5.1 Approved Data vs. Acceptable Data: Legal Standards & Sources

5.1 Approved Data vs. Acceptable Data: Legal Standards & Sources

[!IMPORTANT] The Regulatory Gateway to Return to Service: The distinction between "acceptable data" and "approved data" is the single most critical legal boundary in aviation maintenance. Under 14 CFR § 43.13(a), minor repairs, minor alterations, and standard maintenance procedures require only data that is acceptable to the Administrator. Conversely, under 14 CFR § 65.95(a)(1) and 14 CFR Part 43 Appendix B, approving an aircraft, airframe, powerplant, propeller, or appliance for return to service after a major repair or major alteration strictly requires technical data approved by the Administrator. Approving a major alteration or major repair without bona fide FAA-approved data constitutes a severe violation of federal aviation law, immediately invalidating the aircraft's airworthiness certificate and exposing the Inspection Authorization (IA) holder to administrative revocation under 49 U.S.C. § 44709.

The Statutory Divide: Acceptable Data vs. Approved Data

Federal aviation regulations deliberately establish two tiers of technical documentation governing work performed on civil aircraft. Every practicing IA must navigate this distinction with uncompromising precision:

1. Acceptable Data (The Baseline Maintenance Standard): Codified in 14 CFR § 43.13(a), the general performance rules mandate that each person performing maintenance, alteration, or preventive maintenance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness (ICA), or other methods, techniques, and practices acceptable to the Administrator. Acceptable data describes sound, industry-standard maintenance practices suitable for day-to-day servicing, inspections, parts replacements, and minor repairs. However, acceptable data lacks formal engineering certification that the resulting configuration satisfies specific airworthiness certification bases (such as 14 CFR Part 23 or Part 25).
2. Approved Data (The Major Work Standard): Under 14 CFR § 65.95(a)(1), an Inspection Authorization holder is empowered to inspect and approve for return to service any aircraft, airframe, aircraft engine, propeller, appliance, or component part after a major repair or major alteration, provided the work was performed in accordance with technical data approved by the Administrator. Furthermore, 14 CFR Part 43 Appendix B dictates that major repairs and major alterations recorded on FAA Form 337 must cite specific approved data. Approved data represents technical information that has undergone formal engineering evaluation, testing, substantiation, and statutory endorsement by the FAA Administrator or an authorized designee to prove compliance with applicable airworthiness standards.

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Recognized Sources of FAA-Approved Data

An IA cannot assume or extrapolate data approval; the technical documentation must fall into one of the specifically recognized statutory categories established by FAA Order 8900.1 and Title 14 of the Code of Federal Regulations:

1. Type Certificate Data Sheets (TCDS) and Aircraft Specifications

The Type Certificate Data Sheet (TCDS) and historic Aircraft Specifications constitute the foundational type design approved under 14 CFR Part 21. Any engine, propeller, equipment option, control surface deflection limit, gross weight specification, or operating limitation listed directly in the TCDS or Aircraft Specification is approved data. For example, replacing a fixed-pitch propeller with an alternate propeller model specifically listed under "Propellers" in the aircraft's TCDS is an approved configuration change.

2. Airworthiness Directives (ADs)

Issued under 14 CFR Part 39, Airworthiness Directives are legally enforceable federal regulations addressing unsafe conditions. The technical corrective actions, repair schemes, inspection thresholds, and replacement instructions contained within an AD (or within manufacturer service documents mandated by an AD) represent statutory approved data. An IA may directly reference the specific AD paragraph when executing Block 8 of FAA Form 337 for a major repair mandated by that directive.

3. Supplemental Type Certificates (STCs)

Issued under 14 CFR Part 21 Subpart E, a Supplemental Type Certificate (STC) certifies a major change to the type design of an aeronautical product. The complete STC technical data package—including the certificate, approved model list (AML), installation drawings, engineering reports, flight manual supplements (AFMS), and Instructions for Continued Airworthiness (ICA)—constitutes FAA-approved data. The IA must verify that the specific aircraft serial number is listed on the STC or AML and confirm that the STC does not conflict with previously installed modifications.

4. DER Approved Data (Form 8110-3) and ODA Approved Data (Form 8100-9)

Under 14 CFR Part 183, the FAA delegates engineering evaluation authority to Designated Engineering Representatives (DERs) and Organization Designation Authorizations (ODAs):

• A DER substantiates compliance with specific airworthiness standards (e.g., structural strength, flammability, systems safety) and documents that approval on FAA Form 8110-3 (Statement of Compliance with Airworthiness Standards).
• An ODA engineering unit documents equivalent compliance on FAA Form 8100-9.
• Technical drawings, repair schemes, and test reports endorsed by an active DER on Form 8110-3 or ODA on Form 8100-9 constitute approved data for the specific aircraft or serial numbers identified.

5. FAA Field Approvals (Form 337 Block 3)

An FAA Field Approval is an individualized approval of technical data or a physical alteration granted by an authorized FAA Aviation Safety Inspector (ASI) from a Flight Standards District Office (FSDO). The approval is legally manifested by an official FAA stamp, signature, date, and district office identifier in Block 3 (For FAA Use Only) of FAA Form 337. Once signed by an ASI, the data package cited in Block 8 becomes approved data solely for that specific aircraft serial number.

6. Appliance Manufacturer Manuals with Explicit FAA Approval

Maintenance manuals for certain appliances and technical standard order (TSO) articles—specifically auxiliary power units (APUs), life-limited rotating components, dynamic drive systems, and avionics flight-guidance computers—frequently contain repair sections or overhaul limitations explicitly stamped and designated as FAA Approved. In such cases, the approved sections (e.g., Airworthiness Limitations Sections under 14 CFR § 23.1529 / § 25.1529) constitute approved data.

