14 CFR § 91.413

What does 14 CFR § 91.413 require?

14 CFR 91.413 is the 24-calendar-month recurrent test for any aircraft that has an ATC transponder installed and operates in airspace where §91.215 (or the parallel Part 121 / Part 135 transponder rules) requires the transponder to be on. §91.215 mandates an operating transponder in Class A, Class B, and Class C airspace, in all airspace above 10,000 ft MSL (excluding airspace at and below 2,500 ft AGL), within 30 nautical miles of a Class B primary airport (the Mode-C veil), and in other listed locations — so §91.413 indirectly applies to most powered IFR + most VFR-in-busy-airspace operations. The test must comply with Appendix F to Part 43 (mandatory test procedure: bench test of the transponder if equipment type requires removal, ramp test of the installed transponder, encoder + altimeter correlation within 125 feet, suppression + reply rate + sensitivity tolerances). Sign-off is restricted: an FAA-certificated repair station with appropriate ratings, a Part 121 / Part 135 certificate holder with an approved continuous airworthiness program, or the manufacturer is required. The 24-calendar-month expiration follows the same end-of-month convention as §91.411 + §91.409; most operators couple §91.413 with the §91.411 altimeter + static test on the same avionics-shop visit because the integrated altimeter + encoder + transponder loop is exercised in either test.

Who must comply with 14 CFR § 91.413?

All operators of aircraft with an ATC transponder installed that operate in airspace where §91.215 (or §121.345(c) or §135.143(c)) requires the transponder to be on. §91.215 mandates an operating transponder in: Class A airspace (above 18,000 ft MSL), Class B airspace + the Mode-C veil (30 NM from Class B primary airport surface to 10,000 ft MSL), Class C airspace + 10 NM lateral within 4,000 ft AGL of Class C primary airport, all airspace above 10,000 ft MSL excluding airspace at and below 2,500 ft AGL, and within 30 NM of designated Class B primary airports. In practice, this captures virtually all IFR operations + most VFR operations in or near terminal airspace + all operations above 10,000 ft MSL — so §91.413 applies broadly across Part 91 private + business + corporate, Part 135 commuter + on-demand, and Part 121 air carriers. Aircraft with no installed transponder are not subject to §91.413 (the rule conditions on equipage). Operations in airspace where §91.215 does not require an active transponder + the operator chooses not to use the transponder are not in the operational scope of §91.413, but most operators maintain currency as a practical matter to preserve airspace flexibility.

What happens if you violate 14 CFR § 91.413?

FAA civil penalties typically $1,500–$25,000 for operating in §91.215 airspace with an expired §91.413 test; higher for repeat or willful, or where the operation contributed to an airspace incursion or TCAS incident. The PIC's §91.7 airworthiness determination is also deficient by extension — a transponder that has not been tested in accordance with Appendix F within the preceding 24 calendar months is not in compliance with applicable airworthiness requirements, so any flight through §91.215 airspace creates a parallel §91.7 citation risk. Airman certificate suspension is possible, particularly where logbook records make the overdue test plainly visible. Insurance carriers commonly void coverage on incidents that occurred while §91.413 was overdue. Aircraft can continue to operate in airspace where §91.215 does not require transponder use, but cannot lawfully accept a clearance or transit airspace that triggers §91.215.

How to comply (implementation checklist)

1. 1Track the §91.413 expiration as the last day of the 24th calendar month after the most recent §91.413 sign-off; quarterly reminders 90 + 60 + 30 + 7 days out so a flight into §91.215 airspace is never planned against an expired test.
2. 2Couple the §91.413 ATC transponder test with the §91.411 altimeter + static + altitude-reporting test on the same shop visit — both are 24 calendar months, both restrict sign-off to the same categories of certificated personnel, and the avionics shop is exercising the integrated altimeter + encoder + transponder loop in either test; coupling saves a second downtime + ferry + shop labor charge.
3. 3Verify the §43.9 logbook entry contains: date, total time in service, the words '§91.413' or 'ATC transponder test', the next due date (24 calendar months out, end-of-month), the repair station certificate number + ratings (or Part 121 / 135 program reference), the technician signature, and the Mode capability tested (Mode A, Mode C, Mode S, ADS-B Out where applicable).
4. 4Confirm the test procedure complies with Appendix F to Part 43 — reply rate, sensitivity, suppression, Mode-S address, encoder + altimeter correlation within 125 feet, and antenna pattern check where required by equipment type. Request the shop's data sheet showing each tolerance band met.
5. 5Decide bench-test vs ramp-test cadence per the transponder manufacturer's service manual — equipment types that recommend periodic bench testing should be scheduled accordingly even if ramp-test indications are nominal. Document the bench-vs-ramp decision in the §43.9 entry.
6. 6Cross-check encoder + altimeter correlation against the §91.411 altimeter test result — the encoder must agree with the pilot's altimeter within 125 feet across the tested altitude range. If the §91.411 test was performed under a higher maximum altitude rating, confirm the §91.413 encoder correlation was tested across the same range.
7. 7Do not accept a clearance or transit airspace requiring §91.215 transponder use while §91.413 is overdue; operate outside §91.215 airspace until the test is completed and a fresh §43.9 logbook entry is recorded. The cheapest course of action is staying out of §91.215 airspace, not flying overdue.

Common misinterpretations

• Misinterpretation: '24 months means 730 days from the test date.' Reality: §91.413(a) uses the 24 calendar months convention used throughout Parts 91 + 135. If the §91.413 test was performed on April 8, 2026, it is valid through April 30, 2028 — the last day of the 24th calendar month — not through April 8, 2028. The expiration is end-of-month, identical to §91.411 + §91.409.
• Misinterpretation: '§91.413 is the same rule as §91.411 — one test covers both.' Reality: §91.411 covers the altimeter system + static system + automatic pressure altitude reporting equipment (the encoder); §91.413 covers the ATC transponder itself. Both are 24 calendar months, both require Appendix-to-Part-43 procedures (Appendix E for §91.411, Appendix F for §91.413), and both restrict sign-off to repair stations + Part 121 / 135 holders + the manufacturer — but they are legally distinct. Each requires its own §43.9 logbook entry, each has its own 24-calendar-month cadence, and an aircraft with a current §91.411 but expired §91.413 is still ineligible to operate in §91.215 airspace.
• Misinterpretation: 'Appendix F to Part 43 is a recommended procedure — the avionics shop's process is good enough.' Reality: §91.413(b) makes Appendix F to Part 43 the mandatory test procedure. Appendix F specifies bench-test + ramp-test procedures, reply rate, sensitivity, suppression, encoder + altimeter correlation (within 125 feet), and Mode-S address verification tolerances. The shop's process may exceed Appendix F, but cannot substitute for it. Logbook entries must reflect Appendix F compliance — not a vendor-specific procedure that omits required tolerances.
• Misinterpretation: 'A ramp test is always sufficient — bench testing is optional.' Reality: Appendix F to Part 43 distinguishes between ramp testing (test set connected to the installed antenna or via test antenna) and bench testing (transponder removed from the aircraft and connected directly to the test equipment). Some equipment types + ATC equipment manufacturers' service manuals require periodic bench testing — particularly when ramp-test indications suggest internal sensitivity or reply-rate degradation. Operators who never bench-test risk Appendix F non-compliance even with a current §43.9 entry; the avionics shop's test plan should reflect the equipment manufacturer's recommended interval for bench vs. ramp testing.

Real enforcement examples

Anonymized from public FMCSA enforcement summaries. Penalty amounts reflect assessed and final settled values where disclosed.

Frequently asked questions

Related regulations