Direct Answer — The 24-Calendar-Month Tests and Their Record
Under 14 CFR §91.411, the static pressure system, each altimeter instrument, and each automatic pressure altitude reporting system must be tested and inspected within the preceding 24 calendar months — and found to comply with appendices E and F of part 43 — to operate an airplane or helicopter in controlled airspace under IFR. Under 14 CFR §91.413, the ATC transponder must likewise be tested within the preceding 24 calendar months to appendix F of part 43. These are two independent tests with two independent due dates. Each is recorded as a §43.9 maintenance record entry; appendix E additionally requires the date and the maximum altitude to which the altimeter was tested to be recorded on the altimeter and entered in the airplane log or other permanent record. The 24-month figure is a test interval, not a records-retention period — the record itself is kept under the applicable retention rules.
"24 calendar months" is not a rolling 730 days — and it is not a retention clock
Both §91.411 and §91.413 use the phrase within the preceding 24 calendar months. A calendar-month interval runs through the last day of the final month — a test completed any day in March 2026 is valid through March 31, 2028. That same 24 months is how often you must re-test; it says nothing about how long you keep the paperwork, which is governed separately (Part 91 by §91.417, Part 135 by §135.439).
The Two 24-Month Tests — §91.411 and §91.413 Are Not the Same Sign-Off
Operators routinely conflate these because they are usually performed in the same shop visit — the colloquial "pitot-static and transponder check" — and recorded near each other in the logbook. But they are independent regulatory requirements, against different Part 43 appendices, with different authorized signers and different due dates. An inspector verifies each one separately, by date.
14 CFR §91.411(a) prohibits operating an airplane, or helicopter, in controlled airspace under IFR unless, within the preceding 24 calendar months, each of the following has been tested and inspected and found to comply with appendices E and F of part 43:
- Each static pressure system — the integrity and leak checks in appendix E of part 43
- Each altimeter instrument — the scale-error, hysteresis, friction, case-leak, and barometric-scale tests in appendix E
- Each automatic pressure altitude reporting system — the encoding side that feeds the transponder, verified so its output corresponds to the displayed altitude within the appendix E tolerance
§91.411 also adds interim triggers between the 24-month tests. Under §91.411(a)(2), following any opening and closing of the static pressure system (except the use of system drain and alternate static pressure valves), that system must be tested and inspected to the relevant part of appendix E before it is relied upon again. Under §91.411(a)(3), following installation or maintenance on the automatic pressure altitude reporting system of the ATC transponder where data correspondence error could be introduced, the integrated system must be tested to appendix E. The 24-calendar-month cycle is the floor — certain maintenance events demand an additional test before the next scheduled one.
14 CFR §91.413(a) prohibits using an ATC transponder — one specified in §91.215(a), §121.345(c), or §135.143(c) — unless, within the preceding 24 calendar months, it has been tested and inspected and found to comply with appendix F of part 43.
- Appendix F covers the transponder bench/ramp tests — reply radio frequency, suppression, receiver sensitivity, RF peak output power, and for Mode S, address recognition, reply formats, all-call behavior, and squitter
- It is a different appendix from the §91.411 altimeter/static tests — §91.413 points to appendix F; the §91.411 altimeter/static side points to appendix E
- The transponder test proves the Mode C / Mode S reply and the altitude data being transmitted are correct — distinct from the altimeter accuracy test, even though both touch altitude data
Appendix F is explicit about the paperwork: it directs that the transponder test comply with the provisions of §43.9 as to the content, form, and disposition of the records. So the transponder test sign-off is a §43.9 maintenance record entry — see the dedicated section below. Keep this entry distinct in your filing from any ADS-B Out documentation (§91.225 / §91.227 equipment has its own requirements); an inspector looks for the §91.413 transponder sign-off specifically, by date.
