14 CFR 91.411: Altimeter System Tests and Inspections

Under 14 CFR 91.411, an altimeter system inspection is required every 24 calendar months before you can fly an airplane or helicopter under instrument flight rules in controlled airspace. The rule covers three linked components — the static pressure system, the altimeter instruments, and the automatic pressure altitude reporting equipment — and all three must have been tested and found compliant within that window. Miss the deadline, and the aircraft is grounded for IFR operations no matter how well the instruments seem to be reading.¹

When the Inspection Is Required

The trigger has two parts: controlled airspace and IFR. That includes Classes A, B, C, D, and E whenever you’re operating on an instrument flight plan. Class A above 18,000 feet is IFR by definition, so every flight up there needs a current inspection. In Classes B through E, the requirement only bites when you pick up an instrument clearance.¹

A common misread is that the rule only matters in busy terminal airspace. It doesn’t. Filing IFR into a quiet field in Class E airspace still requires a current inspection. Rotorcraft flown IFR in controlled airspace are covered too, on the same terms as fixed-wing aircraft.

Pure VFR pilots who never accept an IFR clearance aren’t bound by 91.411. The moment you do, you need the inspection to be current.

The 24-Month Clock

Each of the three systems must have been tested within the preceding 24 calendar months. Counting works the same way as other FAA time-limited items: a test done on March 10 stays valid through the last day of March two years later.

Many owners bundle the work with an annual or 100-hour inspection so the airplane only comes off the line once. Fine, but track the two deadlines separately. An annual doesn’t satisfy 91.411, and 91.411 doesn’t satisfy an annual. When the 24 months are up, IFR privileges are gone until a new inspection is signed off.

Maintenance That Resets the Clock Early

Two kinds of work end the current inspection immediately, regardless of where you are in the 24-month cycle.

Opening and closing the static pressure system, other than through the system drain or alternate static valve, requires a fresh test of the entire static system against Appendix E of Part 43 before the aircraft returns to IFR service. Even minor work qualifies: replacing a static port fitting, repairing a cracked line.²

Any installation or maintenance on the altitude reporting system or transponder that could introduce a data correspondence error also requires a re-test. The altitude the transponder sends to ATC and the altitude the altimeter shows the pilot cannot differ by more than 125 feet at any test point.¹³

This is where owners get caught. A quick avionics shop visit to swap a transponder or fix a sticky encoder can ground the airplane for IFR until the post-maintenance test is signed off. Budget the re-test into any work that touches the pitot-static or altitude-reporting chain.

What Gets Checked

The standards come from Appendix E of Part 43. The three components are tested as a single integrated system.

Static Pressure System

A leak check confirms that the path from the external static port through the plumbing to the cockpit instruments is airtight. Any leak feeds false pressure into the altimeter and produces a wrong altitude reading.³

Altimeter Instruments

With the barometric scale set to 29.92, the altimeter is run through simulated pressures up to the aircraft’s maximum expected operating altitude. Readings at each test point must fall within the Appendix E tolerances, which widen with altitude. The technician also runs hysteresis and case-leak checks. You will need to tell the shop your aircraft’s maximum operating altitude — that number sets the top of the scale error test, and it later appears in the logbook entry.

Automatic Pressure Altitude Reporting

The technician interrogates the transponder and compares the altitude it reports against the altimeter reading. The two must agree within 125 feet at every test point. A component that falls outside tolerance must be adjusted or replaced before sign-off. There is no close-enough on this inspection.

Who Can Sign Off the Inspection

The regulation limits testing authority to a specific list of qualified entities. Using anyone else invalidates the inspection.¹

A certificated repair station with an appropriate instrument rating (Class I, Class II, a limited instrument rating for the specific equipment, or an airframe rating carrying a limited rating for the instruments involved).
A certificated repair station with a Class III rating under Part 145.
The manufacturer of the airplane or helicopter on which the equipment is installed.
A certificated mechanic with an airframe rating, but only for the static pressure system test. An A&P working out of a hangar cannot certify the altimeter or the altitude reporting equipment.
A certificated air carrier operating under an approved continuous airworthiness maintenance program, on its own fleet.

Altimeter calibration needs bench-test equipment most independent mechanics don’t have. If someone offers the full inspection with only an airframe certificate, that’s a red flag.

Logbook Entries You Should Verify Before Flying IFR

Appendix E requires the technician to record the date of the test and the maximum altitude to which the altimeter was tested directly on the altimeter itself. The person approving the aircraft for return to service must enter the same information in the aircraft logbook or other permanent maintenance record.³

Under 14 CFR 43.9, every maintenance entry must include a description of the work, the completion date, and the signature, certificate number, and type of certificate of the person approving return to service. That signature is the approval. Without it, the entry is incomplete and the aircraft isn’t legally approved for IFR flight.⁴

Check the entry before every IFR flight, not just for currency but for the maximum tested altitude. If the altimeter was only tested to 20,000 feet and you plan to fly FL250, the inspection doesn’t cover that operation. Ramp inspectors look at these records, and an incomplete or missing entry can bring enforcement action against both the pilot and the owner.

How It Relates to the 91.413 Transponder Check

Section 91.413 is a separate 24-month requirement covering the transponder itself, tested against Appendix F of Part 43 for reply frequency, suppression, receiver sensitivity, and output power.⁵ Because the altitude reporting signal passes through the transponder, most avionics shops offer a combined “pitot-static and transponder” certification and verify the whole chain in one visit. FAA Advisory Circular AC 43-6D treats these as an integrated process where installation or alteration work is involved.⁶

The lists of who can perform the tests aren’t identical. An airframe-rated mechanic can do the static leak check under 91.411 but cannot perform the transponder test under 91.413. If you’re scheduling combined work, confirm the shop holds every rating needed to sign off everything.

If Your Inspection Has Lapsed

An expired 91.411 inspection doesn’t ground the airplane entirely. It bars IFR operations in controlled airspace. VFR flight is still available if the aircraft otherwise meets airworthiness requirements.

When VFR repositioning to a shop isn’t practical, a Special Flight Permit (a ferry permit) lets a U.S.-registered aircraft that doesn’t currently meet all airworthiness requirements make a specific flight the FAA judges can be conducted safely. Applications go through the Flight Standards District Office covering the origin, or through a Designated Airworthiness Representative. An A&P mechanic or Part 145 repair station must inspect the aircraft first and document the inspection in the maintenance records. The permit covers one flight for one purpose, doesn’t waive the Part 91 operating rules, and must be carried in the aircraft with any operating limitations. You can apply online through the FAA’s Airworthiness Certification tool or on paper with FAA Form 8130-6.⁷

The better plan is not to get there. Put the 24-month expiration on the same calendar as your medical, and schedule the inspection with enough lead time that a failed component doesn’t strand you.

1
eCFR. 14 CFR 91.411 – Altimeter System and Altitude Reporting Equipment Tests and Inspections
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eCFR. 14 CFR 91.411 – Altimeter System and Altitude Reporting Equipment Tests and Inspections
3
Electronic Code of Federal Regulations. 14 CFR Appendix E to Part 43 – Altimeter System Test and Inspection
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eCFR. 14 CFR 43.9 – Content, Form, and Disposition of Maintenance, Preventive Maintenance, Rebuilding, and Alteration Records
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eCFR. 14 CFR 91.413 – ATC Transponder Tests and Inspections
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Federal Aviation Administration. Altitude Reporting Equipment and Transponder System Maintenance and Inspection Practices
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Federal Aviation Administration. Special Flight Permits