DIY Aircraft Kits

FAA Regulations For Amateur-Built Airplane Kits

We hear the term “experimental” used within the sport aviation industry regularly. The most common usage of experimental applies to a classification of an airworthiness certificate used for an amateur-built airplane. This is different from the airworthiness category assigned to a plane that’s mass-produced by a manufacturer, which is then sold to the general public.

We will explore the meaning of the word experimental in this article.  The Federal Aviation Regulations (FAR) about the performance of experimental planes can be complicated. We will try to clarify the confusion that exists and also to simplify the regulations as they apply to build an aircraft. Each phase of construction and operating an airplane will be discussed together with the applicable regulations.

Generally, we are very blessed to have a minimal number of regulations that pertain to flying and building our amateur-built airplane. When a manufacturer intends to mass-produce an airplane, FAR’s require them to comply with design criteria that are detailed in FAR Part 23. This regulation is extremely restrictive as to speed, design, weight, etc. Amateur builders are not limited to Part 23 or any other certification regulations. Our only restriction is that we have to construct and build the majority of the airplane. (Most plane kit manufacturers really voluntarily comply with the guidelines of Part 23.)

Part 23 is titled “Airworthiness Standards: Normal, acrobatic, utility, and commuter category airplanes.” As the builder of our airplane, which will not be produced, we’re limited by our creativity and ingenuity. Needless to say, once we build our own plane, we’re likely to impose strict restrictions and limitations concerning the quality of materials used, construction, etc. We definitely want a safe, stable airplane to fly and in which to carry our passengers.


Let’s specify the “experimental” category and see how it applies to our amateur-built airplane. To fly within the USA, we have to have a registration certificate, a registration certificate, an airworthiness certificate, a copy of the operating conditions, and the weight and balance for our airplane.

Airworthiness certificates are categorized under two categories based on FAR 21.175 — special and standard. Standard airworthiness certificates are circulated for most production planes, and they’re usually classed under the normal category. We’re considering special airworthiness certificates, which are further broken down into several additional categories, of which one is “experimental.”

Airworthiness certificates are assigned for different functions. These functions include

(1) research and development,

(2) to conduct flight tests to demonstrate compliance with airworthiness regulations,

(3) for team training,

(4) for display,

(5) for air racing,

(6) to conduct market surveys and sales presentations,

(7) to run an amateur-built plane, and

(8) to run a kit-built aircraft that was assembled by an individual from a kit manufactured by the holder of a production certificate for this kit.

We’ll fundamentally consider individually with purpose number 7, to run an amateur-built aircraft. Fully 95 percent of all planes that we produce from a kit or from a set of programs will be certified under the amateur-built category. Purpose number 8, the kit-built category, only refers to kit manufacturers that have licensed their plane under a type certificate termed a “primary category” aircraft. Up to now, just 1 kitplane manufacturer falls within this category to our knowledge.


The rest of the kit plane manufacturers sell their kits to be classed under the experimental certificate to operate an amateur-built aircraft. FAR 21.191(g) is the core of all regulations for the builder of a plane. This law states the following: “Running amateur-built aircraft.

Operating an aircraft, the significant part of that has been assembled and fabricated by persons who managed the project solely for their own education or recreation.” This regulation is the gist of custom aircraft construction. The intent of this classification is extremely clear. Notice that one or more individuals may construct the airplane, but they need to construct it only for their own pleasure or education.

Ultralight planes fall under a different set of principles. If your finished plane meets the conditions of FAR 103.1, it’s classified as an ultralight vehicle and, as such, does not ask for an airworthiness certificate.

Briefly, these demands are single pilot, weighing less than 254 pounds empty weight, used for recreation only, not able of over 55 knots in level flight, fuel capacity not to exceed 5 U.S. gallons, and the power-off stall speed is not surpassing 24 knots.

As you can easily observe, nearly all custom-built airplanes exceed at least one of these criteria. Frequently, the owner of an ultralight plane will opt to certificate their aircraft under the experimental category.

This is typically done to comply with the regulations regarding passengers, weight, etc. Notice that the operator of an ultralight doesn’t need to be a certified pilot as compared to the operator of an amateur-built airplane, who, obviously, has to be a licensed pilot and the holder of a current medical certificate.

To proceed with our discussion of FAR 21.191(g), it is clear that to certificate a plane under the experimental category for amateur-built operation, we have to assemble and build at least 51 percent of the aircraft. The FAA highlights this limitation in at least two publications.

The first is FAA Order 8130.2C; that’s the airworthiness certification handbook used by FAA Inspectors as a guide to scrutinize an airplane and also to issue an airworthiness certificate. On page 116 of the guide, these guidelines appear under the eligibility section. (1)”Amateur-built aircraft might qualify for an experimental airworthiness certificate while the applicant shows satisfactory proof that the aircraft was fabricated and assembled by a person or group of people.”