Side-by-Side: What Each Test Covers
| Attribute | §91.411 Altimeter/Static | §91.413 Transponder |
|---|---|---|
| Interval | 24 calendar months | 24 calendar months |
| Part 43 appendix | Appendix E (altimeter/static) | Appendix F (transponder) |
| Triggers the requirement | IFR ops in controlled airspace | Use of an ATC transponder |
| What it proves | Altimeter + static system read true | Transponder reply + altitude data correct |
| Record governed by | §43.9 + App E date/max-altitude note | §43.9 (per App F cross-reference) |
For the RVSM dimension — where this same §91.411 altimeter test becomes the airworthiness backbone of legally flying 1,000-foot vertical separation between FL290 and FL410 — see the companion guide on RVSM altimeter and transponder inspection records. This page is the general §91.411 / §91.413 test and the §43.9 record; that page adds the §91.180 / appendix G authorization layer.
The Record Itself — A §43.9 Maintenance Entry, Plus the Appendix E Altimeter Note
A test that was performed but cannot be evidenced is, for compliance purposes, a test that did not happen. The §91.411 and §91.413 tests are recorded as maintenance record entries under 14 CFR §43.9. Appendix F to part 43 expressly cross-references §43.9 for transponder-test records, and the altimeter/static test under appendix E is likewise a maintenance entry — with one extra item appendix E requires.
- 1A description of the work performed, or a reference to data acceptable to the Administrator — e.g., "Altimeter, static system, and automatic altitude reporting system tested and inspected IAW 14 CFR Part 43 Appendix E."
- 2The date of completion of the work performed — this is the date the 24-calendar-month clock runs from.
- 3The name of the person performing the work, if other than the person approving it for return to service.
- 4The signature, certificate number, and kind of certificate held by the person approving the work — the entry that legally returns the work to service.
Appendix E adds a specific altimeter recording requirement
Beyond the four §43.9 items, appendix E to part 43 requires that the person performing the altimeter tests record on the altimeter the date and the maximum altitude to which the altimeter has been tested — and the person approving the airplane for return to service must enter that data in the airplane log or other permanent record. So a complete altimeter test leaves two marks: a notation on the instrument itself, and the maintenance-record entry. An inspector may check that the maximum-altitude figure on the altimeter is consistent with the operation the aircraft is flown in.
This is a §43.9 entry, not a §43.11 inspection entry
It is worth being precise: §43.9 governs entries for maintenance, preventive maintenance, rebuilding, and alteration, and §43.9 by its own terms does not apply to persons performing the inspections covered by §43.11 (the annual, 100-hour, and progressive inspection return-to-service entries under parts 91, 125, §135.411(a)(1), and §135.419). The altimeter and transponder tests are performance tests recorded under §43.9 — they are not the annual inspection. Filing the test sign-off as if it were an inspection entry, or vice versa, muddies which requirement a given logbook line actually satisfies.
For the full anatomy of a compliant maintenance entry, see §43.9 maintenance record entry requirements; for how these test records sit alongside the rest of the aircraft file, see the Part 91 aircraft records requirements; and for the inspection side they are often confused with, see the Part 91 §409 annual inspection requirements.
Who Is Authorized to Perform — and Sign — Each Test
This is where operators most often create a defective record without realizing it. The authorized-performer rules differ between the two tests, and a general A&P certificate does not carry blanket authority for either one in full.
- 1The manufacturer of the airplane, or helicopter, on which the tests are performed.
- 2A certificated repair station holding the appropriate rating for the test being performed.
- 3A certificated mechanic with an airframe rating — but for the static pressure system tests and inspections only. Not the altimeter or altitude-reporting portions.
- 1A certificated repair station properly equipped to perform the function and holding the appropriate radio ratings.
- 2A holder of a continuous airworthiness maintenance program as provided in part 121 or §135.411(a)(2).
- 3The manufacturer of the aircraft on which the transponder to be tested is installed, if the transponder was installed by that manufacturer.
A general A&P certificate alone does not authorize either test in full
For §91.411, a mechanic with an airframe rating may perform only the static system portion — the altimeter and altitude-reporting tests require an appropriately rated repair station or the manufacturer. For §91.413, the transponder test requires a radio-rated repair station, a CAMP holder, or the manufacturer — an A&P certificate by itself is not on the §91.413(c) list. A record signed by someone outside the authorized categories is a defective record, even when the equipment is genuinely within tolerance.
