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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 87 and 1068

[EPA-HQ-OAR-2010-0687; FRL-XXXX-X]

RIN 2060-AO70

Control of Air Pollution From Aircraft and Aircraft Engines; Emission Standards and Test 

Procedures

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

SUMMARY: EPA is adopting several new aircraft engine emission standards for oxides of 

nitrogen (NOx), compliance flexibilities, and other regulatory requirements for aircraft turbofan 

or turbojet engines with rated thrusts greater than 26.7 kilonewtons (kN). We also are adopting 

certain other requirements for gas turbine engines that are subject to exhaust emission standards

as follows. First, we are clarifying when the emission characteristics of a new turbofan or 

turbojet engine model have become different enough from its existing parent engine design that 

it must conform to the most current emission standards. Second, we are establishing a new 

reporting requirement for manufacturers of gas turbine engines that are subject to any exhaust 

emission standard to provide us with timely and consistent emission-related information. Third, 
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and finally, we are establishing amendments to aircraft engine test and emissions measurement 

procedures. EPA actively participated in the United Nation’s International Civil Aviation 

Organization (ICAO) proceedings in which most of these requirements were first developed. 

These regulatory requirements have largely been adopted or are actively under consideration by

its member states. By adopting such similar standards, therefore, the United States maintains 

consistency with these international efforts.

EXECUTIVE SUMMARY: 

A. Purpose of the Regulatory Action

The primary purpose of this rule is to adopt new oxides of nitrogen (NOx) emission 

standards for aircraft engines with rated thrusts greater than 26.7 kN thrust. These are mostly

commercial passenger and freighter aircraft in common use at airports across the U.S. It does 

not include engines used on military aircraft. NOx is strongly correlated with NO2, for which 

EPA has established National Ambient Air Quality Standards (NAAQS), i.e., a criteria pollutant, 

and it is an important precursor gas in the formation of tropospheric ozone and secondary

particulate matter which are common air pollutants in urban areas where airports are located. 

Currently, approximately 154 million people live in areas designated nonattainment for one or 

more of the current NAAQS. This rule will allow us to enforce in the U.S. the emission 

standards adopted by ICAO, and will be useful to states in attaining or maintaining the ozone, 

PM2.5, and NO2 NAAQS standards. This rule also contains several provisions to facilitate the 
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implementation of EPA’s aircraft engine emission regulations and related requirements. It is 

also important to note that adoption of the provisions in this rule meets U.S. treaty obligations 

under the Chicago Convention of 1944 by aligning our regulations with those in the International 

Civil Aviation Organization Annex 16, Volume II (adopted in 2010) that the U.S. helped to 

develop and support as part of the international process. This rule is being implemented under 

the authority provided in section 231 of the Clean Air Act (42 USC 7571), which directs the 

Administrator of EPA to, from time to time, propose aircraft engine emission standards 

applicable to the emission of any air pollutant from classes of aircraft engines which in her

judgment causes or contributes to air pollution that may reasonably be anticipated to endanger 

public health or welfare. 

B. Summary of Major Provisions of the Regulatory Action

The rule contains six major provisions. The first two provisions are new NOx emission 

standards for newly certified-engine models. The first standards, Tier 6, take effect when this 

rule becomes effective. These represent approximately a 12 percent reduction from current Tier 

4 levels. They were actually adopted by ICAO in 2005 with an implementation date in 2008. 

The second standards, Tier 8, were adopted by ICAO in 2008 and take effect in 2014. These 

represent approximately a 15 percent reduction from Tier 6 levels. As noted above, both tiers of 

emission standards are needed to address local air quality concerns (NAAQS) and to meet U.S. 

treaty obligations under the Chicago Convention. The third major provision is a production cut-
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off for newly-manufactured engines (as opposed to newly-certified engines) which basically

requires that after December 31, 2012 all newly-manufactured engines must meet at least Tier 6 

NOx emission standards. This is also needed to meet our obligations under the Chicago 

