Homebuilt Aircraft: How Much is More than Half?

By Scott Spangler on February 27th, 2008

This seems like a simple question, and it is–unless you’re talking about an amateur-built experimental aircraft. Here the answer is critical because these aircraft are certificated under FAR 21.191(g), which requires “…the major portion [more than half, or 51 percent] of which has been fabricated and assembled by persons who undertook the construction project solely for their own education or recreation.”

rv-7_quickbuild_lgOver the past half century homebuilts have gone from simple designs built from scratch to complex, sleek, high-performance, high flying composite kit airplanes with pressurization and turbine engines. Homebuilding was–and still is–the only affordable path to owning an airplane because the builder does the work. With the advent of kit aircraft, it has also become a way of getting comparable–or better–performance capabilities at roughly a third of the cost of store-bought aircraft. The popularity of both explain why homebuilts comprise nearly 15 percent of the single-engine GA fleet.

When builders turn a pile of raw materials into an airplane with a hacksaw, rivet gun, and torch, figuring out who built the major portion of the aircraft is simple. When builders complete a kit aircraft, where its manufacturer has done up to 49 percent of the work, and avail themselves of commercial assistance (paid help), calculating how much work each entity contributed to the finished aircraft  is  not so easy.  Just ask the Amateur-built Aircraft Aviation Rulemaking Committee, chartered in July 2006 to recommend solutions to this problem and others related to it.

In its recently released  final report, the  committee, composed of  representatives from the FAA, aviation organizations, kit airplane manufacturers, and those who offer commercial assistance to builders agreed on enforcement and FAA policy recommendations to deal with the problem of professionally built kit aircraft. Deciding how much is more than half ended in a stalemate, so the FAA will figure out a way to make this calculation and publish their work for public comment later this year. They have my sympathy, for the task will not be easy.

To determine the contribution of the kit maker and the amateur builder, for nearly 30 years the FAA has used Form 8000-38, which is included in AC 20-139, Commercial Assistance During Construction of Amateur-built Aircraft. It lists all the fabrication and assembly operations needed to built an aircraft, and when all is said and done, the builder must have one more checkmark than the kit company.  There is no column for commercial assistance.

This isn’t as simple as it sounds because both kit manufacturers and builders get checks for certain tasks. As Dick VanGrunsven wrote in Pokin’ the Bear, "This at first glance would seem to result in a canceling or neutralizing  effect, but it really doesn’t in the final count. It permits the manufacturer  to contribute his tooling and technology to a task, and the builder to contribute his skilled labor."

But this begs the question: Is building a fuselage of precut, match-hole drilled pieces of sheet metal the same as gluing together the two halves of a composite fuselage? Yes or no, I could make an argument on both sides; fortunately, I don’t have to, but the FAA can’t avoid it.

Further complicating the math is commercial assistance, paying someone to help you build the airplane. It’s different than paying someone to teach you how to build your airplane, which is what I did when building an RV-8. The instructor taught me how to rivet using my tail kit, and then I drilled the prepunched holes to their final size, dimpled, and deburred them, and drove all the rivets. The instructor helped by holding the bucking bar when my arms weren’t long enough.

Had I paid for commercial assistance, I would have built one horizontal stab and elevator, and he would have built the other. In homebuilt math, it could be that the manufacturer did 49 percent of the work in creating the kit, leaving 51 percent for the builder. The question is how to count the percentage of work done by the commercial assistance. In the end, only one thing is certain, to certificate the airplane as an amateur-built experimental aircraft, the builder must do the major portion, because the FAA does not (thankfully) want to change the rule that has served aviation well since it took effect in September 1952. It will be interesting to see what the FAA comes up with. — Scott Spangler

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2 Responses to “Homebuilt Aircraft: How Much is More than Half?”

  1. Grandfathered Kits Don’t Guarantee Amateur-Built Certification - Jetwhine: Aviation Buzz and Bold Opinon Says:

    [...] since the FAA formed an aviation rulemaking committee to take a look at the 51-percent rule (see Homebuilt Aircraft: How Much is More than Half?) Especially anxious were the manufacturers and builders of aircraft on the FAA’s list [...]

  2. Proposed Policy Doesn’t Solve Homebuilt Problem - Jetwhine: Aviation Buzz and Bold Opinion Says:

    [...] If my homebuilding buddies are a typical sample of the amateur-built airplane community, there’s a lot of confusion about what led to the new policy the FAA has proposed. (See Homebuilt Aircraft: How Much is More than Half?) [...]

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