Major vs. Minor Repair & Alteration

Whether a piece of work is a major or a minor repair or alteration is one of the most consequential classifications in general-aviation maintenance, because it determines how the work must be documented and who may approve it for return to service. The definitions and examples live in 14 CFR Part 43 Appendix A, read together with the definitions of "major repair," "major alteration," and "preventive maintenance" in 14 CFR 1.1. Appendix A sorts work into three buckets: major alterations, major repairs, and preventive maintenance, with everything that is a repair or alteration but not "major" falling into the minor category by default.

A major alteration is a change to the type design not listed in the aircraft, engine, or propeller specifications that might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness — or that is not done according to accepted practices or cannot be done by elementary operations. Appendix A gives concrete examples: alterations to wings, tail surfaces, fuselage, control systems, and landing gear on the airframe side; converting an engine from one approved model to another, or changes involving compression ratio or reduction gearing, on the powerplant side; and changes to propeller blade design or the installation of a feathering system on the propeller side.

A major repair is a repair that, if improperly done, might appreciably affect the same airworthiness qualities, or that is not done by elementary operations. Appendix A illustrates these with structural work: repairs to box beams, wing spars, wing ribs, and fuselage longerons, and repairs of stressed skin exceeding a defined size, on the airframe; and disassembly of a crankcase or crankshaft, or structural repair by welding or plating, on the powerplant. The common thread is that major repairs restore primary structure or engine cores in ways that carry real airworthiness risk if done wrong.

Everything that is a repair or alteration but does not meet these thresholds is a minor repair or minor alteration. Separately, Appendix A also lists preventive maintenance — a specific set of simple, listed tasks such as tire replacement, lubrication, spark-plug servicing, battery replacement, and small simple repairs to non-structural fairings and cover plates — which is a narrow category with its own approval rules and is not the same thing as "minor."

The classification drives the approval path directly. Major repairs and major alterations must be done using approved data — for example, an FAA-approved manufacturer manual, a supplemental type certificate, a field approval, or other approved sources — and their completion is recorded on FAA Form 337, Major Repair and Alteration. Return to service after a major repair or major alteration to an airframe, powerplant, propeller, or appliance generally requires an appropriately rated person, and for the classic general-aviation case that means a mechanic holding an Inspection Authorization, or a certificated repair station, must approve the work. Minor repairs and minor alterations can be performed and approved for return to service by an appropriately rated A&P mechanic using acceptable data, without a Form 337. Getting the major/minor call right is therefore the pivot on which the entire documentation and sign-off chain turns.

For flight schools and clubs, the major/minor distinction shows up whenever the fleet is repaired after damage or modified with new equipment. Installing an avionics package, adding a modification under a supplemental type certificate, or repairing structure after a hard landing can all cross into major territory, which means the job needs approved data, a Form 337, and an IA or repair station sign-off — not just an A&P return to service. Misclassifying a major job as minor is a compliance failure that can leave an aircraft with an improperly documented alteration in its records for the rest of its life.

For a maintenance manager or MRO, the classification is a daily judgment with audit consequences. The organization has to recognize when work is major, secure approved data before starting, complete the Form 337 correctly, and route the release to a person authorized for major work. Auditors examine aircraft records for major repairs and alterations that lack a corresponding Form 337 or approved data, and for alterations whose paperwork does not match what is physically installed. Clean, consistent classification and documentation is what keeps a fleet's airworthiness records defensible over decades.

Aviatize's Maintenance Execution and Maintenance Control modules let a maintenance organization record how each job was classified, attach the approved data relied on for major work, and ensure the release is routed to a person authorized to sign for a major repair or alteration. That keeps the major/minor decision — and the paper trail it triggers — visible on the work order rather than left to individual memory.

Through the Digital Data & Records module, the Form 337 and supporting approved data for every major repair and alteration stay linked to the specific aircraft, building a permanent, searchable record that matches the fleet's physical configuration and stands up to authority review.