14 CFR Part 43 Appendix A is the FAA rule that classifies every maintenance task on a certificated aircraft as a major alteration, a major repair, or preventive maintenance. That classification decides three things: who is allowed to touch the aircraft, who has to sign it off before it flies again, and what paperwork the FAA expects afterward. Get the category right and the process is routine. Get it wrong and you can invalidate the airworthiness certificate or draw a civil penalty.
What Counts as a Major Alteration
A major alteration is any change to an aircraft’s basic design that isn’t already listed in the FAA-issued type certificate data sheet or aircraft specifications. Appendix A groups them into four families: airframe, powerplant, propeller, and appliance.
On the airframe side, changes to wings, tail surfaces, the fuselage, engine mounts, control systems, or landing gear qualify when they go beyond the original type design.1Legal Information Institute. 14 CFR Appendix A to Part 43 – Major Alterations, Major Repairs, and Preventive Maintenance The same is true for changes to fuel, oil, cooling, heating, pressurization, electrical, hydraulic, de-icing, or exhaust systems that weren’t part of the original certification.
One trigger catches owners by surprise: adding equipment that shifts the empty weight or center of gravity beyond the maximum certificated limits is a major alteration on its own, even when the equipment itself looks minor.1Legal Information Institute. 14 CFR Appendix A to Part 43 – Major Alterations, Major Repairs, and Preventive Maintenance
For engines, converting from one approved model to another counts as a powerplant major alteration when it involves changes to compression ratio, propeller reduction gear ratios, or the substitution of major engine parts requiring extensive rework and testing. Installing a propeller model not previously approved for the aircraft is a major alteration on the propeller side.
Appliance major alterations include any design change to an appliance that wasn’t recommended by the manufacturer or required by an FAA Airworthiness Directive. For radio and navigation equipment approved under a type certificate or Technical Standard Order, changes affecting frequency stability, sensitivity, selectivity, noise level, or environmental test performance are specifically called out.2eCFR. 14 CFR Part 43 – Maintenance, Preventive Maintenance, Rebuilding, and Alteration
Installing a Supplemental Type Certificate is always a major alteration. By definition an STC introduces a major change in type design, so the full documentation and sign-off chain applies each time one is installed, even though the STC itself is pre-approved.3eCFR. 14 CFR Part 21 Subpart E – Supplemental Type Certificates
What Counts as a Major Repair
Where major alterations change the design, major repairs restore a damaged or worn component. A repair crosses into major territory when it involves strengthening, reinforcing, splicing, or fabricating primary structural members, or replacing them through processes like riveting or welding.
Appendix A names specific structural members whose repair is automatically major: box beams, spars, wing main ribs, compression members, and fuselage longerons among them. Repairing damaged stressed skin on monocoque or semimonocoque wings or control surfaces also qualifies, as does fixing any damaged area in metal or plywood stressed covering that exceeds six inches in any direction.1Legal Information Institute. 14 CFR Appendix A to Part 43 – Major Alterations, Major Repairs, and Preventive Maintenance That six-inch threshold matters. A patch job that looks small can push you across the line.
On the engine, separating or disassembling a crankcase or crankshaft on a reciprocating engine with an integral supercharger or non-spur-type propeller reduction gearing is a major repair. For propellers, repairing or straightening steel blades, machining steel hubs, and overhauling controllable-pitch propellers all qualify.
Appliance major repairs include calibrating instruments, calibrating radio equipment, rewinding field coils of electrical accessories, completely disassembling complex hydraulic power valves, and overhauling pressure-type carburetors or fuel, oil, and hydraulic pumps.2eCFR. 14 CFR Part 43 – Maintenance, Preventive Maintenance, Rebuilding, and Alteration
What Counts as Preventive Maintenance
Preventive maintenance is the routine-preservation category, and Appendix A lists 32 specific tasks that qualify. The list is exhaustive: if a task isn’t on it, it isn’t preventive maintenance, whatever it looks like.2eCFR. 14 CFR Part 43 – Maintenance, Preventive Maintenance, Rebuilding, and Alteration Common items include:
- Landing gear work: replacing tires, servicing shock struts, greasing wheel bearings
- Engine servicing: replacing or cleaning spark plugs, changing oil, cleaning or replacing fuel and oil strainers
- Fluids and hoses: replenishing hydraulic fluid, replacing hose connections other than hydraulic ones
- Electrical: troubleshooting broken landing light wiring, replacing bulbs and lenses on position and landing lights, servicing batteries
- Cosmetics and interior: refinishing decorative coatings where no primary structure is removed, small fabric patches without rib stitching, cabin upholstery repairs
- Miscellaneous: replacing safety wiring, replacing side windows that don’t interfere with operating systems, replacing safety belts, replacing seats with approved parts
The common thread is that none of these tasks require disassembling primary structure or operating systems. The moment you have to pull apart a control system or structural component to finish the job, you have left preventive maintenance.
Where Minor Repairs and Alterations Fit
Work that doesn’t meet Appendix A’s thresholds is minor. A minor repair or minor alteration uses standard practices, doesn’t move weight and balance outside certificated limits, and doesn’t compromise structural strength or airworthiness in a way that would demand the heavy documentation reserved for major work. The practical difference shows up at sign-off: a certificated Airframe and Powerplant mechanic can perform and approve minor work alone, while major work needs a second layer of approval.
