Picture two people standing in the same hangar. The first is a private pilot, pre-flighting a Cessna 182 before a backcountry trip, running a hand along a new set of oversize tires the shop just installed. The second is the A&P/IA who signed off on that installation, flipping through a freshly downloaded PDF because the reference she may have cited on last month’s Form 337 just got replaced by the FAA. Neither of them asked for a new Advisory Circular. But on July 29, 2026, the FAA published AC 43.13-2C, canceling the 2008-vintage AC 43.13-2B. Now, both people will have to live with its requirements should they choose to use it as acceptable data, or in some cases approved data for future alterations.
Quick answer: AC 43.13-2C, effective July 29, 2026, replaces AC 43.13-2B as the FAA’s guidance on acceptable methods, techniques, and practices for inspecting and altering nonpressurized areas of civil aircraft weighing 12,500 pounds or less. The core technical content mostly carries forward, but chapters were renumbered, references modernized, a few load-factor and clearance values were corrected, and an entirely new chapter on larger (tundra) tire installations was added.
What Is AC 43.13-2C, and Why Should You Care Either Way?
AC 43.13-2C is an FAA Advisory Circular that contains methods, techniques, and practices acceptable to the Administrator for inspecting and altering nonpressurized areas of civil aircraft of 12,500 pounds gross weight or less. It is dated July 29, 2026, and it cancels its predecessor, AC 43.13-2B, dated March 3, 2008. If you fly a Cessna, Piper, Beechcraft, or similar light aircraft that has ever had an antenna, radio, ski, oxygen system, shoulder harness, battery, instrument, or cargo tiedown installed, the mechanic who did that work either used this document directly or as guidance and supplemental information to develop approved data.
Here is the piece that gets missed: an Advisory Circular is not a regulation. It is FAA guidance describing one acceptable way to comply with 14 CFR § 43.13(a), which requires that maintenance, alteration, or preventive maintenance be performed using the manufacturer’s current instructions, or other methods acceptable to the Administrator. AC 43.13-2C is one of those acceptable methods. That gap between this pilot’s pre-flight walk-around and this mechanic’s paperwork is smaller than it looks, and this revision changes some of that paperwork’s fine print.
Who Is AC 43.13-2C Actually Written For?
AC 43.13-2C is written primarily for mechanics, repair stations, and other FAA-certificated entities who perform inspections and alterations, not for pilots directly.
While pilots are not the primary audience, they are downstream consumers of every decision an AMT or IA makes using this guidance, which is why this revision belongs on a pilot’s radar too, not just part of a mechanic’s toolbox.
What Aircraft Does AC 43.13-2C Cover—And What Falls Outside It?
AC 43.13-2C covers nonpressurized areas of civil aircraft with a gross weight of 12,500 pounds or less. That scope is unchanged from AC 43.13-2B and is stated in nearly identical language in the “Purpose” section of both versions of the AC.
What falls outside it: pressurized areas of any aircraft, and any civil aircraft over 12,500 pounds gross weight. Within the covered fleet, the new Chapter 14 regarding larger tire installations narrows the scope even further for that specific alteration. Chapter 14 regarding oversized tires applies only to fixed-gear airplanes at or below 6,000 pounds gross weight, where the new tire/wheel combination does not exceed 130 percent of the original tire/wheel size. Therefore, a Beechcraft Bonanza owner and a Piper Super Cub owner are both technically inside the limitations of Chapter 14 of AC 43.13-2C, but only the fixed-gear Super Cub qualifies for the new tundra-tire guidance. The Bonanza’s retractable landing gear puts it outside Chapter 14’s weight limitations.
What Changed in This Revision (Verified Against FAA Source Text)?
The headline change is structural and organizational, not a wholesale rewrite of the underlying engineering. AC 43.13-2C added a new front-matter chapter, renumbered every existing chapter by one, switched from a running numeric paragraph style (100, 101, 102…) to a decimal style tied to chapter number (2.1, 2.2, 2.5.1…), and added one entirely new chapter on larger tire installations. Alongside that reorganization, a handful of specific technical values and references were corrected or modernized.
