Life Limited or Standard Part?

Standard or Life Limited PartsThere have been times in my career, while discussing records or trace, the person I am speaking with and I are not on the same page. Sometimes not even on the same vocabulary track!  It isn’t the fault of either of us, it is the mix mash of abbreviations and acronyms within the aviation industry.

Usually, when I speak of records, especially trace-ability of records; I am referring to Life Limited Parts or LLPs.  However, sometimes a colleague might be referring to standard parts.  As our conversation progresses, they may think I am being too rigid for what they are talking about and I might be thinking they are not taking it seriously enough.  I have learned that it is important for me to define what I am speaking of.

What are life limited parts?  FAA Advisory Circular 33.70-1 definition is as follows:

AC 33.70-1  5. Definitions l. – Life limit. An operational service exposure limit characterized by the application of a finite number of flights or flight cycles. For rotating parts, it is equal to the minimum number of flight cycles required to initiate a crack equal to approximately 0.030 inches in length by 0.015 inches in depth. For life-limited pressure-loaded static parts, the life limit may be based on the crack initiation life plus a portion of the residual crack growth life.

What are standard parts?

The FAA has published a non-regulatory definition of “standard part” as well as interpretative information regarding what criteria parts must meet to come under the standard part category. Advisory Circular 21-29, Detecting and Reporting Suspected Unapproved Parts, provides the following definition of “standard part”:

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 Standard (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).

Life Limited Parts have an entirely different set of reasons and guidelines behind it’s records as does Standard Parts.  BUT, they do have one thing in common; they must be AIRWORTHY.

The FAA goes on to give you some guidelines to consider for standard parts:

When purchasing and installing standard parts, consider the following:

A Certificate of Conformity (C of C) should be provided by the producer of a standard part.

A standard part should carry a mark indicating the part has been produced in accordance with the specification requirements.

A part is no longer considered “standard” if it is used in a critical application that imposes qualification or quality control requirements beyond the standard specification.

 • To facilitate traceability, commingling like fasteners from different lots is not recommended.

Section 21.303(b)(4) provides that acceptable government specifications are limited to those published by the U.S. Government. Parts produced to a foreign standard may, however, be acceptable for installation on foreign type-certificated aircraft and products.

Installation of a standard part must be in accordance with the requirements of part 43. Generally, a standard part may be replaced with an identical standard part; however, substituting standard parts would require a demonstration of acceptability in accordance with part 43.

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