AC 43.13-1B is the FAA advisory circular that sets out acceptable methods, techniques, and practices for aircraft inspection and repair when the manufacturer hasn’t published data for the work you’re doing. The current version, 1B with Change 1, was issued in September 1998 and supersedes the earlier 1A edition.1Federal Aviation Administration. AC 43.13-1B – Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair It covers airframes, engines, propellers, and appliances, and it’s one of the most-referenced documents in general aviation maintenance.
Why the AC Has Authority Without Being a Regulation
Advisory circulars aren’t regulations and don’t carry the force of law. AC 43.13-1B has weight because of the rule it supports. Under 14 CFR 43.13, anyone performing maintenance or alterations must use methods in the manufacturer’s current maintenance manual or “other methods, techniques, and practices acceptable to the Administrator.”2eCFR. 14 CFR 43.13 – Performance Rules (General) The AC fills that second category. When manufacturer repair data doesn’t exist for a particular situation, the AC provides a pre-accepted source that satisfies the rule.
Section 43.13 also sets the quality standard the work must meet. Any repair has to leave the aircraft in a condition at least equal to its original or properly altered state, considering structural strength, aerodynamic function, vibration resistance, and deterioration.2eCFR. 14 CFR 43.13 – Performance Rules (General) The AC’s procedures are designed to meet that bar. The mechanic still owns the judgment call that the chosen technique actually achieves it for the specific aircraft and defect.
What the AC Does Not Cover
Two limits catch people out. First, AC 43.13-1B applies only to nonpressurized areas of civil aircraft, and only when manufacturer repair or maintenance instructions don’t exist for the work.3Federal Aviation Administration. AC 43.13-1B – Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair Published manufacturer procedure takes priority. Work on a pressurized fuselage section, cabin structure, or any pressurized boundary falls outside the AC.
Second, the AC covers repairs, not alterations. Alterations have their own companion document, AC 43.13-2B, which carries the same nonpressurized limitation plus a 12,500-pound gross weight ceiling. That circular is where you find guidance for things like antenna installations, ski installations, oxygen systems in nonpressurized aircraft, and shoulder harness installations.4Federal Aviation Administration. AC 43.13-2B – Acceptable Methods, Techniques, and Practices – Aircraft Alterations
Acceptable Data or Approved Data
How the AC’s content is treated depends on whether the repair is major or minor. This distinction is the single most important thing to understand before you reach for the document.
For minor repairs, the AC’s data qualifies as acceptable data. No specific FAA review is needed before you use it. The mechanic determines the procedure fits the repair, applies it, and signs off the work.5Federal Aviation Administration. AC 43-210A – Standardized Procedures for Obtaining Approval of Data Used in the Performance of Major Repairs and Major Alterations
For major repairs, the AC data can serve as a basis for FAA-approved data only when three conditions are met together: you’ve determined the data is appropriate for the specific product being repaired, it’s directly applicable to the repair being made, and it doesn’t contradict manufacturer data. When you use it this way, the AC chapter, page, and paragraph must appear in Block 8 of FAA Form 337.3Federal Aviation Administration. AC 43.13-1B – Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair Major repairs and alterations always require approved data, meaning data formally reviewed and accepted by the FAA.5Federal Aviation Administration. AC 43-210A – Standardized Procedures for Obtaining Approval of Data Used in the Performance of Major Repairs and Major Alterations
Appendix A to Part 43 draws the line. Major airframe repairs include work on primary structural elements like wing spars, fuselage longerons, and keel beams, and repairs to stressed skin or load-bearing members that involve substituting materials or parts. Major powerplant work includes replacing engine case sections or crankshafts. Anything not listed in Appendix A is a minor repair.6eCFR. Appendix A to Part 43, Title 14
Who Can Use It
Having the AC in front of you doesn’t grant authority to perform work. Under 14 CFR 43.3, mechanic certificate holders can perform maintenance, preventive maintenance, and alterations within the privileges of their ratings. Part 145 repair stations operate under their own authority. Someone working under the direct supervision of a certificated mechanic can perform work the supervisor is authorized to do, if the supervisor personally observes it and remains readily available.7eCFR. 14 CFR 43.3 – Persons Authorized To Perform Maintenance, Preventive Maintenance, Rebuilding, and Alterations
Pilots with at least a private certificate can perform preventive maintenance on aircraft they own or operate, provided the aircraft isn’t used in commercial operations under Part 121, 129, or 135.7eCFR. 14 CFR 43.3 – Persons Authorized To Perform Maintenance, Preventive Maintenance, Rebuilding, and Alterations Preventive maintenance is a defined category in Appendix A. It covers items like replacing landing gear tires, servicing shock struts, replacing safety wire or cotter pins, cleaning spark plugs, and replacing position light bulbs.6eCFR. Appendix A to Part 43, Title 14 A pilot-owner using the AC as reference for a listed task is fine. A pilot-owner tackling a sheet metal skin repair is not, because that’s maintenance rather than preventive maintenance.
