on airspace, altitude, etc.

    The section that answers the question about where you can fly without an operable transponder is 91.215(b) which says you cannot operate in any airspace described in (1)-(5) “unless the aircraft is equipped with an operable coded radar beacon transponder…” The relevant parts of (1)-(5) are Class A, B, and C airspace, mode C veil 30 NM around certain airports, and all airspace above any part of Class B and C airspace. Thus, you can fly without a transponder in Class D, E, and G airspace that is not inside a mode C veil or above Class B or C airspace. But as you adeptly pointed out, if the transponder is off, so is the ADS-B Out so 91.225(f) rains the whole game out unless you have something else on-board that transmits ADS-B Out.

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  2. histriosum on Dec 09, 2021

    Thanks for the answer Bryan! One quick clarification on 91.215(c):

    > You also mentioned 91.215(c). That just says if you’re using a transponder, you have to punch in whatever squawk code ATC gives you. Neither informs usage based on airspace, altitude, etc.

    Isn’t 91.215(c) more broad than that? In particular, this language sticks out to me: “…while in the airspace as specified in paragraph (b) of this section or in all controlled airspace, each person operating an aircraft equipped with an operable ATC transponder maintained in accordance with § 91.413 shall operate the transponder…”

    The keys there to me are “OR in all controlled airspace”, which would clearly cover class E. It reads to me as though 91.215(c) is saying that if you have a transponder on board and it’s maintained according to 91.413, you SHALL operate it in all controlled airspace unless otherwise advised by ATC.

    That obviously wouldn’t have much bearing on the situation I outlined, since the transponder in question is no longer in compliance with 91.413 and so it must NOT be operated. It’s interesting to me, though, that 91.215(c) appears to require transponder use if installed and maintained (kind of similar in spirit to the ADS-B requirement in 91.225) — that definitely wasn’t what I was taught in ground school..

    Thanks much for the second set of eyeballs and your thoughts!
    Joe

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  3. Bryan on Dec 10, 2021

    I think you’re right about 91.215(c).

    As for what you were taught in ground school, a lot has changed fairly recently. Notice most of 91.225 is as of January 1, 2020. So depending on how long ago ground school was, you may not have learned it wrong–it just changed since you learned it.

    Bryan

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