# 14 CFR 91.413: Transponder tests and inspections

> Any transponder required by 91.215 must have been tested and inspected within the preceding 24 calendar months. It also needs a new test after installation or maintenance that could introduce a data correspondence error.

Source: https://www.aerscheduler.com/regulations/91-413
Official text: https://www.ecfr.gov/current/title-14/section-91.413 (eCFR, current as of 2026-10-15; section last amended 2016-12-30)

## In plain English

- A transponder required under 91.215 must pass the Part 43 Appendix F test every 24 calendar months. [(a)](https://www.aerscheduler.com/regulations/91-413#a)
- Installing or working on the transponder in a way that could create a correspondence error needs the Appendix E integrated test. [(b)](https://www.aerscheduler.com/regulations/91-413#b)
- The test is done by a suitably rated repair station, an air carrier's continuous airworthiness program, or the aircraft manufacturer if it installed the transponder. [(c)](https://www.aerscheduler.com/regulations/91-413#c)

## Common questions

**Is the transponder check the same as the pitot-static check?**

They are different checks on the same 24-calendar-month cycle, which is why shops usually do them together. The transponder check applies whenever the transponder is required, including VFR flight; the pitot-static check in 91.411 applies to IFR.

**Can an A&P sign off the transponder check?**

No. Paragraph (c) lists repair stations with the right radio rating, certain air carrier programs and the manufacturer. A mechanic's certificate alone is not on the list.

## Official text of 14 CFR 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

(b) Following any installation or maintenance on an ATC transponder where data correspondence error could be introduced, the integrated system has been tested, inspected, and found to comply with paragraph (c), appendix E, of part 43 of this chapter.

(c) The tests and inspections specified in this section must be conducted by:

  (1) A certificated repair station properly equipped to perform those functions and holding:

    (i) A radio rating, Class III;

    (ii) A limited radio rating appropriate to the make and model transponder to be tested;

    (iii) A limited rating appropriate to the test to be performed;

  (2) A holder of a continuous airworthiness maintenance program as provided in part 121 or § 135.411(a)(2) of this chapter; or

  (3) The manufacturer of the aircraft on which the transponder to be tested is installed, if the transponder was installed by that manufacturer.

## Related

- [14 CFR 91.411: Altimeter and pitot-static checks for IFR](https://www.aerscheduler.com/regulations/91-411.md)
- [14 CFR 91.225: ADS-B Out: where it is required](https://www.aerscheduler.com/regulations/91-225.md)
- [14 CFR 91.409: Annual and 100-hour inspections](https://www.aerscheduler.com/regulations/91-409.md)

AerScheduler tracks the annual, 100-hour, transponder, pitot-static, ELT and VOR checks by hours and calendar months, and takes an aircraft off the schedule when its annual lapses. [https://www.aerscheduler.com/features/inspections](https://www.aerscheduler.com/features/inspections)

_The plain-English summary is AerScheduler's reading of the rule, not legal advice. The official text above is the eCFR's, published by the Office of the Federal Register; the eCFR is the current text._