FAA Seeks Analysis of Major/Minor STC Changes

 - September 2, 2009, 10:33 AM

The FAA has issued a draft Advisory Circular (AC) that is intended to help supplemental type certificate applicants determine whether a modification involves a minor or major change to type design. While FAR 21.93(a) defines a minor change as “one that has no appreciable effect on the weight, balance, structural strength, reliability, operational characteristics or other characteristics affecting the airworthiness of the product,” figuring out the difference between a major or minor change has always been difficult for technicians. According to the draft AC, “When you propose a change to an existing type design, you must classify the change as minor or major in accordance with 21.93.” This is not precisely true, according to the Modification and Replacement Parts Association, which pointed out that “the existing language of 21.93 does not impose a burden to identify whether a proposed change is a major or minor change to type design. While affirmative classification of minor changes can aid in compliance, it is not a requirement of the regulations.”