(a) During the 12 months following the effective date of any change in the provisions of this part, you may ask to apply the previously applicable provisions. Note that the effective date is generally 30 or 60 days after publication in the Federal Register, as noted in the final rule. We will generally approve your request if you can demonstrate that it would be impractical to comply with the new requirements. We may consider the potential for adverse environmental impacts in our decision. Similarly, in unusual circumstances, you may ask for relief under this paragraph (a) from new requirements that apply under the standard-setting part.

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(b) During the 60 days following the effective date of any change in the provisions of this part, you may use the previously applicable provisions without request if they meet either of the following criteria:

(1) The new provisions require you to redesign your engines/equipment, modify your engine/equipment labels, or change your production procedures.

(2) The new provisions change what you must include in an application for certification that you submit before the end of this 60-day period. You are not required to amend such applications to comply with the new provisions for that model year; however, this allowance does not apply for later model years, even if you certify an engine family using carryover emission data. This allowance does not affect your obligation to provide information that we request separate from an application for certification.

[75 FR 23059, Apr. 30, 2010, as amended at 81 FR 74222, Oct. 25, 2016]