The Environmental Protection Agency (EPA) has adopted the first-ever Clean Air Act (CAA) aircraft emission standards for greenhouse gases (GHGs), assuring the worldwide acceptance of U.S. manufactured airplanes and airplane engines. The final rule, “Control of Air Pollution from Airplanes and Airplane Engines: GHG Emission Standards and Test Procedures,” flows from the agency’s 2016 twin findings that: (1) GHG emissions from the engines of certain aircraft “cause or contribute to” elevated GHG concentrations in the atmosphere, and (2) these emissions endanger the public health and welfare via climate change. These findings form the basis for regulation of a pollutant under CAA section 231(a), the legal foundation for EPA’s authority for this aircraft emissions rule, promulgated December 23, 2020.

Key Takeaways

• EPA drew heavily from the 2017 Airplane CO₂ Emission Standards established by the United Nations’ International Civil Aviation Organization (ICAO), resulting in alignment with the ICAO standards and assuring the worldwide acceptance of U.S. manufactured airplanes and airplane engines.
• The final rule does not require emission reductions beyond those adopted by ICAO, and does not require significant changes to aircraft production beyond those already planned.
• The final rule applies to manufacturers of new civil aircraft beginning either: (A) on the rule’s effective date (Federal Register publication date) for “new” models of aircraft that the Federal Aviation Administration (FAA) has not yet type certificated, or (B) on January 1, 2028 for most “in-production” models that already have such certification.
• The final rule does not apply to certain  aircraft  covered by various exemptions and exceptions identified in the rule.
• The final rule requires certain new airplanes to meet a “fuel efficiency metric” based on the airplane’s certified weight.

Alignment with International Standards

In developing this rule, EPA drew heavily from the 2017 Airplane CO₂ Emission Standards established by ICAO. EPA chose standards equivalent to ICAO in part because, according to EPA, without this final action, other nations could ban the use of any airplane within their airspace that does not meet ICAO standards. In addition, the EPA determined that matching standards will have “substantial benefits for future international cooperation” on aircraft emissions, which the agency deemed “key for achieving worldwide emission reductions.” Accordingly, the rule does not result in emission reductions beyond those ensured by the ICAO standards, and imposes “no additional burden on manufacturers” beyond certain reporting requirements.

Reporting Requirements

Because the rule’s emission standards and compliance dates mirror ICAO’s, the only additional burden on manufacturers will be an annual reporting requirement. Specifically, the rule requires airplane manufacturers to submit an annual production report to EPA—not the FAA—for each airplane sub-model that already has a type certificate, is subject to the GHG standards, and is designed to operate at subsonic speeds. For each affected airplane sub-model, the reporting requirement requires annual reports to include:

• the certificate type number issued by FAA;
• the month and year that FAA issued the type certificate;
• the number of engines on the airplane;
• the prior year’s production volume for that sub-model;
• the number of any exempt airplanes produced in that sub-model;
• the certificated MTOM; and
• the sub-model’s fuel efficiency metric as compared to the maximum fuel efficiency metric permitted.

Applicability

The final rule applies to manufacturers of two types of civil aircraft: (1) subsonic jet aircraft with a maximum takeoff mass (MTOM) greater than 5,700 kg, and (2) large turboprops and other subsonic propeller-driven aircraft with an MTOM over 8,618 kg. Examples include business jets, such as the Cessna Citation CJ3+, commercial jet aircraft, including the Boeing 777 and the Boeing 787, and civil turboprop airplanes, such as the ATR 72 and the Viking Q400.  According to EPA, these aircraft are responsible for 10% of domestic transportation emissions, and 3% of total domestic GHG emissions.

The compliance deadlines and emission standards depend on whether the covered aircraft: (A) has a “new type design” never previously certified by the FAA, or (B) is an “in-production” aircraft, already covered by an FAA type-certification.

• For new type designs, the certification requirement applies to any designs submitted for FAA certification on or after the rule’s effective date (publication in Federal register). The rule extends the applicability date to January 1, 2023 for new type designs of smaller airplanes—i.e., those less than 60,000 kg with no more than 19 passenger seats.
• For in-production type designs, manufacturers must test and verify emissions compliance for each design before 2028; otherwise, FAA will deny certification for any newly manufactured airplanes beginning January 1, 2028. This requirement could apply as early as January 1, 2023 if certain aircraft modifications increase its MTOM or impair fuel efficiency beyond certain thresholds.

