FAA Withdraws Major Design Change Guidance for Overhaul

The FAA plans to rewqrite AC 21.93-1 and will present a new draft in the third quarter of 2010.


Last Fall, MARPA and MARPA’s members submitted comments on the FAA’s proposed draft Advisory Circular 21.93. This draft would have provided guidance on how to determine whether a change to type design was major or minor (or somewhere in-between). MARPA applauded the FAA’s desire to provide much-needed guidance on this subject, but critiqued the actual guidance because it appeared to introduce more uncertainty into the compliance equation, rather than resolving the compliance issues facing the industry. In particular, the guidance appears to drive certain PMAs to a requirement for STC, even where the regulations clearly did not support classification of the PMA as a major change in type design.

The FAA responded to our comments on Thursday, April 1 with the following short email:

"Thank you for your participation in the review of draft Advisory Circular (AC) 21.93-1, “Determining the Classification of a Change to Type Design,” in 2009. The FAA values your comments and has made the decision to rewrite the AC. We plan to publish a new draft in the third quarter of 2010 for a new round of public comment. We look forward to your inputs again on this new draft later this year."

In short, the FAA took our industry’s comments seriously, and withdrew the draft guidance so that they could make major improvements to it.

MARPA’s comments can be found on-line at the MARPA website. In addition, MARPA provided a draft rewrite pmamarpa.com/gvt/2009-10-09DraftAC21-93asModifiedByMARPA.pdf to correct some of the most glaring issues. We hope that these documents will help guide the FAA toward a better draft advisory circular.

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