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a. The two objectives of Aircraft certification is to encourage and foster the development of civil aviation, and to ensure aviation safety. One method used by the Federal Aviation Administration (FAA) to fulfill these objectives is the aircraft certification system through which aircraft design and modification must be approved. Title 14 of the Code of Federal Regulations (14 CFR) and the Civil Air Regulations (CAR) define the minimum required safety standards for FAA certification. By demonstrating compliance with these regulations, an aircraft modifier may obtain the necessary FAA approval for a modification.

b. Types of aircraft certification design approvals are determined by the magnitude and complexity of the change. Aircraft modifications can be subdivided into minor and major changes (14 CFR part 21, section 21.93). Minor changes are those which do not appreciably affect weight, balance, structural strength, reliability, operational characteristics, airworthiness characteristics, power and noise characteristics, or emissions. Minor changes may be approved under a method acceptable to the Administrator before submitting to the Administrator any substantiating or descriptive data (14 CFR part 21, section 21.95). Major changes are those which are not minor. The type of FAA approval is applicable to a given modification. Supplemental Type Certificates (STC) are required for most major changes to existing Type Certificate (TC) products affected by a modification or installation when the change is not so intensive as to require a new TC (14 CFR part 21, section 21.19). STC's are not issued for minor changes or for approval of replacement and modification parts meeting the provisions of 14 CFR part 21, section 21.303. More than one STC may be necessary for a given modification. One STC may be required to approve the change to an engine or propeller, while a second STC may be necessary to approve the aircraft installation of the modified engine or propeller. An STC will probably be required if a significant amount of analysis or flight tests are required, or if extensive flight manual changes are necessary. An STC is issued through the FAA ACO or Engine Certification Office (ECO) which serves the geographic area of residence of the STC owner. Significant STC applications will require coordination with the Directorate, and may involve more time to process the application. See Order 8100-5.

NOTE: If there are any questions whether the modification is major or minor, the applicant should contact the ACO.


a. Privileges are associated with the issuance of an STC.

(1) Standard Airworthiness Certificates may be granted to specified aircraft that are modified in accordance with the STC.

(2) Multiple installations may be achieved on any certificated aircraft designated in accordance with the STC.

(3) Parts Manufacturer Approval (PMA) may be obtained by the STC holder to manufacture and sell parts/kits when it is demonstrated to the FAA Manufacturing Aviation Safety Inspector that the applicant has established a Fabrication Inspection System which meets the requirements of 21.303(h) to ensure that production is consistent to adequately duplicate the parts.

NOTE: The STC must be a "Multiple" Installation STC.

b. Responsibilities of the STC holder are the accomplishments of the modification or installation in accordance with the STC, and reporting to the FAA any failures, malfunctions, or defects per 14 CFR part 21, section 21.3. The holder of an STC, is also required to maintain an updated data file related to the STC.

c. Types of STC's are classified as either "one-only" STC (aircraft/engine/propeller) or "multiple" STC (aircraft/engine/propeller).

(1) "One-only" STC's apply to only one aircraft/engine/propeller serial number.

(2) "Multiple" STC's are necessary if two or more aircraft/engines/propellers are to be modified, and it must be demonstrated that the modification can be duplicated.

d. AC 21-5M, Announcement of Availability: Summary of STC's, is an FAA publication listing all existing MULTIPLE STC's for each aircraft model. A copy of this publication is available for review at the local FAA ACO, FSDO, and MIDO and a disk (updated once a year) may be purchased from the National Technical Information Service (NTIS). This publication may be reviewed to determine if another STC has been issued that would satisfy the intended requirement, and thereby prevent a duplication of effort.

NOTE: Pursuant to 49 U.S.C 44704; If the holder of an STC agrees to permit another person to use the certificate to modify an aircraft, aircraft engine, propeller, or appliance, the holder will provide the other person with written evidence, in a form acceptable to the administrator, of that agreement. A person may change an aircraft, aircraft engine, propeller, or appliance based on an existing STC only if the person requesting the change is the holder of the STC or has permission from the holder to make the change. See chapter 9.

e. No STC activity is covered under our bilateral airworthiness agreements in any country except Canada. Additional guidance should be sought from AIR head quarters before proceeding on any STC project involving a foreign entity to any degree.

f. 14 CFR part 21, sections 21.137 and 21.601 require the FAA to make a determination that there will be no undue burden on the United States in administering the applicable requirements of Title 49, U.S. Code (Transportation), and Title 14 of the Code of Federal Regulations when production approvals are requested at manufacturing facilities located outside the United States. Once the foregoing criteria have been satisfied by the certificate management Directorate and the PC holder, the FAA office responsible for certificate management of the PC holder should prepare a decision paper.

NOTE: The decision paper should be signed by the Aircraft Certification Directorate Manager who has certificate management responsibility for the PC holder prior to forwarding the decision paper to AIR-200 for concurrence and to AIR-1 for approval. See AC 21-24..


a. The applicant's responsibility for substantiating the modification is accomplished by showing the FAA that the modified aircraft/ engine/propeller complies with the applicable regulations.

b. FAA Form 8110-12, Application For Type Certificate, Production Certificate, or Supplemental Type Certificate, should be submitted to the geographically responsible ACO. See appendix 8. The most current version of AC 20-126, Aircraft Certification Service Field Office Listing, contains an address, telephone number, and geographic area listing of all ACOs.

c. Certification requirements are located in title 14 CFR's, or the predecessor to them, Civil Air Regulations. These regulations are extensive but only certain portions apply to a particular STC. See chapter 3.

d. Design feasibility should be discussed with a local FAA engineer to determine if the proposed modification design is feasible for approval BEFORE MODIFYING THE AIRCRAFT. An unapproved modified aircraft may be subject to grounding and Airworthiness Certificate removal.

e. Data submittals are to contain sufficient descriptive and substantiating/compliance data to completely describe the design of the modification or installation, and demonstrate that the design meets the applicable regulations. See chapter 5.

f. Inspections are for conformity and compliance. The conformity inspection verifies that the modification conforms to the descriptive data, while the compliance inspection verifies that the modification meets the applicable regulations. See chapter 6.

g. Tests may include verifying the component, ground requirements, and flight requirements. Component or certification testing demonstrates that detail parts, components, or subassemblies function as required to meet the applicable regulations. Ground testing and flight testing are performed to demonstrate the completed modification or installation complies with the regulations. See chapter 8.

h. Timing/scheduling necessary for obtaining FAA approval varies with the complexity of each modification. Inspections, meetings, tests, etc., should be planned, scheduled, and provided well in advance to the FAA to assure appropriate personnel are available. Scheduling flight tests has the added complication of weather. All proposed changes to the schedule should be kept to a minimum and provided to the FAA immediately for concurrence.

i. Use of designees authorized by the FAA to approve data, conduct inspections, witness tests, etc., may expedite the approval of a modification. See chapter 4.

j. Issuance of an STC is the final product and goal of the application process. See chapter 2 and chapter 9.

k. Subsequent change procedures to the original substantiating data should be submitted for approval and inclusion in the FAA data files. Major changes must be FAA approved prior to inclusion in the design data. Minor changes may be accom-plished in any manner found acceptable to the FAA. See 14 CFR part 21, sections 21.95 and 21.97.

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