Airbus Model A321-100 and -200 Series Airplanes

Many, if not most, airworthiness directives(AD) are merely restatements of manufacturer's service documents. Problems can arise from this procedure with respect to 14 CFR § 21.303 (PMA) since the ramifications of this law are generally ignored in the service documents. The most frequent problem that arises is the service document specifying a defective part numbered part with the requirement that the defective part be replaced by a "new and improved" part numbered part. The service document and, all too frequently, the resulting AD fail to address the possibility that a PMA part may be installed in lieu of the original part. Since the PMA part may often share the identical design data with the original part while carrying a completely different part number it is possible the AD will not address certain defective PMA parts installed on the aircraft thereby permitting the unsafe condition to continue. It is also possible that a "new and improved" PMA version of the defective original part may already exist in the marketplace. Therefore, specifying one approved part in preference to a different, but also approved part imparts a commercial advantage to one manufacturer over the other. In either case, simply echoing part numbers without some qualifying language places the AD in conflict with existing law (FAR 21.303) AD writers frequently refer to the clause in the AD or proposed AD allowing alternative methods of compliance thereby implying that the use of a PMA part is such a method. It is not. A PMA part is already approved and needs no further approval for installation and use. Therefore, this commenter, Modification and Replacement Parts Association (MARPA) requests that the final action include the phrase "or other FAA-approved equivalent part." after the part number of the part mandated to be installed. Jack Buster AD Committee