Convention. The production cut-off is needed to ensure that the emission reductions envisioned 

by the emission standards are achieved on new production engines. The fourth major provision is 

related to potential exemptions or exceptions to the production cut-off requirement. These 

include revised provisions allowing manufacturers to request that FAA in consultation with EPA 

grant exemptions from the production cut-off for a designated number of engines within a 

prescribed time frame. These also include a low-volume, time-limited exception provision that 

will exclude several engines from the production cutoff. Both of these provisions help to assure 

an orderly transition to the new standards for engines needing more time to comply or for a few 

engines at the end of their production life. Finally, the rule includes a set of provisions which 

may be considered as minor if viewed separately, but collectively are important in upgrading 

EPA’s regulations by incorporating some related agreements from our ICAO process and 

clarifying and improving existing provisions. Examples of this include special provisions for 

spare engines, provisions related to derivative engine models, test procedure specifications and 

reporting requirements. These changes are important for an effective implementation of the new 

requirements, and in many cases are also needed to meet our obligations under the Chicago 

Convention.

C. Costs and Benefits
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This is not an economically significant regulatory action. Aircraft engines are 

international commodities used on aircraft manufactured and sold around the world. When 

developing new engine models manufacturers not only consider current emission requirements 

but also try to anticipate the stringency of future standards and respond appropriately. Engine 

manufacturers participated in the deliberations leading up to ICAO decisions on the aircraft 

engine NOx emission standards and after the ICAO decisions they incorporated engine 

technology changes as needed to meet the new ICAO requirements. This helps to ensure the 

world wide acceptability of their products. Essentially all of these changes are now complete. 

Thus, while there is some cost to a manufacturer for responding to the new ICAO provisions, 

there is no significant further direct cost to the manufacturers created by EPA’s adopting the 

requirements into U.S regulations. In fact, it is likely that our adopting these requirements 

facilitates the acceptance of U.S. type certificates by aircraft manufacturers and airlines around 

the worldDATES: These final rules are effective on [insert date 30 days after publication in the 

Federal Register.] The incorporation by reference of certain publications listed in this regulation 

is approved by the Director of the Federal Register as of [insert date 30 days after publication in 

the Federal Register.]

ADDRESSES: EPA has established a docket for this action under Docket ID No. EPAHQ-OAR-2010-0687. All documents in the docket are listed on the http://www.regulations.gov

Web site. Although listed in the index, some information is not publicly available, e.g., 

confidential business information or other information whose disclosure is restricted by statute. 
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Certain other material, such as copyrighted material, is not placed on the Internet and will be 

publicly available only in hard copy form. Publicly available docket materials are available 

electronically through http://www.regulations.gov or in hard copy at the EPA Docket Center, 

EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW, Washington, DC. The Public 

Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal 

holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the 

telephone number for the Air Docket is 202-566-1742.

FOR FURTHER INFORMATION CONTACT: Richard Wilcox, Office of 

Transportation and Air Quality, Office of Air and Radiation, Environmental Protection Agency, 

2000 Traverwood Drive, Ann Arbor, MI 48105; telephone number: (734) 214-4390; fax number: 

(734) 214-4816; email address: wilcox.rich@epa.gov.

SUPPLEMENTARY INFORMATION:

 Does This Action Apply to Me?

Entities potentially regulated by this action are those that manufacture and sell aircraft 

engines and aircraft in the United States. Regulated categories include:

Category NAICSa Codes SIC

b Codes Examples of potentially affected entities

Industry .......... 336412 3724 Manufacturers of new aircraft engines

Industry .......... 336411 3721 Manufacturers of new aircraft 

a North American Industry Classification System (NAICS) b

Standard Industrial Classification 

(SIC) system code
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This table lists the types of entities that EPA is now aware could potentially be regulated 

by this action. Other types of entities not listed in the table could also be regulated. To 

determine whether your activities are regulated by this action, you should carefully examine the 

applicability criteria in 40 CFR 87.1 (part 87). If you have any questions regarding the 

applicability of this action to a particular entity, consult the person listed in the preceding FOR 

FURTHER INFORMATION CONTACT section.