7. Manufacturer Structural Repair Manuals (SRM) with FAA-Approved Sections

While general maintenance manuals provide acceptable data, modern commercial and general aviation Structural Repair Manuals (SRMs) often contain specific structural repair schemes (such as fuselage skin doublers, wing skin patches, and frame splices) within chapters designated as FAA Approved. When an SRM chapter or repair drawing explicitly carries FAA approval notation, an IA may use those specific structural repair schemes as approved data for major repairs on that make and model.

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Recognized Sources of Acceptable Data

Acceptable data encompasses technical documentation that demonstrates sound aviation maintenance practices, but which has not been individually certified by FAA engineering for a specific major alteration or major structural redesign:

• FAA Advisory Circulars AC 43.13-1B and AC 43.13-2B: AC 43.13-1B (Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair) and AC 43.13-2B (Aircraft Alterations) provide industry-standard methods for inspecting, repairing, and altering aircraft. They are acceptable data under 14 CFR § 43.13(a).
• Manufacturer Maintenance and Service Manuals: Standard airframe, engine, and propeller maintenance manuals provide acceptable data for routine maintenance, inspections, component replacements, and minor repairs, unless a specific section explicitly denotes FAA approval.
• Manufacturer Service Letters and Service Bulletins: Unless specifically mandated by an Airworthiness Directive or bearing an FAA engineering approval stamp, manufacturer service bulletins (SBs) and service letters (SLs) are advisory and represent acceptable data.
• Industry Standards: Mil-Spec, AN/MS/NAS hardware specifications, SAE standards, and standard shop practices represent acceptable data.

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When Can AC 43.13-1B Be Used as Approved Data?

One of the most heavily tested concepts on the FAA IA Knowledge Exam is the precise legal status of AC 43.13-1B.

Many technicians mistakenly assume that because AC 43.13-1B is published by the FAA, it automatically serves as approved data for any major repair. This is legally incorrect. By regulatory definition, AC 43.13-1B contains methods, techniques, and practices acceptable to the Administrator. It is the baseline standard for acceptable data.

However, AC 43.13-1B may serve as approved data only under strictly defined statutory exceptions:

1. Explicit Regulatory or Directive Incorporation: When an Airworthiness Directive (AD) specifically mandates a repair to be accomplished in accordance with a designated chapter, section, or figure of AC 43.13-1B, the Advisory Circular acquires the force of approved data for that specific mandated repair.
2. Approved by the Administrator for Make and Model: In certain legacy aircraft type certifications, the FAA Administrator has officially approved specific repair schemes in AC 43.13-1B (such as standard fabric covering testing, rib stitching, or standard sheet metal lap splices) as an approved standard practice for that make and model.
3. Incorporated into an FAA Field Approval: When an applicant submits a Form 337 package for an FAA Field Approval and cites AC 43.13-1B as the technical basis, and an FAA ASI signs Block 3 granting the field approval, the specific cited sections of AC 43.13-1B become approved data for that specific aircraft serial number.
4. Advisory Circular AC 43.13-2B Caution: Unlike AC 43.13-1B (which addresses repairs), AC 43.13-2B (Alterations) is never automatically approved data for a major alteration. An alteration alters the configuration of the aircraft away from its original type design; therefore, using AC 43.13-2B for a major alteration invariably requires an STC or an FAA Field Approval.

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Approved vs. Acceptable Data Comparison Matrix

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The IA's Legal Exposure and Liability

The Inspection Authorization holder is the final gatekeeper of civil aviation airworthiness. An A&P mechanic may perform a major repair or major alteration, but only an IA, a certificated repair station, or the manufacturer possesses the statutory authority under 14 CFR § 43.7 and § 65.95 to inspect and approve that work for return to service.

If an IA signs Block 7 of FAA Form 337 approving a major repair or major alteration that was performed with only acceptable data:

• Immediate Unairworthy Status: The aircraft is legally unairworthy. Under 14 CFR § 91.403(a), the owner/operator cannot lawfully operate the aircraft, and any operation constitutes an illegal flight.
• Administrative Enforcement: Under 49 U.S.C. § 44709 and 14 CFR § 65.93, the FAA initiates certificate action against the IA. Signing Block 7 without approved data is treated by FAA enforcement counsel as a failure to exercise the care, skill, and judgment required of an IA, routinely resulting in the emergency suspension or permanent revocation of both the Inspection Authorization and the underlying mechanic certificate.
• Civil and Criminal Liability: Under 14 CFR § 43.12, making a fraudulent or intentionally false entry on FAA Form 337 is a federal offense punishable by fines and imprisonment. Furthermore, in the event of an accident, civil courts hold the signing IA personally liable for damages resulting from an unapproved modification.

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High-Yield Exam Traps & Regulatory Distinctions

• AC 43.13-1B is NOT Automatically Approved Data: The FAA IAR exam repeatedly tests whether an IA can approve a major repair based solely on AC 43.13-1B. The answer is no, unless the repair is specifically approved by the Administrator (e.g., in an AD or field approval).
• AC 43.13-2B is NEVER Approved Data for Alterations: AC 43.13-2B provides guidance on how to mount hardware or run cables, but it does not approve the alteration itself. Major alterations require an STC or FAA Field Approval.
• DER Data Approves Data, Not the Aircraft: A DER signing Form 8110-3 does not return the aircraft to service. The DER approves the engineering data; the IA must physically inspect the work, verify conformity to that data, and sign Block 7 of Form 337.
• Service Bulletins are NOT Mandatory or Approved Data Unless Tied to an AD: An aircraft manufacturer cannot issue an Airworthiness Directive. An OEM service bulletin—even if labeled "Mandatory"—is acceptable data unless it is formally incorporated by reference into an FAA AD.