Explainer
Operator Maintenance Manuals Under 14 CFR 43.13(c)
The Rule
Three Paragraphs, Three Different Jobs
14 CFR 43.13(a) tells a person doing maintenance, preventive maintenance, or alterations to use the methods, techniques, and practices in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness (ICA), or other methods, techniques, and practices acceptable to the Administrator. Paragraph (b) sets the outcome: the work must leave the product at least equal to its original or properly altered condition, with regard to aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness.
Paragraph (c) is the one this page is about. Unless the Administrator notifies otherwise, the methods, techniques, and practices in the maintenance manual, or maintenance part of the manual, of a part 121 or 135 certificate holder (and of part 129 operators whose operations specifications require a continuous airworthiness maintenance and inspection program) constitute acceptable means of compliance with section 43.13. The paragraph was amended in the rule published at 90 FR 35211 on 24 July 2025. For an operator that follows its manual, FAA AC 120-77B reads that as compliance with 43.13(a) and (b) both.
In plain terms: for these operators, the document that governs the technician is the operator's manual, not the manufacturer's. The manufacturer's publications are usually the baseline for it. For where those publications come from, see where aircraft manuals come from, and for the ICA behind them, our explainer on instructions for continued airworthiness. The operator's manual is also one book in the larger set of manuals a Part 121 or Part 135 certificate holder must keep; see air operator manuals.
Who Can Use It
Operators, Not Everyone
AC 120-77B is addressed to operators under 14 CFR part 121 and sections 129.14(b)(3) and 135.411(a)(2) that use the 43.13(c) provisions. It covers aircraft type certificated under parts 23, 25, 27, and 29 (and Civil Air Regulations 4b). Part 129 is narrower than it looks: a note in the AC says only operators with a continuous airworthiness maintenance and inspection program qualify, and for leased aircraft maintained under a U.S. operator's program, eligibility depends on traceability to that operator's OpSpec D072.
The AC itself is guidance. It says it is one means of compliance, not the only one, that it is not legally binding in its own right, and that conformity is voluntary. The operating rules it leans on are binding: for example 121.369 and 135.427 require the operator's manual to contain the method of performing routine and nonroutine maintenance, and the AC says those rules also require the operator to follow its manual. Whether your operation qualifies is a question for your operations specifications and your principal inspector, not for this page.
Approved vs. Acceptable
Two Words the FAA Uses Differently
Approved data is data approved by the FAA. The AC grounds the term in 14 CFR 1.1: approved means approved by the FAA, by a person to whom it has delegated its authority in the matter, or under a bilateral agreement with a foreign country or jurisdiction. The FAA does not approve all service documents. The AC singles out the Airworthiness Limitations section of the ICA, which is FAA-approved and can be changed only with FAA approval, along with FAA-approved sections of a structural repair manual, service bulletins approved as described in AC 20-77, and Maintenance Review Board-approved data.
Acceptable is the lower bar and the one 43.13 mostly uses. Methods, techniques, and practices in a manufacturer's maintenance information are considered acceptable, and 43.13(c) makes an operator's own manual an acceptable means of compliance. The AC draws a second line that is easy to miss. Methods, techniques, and practices are the step-by-step how-to instructions. Technical data is the drawings, specifications, test data, and engineering analysis behind them. A manufacturer's manual typically carries the first, based on approved technical data it usually does not publish. The operator must substantiate any change to technical data for the new methods to be acceptable.
Two further points from the AC. A “no technical objection” letter, or a statement that a repair is “DER approvable,” is not FAA approval, though it can inform an evaluation. And the approved-data requirement for major repairs and alterations in 121.379(b) and 135.437(b) still applies to an operator using 43.13(c). For the structural side of that line, see our explainer on the structural repair manual. For the broader question of what counts as approved or acceptable maintenance data, see approved vs. acceptable maintenance data.
Ownership
Whose Document Is It?
The AC is blunt about responsibility. Performance-based maintenance rules put the airworthiness and reliability of the aircraft on the operator, and operators do not share that responsibility with manufacturers or design approval holders. Manufacturers' service documents, meaning maintenance manuals, restoration or overhaul manuals, ICA, component maintenance manuals, structural repair manuals, service bulletins, and service letters, “may be incorporated into the operator's manual and are subject to the operator's control.”