Table of Contents

I. Overview and Background

A. Contents of the Final Rule

B. EPA’s Responsibilities Under the Clean Air Act

C. Interaction with the International Community

D. Brief History of EPA’s Regulation of Aircraft Engine Emissions 

E. Brief History of ICAO Regulation of Aircraft Engine Emissions 

II. Why is EPA Taking this Action? 

A. Inventory Contribution

B. Health, Environmental and Air Quality Impacts
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1. Background on Ozone, PM and NOx

a. What is Ozone?

b. What is Particulate Matter?

c. What is NOx?

2. Health Effects Associated with Exposure to Ozone, PM and 

NOx

a. What are the Health Effects of Ozone?

b. What are the Health Effects of PM?

c. What are the Health Effects of NOx?

3. Environmental Effects Associated with Exposure to Ozone, PM 

and NOx

a. Deposition of Nitrogen

b. Visibility Effects

c. Plant and Ecosystem Effects of Ozone

4. Impacts on Ambient Air Quality
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III. Details of the Final Rule

A. NOx Standards for Newly-Certified Engines

1. Tier 6 NOx Standards for Newly-Certified Engines

a. Numerical Emission Limits for Higher Thrust Engines 

b. Numerical Emission Limits for Lower Thrust Engines

2. Tier 8 NOx Standards for Newly-Certified Engines

a. Numerical Emission Limits for Higher Thrust Engines 

b. Numerical Emission Limits for Lower Thrust Engines

B. Application of NOx Standards for Newly-Manufactured Engines

1. Phase-In of the Tier 6 NOx Standards for NewlyManufactured Engines

2. Carryover of Previously Generated Emission Data

3. Exemptions and Exceptions from the Tier 6 Production Cutoff

a. New Provisions for Spare Engines

b. New Provisions for Engines Installed in New Aircraft
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i. Time-Frame and Scope

ii. Production Limit

iii. Exemption Requests

iv. Coordination of Exemption Requests

v. Low-Volume, Time-Limited Transitional Exception 

program

c. Voluntary Emission Offsets

4. Potential Phase-In of New Tier 8 NOx Standards for NewlyManufactured Engines

C. Application of Standards for Derivative Engines for Emission 

Certification Purposes

D. Annual Reporting Requirement

E. Standards for Supersonic Aircraft Turbine Engines

F. Amendments to Test and Measurement Procedures

G. Possible Future Revisions to Emission Standards for New Technology

Turbine Engines and Supersonic Aircraft Turbine Engines
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IV. Description of Other Revisions to the Regulatory Text

A. Applicability Issues

1. Military Engines

2. Noncommercial Engines

B. Non-Substantive Revisions

C. Clarifying Language for Regulatory Text

V. Technical Feasibility, Costs, and Emission Benefits

VI. Consultation with FAA

VII. Public Participation 

VIII. Statutory Provisions and Legal Authority

IX. Statutory and Executive Orders Review

A. Executive Order 12866: Regulatory Planning and Review, and Executive 

 Order 13563: Improving Regulation and Regulatory Review

B. Paperwork Reduction Act

C. Regulatory Flexibility Analysis
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D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation and Coordination with Indian 

Tribal Governments 

G. Executive Order 13045: Protection of Children from Environmental 

Health & Safety Risks

H. Executive Order 13211: Actions that Significantly Affect Energy

Supply, Distribution, or Use

I. National Technology Transfer Advancement Act

J. Executive Order 12898: Federal Actions to Address Environmental Justice in 

Minority Populations and Low Income Populations

K. Congressional Review Act

I. Overview and Background

This section summarizes the major provisions of the final rule for aircraft gas turbine 

engines. It also contains background on the EPA’s standard setting authority and responsibilities 
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under the Clean Air Act, the connection between our emission standards and those of the 

international community, and a brief regulatory history for this source of emissions.

A. Contents of the Final Rule

We are adopting several new emission standards and other regulatory requirements for 

aircraft turbofan and turbojet engines1 with rated thrusts greater than 26.7 kilonewtons (kN). 

First, we are establishing two new tiers of more stringent emission standards for oxides of 

nitrogen (NOx).