| What Changed | 2B (2008) | 2C (2026) | Who It Affects | Why It Matters |
|---|---|---|---|---|
| Document length/chapters | 137 pages, 12 chapters | 196 pages, 14 chapters | AMTs, IAs, DERs | New Chapter 1 (General) and Chapter 14 (Larger Tire Installations) added; every old chapter shifts by +1 |
| Paragraph numbering | Running numbers (100, 101…) | Decimal, per chapter (2.1, 2.2…) | AMTs citing Form 337 Block 8 | Every old paragraph citation on a shop card or prior Form 337 no longer matches the current AC |
| Load factor table title (structural chapter) | “Limit Load Factors” | “Ultimate Load Factors” | AMTs performing static tests | Corrects a labeling error; the values were always being used as ultimate factors |
| Sideward load factor, normal-utility occupant | 3.0g | 1.5g | AMTs sizing equipment mounts | Aligns the table with the AC’s own worked example, which already used 1.5g |
| Worked example, downward load | 6.0g / 42.0 lb | 6.6g / 46.2 lb | AMTs using the sample as a template | Shop worksheets built on the old example understate the downward load by about 10 percent |
| Material strength standard | MIL-HDBK-5 (misspelled MIL-HNDK-5 in 2B) | MMPDS (mmpds.org) | AMTs, DERs sourcing design values | MIL-HDBK-5 was canceled in 2004; MMPDS is the current industry standard |
| Wire bundle separation from flammable fluid lines | Mount above, never clamp to fluid lines | May mount above or level with; 6-inch minimum separation; clamp only within a 1/2 to 2 inch band, per AC 43.13-1 | AMTs installing avionics wiring | Directly changes an installation practice, not just wording |
| Anticollision light regulatory citation | § 91.205 plus two date-specific rules (1996, 1971) | § 91.205 for operation, §§ 23.1401/27.1401 for installation; date-specific rules removed | AMTs, pilots checking equipment requirements | Simplifies where to look, without changing what’s required |
| Larger (tundra) tire installations | Not covered | New Chapter 14, with eligibility limits, load formulas, and a job-aid checklist | AMTs handling field approvals; owners of fixed-gear aircraft ≤ 6,000 lb | First standardized path for a job that previously required case-by-case approval or an STC |
Items and subjects not listed in the above table, including the core structural design process, antenna bonding, and torque values, and most of the ski, oxygen, tow-hitch, and cargo-tiedown chapters, carries forward with only renumbering and modernized cross-references. However, before using the AC for alterations or inspections after July 29, the mechanic should review the applicable sections for any new or changed information.
Why Does an Alterations AC Matter If You’re Just the Pilot?
An alterations AC matters to a non-mechanic pilot because every piece of non-original equipment on your aircraft, from the antenna on your belly to the shoulder harness you buckle before every flight, was likely installed using this exact document or in addition to other data such as an STC as its technical justification. When the load factors, material standards, or wiring clearances in this AC change, the engineering behind future alterations to your aircraft changes with it, even if the airframe itself never gets touched again after your last annual.
The practical pilot takeaway is narrower than it sounds: you do not need to memorize chapter numbers. However, the pilot does need to know of any applicable Instructions for Continued Airworthiness, placards, and the current weight and balance document. If you’re an aircraft owner considering an oversize tire upgrade for backcountry flying, AC 43.13-2C’s new Chapter 14 is the first standardized FAA path for that job on a fixed-gear airplane at or below 6,000 pounds gross weight, replacing what used to be a case-by-case field approval or an STC search.
How Do AMTs and IAs Apply AC 43.13-2C on the Hangar Floor?
AMTs and IAs apply AC 43.13-2C to an alteration by citing the specific chapter, page, and paragraph in Block 8 of FAA Form 337 when it can be used as approved data for a major alteration. That provision carried forward from AC 43.13-2B’s paragraph 1 into AC 43.13-2C’s paragraph 1.1, and it still requires three determinations before the data can be used: the guidance must be appropriate to the product being altered, directly applicable to the alteration being made, and not contrary to the manufacturer’s data.
The day-to-day discipline this revision demands is citation hygiene. Every paragraph number an AMT has ever written on a Form 337, a shop procedure card, or a training handout is now wrong for new citations under the new decimal numbering. “AC 43.13-2B, Chapter 9” for a shoulder harness installation is now found under AC 43.13-2C, Chapter 10. Beyond renumbering, the wire bundle separation change in the communication/navigation chapter and the load factor corrections in the structural chapter are the two updates most likely to change an actual maintenance action, not just a citation, so those two areas deserve a second look even from technicians who feel confident they already know this AC cold.
AC 43.13-1B or AC 43.13-2C: Which One Applies to This Job?
AC 43.13-1B and AC 43.13-2C are two separate documents covering two separate categories of work: 43.13-1B addresses aircraft inspection and repair, while 43.13-2C addresses aircraft alterations. A common point of confusion in the hangar is treating these as versions of the same document. If the work performed restores an aircraft to its original type-certificated configuration, or in accordance with other approved data then AC 43.13-1B is the relevant reference. If the work adds, removes, or changes equipment or configuration beyond the type-certificated baseline, AC 43.13-2C is the relevant reference; either as approved data when allowed, or in conjunction with other approved data.
