(a) Overview. For purposes of compliance with exhaust emission standards of this part, a type certificate applicant may request from the FAA a determination that an engine configuration be considered a derivative engine for emissions certification purposes. The applicant must demonstrate that the configuration is derived from and similar in type design to an engine that has a type certificate issued in accordance with 14 CFR part 33, and at least one of the following circumstances applies:

(1) The FAA determines that a safety issue requires an engine modification.

(2) All regulated emissions from the proposed derivative engine are lower than the corresponding emissions from the previously certificated engine.

(3) The FAA determines that the proposed derivative engine's emissions are similar to the previously certificated engine's emissions as described in paragraph (c) of this section.

(b) Determining emission rates. To determine new emission rates for a derivative engine for demonstrating compliance with emission standards under § 1031.30(a)(4) and for showing emissions similarity in paragraph (c) of this section, testing may not be required in all situations. If the previously certificated engine model or any associated sub-models have a characteristic level before modification that is at or above 95% of any applicable standard for smoke number, HC, CO, or NOX or at or above 80% of any applicable nvPM standard, you must test the proposed derivative engine. Otherwise, you may use engineering analysis to determine the new emission rates, consistent with good engineering judgment. The engineering analysis must address all modifications from the previously certificated engine, including those approved for previous derivative engines.

(c) Emissions similarity. (1) A proposed derivative engine's emissions are similar to the previously certificated engine's emissions if the type certificate applicant demonstrates that the engine meets the applicable emission standards and differ from the previously certificated engine's emissions only within the following ranges:

(i) ±3.0 g/kN for NOX.

(ii) ±1.0 g/kN for HC.

(iii) ±5.0 g/kN for CO.

(iv) ±2.0 SN for smoke number.

(v) The following values apply for nvPMMC:

(A) ±200 µg/m 3 if the characteristic level of maximum nvPMMC is below 1,000 µg/m 3.

(B) ±20% of the characteristic level if the characteristic level for maximum nvPMMC is at or above 1,000 µg/m 3.

(vi) The following values apply for nvPMmass:

(A) 80 mg/kN if the characteristic level for nvPMmass emissions is below 400 mg/kN.

(B) ±20% of the characteristic level if the characteristic level for nvPMmass emissions is greater than or equal to 400 mg/kN.

(vii) The following values apply for nvPMnum:

(A) 4 × 10 14 particles/kN if the characteristic level for nvPMnum emissions is below 2 × 10 15 particles/kN.

(B) ±20% of the characteristic level if the characteristic level for nvPMnum emissions is greater than or equal to 2×10 15 particles/kN.

(2) In unusual circumstances, the FAA may, for individual certification applications, adjust the ranges beyond those specified in paragraph (c)(1) of this section to evaluate a proposed derivative engine, consistent with good engineering judgment.