2

The standards apply differently to two classes of these engines, i.e., “newlycertified engines” and “newly-manufactured engines.” The newly-certified engine standards 

apply to aircraft engines that have received a new type certificate and have never been 

manufactured prior to the effective date of the new emission standards. Requirements for newlymanufactured engines apply to aircraft engines that were previously certified and manufactured 

in compliance with preexisting standards, and they require manufacturers to either comply with 

the newer standards by a specified future date or cease production of the affected engine models. 

 

1 Turbofan and turbojet engines will be collectively referred to as turbofan engines hereafter for 

convenience.

2 As previously mentioned, these new NOx standards are identical to requirements established by ICAO. 

The stringency of any new emission standard is selected based on an assessment of the technical feasibility, cost, 

and environmental benefit of potential requirements. The NOx standards we are promulgating today will not affect 

fuel economy or have any practical effect on CO2 emissions. (See International Civil Aviation Organization (ICAO), 

“Committee on Aviation Environmental Protection (CAEP), Eighth Meeting, Montreal, 1 to 12 February 2010, 

CAEP/8 NOx Stringency Cost –Benefit Analysis Demonstration Using APMT-IMPACTS,” CAEP/8-IP/30, 

December 1, 2010. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.)
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Newly-manufactured engine standards are also sometimes referred to as “production cutoff”

standards. Second, we are adopting certain time-limited flexibilities, i.e., the potential for 

exemptions or exceptions as defined in the regulations for newly-manufactured engines that may

not be able to comply with the first tier of the NOx standards because of specific technical or 

economic reasons.3 

We are also making a number of additional changes that would apply to a wider range of 

aircraft gas turbine engines4than those that would be subject to the new emission standards.5 

First, we are defining the meaning of a derivative engine for emissions certification purposes. 

The intent of this definition is to distinguish when the emission characteristics of a new turbofan 

engine model vary sufficiently from its existing parent engine design, and must show compliance 

with the emission standard for a newly-certificated engine. Second, we are establishing new 

reporting requirements for manufacturers that produce gas turbine engines subject to any exhaust 

emission standard. This will provide us with timely and consistent emission data and other 

information that is necessary to conduct emission inventory and air quality analyses and develop 

appropriate public policy for the aviation sector. Specifically, reports are required for turbofan 

 

3 These exemption or exception provisions are conceptually the same as the ICAO exemption provisions 

and provide the same regulatory flexibilities to all engine manufacturers. 

4 The term gas turbine engine includes turbofan, turbojet, and turboprop engines designs. The rated output 

for turbofan and turbojet engines is normally expressed as kilonewtons (kN) thrust. The rated output for turboprop 

engines is normally expressed as shaft horsepower (hp) or shaft kilowatt (kW). 

5 This includes turbofan and turbojet engines less than 26.7 kN thrust and all turboprop engines that are 

subject to any emission standard, e.g., smoke. 
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engines with rated thrusts greater than 26.7 kN, which are subject to gaseous emission and 

smoke standards, in addition to turbofans less than or equal to 26.7 kN, and all turboprop 

engines, that are only subject to smoke standards.6 Third, we are adopting minor amendments to 

the test and measurement procedures for aircraft engines. Finally, as described in section IV, we 

are making minor amendments to regulator provisions addressing definitions, acronyms and 

abbreviations, general applicability and requirements, exemptions, and incorporation by 

reference. 

Most of these new regulatory requirements have already been adopted by the United 

Nation’s International Civil Aviation Organization (ICAO). The requirements contained in this 

final rule bring the United States into alignment with the international standards and 

recommended practices. 

B. EPA’s Authority and Responsibilities under the Clean Air Act

Section 231(a)(2)(A) of the Clean Air Act (CAA) directs the Administrator of EPA to, 

from time to time, propose aircraft engine emission standards applicable to the emission of any

air pollutant from classes of aircraft engines which in her judgment causes or contributes to air 

pollution that may reasonably be anticipated to endanger public health or welfare. (See 42 

U.S.C. § 7571(a)(2)(A).) Section 231(a)(2)(B) directs EPA to consult with the Administrator of 

 

6 As discussed further in section III.D., the voluntary emission data report to ICAO does not include 

turbofans at or below 26.7 kN or turboprops subject to any emission standard. 
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the Federal Aviation Administration (FAA) on such standards, and prohibits EPA from changing 

aircraft emission standards if such a change would significantly increase noise and adversely

affect safety. 42 U.S.C. § 7571(a)(2)(B)(i)-(ii). Section 231(a)(3) provides that after we propose 

standards, the Administrator shall issue such standards “with such modifications as he deems 

appropriate.” 42 U.S.C. § 7571(a)(3). The U.S. Court of Appeals for the D.C. Circuit has held 

that this provision confers an unusually broad degree of discretion on EPA to adopt aircraft 

engine emission standards as the Agency determines are reasonable. NACAA v. EPA, 489 F.3d 

1221 (D.C. Cir. 2007). 

