Regulations, approved data and maintenance records

A heavily regulated profession

Aircraft maintenance is one of the most heavily regulated professions in aviation. Every inspection, repair, alteration and return-to-service decision must comply with federal regulations and be supported by proper technical data. Understanding where the rules come from, what data you are allowed to use, and how to create a legally valid maintenance record is a core skill for every aircraft technician.

In maintenance, the work is not complete until it is properly documented. A perfectly executed repair without the required record entry is legally incomplete.

The regulatory framework

In the United States, civil aviation maintenance is governed by Title 14 of the Code of Federal Regulations (14 CFR), commonly known as the Federal Aviation Regulations (FARs). While dozens of parts affect aviation maintenance, a handful form the foundation of a technician's daily work.

Part 21: certification procedures

Part 21 governs how aviation products and parts are approved and certificated. It defines what a product was originally approved to be and how changes to that design may be approved. It covers:

• Type certificates (TC)
• Supplemental type certificates (STC)
• Production approvals
• Parts manufacturer approval (PMA)
• Airworthiness certificates

Parts 23, 25, 27, 29, 33 and 35: airworthiness standards

These parts contain the design standards that aircraft and components must meet before certification. Although technicians may not reference these regulations daily, they establish the engineering requirements behind approved designs.

• Part 23: normal category airplanes
• Part 25: transport category airplanes
• Part 27: normal category rotorcraft
• Part 29: transport category rotorcraft
• Part 33: aircraft engines
• Part 35: propellers

Part 39: airworthiness directives (ADs)

An airworthiness directive (AD) is a legally enforceable regulation issued to correct an unsafe condition. Compliance with applicable ADs is mandatory. An aircraft that does not comply with a required AD is generally not airworthy. ADs may require:

• Additional inspections
• Part replacements
• Modified maintenance procedures
• Operating limitations

Part 43: maintenance rules

Part 43 is one of the most important regulations for maintenance personnel. It governs maintenance, preventive maintenance, rebuilding, alterations, maintenance records and return-to-service requirements. It also contains:

• Performance rules
• Recordkeeping requirements
• Appendix A (major repairs and alterations)
• Appendix D (scope of annual and 100-hour inspections)

Part 65: certification of maintenance personnel

Part 65 establishes the privileges, limitations and certification requirements for aviation maintenance personnel. It defines who may perform certain work and who may approve aircraft for return to service. It covers:

• Airframe and powerplant (A&P) mechanics
• Inspection authorization (IA) holders
• Repairmen
• Parachute riggers

Part 91: aircraft operation and recordkeeping

Part 91 places responsibilities on aircraft owners and operators. While technicians perform maintenance, owners and operators are ultimately responsible for ensuring required maintenance is accomplished. Their responsibilities include:

• Maintaining airworthiness
• Performing required inspections
• Ensuring AD compliance
• Maintaining aircraft records

Repairs

Before beginning any maintenance task, determine what type of work is being performed. A repair restores an aircraft, engine, propeller or component to its original approved condition or an approved altered condition. The goal of a repair is restoration, not design change. Examples include:

• Replacing brake components
• Repairing sheet metal damage
• Replacing a damaged control surface
• Installing an approved replacement engine

Alterations

An alteration changes the aircraft's original design or configuration. Alterations change the approved design and therefore require additional regulatory consideration. Examples include:

• Installing new avionics
• Adding winglets
• Modifying interior configurations
• Installing additional equipment

Major vs. minor work

Both repairs and alterations are classified as either major or minor. This distinction determines documentation requirements, data requirements and approval processes.

Major repairs and major alterations

Part 43 Appendix A provides examples of major repairs and major alterations. Major work typically requires approved data, detailed documentation and FAA Form 337. Major work generally involves:

• Structural changes
• Significant systems modifications
• Work affecting weight and balance
• Performance changes
• Flight characteristics
• Structural strength

Minor repairs and minor alterations

Minor work is any repair or alteration that does not meet the criteria for major work. Most routine maintenance falls into this category. Even minor work must comply with Part 43 and be properly documented.