In preparing its manual, the operator may designate the manufacturer's manuals as its own, develop its own maintenance information (which must be traceable to standards acceptable to the Administrator), or combine the two. The manual has two kinds of content: product-specific methods for the aircraft, engines, and components, and the operator's own policies and procedures, usually in a general maintenance manual or similar document. Once the manual is accepted under 43.13(c), the operator must comply with its terms.
For a publications team this has a practical consequence. A revision to the manufacturer's aircraft maintenance manual is the manufacturer's change to its document. What the technician follows is what the operator's manual says, and keeping the two aligned is the operator's job under its own change procedures. See also keeping service bulletins and revisions current.
Changes
What an Operator May Change, and What It Takes
The AC defines a change as a variation from the method, technique, practice, or continue-in-service condition in the manufacturer's service document as incorporated in the operator's manual. Its examples: developing a new repair design, revising a work instruction or an inspection interval, using a substituted part other than the one the maintenance manual calls out, and revising a damage limit or wear tolerance.
Before an operator or someone acting for it changes a repair design, limit, or procedure in a service document, the AC says three things must be true. The change is processed under the procedures in the operator's manual and results in methods traceable to standards acceptable to the Administrator. It is shown to comply with the relevant airworthiness standards, and documented. And major repairs or alterations are done to FAA-approved technical data.
Some things are off the table without prior FAA approval. The AC names airworthiness directives (changes go through an alternative method of compliance), airworthiness limitations, and certification maintenance requirements incorporated in the type certificate data sheet. Our explainer on the Airworthiness Limitations section covers the last two.
The operator's manual should itself contain procedures for evaluating a proposed change. Paragraph 16.2 of the AC lists these elements:
- Qualified people
- A procedure ensuring only appropriately qualified and experienced personnel make the engineering determinations.
- FAA approval triggers
- A procedure for deciding whether the change needs FAA approval because it touches an airworthiness directive, certification maintenance requirement, airworthiness limitation, minimum equipment list, or maintenance program task or interval, and how to obtain that approval.
- Major or minor
- A procedure for classifying the change as minor or major, and for obtaining FAA approval of the supporting data when the result is a major repair or alteration.
- Technical and substantiating data
- A documented review of whether existing technical data is enough, consultation with the manufacturer as appropriate, a route to more substantiating data, and documented compliance that cites the specific parts of 14 CFR the change was checked against.
- Reporting and coordination
- How changes are reported to the FAA principal inspector, as appropriate, and how anyone working on the operator's behalf coordinates with the operator.
- Records
- A method of retaining the record of each action, consistent with the recordkeeping requirements of 14 CFR.
What Is New
AC 120-77B Against 120-77A
AC 120-77B is dated 10 September 2026 and cancels AC 120-77A, dated 24 October 2023. The two share a title, the same 18 numbered paragraphs, and most of their text. These are the differences visible when the documents are read side by side; the AC does not summarize its own changes.
- Scope sentence
- 120-77A applied to operators "required to provide a CAMP under § 43.13(c)." 120-77B instead says it offers guidance on methods, techniques, and practices in the maintenance manual or maintenance sections of the manual used by part 121, 129.14(b)(3), and 135.411(a)(2) operators.
- Guidance status and part 129 eligibility
- 120-77B adds an explicit note that it is guidance, not legally binding, and that conformity is voluntary, in place of 120-77A's "not mandatory" paragraph. It also adds a note that only some part 129 operators can use 43.13(c): eligibility for leased aircraft rests on traceability to the U.S. operator's OpSpec D072.
- ICA definition
- 120-77A described manufacturer methods as acceptable "if the information is incorporated into the operator's manual as their maintenance practices." 120-77B drops that condition and states that methods the design approval holder or its component manufacturers provide are considered acceptable under 43.13(c).
- Structural repair section
- Paragraph 12 was about the SRM alone. It is now titled for the SRM and the maintenance, restoration, or overhaul manuals, "which are all ICA," and its purpose paragraph speaks of ICA rather than the SRM.
- Manual changes before return to service
- 120-77A said operators may change their manuals "without obtaining prior FAA acceptance." 120-77B says they may change them in accordance with their procedures, and adds that the manuals must be updated and the changes acceptable to the FAA before an aircraft returns to service.
