AFAIK, the builder of an Experimental category aircraft has to build 51% of it. The intent, I believe, is to prevent an aircraft maker from building an entire aircraft and getting around the certification by, say, leaving out a single rivet or something.
But what if an amateur builder all but completes an airframe? Say he’s built all of the components but has not put them together yet. For whatever reason (starts a family, runs out of money, loses his medical, or whatever) he decides to sell the kit. Obviously, the buyer did not do 51% of the work. On the other hand, the unfinished airframe would still be “amateur built” (even if the bulder as an A&P).
So how is this handled by the FAA? Do they say, “51% or more was amateur-built, therefore it is eligible to be registered in the Experimental category.”? Who is the builder of record? The person who started (and built most of) it, or the one who finishes it? When is the airframe inspected?
The key FAR that addresses this is 21.191(g), which states:
The key here is “persons”. A group (or succession) of people may assemble the aircraft, as long as it’s for their own education or recreation. It doesn’t have to be by a single person.
Exactly. If 51% was built by persons who undertook the project for their own education or recreation, it qualifies.
Ceritification of repairmen for experimentals is covered in Advisory Circular 65-23A. When the aircraft is built by more than one person, one must be picked as the primary builder. This person (to get the repairmans certificate for that particular aircraft) may have to demonstrate to the FAA inspector their ability to perform the condition inspections and determine whether or not the aircraft is in condition for safe operation. It doesn’t necessarily have to be the person that started it, finished it, or that built most of it. If you buy a partially completed kit, you need to obtain documentation from the builder to prove the aircraft complies with the major portion rule.