Approved data

One of the most important concepts in aircraft maintenance is understanding the difference between approved data and acceptable data. The two terms are not interchangeable.

Approved data has received formal FAA approval or approval through an FAA-authorized process. Approved data is generally required for major repairs and major alterations. Examples include:

• Type certificate data sheets (TCDS)
• Airworthiness directives (ADs)
• Supplemental type certificates (STCs)
• FAA-approved portions of manufacturer manuals
• FAA-approved engineering drawings
• Designated Engineering Representative (DER)-approved data
• FAA-approved field approval data

Acceptable data

Acceptable data consists of methods, techniques and practices that the FAA recognizes as suitable for performing maintenance. Acceptable data often supports routine maintenance and minor repairs. Examples include:

• Aircraft maintenance manuals (AMM)
• Component maintenance manuals (CMM)
• Service instructions
• FAA advisory circulars
• AC 43.13-1B
• AC 43.13-2B

Understanding AC 43.13-1B

One of the most frequently referenced maintenance documents is FAA Advisory Circular 43.13-1B, which provides accepted methods, techniques and practices for aircraft inspection and repair. Technicians often use AC 43.13 when:

• Manufacturer data is unavailable
• A repair method is needed for common structures
• Guidance is required for standard maintenance practices

AC 43.13 is not automatically approved data

However, AC 43.13 is not automatically approved data. Always verify the applicable requirements before relying on it for major work. It may support major repair documentation only when:

• The guidance is directly applicable
• It is appropriate to the aircraft product involved
• It does not conflict with manufacturer instructions
• Regulatory requirements permit its use

FAA Form 337

FAA Form 337, Major Repair and Alteration, documents major repairs and major alterations performed on aircraft. Form 337 becomes a permanent part of the aircraft's maintenance history. It typically includes:

• Aircraft identification
• Description of work performed
• Reference data used
• Approval information
• Return-to-service documentation

Maintenance records and logbook entries

Maintenance records are legal documents. Future technicians, operators, inspectors and buyers depend on the accuracy of these records. They provide a permanent history of:

• Work performed
• Inspections completed
• Airworthiness status
• Regulatory compliance

Required elements under 14 CFR 43.9

A maintenance record entry must include:

• Description of the work: the entry must describe the work performed or reference the approved or acceptable data used. The description should be detailed enough that another qualified technician can understand what was accomplished.
• Completion date: the date the maintenance was completed must be recorded.
• Identification of the person performing the work: the record must include the name of the person who performed the work.
• Return-to-service approval: when approving the item for return to service, the entry must also include a signature, certificate number and certificate type.

What a signature certifies

The signer is certifying that the work was performed in accordance with applicable regulations and data.

Inspection record requirements

Inspection entries are governed by 14 CFR 43.11 and require additional information. Inspection records generally include:

• The type of inspection performed
• Aircraft total time in service
• The inspection date
• Airworthiness determination
• Any required discrepancy list

Airworthy or not

The entry must clearly indicate whether the aircraft:

• Was found airworthy and approved for return to service, or
• Was found unairworthy and provided with a list of discrepancies.

Why records matter

Poor documentation can create serious airworthiness and liability issues years after maintenance is completed. Maintenance records serve several critical functions:

• Demonstrate regulatory compliance
• Establish aircraft history
• Track inspections and AD compliance
• Support aircraft value and resale
• Provide legal documentation
• Help future technicians understand prior work

Key takeaways

• Classify the work first: repair or alteration, major or minor.
• Use the correct data: understand whether approved or acceptable data is required.
• Major repairs and alterations generally require approved data and FAA Form 337.
• Maintenance records are legal documents, not administrative paperwork.
• Every return-to-service approval carries regulatory and professional responsibility.
• If it isn't documented, from a regulatory perspective, the maintenance is not complete.

The bottom line

Aircraft maintenance is governed by a framework of regulations designed to ensure safety, consistency and traceability. Successful technicians understand not only how to perform maintenance, but also how to determine the correct classification of work, select the proper technical data, and create complete and accurate maintenance records. In aviation, the wrench and the logbook carry equal importance, because both are essential to maintaining airworthiness.