- Minor deviations and changed approved data
- 120-77B adds a statement that the FAA allows minor deviations from approved data provided the condition stays at least equal to original or properly altered. The 120-77A appendix paragraph clarifying that changing approved data for a major repair or alteration makes it no longer approved does not appear in 120-77B; a footnote now points to FAA Order 8300.16 on minor deviations.
- Designee paragraphs and references
- Two passages in the procedures list, on operators without an engineering department using designees and on naming a responsible individual, are gone. The order list gains FAA Order 8100.15 (organization designation authorization), and the regulations list gains part 38.
For Publishers
What OEM Publication Teams Should Expect
Read together, the AC and the rule suggest what happens to OEM data after delivery. Operators will incorporate it, sometimes unchanged and sometimes altered: new intervals, substituted parts, revised damage limits, and repair designs that never appeared in the manufacturer's manual. The AC expects operators to consult the manufacturer as appropriate when they do, and expects the supporting substantiation to be documented and traceable.
That makes the structure of the source data matter. Clear applicability, stable task identifiers, visible revision status, and clean separation of limitations from ordinary instructions all make it easier for an operator's engineering group to trace a change back to its baseline. For how manufacturer manuals are organized, see aircraft manual types, and for the general practices that sit beside them, the standard practices manual.
Shakewell writes and revises operator maintenance manuals, including general maintenance manuals, for air carriers and other operators.
FAQ
Questions We Hear
What is AC 120-77B?
AC 120-77B, "Performance Rules: Provisions Contained in an Operator Manual Under § 43.13(c)," is an FAA advisory circular dated 10 September 2026. It describes one acceptable means for part 121, 129.14(b)(3), and 135.411(a)(2) operators to develop and change the methods, techniques, and practices in their maintenance manuals. It cancels AC 120-77A of 24 October 2023. Like all advisory circulars it is guidance, not a regulation.
What does 14 CFR 43.13(c) say?
Unless the Administrator notifies otherwise, the methods, techniques, and practices in the maintenance manual (or the maintenance part of the manual) of a part 121 or 135 certificate holder, or of a part 129 operator whose operations specifications require a continuous airworthiness maintenance and inspection program, are acceptable means of compliance with 43.13. That is the operator-side counterpart to 43.13(a), which points everyone else to the current manufacturer's manual or ICA, or other acceptable methods.
What is the difference between approved data and acceptable data?
Approved data has been approved by the FAA or a person it has delegated; 14 CFR 1.1 defines "approved" that way, and AC 120-77B applies it to technical data. Acceptable data is a looser category: methods, techniques, and practices the FAA finds an acceptable way to comply, such as most manufacturer maintenance manuals and, for qualifying operators, the operator's own manual under 43.13(c). The distinction matters most for major repairs and alterations, which sections 121.379(b) and 135.437(b) require to be done to technical data approved by the Administrator.
Does 43.13(c) let an operator skip approved data for major repairs?
No. AC 120-77B says in so many words that the special provisions of 43.13(c) do not exempt operators from the approved-data requirement of 121.379(b) and 135.437(b) for major repairs and alterations. The operator classifies the work as major or minor under its manual procedures, and if it is major, the supporting technical data must be approved by the FAA or its designee before the aircraft is returned to service.
Is a manufacturer's manual revision automatically a revision to the operator's manual?
The AC treats them as separate documents. It says manufacturers' service documents may be incorporated into the operator's manual and are then subject to the operator's control, and that the operator may adopt the manufacturer's manuals as its own, write its own, or combine the two. Once its manual is accepted under 43.13(c), the operator must follow it. How a manufacturer revision enters that manual is a matter for the operator's own change procedures, so read your manual and your operations specifications for the rule that applies to you.
Does a repair station use 43.13(c)?
Not on its own certificate. The text of 43.13(c) and AC 120-77B are addressed to part 121 and 135 operators and the qualifying part 129 operators. A repair station working for an operator can be authorized to work under that operator's procedures and manual, and AC 120-77B says contract maintenance functions must be covered by procedures in the operator's manual. A repair station's own data obligation is in 14 CFR 145.109(d), which requires current and accessible data including maintenance manuals, ICA, and other data acceptable to or approved by the FAA.
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Maintenance Data That Traces to Its Source
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