Advisory Circular Merits Comments, because Identicality Statistical Analysis, once finalized, will be THE Standard

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SOURCE: Statistical Analysis Considerations for Comparative Test and Analysis Based Compliance Findings for Turbine Engine

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The Federal Aviation Administration (FAA) is attempting to make one of its most subjective tests, the identicality determination of 14 CFR §21.303, more objective. In engineering terms, this regulatory requirement is extremely complex. The FAA has proposed in Draft Advisory Circular 33-XX, a lengthy explanation of the past practice and a detailed explanation of the proposed methodology.

Equally important, the new proposed standard would apply to parts manufacturer approval (PMA), type certificate (TC), supplemental type certificate (STC), or repair or alteration. Thus, all of the regulatory judgments involving the same words must meet the same statistical determination.

It should be noted that this is an advisory circular (AC) and therefore, it is not THE ONLY standard. The template for the introduction to an AC bears repetition here:

This material is neither mandatory nor regulatory in nature and does not constitute a regulation. It describes acceptable means, but not the only means, for demonstrating compliance with the applicable regulations. The FAA will consider other methods of demonstrating compliance that an applicant may elect to present.

Theoretically, an applicant for one of these certificates can propose a different analytical basis for proving identicality.

The actual explanation of the mathematical calculations, including mathmust be carefully scrutinized by anyone intending to file for a PMA, TC, STC, etc. In reality, if the proposed product cannot meet this test, it will be virtually impossible to convince an aircraft certification office (ACO) to accept a different analysis.

The due date for comments is July 11, 2013. The document should reference AC No. 33-XX –Statistical Analysis Considerations for Comparative Test and Analysis Based Compliance Findings for Turbine Engine and Auxiliary Power Unit Replacement, Redesign and Repaired Parts. Comments should be addressed to:

Email: marc.bouthillier@faa.gov
Mail or hand delivery:
Federal Aviation Administration
Engine and Propeller Directorate
Standards Staff, ANE-111
12 New England Executive Park
Burlington, MA 01803
Fax: 781-238-7199

This area of FAA certification has been extremely contentious. The goal of this AC is to reduce the controversy. It would not be surprising if some of the comments take exception to this draft.

If you find fault with the FAA’s statistical standard, please copy your submission to the FAA into comment box below. With such feedback, a follow-up post may be generated.

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