FAA Aviation Mechanic General (AMG)Regulations, Records and Human FactorsEasy
A single-engine airplane operated under IFR in controlled airspace has a functioning ATC transponder installed. According to 14 CFR 91.413, how often must the transponder system be tested and inspected?
- AOnly when the transponder malfunctions
- BEvery 12 calendar months
- CEvery 100 hours of time in service
- DEvery 24 calendar months
Show answer & explanationAnswer & explanation
Correct answer: D. Every 24 calendar months
14 CFR 91.413 requires that the ATC transponder system be tested and inspected in accordance with Part 43, Appendix F, at intervals not exceeding 24 calendar months, similar to the altimeter/static system requirement in 91.411.
Why the other options are wrong
- A. A scheduled periodic test is required regardless of reported malfunctions.
- B. 12 calendar months is the annual inspection interval, not the transponder test interval.
- C. The interval is based on calendar time, not hours of operation.
91.413 Transponder Test
14 CFR 91.413 requires ATC transponders to be tested and inspected per Part 43 Appendix F at intervals not exceeding 24 calendar months for operation in controlled airspace requiring a transponder.
- Same 24-month interval applies to altimeter/static system checks under 91.411
- Test must be performed by an appropriately certificated repair station, or the manufacturer
- Required for operations in most controlled airspace per 91.215
Memory trick: 'Transponder & Altimeter: Two-Year Twins' — both use 24-month cycles.