Buying someone else’s unfinished aircraft project can save money and years of work, or it can hand you a pile of parts you can never legally certificate. This guide shows how to inspect a partial build, why the builder log and the major-portion rule decide everything, and the questions to ask before you pay. The goal: know what you are actually buying.
Why unfinished projects get sold
Most abandoned projects are not abandoned because the aircraft is bad. Life changes, health changes, skills run out, or the builder underestimated the time. That means good projects exist at fair prices. It also means you must judge the work of a stranger, sometimes an inexperienced one, and sometimes work that is undocumented.
The paperwork decides more than the parts
For an amateur-built aircraft in the United States, the certificate is granted for education and recreation, and the builder must have completed the major portion of the work. This is the 51% rule, and it follows the airframe, not the person.
Why this matters when buying
If a previous owner built most of the aircraft, you can usually still complete it and register it as amateur-built, but the builder log and documentation of who did what become critical. What you cannot do is claim you completed the major portion if you did not. That affects your eligibility for the repairman certificate, which lets the primary builder do the annual condition inspection.
The repairman certificate trap
The repairman certificate for an amateur-built aircraft is issued to one person, typically the primary builder, and it does not transfer with a sale. If you buy a mostly finished project, you likely will not qualify for that certificate, which means you will pay a mechanic for condition inspections for the life of the aircraft. That is not a dealbreaker, but it is a cost you must price in.
The builder log is the asset
A complete builder log with dated photos is worth more than the parts. It proves what was done, how, and by whom. A project with no log is not automatically worthless, but it raises real questions about airworthiness documentation and the eventual FAA inspection.
- Photos at each stage, dated, showing the actual work.
- Receipts for the kit, engine, avionics, and major parts.
- Records of any factory quick-build portions, which count differently toward the major portion.
- Any Technical Counselor visit notes.
Inspecting the physical build
Bring someone who knows the type. An EAA Technical Counselor can help you assess unfamiliar work. Look for consistency: good work tends to be consistent, and sudden changes in quality suggest the build changed hands or the builder rushed.
- Check hidden work through inspection panels where possible.
- Verify serial numbers on airframe and engine match the paperwork.
- Assess corrosion on metal, resin quality on composite, glue joints on wood.
- Confirm the kit is a current, supported design with parts still available.
A real scenario
A buyer finds a composite project at half the cost of a new kit. The airframe looks clean, but there is no builder log and no photos of the internal layups. A Technical Counselor points out that the buried structure cannot be verified without destructive inspection, and the FAA inspection will be difficult without documentation. The buyer negotiates the price down sharply to reflect that risk, then decides the discount is not worth the uncertainty and walks away. That is a good outcome, because the decision was informed.
Common mistakes and how to fix them
- Paying kit prices for an undocumented project. Fix: price the missing log and unknown work as risk, not as saved labor.
- Assuming you get the repairman certificate. Fix: confirm eligibility; if not, budget for paid condition inspections.
- Ignoring parts availability. Fix: verify the design is still supported and parts exist.
- Skipping an expert inspection. Fix: bring a counselor or type-experienced builder before you pay.
- Overlooking engine and avionics condition. Fix: these are large costs; assess them separately from the airframe.
Action steps
- Ask for the full builder log and photos before viewing.
- Verify airframe and engine serial numbers against documents.
- Bring a Technical Counselor or type expert to inspect.
- Confirm the design is current and parts are available.
- Clarify your repairman certificate eligibility and inspection costs.
- Price undocumented or hidden work as risk in your offer.
Conclusion and next step
A partial project is a paperwork purchase as much as a parts purchase. The builder log and your legal eligibility matter as much as the airframe quality. Your next step: before you visit any project, ask the seller to send the complete builder log and part receipts. If they cannot, treat that as your first data point.
FAQ
Can I finish someone else’s project and register it as amateur-built?
Often yes, if the major portion was built for education and recreation and documentation supports it. The details depend on the build history and FAA review.
Will I get the repairman certificate?
Usually not if you were not the primary builder. That certificate is issued to one person and does not transfer with the aircraft.
Is a project without a builder log worthless?
Not worthless, but riskier. Missing documentation complicates the FAA inspection and hides work you cannot verify, so it should lower the price.
How do I judge build quality I cannot see?
Bring an EAA Technical Counselor or an experienced builder of the same type, and rely on documentation for buried structure.
References
- U.S. Federal Aviation Administration (FAA) — amateur-built aircraft certification and repairman certificate guidance.
- Experimental Aircraft Association (EAA) — Technical Counselor program and homebuilder resources.