Subject: Airworthiness Compliance Checklists
Used to Substantiate Major Alterations for
Small Airplanes
Date: 9/30/04
Initiated By
: ACE-100
AC No: 23-21
Change:
1. PURPOSE.
a. This advisory circular (AC) provides guidance material for the creation and use of
airworthiness compliance checklists that aid in substantiating requirements when performing
major alterations to small airplanes. These checklists may be used by Airframe and Powerplant
(A&P) mechanics and those holding Inspection Authorization (IA) privileges and by persons
performing alterations (modifiers), under the privileges of an FAA Certificated Repair Station
(CRS) operating under Title 14 Code of Federal Regulations (CFR) part 145 as well as by
Federal Aviation Administration (FAA) Airworthiness Aviation Safety Inspectors (ASIs) to
assist in determining that such alterations meet compliance with the Federal Aviation
Regulations. These checklists will help identify all the data requirements and outline the data
approval methods for a particular major alteration, as well as identify documentation required to
further substantiate approval for returning the product to service.
b. Use of these compliance checklists should be limited to alterations that have been
determined to be “major” alterations, as defined in 14 CFR part 1, and are not major changes to
the type design of the product as denoted in 14 CFR part 21, § 21.97, and which are not so
complex that they require a Supplemental Type Certificate (STC), per FAA Order 8300.10.
c. This AC is intended to aid persons performing an alteration using the guidance of
AC 43-210, Standardized Procedures for Requesting Field Approval of Data, Major Alterations,
and Repairs, as well as the ASI in determining requirements are met to satisfy airworthiness.
d. This AC does not change any previously released FAA guidance material such as FAA
Orders and advisory circulars listed in section 4 of this AC. The intent of this AC is to provide
an aid to assist industry and the FAA with existing approval processes.
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