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Aircraft AlterationsAircraft alterations are usually done to improve upon a current aircraft design or performance standard. They are also performed to equip an aircraft for special purpose operations (photography, crop spraying, etc.) Meeting an aircraft’s type design or properly altered condition is one of the requirements to maintain the validity of a standard airworthiness certificate. Properly altered condition means an alteration that is performed correctly in accordance with FAA approved data. The owner/operator of an aircraft must make sure that any alterations or modifications accomplised on the aircraft are accomplished in accordance with FAA-approved data. Supplemental Type Certificates (STC) Supplemental type certificates are issued for aircraft alterations and alterations to other aviation articles. The applicant must submit the engineering data used in the design of the alteration for review. Instructions for continued airworthiness and any flight manual supplements must also be submitted. STC’s are reviewed and approved by the FAA Aircraft Certification Office (ACO) that serves the geographic area of the supplemental type certificate owner’s residence. The STC and all referenced drawings, data, and specifications are the property of the supplemental type certificate holder, so the aircraft owner (installer) must have written permission from the owner of the STC before it can be installed. If you vary from the instructions or the materials referenced in the STC, you must seek further FAA approval. We were asked a question in our “Submit a Question” section about the STC numbering system. I have repeated that answer below for your convenience. Supplemental Type Certificate Numbering System is as follows: Certificate Number = SX NNNNN YY-D S indicates a supplemental type certificate (blank if a type certificate) X = An alpha digit to identify the type of product that it is: A = Small AirplaneB = BalloonE = EngineG = GliderP = PropellerR = RotorcraftS = AirshipT = Transport Airplane NNNNN = assigned number automatically generated by ACOS; for example, 00146. YY = Two alpha digits to identify the issuing Aircraft Certification Office (ACO) AC = ASW-150, Ft. Worth Airplane Certification Office D = indicates Designated Alteration Station (DAS) issued STC (blank if not DAS issued) As an example, SA00125AT would be an STC issued by the Atlanta ACO on a small airplane with the assigned number 00125. You can find this information in FAA Order 8110-4C Manufacturers Service Bulletins The FAA relies on the manufacturer to recommend in-service improvements as necessary to improve the design or safety of a product. The manufacturer has internal quality procedures in place that are approved by the FAA. When these procedures are followed, the data they develop to perform the aircraft alteration is considered FAA Approved Data. Other Data Approved by the FAA Other data means the engineering data (design analysis) and installation instructions used to accomplish the aircraft alteration. This data is reviewed and approved by the FAA or an FAA Designee. They use FAA Forms 8100-9 or FAA Form 8110-3 to approve the data. This does not approve the installation. The installation must be performed and approved by an authorized individual. The record entry required by FAR 43.9 must also be made. FAA Field Approvals This is another way that the FAA can approve technical data used to accomplish a major repair or major alteration. It is an approval by the FAA of technical data and/or installations used to accomplish a major repair or major alteration. Technical data so approved becomes technical data approved by the Administrator. This type of approval may be accomplished for one-time approval. The FAA is moving away from this type of approval with the exception of light aircraft, and even then they shy away because of the potential liabilities. Approvals from Other Countries The FAA has a growing number of bilateral agreements with different countries. They are accepting repair and alteration data approved by a country with which the United States has a bilateral avation safety agreement (BASA) with implementation procedures for airworthiness (IPA), if those documents speak to the acceptance of that data. Acceptance of these approvals is for aircraft alterations up to the level of an STC. If a foreign STC was issued for the alteration, it will need to be validated by the FAA before an aircraft could be certificated in the United States.
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