For Part 135 operators, the maintenance program and the continuous-airworthiness arrangements under §135.411 govern who performs and signs these tests — see what records a Part 135 operator must keep and Part 145 repair station recordkeeping requirements for the shop side of the sign-off and what the repair station retains on its end.
Related Aviation Compliance Guides
The Interval Is a Test Clock, Not a Retention Clock
One of the most common — and most consequential — misreadings of §91.411 and §91.413 is to treat the "24 calendar months" as if it tells you how long to keep the record. It does not. The 24 months tells you only how often the test must be re-accomplished. Two completely separate sets of rules govern how long the resulting records are retained.
Tells you when to re-test: within the preceding 24 calendar months. Once a test is older than its 24-calendar-month window, the aircraft is no longer eligible for the operation that test enables — IFR in controlled airspace for §91.411, transponder use for §91.413 — until a fresh test is accomplished and recorded.
Source: 14 CFR §91.411(a), §91.413(a)
Tell you how long to keep the paperwork. For Part 91 aircraft, maintenance records are kept under §91.417 — records of the work generally until the work is superseded or the aircraft is sold, with certain records transferred with the aircraft. For Part 135 operators, §135.439 governs retention. The current test sign-off is the operative proof and must always be available.
Source: 14 CFR §91.417, §135.439
Why the distinction matters in practice
An operator who reads the 24 months as a retention period may discard a test record at 24 months and one day — exactly when an inspector might ask to see the last several tests to establish a continuous compliance history, or when a buyer's pre-purchase inspection wants to trace the altimetry maintenance trail. The reverse error is equally common: keeping every test forever but never tracking the next-due date, so the aircraft quietly flies past an expired test.
The disciplined position is simple — re-test on the 24-calendar-month clock, retain the records under the applicable retention rule, and track both the test date and the computed next-due date for each of the two tests independently. For how long different aviation records must be kept across the board, see the aviation records retention schedule.
These recurring tests sit alongside the other recurring obligations that quietly ground an aircraft when they lapse — see airworthiness directive compliance records and the Part 91 §409 annual inspection requirements for the other recurring intervals an inspector cross-checks against the logbooks. The companion RVSM records guide shows how the §91.411 test additionally anchors RVSM altitude-keeping.
Record Discipline — What an Inspector Actually Looks For
The recurring tests are only as good as the records that prove them. Here is what a complete, audit-ready record set for the §91.411 / §91.413 tests looks like — and the specific ways these records fail.
Complete Record Set
- §91.411 altimeter/static/altitude-reporting sign-off with the §43.9 description, test date, and the computed 24-calendar-month next-due date
- §91.413 transponder sign-off with its own §43.9 entry, test date, and next-due date
- The appendix E date-and-maximum-altitude notation reflected on the altimeter and in the permanent record
- Identity and authority of the performer — repair station certificate number and ratings, manufacturer, CAMP reference, or (static-only) the airframe-rated mechanic
- The signature, certificate number, and kind of certificate of the person approving return to service
- ADS-B Out documentation, where applicable, filed separately from the §91.413 entry
How These Records Fail
- Treating one combined "pitot-static / transponder" entry as covering both tests, with only a single date
- Letting the two tests drift to different months, then losing track of the earlier next-due date
- A static-system-only airframe-mechanic sign-off used to claim the full §91.411 test
- Calculating the next-due as 730 days instead of to the end of the 24th calendar month
- Discarding the record at 24 months because the interval was mistaken for a retention period
- Missing the appendix E maximum-altitude notation, or an altitude inconsistent with the operation
A missing record reads the same as a missing test
An FAA inspector who cannot find a current §91.411 or §91.413 sign-off cannot distinguish "the test was done but the record is missing" from "the test was never done" — both are treated as the aircraft being ineligible for the operation until a current test is accomplished and recorded. Operating an aircraft in violation of these rules can expose a certificate holder to civil penalties; under 14 CFR §13.301 the maximum civil penalty for a violation occurring on or after December 30, 2024 is up to $75,000 per violation in general, and up to $1,875 per violation for an individual or small business concern. The records are the cheapest part of staying clear of that exposure.
