Aircraft inspection & repair: FAA AC 43.13 acceptable methods and AMT handbooks
This base gathers the FAA's AC 43.13-1B (acceptable methods, techniques, and practices for aircraft inspection and repair) and AC 43.13-2B (alterations) chapters, together with 14 CFR Part 43 and the FAA AMT General Handbook: rivets, torque values, safety wiring, control cables, fabric and wood repairs, welding, corrosion, electrical wiring, tires and brakes, weight and balance, and the major-vs-minor repair/alteration criteria of Part 43 Appendix A. It is built for A&P mechanics, maintenance shops, light-aircraft owners, and aviation students who need an exact spacing, torque figure, wire gauge, or regulatory threshold. These are FAA-accepted methods for airframe work, not a substitute for the aircraft manufacturer's own maintenance data, not an FAA approval for a specific major repair, and not an EASA reference. Curated by Kopik from public sources: U.S. Federal Aviation Administration and eCFR (U.S. government works, public domain).
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This assistant answers practical questions about inspecting and repairing light aircraft under FAA rules: rivet spacing, hardware, corrosion rework, fabric, cables, wiring, weight and balance, and the paperwork that goes with each job. Questions can be as precise as an exact rivet spacing, a torque figure, a fabric strength limit or a regulatory threshold. It is meant for A&P mechanics, maintenance shops, aircraft owners and aviation students. Every answer comes from FAA public documents: AC 43.13-1B, chapters of AC 43.13-2B, 14 CFR Part 43 and the FAA AMT General Handbook.
What AC 43.13 is, and what it is not
Under 14 CFR 43.13(a), anyone performing maintenance, alteration or preventive maintenance must use the methods in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness, or other methods, techniques and practices acceptable to the Administrator.
The FAA AMT General Handbook explains that when the manufacturer's documents do not give the guidance a technician needs, AC 43.13-1 or AC 43.13-2 contain examples of those other acceptable methods. For minor repairs and alterations, AC 43.13-1 is cited as an example of acceptable data.
The assistant therefore treats AC 43.13 as acceptable data, not as approved data for a specific major repair, and not as a replacement for your aircraft manufacturer's instructions.
Sheet metal: rivet edge distance and spacing
AC 43.13-1B defines edge distance as the distance from the center of the rivet hole to the nearest edge of the sheet, and spacing as the distance between the centers of adjacent rivet holes. Unless structural deficiencies are suspected, both should duplicate the original aircraft structure.
When deficiencies are suspected, a single row of rivets should have an edge distance of at least 2 times the rivet diameter and a spacing of at least 3 times the diameter. Double and multiple rows follow the minimums of Figure 4-5.
The chapter also notes that 2117 rivets may be driven as received, while 2017 rivets above 3/16 inch and all 2024 rivets must be kept refrigerated or in dry ice in the quenched condition, or be reheat-treated just before driving.
Corrosion rework on aluminum structure
Chapter 6 asks that depressions left by corrosion removal be faired into the surrounding surface as smooth dish-outs with a length to depth ratio of 20:1. In critical, highly stressed areas, remaining pits should be blended out to avoid stress risers that can lead to stress corrosion cracking.
Steel nut-plates and fasteners should be removed before blending aluminum, because embedded steel or copper particles can start new corrosion. All corrosion products must be removed.
After rework, a chemical conversion coating (MIL-C-81706) is applied. If 48 hours or more pass before primer or paint, the conversion coating should be reapplied.
Bolts, nuts and safetying hardware
Chapter 7 of AC 43.13-1B asks that all bolts and nuts be locked or safetied, except self-locking nuts. The three basic safetying methods are safety wire, cotter pins and self-locking nuts. Cotter pins and safety wire must not be reused, while spring pins may be reused if careful inspection shows no deformation of the pin or hole.
Self-locking nuts come in all-metal and fiber or nylon types. They must not be used on parts subject to rotation, on access panels or doors, or on parts routinely taken apart before or after each flight. On turbine engine airplanes, they should not be used where a loose nut, bolt or washer could fall or be drawn into the engine air intake.
Fiber or nylon locknuts are not installed where temperatures exceed 250 ºF, and a fiber or nylon locknut that cannot meet the minimum prevailing torque values of the AC table must not be reused.
Frequently asked questions
Can I use AC 43.13-1B instead of my aircraft's maintenance manual?
Part 43 lists the manufacturer's current maintenance manual or Instructions for Continued Airworthiness first. AC 43.13 offers other methods acceptable to the Administrator, which the FAA handbook presents as useful when the manufacturer's documents do not cover what you need.
Which aircraft does AC 43.13-2B cover?
As quoted in the AMT General Handbook, AC 43.13-2B gives acceptable methods for the inspection and alteration of non-pressurized areas of civil aircraft of 12,500 lbs gross weight or less.
What does the empty weight of an aircraft include?
Chapter 10 of AC 43.13-1B says the empty weight includes all operating equipment that has a fixed location and is actually installed in the aircraft. The fluids that must be included are listed in the Aircraft Specifications or the TCDS. The useful load is the maximum weight minus the empty weight.
Can I clean corroded aluminum with kerosene?
No. The corrosion rework steps in Chapter 6 say to clean the reworked area with dry cleaning solvent and not to use kerosene or any other petroleum based fuel as a cleaning solvent.
What is the minimum prevailing torque for a reused self-locking nut on a 3/4-16 bolt?
The AC 43.13-1B table gives 27 inch-pounds for a 3/4-16 fine thread nut. The coarse thread 3/4-10 size has the same value, 27 inch-pounds. For comparison, a 1/2-20 fine thread nut needs at least 10 inch-pounds.
Where do I find the data to update a weight and balance record?
AC 43.13-1B points to the Aircraft Specifications, the Type Certificate Data Sheet, the prescribed operating limitations, the Aircraft Flight Manual, the aircraft weight and balance report and the maintenance manual. The removal or addition of equipment changes the center of gravity, and the empty weight and permissible useful load are affected accordingly. The empty weight center of gravity is an essential part of the weight and balance record, and Chapter 10 gives the formulas for tailwheel and nosewheel aircraft.
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