A type certificate is issued to signify the airworthiness of an aircraft manufacturing design. The certificate is issued by a regulating body, and once issued, the design cannot be changed. The certificate reflects a determination made by the regulating body that the aircraft is manufactured according to an approved design, and that the design ensures compliance with airworthiness requirements. The regulating body compares design documents and processes to determine if the design meets requirements established for the type of equipment. Requirements established by a regulating body typically refer to Minimum Operating Performance Standards (MOPS) and related documents (such as DO-178 series, DO-160 series and DO-254 series), which are developed jointly by RTCA, Inc. and EUROCAE. Once issued, the aircraft “type” meets appropriate requirements. The determination process includes a step called “First Article Inspection”, for it and for each of its subassemblies. This is a quality control assessment whereas those prior to it are part of quality assurance. With respect to “cannot be changed”: When an airframer wants to change something it has two options. One is to request a Supplemental Type Certificate (STC), the other is to create an entirely different design. The choice is determined by considering whether or not the change constitutes a new design (i.e. introduces risk not considered in the first design). If the manufacturer believes the change doesn’t introduce new risk the manufacturer typically requests an STC. This is less expensive. If the regulatory authority agrees with the rationale for choosing STC, the STC is granted. The type certificate (TC) implies that aircraft manufactured according to the approved design can be issued an Airworthiness Certificate. Examples of regulatory authorities are the Civil Aviation Authority (CAA), the Federal Aviation Administration (FAA) and the (European Aviation Safety Agency (EASA). To meet those requirements the aircraft and each sub-assembly must also be approved. For example, in the U.S. these sub-assemblies must meet requirements in the applicable Technical Standard Order (TSO). To meet those requirements the design documents are examined for compliance with the applicable Minimum Operating Performance Standards (MOPS) applicable to that sub-assembly. MOPS are published by RTCA, Inc. When aircraft are produced to meet a given TC, each one need not be tested as rigorously but the confidence demonstrated by the TC is conferred, when the aircraft has been assigned an Airworthiness Certificate. An “Airworthiness Certificate” is issued for each aircraft that is properly registered if it conforms to its type design. The airworthiness certificate is valid and the aircraft may be operated as long as it is maintained in accordance with the rules issued by the regulatory authority. A supplemental type certificate (STC) is issued following a modification. The STC defines the product design change, states how the modification affects the existing type design, and lists serial number effectivity. It also identifies the certification basis listing specific regulatory compliance for the design change. Information contained in the certification basis is helpful for those applicants proposing subsequent product modifications and evaluating certification basis compatibility with other STC modifications.