FileFlo as the Altimeter / Transponder Records Layer
FileFlo is a compliance document intelligence platform — a read-only proof layer that sits alongside your maintenance-tracking stack and completes it. It does not perform the §91.411 or §91.413 tests, sign off airworthiness, or run a maintenance-tracking, dispatch, or flight-operations system. What it does is make the records that prove these tests instantly producible.
- Classifies uploaded sign-offs against their governing rule (§91.411 altimeter/static, §91.413 transponder) and separates them so neither is mistaken for the other
- Reads the test date out of the document and tracks the 24-calendar-month next-due date for each test independently, with expiration alerts at 90/60/30 days
- Keeps the §43.9 entry indexed alongside the appendix E maximum-altitude notation so the full proof of one test is in one place
- Distinguishes the test records from the §43.11 annual/100-hour inspection entries and from ADS-B documentation, so the right logbook line answers the right requirement
- Generates an inspector-format records binder on demand, organized by requirement and due date
FileFlo classifies 600+ compliance document types and manages records across Part 91, Part 135, and Part 145 operators in a single platform. Pricing: Starter $89/mo, Professional $299/mo. 5-day free trial, no credit card required. FileFlo keeps the documents that prove compliance audit-ready — it does not provide or run a safety management system (SMS), dispatch system, or flight operations system.
The Tests Apply Across Operators — What Changes Is Accountability
The §91.411 and §91.413 tests are general Part 91 operating rules, with one structural carve-out: under §91.401(b), §91.411 does not apply to an aircraft maintained in accordance with a continuous airworthiness maintenance program (Part 121, or 10-or-more-seat Part 135 aircraft under §135.411(a)(2)) — whose parallel requirements live in the CAMP. The §91.413 transponder test applies to any aircraft using a transponder in the airspace specified by §91.215. What changes by operator is who is accountable for the test record and the consequence of letting it lapse.
Who is responsible
Owner/operator
Owner tracks both test due dates and retains the records under §91.417. Most exposed to silent drift between the two 24-month dates.
Who is responsible
DOM via maintenance program
Tests fold into the §135.411 maintenance program; records retained under §135.439. A Principal Maintenance Inspector reviews them on surveillance.
Who is responsible
Continuous airworthiness program
Under §91.401(b), §91.411 is satisfied through the CAMP rather than the standalone rule — but the parallel test and its record are still required and tracked.
Because these tests are part of the broader recurring-compliance picture a modern fleet must keep current, the same discipline applies to Part 135 CAMP maintenance recordkeeping, the FAA Part 135 SMS 2027 deadline, and the way a surveillance team examines the whole file — how to prepare for a Part 135 FAA surveillance audit.
Frequently Asked Questions
How often must the altimeter and static pressure system be tested under 14 CFR §91.411?
Every 24 calendar months. 14 CFR §91.411(a) prohibits operating 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 and inspected and found to comply with appendices E and F of part 43. A calendar-month interval runs through the last day of the 24th month after the test — a test completed any day in March 2026 is valid through March 31, 2028. It is not a rolling 730 days measured from the exact test date.
How often must the ATC transponder be tested under 14 CFR §91.413?
Every 24 calendar months. 14 CFR §91.413(a) states that no person may use an ATC transponder specified in §91.215(a), §121.345(c), or §135.143(c) unless, within the preceding 24 calendar months, the transponder has been tested and inspected and found to comply with appendix F of part 43. The transponder test and the altimeter/static test are both on a 24-calendar-month cycle, but they are independent tests with independent due dates — a §91.411 sign-off does not satisfy §91.413 and vice versa. Many shops do them in one visit, but each must appear in the records on its own terms.
What record proves the altimeter and static system test was done, and what must it contain?