Who Can Perform the Work and Who Signs It Off
The FAA draws a sharp line between doing the work and approving the aircraft for return to service. Most of the confusion in this area lives on that line.
Performing the Work
A certificated A&P mechanic can perform maintenance, preventive maintenance, and alterations within the scope of the ratings held.4eCFR. 14 CFR 43.3 – Persons Authorized to Perform Maintenance, Preventive Maintenance, Rebuilding, and Alteration An uncertificated person can also do the physical work, but only under the direct supervision of a certificated mechanic or repairman who personally observes the work and stays available for consultation. A supervised worker cannot perform any required inspection, and cannot perform any inspection following a major repair or major alteration. Certificated repair stations under Part 145 and air carriers under Part 121 or Part 135 operate under their own maintenance authority.
Any pilot holding a Part 61 certificate (other than a sport pilot on a standard-category aircraft) may perform the 32 preventive maintenance tasks on an aircraft they own or operate, provided the aircraft isn’t used under Part 121, Part 129, or Part 135.4eCFR. 14 CFR 43.3 – Persons Authorized to Perform Maintenance, Preventive Maintenance, Rebuilding, and Alteration Sport pilot certificate holders can do preventive maintenance only on aircraft they own or operate that hold a special airworthiness certificate in the light-sport category.
One narrow commercial carve-out exists. The FAA may authorize a Part 135 rotorcraft operator in a remote area to let pilots handle specific preventive maintenance items when no mechanic is available, the problem arose en route, and the pilot has completed an approved training program for those tasks. Outside that scenario, pilots on commercial operations should not be performing maintenance.
Approving Return to Service
An A&P mechanic can approve return to service for minor repairs and minor alterations. Major repairs and major alterations are different. Approval for those has to come from someone who holds an Inspection Authorization, a credential that sits on top of the A&P certificate.5eCFR. 14 CFR 65.95 – Inspection Authorization Privileges and Limitations The IA holder verifies the work was done using FAA-approved technical data and signs the approval block on the required paperwork. IA holders also perform annual inspections and supervise progressive inspections.
Put practically: an A&P can do the hands-on labor of splicing a wing spar, but the aircraft can’t fly again until an IA holder inspects the work and signs it off.6eCFR. 14 CFR 43.7 – Persons Authorized to Approve Aircraft, Airframes, Aircraft Engines, Propellers, Appliances, or Component Parts for Return to Service After Maintenance, Preventive Maintenance, Rebuilding, or Alteration
Documentation Requirements
Every person who performs maintenance, preventive maintenance, rebuilding, or alteration has to make a maintenance record entry with a description of the work, the completion date, the name of the person who performed the work (if different from the approver), and the signature, certificate number, and certificate type of the person approving the work.7eCFR. 14 CFR 43.9 – Content, Form, and Disposition of Maintenance, Preventive Maintenance, Rebuilding, and Alteration Records That signature is the return-to-service approval for the specific work performed.
Major repairs and major alterations require FAA Form 337 on top of the logbook entry. The form is prepared in at least duplicate. One signed copy goes to the aircraft owner. A second copy has to reach the FAA Aircraft Registration Branch in Oklahoma City within 48 hours after the aircraft is approved for return to service.8Legal Information Institute. 14 CFR Appendix B to Part 43 – Recording of Major Repairs and Major Alterations For extended-range fuel tanks installed in the passenger or baggage compartment, a third copy must be kept on board.9Federal Aviation Administration. AC 43.9-1G – Instructions for Completion of FAA Form 337 Questions about completing the form go to the local Flight Standards District Office, but the completed form itself goes to Oklahoma City.
Penalties for Getting the Classification Wrong
Performing maintenance without proper authorization, skipping required documentation, or misclassifying work can produce serious consequences. Under 49 U.S.C. § 46301, the FAA can impose civil penalties for violations of aviation safety regulations, including the maintenance rules.
Following the FAA Reauthorization Act of 2024, the maximum civil penalty the FAA can impose administratively is $100,000 for an individual and $1,200,000 for a company or other non-individual person.10Office of the Law Revision Counsel. 49 USC 46301 – Civil Penalties A separate provision for individuals and small business concerns caps liability at $10,000 per violation for most maintenance-related infractions. Penalties apply per violation, so a pattern adds up quickly.
Beyond fines, the FAA can suspend or revoke airman certificates, including mechanic certificates, inspection authorizations, and pilot certificates, for performing unauthorized maintenance or falsifying records. Insufficient or missing maintenance records can also render a Standard Airworthiness Certificate invalid, effectively grounding the aircraft until the records are reconstructed and the aircraft is re-inspected.
How Commercial Operations Change the Picture
Appendix A’s classifications apply regardless of how the aircraft is operated. A spar splice is a major repair whether the aircraft flies charter passengers or weekend trips. What changes with commercial operations is the oversight around that work.
Aircraft operated under Part 91 are largely self-policed. The owner is responsible for keeping the aircraft airworthy, and pilots can perform the 32 preventive maintenance tasks on aircraft they own or operate. Part 135 and Part 121 operators layer additional requirements on top of Part 43: they must maintain aircraft to their operational standards, employ designated maintenance personnel, and follow structured inspection programs. Pilot-performed preventive maintenance is generally prohibited under Parts 121 and 135, with the narrow remote-rotorcraft exception noted earlier.