51% Rule

Gyroplanes and really anything certified as an amatuer-built experimental aircraft is required to meet a manufacturing requirement typically known as the 51% rule (FAR 21.191(G)). The FAA has in place a rule that states (in laymans terms) The builder must perform between 51 and 100 percent of the total work.

Before purchasing a kit, first check with the FAA to see if the FAA or your countries governmental aviation authority has already evaluated your kit selection and see if it in fact does meet the 51 percent rule. This starts you out on the right foundation.

Now simply build the kit. Keep in mind if assembled sub-kits are offered by the kit manufacturer that reduces your build time and you can reach a point that the construction will no longer meet the 51% rule. If you reduce your build input below 51% you will not be able to get the kit certified for flight. This should not be an area to be too overly concerned about, as you will more than likely be adding more build time to the basic kit when you install all the "goodies" like a GPS reciever.

For those with a real need to know, look at FAR's 21.191(g) and 65.104. Title 14 CFR part 21, section 21.191(g) lays out the following to define an amatuer-built aircraft as " an aircraft the major portion of which has been fabricated and assembled by persons who undertook the construction project solely for their own education or recreation". I'm sure that really clears the mud for most of us.

Check with the FAA and EAA or EAA technical counslor for any questions.

Click for link to the FAA

Click for link to the EAA

Background Information on the 51% Rule

1926- This year brought to fruition the first Federal Regulation to cover aspects of Civil Aviation in the Air Commerce Act of 1926.

This Act entrusted the Secretary of Commerce to foster air commerce, issue and enforce air traffic regulations, license pilots, certificate aircraft, establish airways and to operate and maintain air navigation aids.

1931-1941- The Department of Commerce set about writing regulations addressing safety issues and certification of pilots and aircraft. What is rather interesting is that only aircraft used for interstate commerce were required to have an airworthiness certificate. By 1931 many states had signed into law their own sets of regulations regarding civil aviation with application to all aircraft. These actions by the states essentially outlawed homebuilt aircraft construction due to there being no due process for an amateur built aircraft to receive an airworthiness certificate. This trend continued to spread across the country and by 1941 every state, with the exception of Oregon, had similar laws.

1940-1952- In 1940 the Civil Aeronautics Administration (CAA and predecessor agency to the Federal Aviation Administration (FAA)) was created to oversee the civil aviation market within the United States and with agreement to consider a permanent category for homebuilt aircraft.

World War II effectively halted any continued advancement for civil aviation within the U.S.. Aviation efforts during this time concentrated on the needs of the of the war effort.

Following World War II, the building and flying of homebuilt aircraft began again. By 1947 the CAA again started to address the needs of the civil homebuilt aircraft group.

By 1951 enough progress was made within the CAA to mandate an amendment to the Civil Air Regulations. This amendment recognized a category of aircraft with “experimental” airworthiness certificates. This action in turn lead to the official establishment, in September of 1952, of the amateur built category within the experimental aircraft category.

1972- Like any industry that must deal with new technology, so did the homebuilt aviation needs require some updated regulations to carry the sport forward. Paul Poberezny, founder of the Experimental Aircraft Association (EAA), sought to work with the now FAA for improved regulations to streamline the certification process of homebuilt aircraft. The goals of these changes sought to reduce the amount of time and number of times the aircraft needed to be inspected during the build process thus reducing the strain on the FAA with inspectors, inspections and paperwork. The collective regulation changes that resulted have come to be known as the 51 percent rule.

Since the 1952 legal establishment of the experimental amateur-built category, many individuals have had the privilege to construct an aircraft project for their personal education and/or recreation. Currently, the amateur-built aircraft market represents about 20 percent of the single-engine general aviation active fleet.

The impact of the 51 percent rule has established the standards of qualification/disqualification of acceptable kits, this in turn has opened a market of parts suppliers, technological support, component manufacturing (to include subcontracted parts and services) that have resulted in greater standards of safety within the homebuilt market.

The technological advancement and creative innovations from the amateur-built community cannot go unnoticed. The now accepted use of composite materials within aviation, cockpit design incorporating ergonomic designs and smaller components, continuing advances in aircraft lighting and cockpit display and management systems have become standards within the commercial and military marketplace.

By understanding and applying the 51 percent rule to your project you help ensure your project will not only meet certification requirements for your airworthiness certificate but also help preserve the privilege for further generations to experience the creative passion of building and flying their own dreams.

Since the landmark 1972 rule changes many nations around the world have adopted similar regulations within their own laws regarding homebuilt certification standards. Most have used the 51 percent rule as the standard for their own certification process. Be sure to fully understand the requirements of certification and ensure that your kit meets the legal standards for the country in which plan to build and operate within.

For further information on U.S. Civil Aviation history see www.Centennial of Flight.gov.

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