(a) Any significant revision to a State plan shall be adopted by such State after reasonable notice, public hearing, and meaningful engagement. For plan revisions required in response to a revised emission guideline, such plan revisions shall be submitted to the Administrator within fifteen months, or as determined by the Administrator, after publication in the Federal Register of a final revised emission guideline under § 60.22a. All plan revisions must be submitted in accordance with the procedures and requirements applicable to development and submission of the original plan.

(b) A revision of a plan, or any portion thereof, shall not be considered part of an applicable plan until approved by the Administrator in accordance with this subpart.