This section goes on to say that the project must be undertaken for recreational or educational purposes, and the FAA must realize that the airplane complies with satisfactory criteria. Aircraft that are built and assembled as a business for sale is not considered to be amateur-built. This statement appears within the Order: “NOTE: amateur-built kit proprietor (s) will jeopardize eligibility for certification under FAR 21.191(g) if somebody else builds the plane.” The applicant for an amateur-built certificate must sign a notarized form (FAA Form 8130-12), certifying the significant part was fabricated and constructed for recreational or educational purposes, that evidence is available to support the statement. The next place that the 51% rule is highlighted is in Advisory Circular 20-27D on page 5 under 7(b). This section simply highlights the significant portion rule.

When you purchase a plane kit from a manufacturer, the kit ought to be recorded on the FAA listing of kits, which have been evaluated to make sure that 51 percent of the construction will be finished by the purchaser (that is usually called the “major portion” principle). We need to highlight that the FAA in no way supports any of those kits, nor do they support kit makers. They just evaluate the kits solely to determine if an aircraft built in the kit will satisfy the significant portion criteria. A listing of those kits is available in the regional FAA office. We don’t recommend buying a kit that is not on this list unless you’re ready to prove to the FAA Inspector that the kit meets the appropriate criteria.

The FAA doesn’t expect the builder to fabricate every part of the airplane personally. A variety of items can be bought, and tasks can be obtained. FAA Advisory Circular 20-139 named “Commercial Assistance During Construction of Amateur-Built Aircraft” presents a very comprehensive guide regarding what can be bought complete and what could be contracted commercially. Propellers, engines, standard aircraft hardware, and wheel and brake assemblies are examples of items that may be bought.

Painting an airplane, installation of avionics, and upholstery items are examples of tasks that may be contracted. The main point of the whole discussion is that you need to prove to the FAA Inspector, who issues the airworthiness certification that you have complied with FAR 21.191(g).

If you choose to let someone build your plane to be certificated as amateur-built, you’ll be asked to license it under the experimental category for the purpose of the exhibition. This category is more restrictive than amateur-built. The objective of this class is to permit the holder to display their plane at air shows, television filming, motion pictures, etc., and of course, to fly to and from those productions.

Now that we’ve reviewed the common regulations concerning developing your airplane, we will show particular ordinances as they refer to each phase of construction, flying, and repairing an amateur-built aircraft. We would advise that you get a copy of the regulations for your reference. Several books are available that contain the FAR’s along with computer disks containing all the FAA regulations. The FAA also owns a website with all regulations.

Initial Building Phase

The first phase of construction is the building phase. We would recommend that before you start your job, you ask your regional FAA office for their information packet that is available relating to an amateur-built airplane. Part of the packet is Advisory Circular 20-27D, you will refer to frequently. Regarding regulations governing the initial stage, we’ve discussed in detail FAR21.191(g). Another law, FAR 21.173, presents the eligibility for an airworthiness certificate. FAR 21.191 defines all functions which are allowed for licensing under the experimental group such as, obviously, amateur-built.

FAR 21.175 defines the categories of airworthiness certificates. FAR 21.193 holds the information that must be filed for an experimental certificate. Advisory Circular 20-27D presents this information much more thoroughly.

Amateur-Built Airplane

FAA Part 45 details the markings that are essential to your aircraft concerning what’s required, dimensions, location, etc. FAR 45.23 is where we’re told that we’ll show the term “experimental” in letters not less than two inches high nor more than 6 inches high close to the entrance to the cockpit or cabin. FAR 45.29 provides us with the size of registration marks and especially allows us, as owners of experimental aircraft, to use 3-inch-high numbers and letters giving our maximum cruising rate is less than 180 knots. If our speed is greater than 180 knots, we’re expected to utilize 12-inch letters and numbers. Another regulation applies if our plane had an experimental certificate issued. This regulation enables us to use letters and numbers only 2 inches high. FAR45.22 defines the principles as they apply to the older planes.

Continuing the building stage, FAR 47.15 informs us about registration numbers. You may pick an “N” number of your choice providing the number is currently not in use on another plane. FAR 47.33 lists the information that should be submitted with your application for the “N” number. You’re required to have specific gear if you wish to fly your plane at night or under Instrument Flight Rules. The essential equipment, including tools, radios, etc., are outlined in FAR 91.205. This law also tells you what’s required during the day for VFR flight. FAR 91.207 summarizes the requirements for emergency locator transmitters (ELT). The prerequisites for an ELT are the same for all planes. It should be noted that you’re engaged in flight training, and in case you stay within 50 miles of your home airport, you’re not required to have an ELT. If you have a single-place airplane, you’re not required to install an ELT.

Airworthiness Testing Guidelines

FAR 91.305 defines a flight test area. It states you must conduct your flight testing over sparsely populated areas having light air traffic. FAR 91.319 provides a list of operating limitations. As soon as your aircraft is inspected, you’ll be provided a copy of the constraints. The inspector will issue Phase 1 and Phase 2 in the time of review, providing you with two sets of limitations; flight testing and consequent operation. The flight test area is described within the Phase 1 limitations along with the required number of hours you must fly the aircraft. The principal limitations regarding flight testing are: (1) no passengers, (2) day, VFR only, (3) no flight within congested areas, (4) you have to advise ATC that you’re experimental, and (5) the pilot must have the appropriate ratings. Needless to say, the general rules under FAR Part 91 are applicable.