The test is recorded as a maintenance record entry. Under 14 CFR §43.9(a), the entry for maintenance, preventive maintenance, rebuilding, or alteration must include a description of the work performed (or a reference to acceptable data), the date of completion, the name of the person performing the work if different from the approver, and the signature, certificate number, and kind of certificate held by the person approving the work for return to service. Appendix E to part 43 adds a specific requirement for the altimeter: the person performing the altimeter tests must record on the altimeter the date and the maximum altitude to which it has been tested, and the person approving the aircraft for return to service must enter that data in the airplane log or other permanent record.
Who is authorized to perform the §91.411 altimeter and static system test?
Per 14 CFR §91.411(b), the tests may be performed by the manufacturer of the airplane or helicopter on which they are performed; by a certificated repair station holding the appropriate rating; or by a certificated mechanic with an airframe rating — but the mechanic is limited to the static pressure system tests and inspections only. A certificated mechanic with an airframe rating cannot, on that certificate alone, perform the altimeter or automatic altitude-reporting portions of the §91.411 test; those require an appropriately rated repair station or the manufacturer.
Who is authorized to perform the §91.413 transponder test?
Per 14 CFR §91.413(c), the transponder test may be conducted by a certificated repair station properly equipped to perform the function and holding the appropriate radio ratings; by a holder of a continuous airworthiness maintenance program as provided in part 121 or §135.411(a)(2); or by the manufacturer of the aircraft on which the transponder to be tested is installed, if the transponder was installed by that manufacturer. A general airframe-and-powerplant mechanic is not, by that certificate alone, on the list of those who may perform the §91.413 transponder test.
Are these tests a records-retention period? Do I throw the record away after 24 months?
No — and this trips operators up. The 24 calendar months in §91.411 and §91.413 is the test interval (how often the test must be re-accomplished), not a retention period for the record. The current test sign-off must be kept as long as it is the operative proof of compliance, and the underlying maintenance records are governed by the applicable retention rules — for example §91.417 for Part 91 aircraft and §135.439 for Part 135 operators. The interval tells you when to re-test; the retention rules tell you how long to keep the paperwork. Confusing the two is how operators discard a record that an inspector later asks to see.
Is the §91.411 / §91.413 test entry a §43.9 maintenance entry or a §43.11 inspection entry?
It is a §43.9 maintenance record entry. Appendix F to part 43 expressly says the transponder test must comply with the provisions of §43.9 as to the content, form, and disposition of the records, and the altimeter/static test under appendix E is likewise recorded as a maintenance entry with the date-and-maximum-altitude data noted. §43.9 governs maintenance, preventive maintenance, rebuilding, and alteration entries; §43.11 governs the separate return-to-service entries for inspections conducted under parts 91, 125, §135.411(a)(1), and §135.419. The altimeter and transponder tests are performance tests recorded under §43.9, distinct from the annual or 100-hour inspection entries that fall under §43.11.
Does FileFlo perform the altimeter, static system, or transponder tests?
No. FileFlo is a compliance document intelligence platform — a read-only proof layer. It does not perform the §91.411 or §91.413 tests, sign off airworthiness, or run a maintenance-tracking, dispatch, or flight-operations system. What FileFlo does is classify and index the test sign-offs, read the test dates, track the 24-calendar-month next-due date for each test independently, and surface expiration alerts so an expired altimeter or transponder test never surprises you at a ramp check or in a records audit. The tests themselves are performed by an appropriately rated repair station, a CAMP holder, a qualifying mechanic, or the manufacturer.
Never let an altimeter or transponder test expire under you
FileFlo classifies your §91.411 and §91.413 sign-offs, reads each test date, tracks both 24-calendar-month next-due dates independently, keeps the §43.9 entries and appendix E notations indexed, and generates a complete inspector-format records binder on demand. Starter plan $89/mo. Professional $299/mo. 5-day free trial — no credit card required.
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Written by Chad Griffith, Founder & CEO of FileFlo — compliance document intelligence. Reviewed June 13, 2026. FileFlo is a compliance document intelligence platform, not legal counsel, an A&P, or a repair station. Verify all test intervals, recording requirements, and who-may-perform rules with a certificated A&P or IA, your repair station, and your FSDO.