The two documents also cross-reference each other. AC 43.13-2C’s updated wire-bundle-separation guidance, for example, directs the reader to AC 43.13-1, Chapter 11, Paragraph 11-127, for the governing flammable-fluids-and-gases language rather than restating it. An AMT working a wiring installation next to a fuel line needs both documents open, not just one, to fully justify the work on a Form 337.
What is a Common Misconception About This AC’s Authority?
A common misconception is that an Advisory Circular like AC 43.13-2C carries the same binding force as a Federal Aviation Regulation. AC 43.13-2C’s new Chapter 1 explicitly states that the AC is a guidance document, that conformity with it is voluntary, and that nonconformity does not, by itself, change an operator’s or mechanic’s obligations under the actual regulations. The AC also states plainly that it describes an acceptable means of compliance, not the only means; a different method can be used if the FAA finds it acceptable, and referencing an established standard or publication supports that acceptability.
The corollary misconception, common among pilots rather than mechanics, is assuming that a maintenance-alteration AC revision is purely an internal AMT concern with no bearing on how a pilot’s aircraft flies, feels, or gets inspected. Given how many of the covered alterations (harnesses, avionics, tires, oxygen systems) sit directly in a pilot’s field of use, that assumption does not hold up.
Quick-Reference: AC 43.13-2C at a Glance
| Item | Detail |
|---|---|
| Full title | Acceptable Methods, Techniques, and Practices – Aircraft Alterations |
| AC number | 43.13-2C |
| Date issued | July 29, 2026 |
| Cancels | AC 43.13-2B (March 3, 2008) |
| Scope | Nonpressurized areas of civil aircraft, 12,500 lb gross weight or less |
| Primary audience | Mechanics, repair stations, other FAA-certificated entities |
| Chapters | 14 (was 12 in 2B); new Chapter 1 (General) and Chapter 14 (Larger Tire Installations) |
| Paragraph style | Decimal, per chapter (e.g., 3.8.7); was running numeric (e.g., 207) in 2B |
| Biggest new technical content | Larger (tundra) tire installation guidance for fixed-gear aircraft ≤ 6,000 lb |
| Notable corrected values | Sideward load factor 3.0g → 1.5g; downward worked example 6.0g/42.0 lb → 6.6g/46.2 lb |
| Companion document | AC 43.13-1B (inspection and repair, separate scope from alterations) |
| Legal status | Guidance only; voluntary; one acceptable means among possibly others |
Frequently Asked Questions
What is AC 43.13-2C and why does it matter to me as a pilot?
AC 43.13-2C is the FAA’s guidance document listing acceptable methods for inspecting and altering nonpressurized areas of light civil aircraft. It matters to pilots because equipment on your aircraft, from antennas to shoulder harnesses to oxygen systems, was likely installed using this AC’s guidance. When the AC updates load factors, wiring clearances, or adds new alteration categories like larger tires, the engineering behind your aircraft’s non-original equipment is affected even if you never open the document yourself.
Does AC 43.13-2C apply to my aircraft if it is pressurized or over 12,500 pounds?
No. AC 43.13-2C’s stated scope covers only nonpressurized areas of civil aircraft weighing 12,500 pounds gross weight or less. If your aircraft is pressurized, or exceeds that weight, this specific AC does not apply to alterations on those areas or that aircraft; other FAA guidance and certification requirements govern that work instead.
What is the difference between AC 43.13-1B and AC 43.13-2C?
They cover various categories of work. AC 43.13-1B addresses aircraft inspection and repair, meaning work that restores an aircraft to its original type-certificated condition. AC 43.13-2C addresses aircraft alterations, meaning work that adds, removes, or changes equipment beyond that original configuration. They are companion documents, not revisions of each other, and mechanics sometimes need to reference both on a single job.
What changed in the latest revision of AC 43.13-2C?
The biggest changes are a new front-matter chapter, chapter renumbering across the board, a switch to decimal paragraph numbering, and an entirely new chapter on larger tire installations. Within the existing technical content, a handful of specific corrections were made, including a load factor value, a worked structural example, the material strength standard reference, and wiring separation guidance near flammable fluid lines. Most core technical guidance carried forward unchanged in substance.
Is AC 43.13-2C mandatory, or is it just guidance an AMT can deviate from with FAA approval?
AC 43.13-2C is guidance, not a binding regulation on its own. The AC itself states that conformity is voluntary and that it represents one acceptable means of compliance, not the only means. An AMT or IA can use a different method if the FAA finds it acceptable for that specific product and alteration, but citing this AC in Form 337 Block 8 remains the most common, well-documented path for showing compliance.
[SME/Author Credit Placeholder: reviewed by [Name], A&P/IA/CFI, Gleim Aviation]
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