FAR 91.409, 91.411, 91.413 — Annual, Altimeter, Transponder Checks Explained

Three regulations. Six calendar dates to remember. Most owners can quote you the first one and have to look up the other two. Here's the field-guide version of all three — with what gets logged, who can sign it off, and what happens if you fly without one current.

TL;DR — the cheat sheet

| Regulation | What it requires | Interval | Who signs |

|---|---|---|---|

| 91.409(a) | Annual inspection | 12 calendar months | IA |

| 91.409(b) | 100-hour inspection (only if for hire / instruction) | Every 100 hours tach time | A&P (does not need IA) |

| 91.411 | Altimeter, encoder, static system check (IFR only) | 24 calendar months | Repair station (some A&Ps with cert) |

| 91.413 | Transponder check (all aircraft with one installed) | 24 calendar months | Repair station |

If any one of those is out of date and you fly, you're not airworthy. (Yes — even the transponder check on a VFR-only airplane that flies with a working transponder installed.)

91.409(a) — Annual inspection

> "no person may operate an aircraft unless, within the preceding 12 calendar months, it has had an annual inspection..."

The big one. Calendar-month math: if it's signed off on March 17, 2025, you're good through March 31, 2026. You don't lose the rest of March because the inspection was mid-month — the clock rounds UP to the end of the calendar month.

Who signs: Only an A&P holding Inspection Authorization (an "IA"). Some IAs are independent; some work for FBOs; some come on-site. Average rate runs $95–$135/hr for the inspection labor in 2026. See our [annual inspection cost ranges](/blog/aircraft-annual-inspection-cost-2026) for what 12 common GA airframes typically run.

What gets logged: An entry in the airframe logbook with the IA's certificate number, the date, the tach/Hobbs at inspection, and the exact phrase _"I certify that this aircraft has been inspected in accordance with an annual inspection and was determined to be in an airworthy condition."_ (Per FAR 43.11.)

Where owners get burned: Buying an aircraft mid-annual cycle. If the previous owner's annual was March 2025 and you buy in October 2025, your next annual is due March 31, 2026 — five months after you take possession.

91.409(b) — 100-hour inspection

Only applies if the aircraft is used for hire OR for flight instruction (where the school provides the airplane). If you're a private owner who never rents the airplane out, you don't track this.

Who signs: A regular A&P — no IA required.

The 10-hour overrun rule: You can exceed the 100-hour interval by up to 10 hours, BUT only if necessary to reach a place where the inspection can be done. Those overrun hours come off your next 100-hour interval. (Per FAR 91.409(b)(1).)

91.411 — Altimeter, encoder, static system check

> "no person may operate an airplane, or helicopter, in controlled airspace under IFR unless ... within the preceding 24 calendar months, each static pressure system, each altimeter instrument, and each automatic pressure altitude reporting system has been tested..."

Required for: IFR flight in controlled airspace. If your aircraft is VFR-only (or even IFR-capable but you fly only VFR), 91.411 doesn't apply to you.

What gets tested: static-system leak rate, altimeter accuracy through the operating altitude range, automatic altitude reporting (mode-C / mode-S encoder).

Who signs: A certified repair station with the right ratings — usually an avionics shop. Some A&Ps with specific certifications can sign the static-system portion; the altimeter and encoder generally require the repair station.

Where it's logged: Both the airframe logbook AND the avionics logbook (if you keep them separately). Should include the test results, the certifying technician, and the certificate number of the repair station.

Cost in 2026: $180–$320 for the 91.411 work alone, usually bundled with 91.413 as a combined "pitot-static / transponder check" for $300–$500 total.

91.413 — Transponder check

> "no person may use an ATC transponder ... that has been installed in an aircraft ... 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..."

Required for: Any aircraft with a transponder installed — whether or not you ever turn it on. (If you have one, it must be current.)

Combined with 91.411: Almost always done in the same visit. The 24-month clocks aren't required to be synchronized, but most shops align them so the owner makes one trip every two years.

Who signs: Certified repair station. Same paper trail as 91.411.

Real owner pitfalls

"I'm VFR-only — do I really need the transponder check?"

Yes, if a transponder is installed. The reg attaches to the transponder being installed, not to the flight rules you use.

"We let the annual lapse by 8 days — does the prior annual still count?"

No. The aircraft is non-airworthy starting on the first day of the month AFTER the inspection month ended. There is no grace period in 91.409. You'd need a ferry permit to fly to a shop for a new annual.

"My 91.411 is good through October but my 91.413 expired in July — can I fly IFR?"

No. You also can't fly with the transponder turned on (any flight rules). Realistically, you can't fly an aircraft with a transponder installed AT ALL until 91.413 is current. (You can request the transponder be physically removed and the panel placarded INOP, but that's rare.)

"The shop signed only one logbook entry covering both 91.411 and 91.413 — is that OK?"

Yes. Combined entries are standard practice as long as they clearly cite both regs, the test results, and the repair-station cert. The IA at next annual will look for both — make sure both are mentioned by name.

Where myaircraft.us helps

We surface every calendar-month deadline against your tail in one view:

• 91.409(a): "Annual due in 47 days" with the IA who signed the last one
• 91.411: "Altimeter/static next due 2026-10-31"
• 91.413: "Transponder next due 2026-10-31"
• 91.409(b): tracked only if you've flagged the aircraft as "for hire / instruction"

Every deadline links to the logbook page proving the last compliance — auditable for the IA, owner-friendly for you. [Try it free](/signup).

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This post is general guidance. Read the actual regulations and consult your IA for anything tail-specific. We are not the FAA.