Are experimental aircraft exempted from the 2 year verification test for avionics, transponder and altitude encoder? Or must they comply?

  • 2
    $\begingroup$ Which legislation? $\endgroup$
    – DeltaLima
    Jul 2, 2017 at 9:05
  • 1
    $\begingroup$ What's BL? Are you asking about the regulations under FAR 91.411 and 91.413? $\endgroup$
    – Simon
    Jul 2, 2017 at 9:36

1 Answer 1


When you operate in airspace that is under FAA regulations, FAR 91 applies (unless you are flying military)

FAR 91.413 a) states:

(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;

So when you haven't performed the two year transponder check, you are not allowed to use the transponder. The way to fly then is to fly VFR in airspace where no transponder is required AND not to use the transponder at all.

This is not specific to experimental aircraft, there is no exemption.

There is good reason not to have an exemption for experimental aircraft; a malfunctioning transponder can cause many problems to the ATC radar systems.

  • $\begingroup$ If you have a transponder installed, it must be turned on (except in Class G airspace) §91.215 (c) Transponder-on operation. 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 of this part shall operate the transponder, including Mode C equipment if installed, and shall reply on the appropriate code or as assigned by ATC. $\endgroup$
    – JScarry
    Sep 7, 2018 at 15:33
  • 1
    $\begingroup$ @JScarry According to §91.215(c) the transponder must be turned on if it is maintained in accordance with §91.413. The case that is being discussed here is when the transponder is not maintained in accordance with §91.413. $\endgroup$
    – DeltaLima
    Sep 7, 2018 at 15:47
  • $\begingroup$ You stated that if you fly in airspace where it is not required then you can turn it off. That is not true. If you have a transponder, it must be maintained and turned on. You can’t fly in controlled airspace with it turned off or not maintained. An interesting loophole is that if it was inspected and subsequently fails, you can turn it off and fly in controlled airspace. $\endgroup$
    – JScarry
    Sep 7, 2018 at 16:27

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