Phase 1 limitations have an expiration period of 12 months from the date of the issue. All flight testing must be performed within that period, or the aircraft has to be re-inspected. Among the constraints, in FAR 91.319, that’s interesting is that to have the Phase 1 restrictions lifted, you have to demonstrate that the aircraft has no hazardous operating characteristics.

It is manageable throughout its standard range of speeds and maneuvers. The FAA includes an Advisory Circular that is extremely useful in presenting guidelines for flight trials. This circular, Advisory Circular 90-89, is necessary to read before your first flight. Also, the EAA Flight Advisor program is highly significant. The flight testing phase should be a fun result in your building experience, and it will be if designed and executed properly.

Operation of Your Amateur Self-Built

All of the operating rules under FAR Part 91 apply to the daily operations of your aircraft. Moreover, the operating conditions are given under FAR 91.319 and issued by the FAA Inspector at the time of inspection command. After completion of Phase 1, you’re then permitted to carry passengers and fly at night or IFR if so outfitted. Phase 2 limitations do include some constraints that merit discussion.

To start with, you may not carry passengers or property for hire. Secondly, any significant changes which are made to the plane, as defined by FAR 21.93, require scrutiny by the FAA before the next flight. A minor change is defined as a one that has no apparent effect on the weight, balance, structure, or anything.

Examples of a significant change would be a separate a different pitch propeller, horsepower engine, a change in the basic design, etc. If there is a change made to notify the FAA in writing, providing the particulars of the change to determine whether or not an inspection will be needed. Thirdly, you may not run your airplane unless it has obtained a state inspection (annual inspection).

Amateur-built Airplane Maintenance

Like we described in the previous section, a condition inspection is needed every 12 months on amateur-built aircraft. This test is similar to a yearly inspection wanted by FAR Part 43 on production airplanes. Phase 2 Running Limitations refers to FAR Part 43, Appendix D, as the guide to performing this inspection. The inspection can be done by any certified A & P technician, an FAA Approved Repair Station, or from the manufacturer of the airplane presented the contractor receives a “Repairman’s Certificate.” FAA Advisory Circular 65-23A is accessible for advice regarding the application and perquisites of the certification.

In short, the primary builder of the plane is eligible to apply for this certification that permits a logbook endorsement of this condition check and inspection of the plane. It’s noteworthy that the primary builder must be one individual. If a group of individuals builds an airplane, only one could be designated as the primary builder. Furthermore, the issuance of the repairman’s certificate only applies to the one aircraft that has been built by the primary builder and no other plane, regardless of the same kind, etc..

Normal maintenance on an experimental plane can be performed virtually by anyone regardless of credentials. Furthermore, this does not refer to the condition check earlier explained. You may perform maintenance items on the engine, whether it is “certified.” After a certified engine is set on an amateur-built airplane and is run, it no longer conforms to its type design. This means that the motor can’t be placed on any aircraft other than an amateur-built until it has been examined and found to meet its type design.

Additionally, it has to be found to be in a condition for safe operation “airworthy.” Common sense is required. We do not want to repair an engine on our airplane unless we are furnished to do so with tools and precise knowledge.

We will point out that FAR. Part 43 states explicitly that the rules of that part do not apply to amateur-built airplanes. With that in mind, the aircraft can be maintained by anyone. Although, remember in our earlier discussion that Part 43, Appendix D, was referenced in Phase 2 operating limitations given to the builder at the time of inspection. It is referenced as a reference to be used in administering condition inspections. That implies Part 43, Appendix D does apply to the condition inspection due to this reference.

The FAA has further explained AD (Airworthiness Directives) as they apply to amateur-built airplanes. AD cannot apply to any part on an amateur-built airplane until that specific plane is mentioned along with who should do the work and to what standards. The cause of this is because once an approved part is set on an experimental airplane, it is no longer considered an approved component. Again, let me emphasize that just because the regulation does not want action, it still may be reasonable and within our best interest to agree to an AD note. We’re attempting to improve the industry’s safety record. In most cases, we have to act on the side of good practice and common sense.

Rules For Selling Your Amateur-Built Airplane

Few regulations are governing the sale of your airplane. The AD is transferable with the airplane even though it is experimental. (FAR 21.179) The appropriate bill of sale and registration documents must be completed when you sell the aircraft. Of particular interest is how the newly purchased plane may be maintained by the new owner, but may not perform the condition check. The repairman’s certificate is not transferred with the flight. It stays with the original primary builder. That person lawfully may still execute the condition check if you can persuade them to do so. If you are buying a partly completed kit, you require to obtain the precise documentation to assure you will satisfy the primary portion rule.

FAA Advisory Circular 20-27D gets the following warning: “CAUTION: Buyers of partly completed kits should get all fabrication and assembly documents from the previous owner(s). This will enable builder who completes the aircraft to be eligible for amateur-built certification.” Again, a call to your FAA Inspector will avoid future problems. The time spent by the primary builder is normally applied toward the total time required to build the airplane. Documentation is necessary.

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