On May 28, 2004, the FAA published a Notice of Proposed Advisory Circular relating to the creation and use of airworthiness compliance checklists used when making major alterations to small airplanes. Proposed AC 23-XX-21 would provide guidance material for use of these compliance checklists in connection with “major” alterations, as defined in 14 CFR 1.1, but not with alterations that would otherwise require a Supplemental Type Certificate (STC). The FAA recognizes that data and documentation requirements for major alterations can vary considerably. The AC is proposed to assure the standardization of particular airplane alterations data submission and process through the use of the airworthiness compliance checklists. However, the guidance provided in this AC does not constitute a regulation and is not mandatory. If you would like to comment on this proposed AC, you should send your comments to: FAA, Small Airplane Directorate, Aircraft Certification Service, Kansas City, MO 64106. For further information, you may contact the FAA and speak with Mr. Taylor Martin at (816) 329-4138.