In the United States, several distinct groups of aircraft may be flown as light-sport. Existing certificated aircraft and experimental, amateur-built aircraft that fall within the definition listed in 14CFR1.1 are acceptable, as are aircraft built to an industry consensus standard rather than FAA airworthiness requirements. The accepted consensus standard is defined by ASTM International Technical Committee F37. Aircraft built to the consensus standard may be factory-built and sold with a special airworthiness certification (S-LSA) or may be assembled from a kit under the experimental rules (E-LSA) under experimental airworthiness. A company must have produced and certified at least one S-LSA in order to be permitted to sell E-LSA kits of the same model. E-LSA kits are not subject to the normal experimental amateur built (E-AB) requirement 14 CFR 21.191 which identifies 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."