To avoid potential concerns raised in comments during the rule’s public comment period and because it did not affect harmonization with ICAO standards, the EPA adopted standards that apply upon the effective date of this rule (the final rule’s Federal Register publication date), rather than retroactively to January 1, 2020 as outlined in the Notice of Proposed Rulemaking. Additional applicability criteria can be found in the United States Code of Federal Regulations (CFR) at 40 CFR parts 87 and 1030.

Aircraft Exceptions and Exemptions

The final rule exempts certain aircraft types and contains pathways to obtain exemptions or temporary reprieves from enforcement in certain instances.

The rule categorically exempts certain aircraft types including: amphibious airplanes; “very rare” airplanes designed with an unpressurized compartment; airplanes specifically designed or modified and used for fire-fighting purposes; and airplanes initially designed or modified and used for specialized operational requirements. EPA does not define “specialized operational requirements” but provides a few examples and notes that all such aircraft “require performance that was outside of the scope considered” by ICAO when developing its own standards.

Regulated entities may also petition the FAA for a temporary request for relief from enforcement, pursuant to the FAA’s existing regulatory framework for such petitions. Although the decision to withhold enforcement is ultimately the FAA’s, enforcement discretion will be conducted in consultation with EPA.

Additionally, the rule adopts ICAO’s exemptions from recertification requirements for certain modifications that cause only “slight changes” in GHG emissions. Those thresholds can range from a maximum 0.7% effect on fuel economy for the heaviest airplanes, up to a maximum 1.35% effect for the lightest.

How the Final Rule Works

As with many other mobile source GHG standards, these standards rely heavily on fuel efficiency as a surrogate for assessing GHG emissions. The EPA used fuel efficiency because the only two GHGs emitted by covered aircraft—carbon dioxide (CO₂) and nitrous oxide (N₂O)—“scale with” fuel consumption. In focusing the standards on fuel efficiency, the rule accommodates a wide variety of efficiency-boosting measures, including improvements for aerodynamics, for engine performance, and functionally for measures that reduce an aircraft’s MTOM. However, because compliance is determined at the design certification stage, the rule excludes many other operational techniques to reduce emissions, including the use of biofuels.

The emission standards themselves are logarithmic equations establishing a maximum so-called “fuel efficiency metric”—identical to ICAO’s “CO₂ emissions metric”—based on the MTOM and whether the FAA has already certified the type design. Fuel efficiency metric calculations are based on a combination of the design’s fuselage size and fuel economy, with the most stringent standards generally reserved for the heaviest aircraft.

Determining the Applicable Standard

The applicable emission standards (the specific logarithmic equation), depends first on whether the aircraft is a new design or has a design already in-production. Within these categories, the relevant emission standard further depends on the aircraft’s certified MTOM, with the emission standard equations generally imposing tighter standards for each marginal increase in the certified MTOM.

As noted above, the emission standard itself is a “fuel efficiency metric” that depends on the novelty of the type design and the design’s certified MTOM. Like ICAO’s CO₂ emissions metric, EPA’s fuel efficiency metric is a function of two aircraft design characteristics: (1) the reference geometric factor (RGF), and (2) the specific air range (SAR). The RGF is a measure of fuselage size “generally considered to be the shadow area of the airplane’s pressurized passenger compartment.” By contrast, the SAR is the “traditional measure” of cruise performance, measured in kilometers-per-kilogram of fuel. To account for variations in operating weights, fuel efficiency metric calculations require manufacturers to measure the design’s SAR during high-, mid-, and low-gross mass operating conditions. The fuel efficiency metric is then calculated by averaging the reciprocals of each SAR and dividing that average by the design’s RGF to the power of 0.24. A separate set of equations based on certified MTOM—the “correlating parameter”— dictates the stringency of the fuel efficiency metric the aircraft must achieve to obtain FAA certification.

What’s Next?

Various aviation and air transport groups have praised this rule as a sensible domestic alignment with international standards. On the other hand, several environmental non-governmental organizations have already voiced their opposition, and may challenge the rule in the D.C Circuit. These groups are focused on the lack of additional emission reductions beyond the ICAO standards, calling the standards “wholly inconsistent” with the Paris Agreement. The Paris Agreement covers a nation’s domestic aviation emissions but specifically excludes international aviation emissions. International aviation emissions are managed through ICAO’s Carbon Offsetting and Reduction Scheme for International Airlines (CORSIA), which launches this year in a pilot phase.

Meanwhile, the FAA is developing an aircraft certification rule to incorporate the final EPA emissions standards and to provide for FAA enforcement of those standards. The FAA anticipates publishing a Notice of Proposed Rulemaking in 2021 for public comment.