FREQUENTLY ASKED QUESTIONS > Incorporating the STC > Q: I thought the STC was a done deal. Why do I need an FAA Form 337 and "Approval for Return to Service"?

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Q: I thought the STC was a done deal.  Why do I need an "Approval for Return to Service"?

A:  It is true that no further FAA/EASA approvals or signatures are required.  Although no physical changes are being made, this STC is considered a major airframe alteration.  All STC's, regardless of type, include a "Limitations and Conditions" section which states to the effect:

"This approval should not be extended to other aircraft of this model on which other previously approved modifications are incorporated, unless it is determined by the installer that the interrelationship between this change and any other previously approved modifications will produce no adverse effect upon the airworthiness of that airplane."

An authorized person must make this determination and sign the FAA Form 337 or EASA CRS, effectively returning the airplane to service after the "major alteration."