AIRCRAFT PARTS MANUFACTURING ASSISTANCE (PMA)
AIRWORTHY / AIRWORTHINESS
The FAA's definition of "airworthy" is "meets its type design and is in a condition for safe operation." This definition is difficult to find. The Philadelphia FSDO has an excellent treatise on this topic that is not well understood by most aviation professionals in this country. You can find it at Airworthiness.
NOTE: this AC has been replaced by the following document: Plane Sense, General Aviation Information.
MAJOR ALTERATION OR CHANGE VERSUS MINOR ALERATION OR CHANGE TO TYPE DESIGN
Many people in the aviation industry think that a minor change is one that does not affect "form, fit, or function". Two regulatory definitions can be found in 14 CFR §1.1 and §21.93. 14 CFR §1.1 defines a major alteration as one that "means an alteration not listed in the aircraft, aircraft engine, or propeller specifications--
Confusion exists as to the definition of "standard parts." The official FAA definition is: "Standard parts (such as bolts and nuts) conforming to established industry or U.S. specifications." This definition is found in Title 14 CFR § 21.303(b)(4) and is not otherwise defined.
Standard parts are one of four categories of parts that are exempted from the requirement to have PMA in order to be sold for installation on type certificated products.
AC21-29, paragraph 4j defines a "Standard Part" as: A part manufactured in complete compliance with an established industry or U.S. government specification which includes design, manufacturing, test and acceptance criteria, and uniform identification requirements; or for a type of part which the Administrator has found demonstrates conformity based solely on meeting performance criteria, is in complete compliance with an established industry or U.S. Government specification which contains performance criteria, test and acceptance criteria, and uniform identification requirements. The specification must include all information necessary to produce and conform the part, and be published so that any party may manufacture the part. Examples include, but are not limited to, National Aerospace Standards (NAS), Army-Navy Aeronautical Standard (AN), Society of Automotive Engineers (SAE), SAE Sematec, Joint Electron Device Engineering Council, Joint Electron Tube Engineering Council, and American National Standards Institute (ANSI).
On March 5, 1997, the FAA published in the Federal Register (Volume 62, Number 43) a "Notice of Interpretation" regarding standard parts. It states in part "Section 21.303(b)(4) has come to be understood by the aviation and manufacturing public as meaning a part, the specification for which has been published by a standard setting organization or by the U.S. government, and the FAA has traditionally regulated parts production with that understanding. Examples of such "traditional" standard part specifications include National Aerospace Standards (NAS), Air Force-Navy Aeronautical Standard (AN), Society of Automotive Engineers (SAE), SAE Aerospace Standard (AS), and Military Standard (MS)."Reference material:
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