What’s Inside the AC
Sheet Metal Structure
The sheet metal chapters give dimensional standards for riveted repairs that restore original load-carrying ability. Edge distance from the center of a rivet hole to the nearest sheet edge cannot be less than two times the rivet diameter. Single-row rivet spacing must be at least three times the rivet diameter, with additional minimums for multi-row patterns shown in the AC’s figures.3Federal Aviation Administration. AC 43.13-1B – Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair The AC also specifies rivet alloy selection based on the skin being repaired. A harder rivet in softer skin can crack surrounding material or cause galvanic corrosion.
Composites
Composite repair procedures cover laminate structures using materials like fiberglass. Replacement material must match the original in chemical composition, or be a substitute approved by the manufacturer, to preserve strength, weight, and aerodynamic properties. Scarf joints maximize bonding surface for bonded repairs, and patches should be round or oval where possible, with rounded corners on larger repairs to avoid stress concentrations.3Federal Aviation Administration. AC 43.13-1B – Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair Advanced composites like carbon fiber and aramid structures on newer aircraft often need manufacturer-specific data that goes beyond the AC, especially for primary structure.
Electrical Systems
Wire routing must protect conductors from chafing against structure or moving parts, and bends must maintain a minimum radius to avoid cracking the conductor. Splices use approved crimp-type terminal lugs and connectors for low-resistance, vibration-resistant connections. When wires run in bundles, each wire’s rated ampacity must be reduced, a process called derating, because bundled wires generate heat that can’t dissipate as easily. The AC provides continuous-duty current tables for copper and aluminum wire at different temperature ratings, along with derating curves based on conductor count and altitude.8Federal Aviation Administration. AC 43.13-1B – Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair Skipping derating is how electrical fires start. A wire that runs cool in free air can overheat inside a tight harness with dozens of energized conductors.
Fluid Lines and Control Cables
Hydraulic, fuel, and oil lines require proper routing and support to prevent movement and abrasion. The AC details flaring techniques for metal tubing, typically single or double-lap flares, for leak-proof connections at fittings. For control cables, tension is measured with a tensiometer and varies with ambient temperature because cables expand and contract with heat and cold. Fairleads guide cables through bulkheads and around structure with minimum friction.
Torque and Safetying
The AC provides torque tables organized by fastener size and material. A detail that gets missed: published values are dry, meaning no lubricant on the threads. Adding lubricant increases effective clamping force at the same torque reading, so applied torque must be reduced, and the AC gives guidance for the adjustment. Over-torquing can stretch a bolt past its yield point or crush the material underneath. Under-torquing leaves it vulnerable to vibration loosening.
Safetying keeps fasteners from backing out in flight. The AC describes two primary safety wire techniques: the double-twist method, used for most bolts, and the single-wire method, used for closely spaced fasteners in geometric patterns and on some electrical components.3Federal Aviation Administration. AC 43.13-1B – Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair A properly installed job shows about six to eight twists per inch and keeps light tension pulling the fastener in the tightening direction.9Federal Aviation Administration. Safety Wire Cotter pins with castellated nuts and self-locking nuts are also covered, each with its own installation rules.
Documenting a Repair That Uses the AC
The work isn’t finished until the record is. Under 14 CFR 43.9, every maintenance entry must contain four things: a description of the work performed or a reference to acceptable data, the date the work was completed, the name of the person who did the work if different from the person signing it off, and the signature, certificate number, and certificate type of the person approving the return to service.10eCFR. 14 CFR 43.9 – Content, Form, and Disposition of Maintenance, Preventive Maintenance, Rebuilding, and Alteration Records That signature only approves return to service for the specific work described.
When AC 43.13-1B is your data source, the logbook entry should reference the specific chapter, page, and paragraph used. For major repairs and alterations, that reference goes in Block 8 of FAA Form 337 along with a clear description including the location of the repair on the aircraft.11Federal Aviation Administration. AC 43.9-1G – FAA Form 337 If any portion of the repair will be concealed by skin or other structure, the form should include a pre-closure certification with a signature confirming covered areas were inspected and found satisfactory before being closed.
Only certain people can sign the return-to-service approval. Mechanic certificate holders, inspection authorization holders, Part 145 repair stations, and manufacturers working under their own authority can approve maintenance. Pilots performing preventive maintenance on their own aircraft can approve their own work.12eCFR. 14 CFR 43.7 – Persons Authorized To Approve Aircraft, Airframes, Aircraft Engines, Propellers, Appliances, or Component Parts for Return to Service Incomplete documentation is one of the most common findings on ramp checks and repair station inspections, and it can ground an aircraft as effectively as a mechanical defect.