In addition, under CAA section 231(b) EPA is required to ensure, in consultation with the 

U.S. Department of Transportation (DOT), that the effective date of any standard provides the 

necessary time to permit the development and application of the requisite technology, giving 

appropriate consideration to the cost of compliance. 42 U.S.C. § 7571(b). Section 232 then 

directs the FAA to prescribe regulations to ensure compliance with EPA’s standards. 42 U.S.C. 

§ 7572. Finally, section 233 of the CAA vests the authority to promulgate emission standards for 

aircraft or aircraft engines only in EPA. States are preempted from adopting or enforcing any 

standard respecting aircraft engine emissions unless such standard is identical to EPA’s 

standards. 42 U.S.C. § 7573. Section VI of today's final rule further discusses our coordination 
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with DOT through the FAA.

7

 It also describes DOT’s responsibility under the CAA to enforce 

the aircraft emission standards established by EPA.

C. Interaction with the International Community

We began regulating the air pollution emissions from aircraft engines in 1973. Since that 

time, we have worked with the FAA and later with the International Civil Aviation Organization 

(ICAO) to develop international standards and other recommended practices pertaining to 

aircraft engine emissions. ICAO was established in 1944 by the United Nations (by the 

Convention on International Civil Aviation, the “Chicago Convention”) “... in order that 

international civil aviation may be developed in a safe and orderly manner and that international 

air transport services may be established on the basis of equality of opportunity and operated 

soundly and economically.”8 ICAO’s responsibilities include developing aircraft technical and 

operating standards, recommending practices, and generally fostering the growth of international 

civil aviation. The United States is currently one of 191 participating member States of 

ICAO.9,10 

 

7The functions of the Secretary of Transportation under part B of title II of the Clean Air Act (§§ 231-234, 

42 U.S.C. 7571-7574) have been delegated to the Administrator of the FAA. 49 CFR 1.47(g).

8

ICAO, “Convention on International Civil Aviation,” Ninth Edition, Document 7300/9, 2006. Copies of 

this document can be obtained from the ICAO website located at www.icao.int.

9 Members of ICAO’s Assembly are generally termed member States or contracting States. These terms 

are used interchangeably throughout this preamble.

10 There are currently 191 Contracting States according to ICAO website located at www.icao.int.
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In the interests of global harmonization and international air commerce, the Chicago 

Convention urges a high degree of uniformity by its member States. Nonetheless, the 

Convention also recognizes that member States may adopt their own unique airworthiness 

standards and that some may adopt standards that are more stringent than those agreed upon by

ICAO. 

The Convention has a number of other features that govern international commerce. 

First, States that wish to use aircraft in international transportation must adopt emission standards

and other recommended practices that are at least as stringent as ICAO’s standards. States may

ban the use of any aircraft within their airspace that does not meet ICAO standards.11 Second, 

States are required to recognize the airworthiness certificates of any State whose standards are at 

least as stringent as ICAO’s standards, thereby assuring that aircraft of any member State will be 

permitted to operate in any other member State.12 Third, and finally, to ensure that international

commerce is not unreasonably constrained, a participating nation which elects to adopt more 

stringent standards is obligated to notify ICAO of the differences between its standards and 

 

11 ICAO, “Convention on International Civil Aviation,” Article 87, Ninth Edition, Document 7300/9, 2006. 

Copies of this document can be obtained from the ICAO website located at 

www.icao.int/icaonet/arch/doc/7300/7300_9ed.pdf.

12 ICAO, “Convention on International Civil Aviation,” Article 33, Ninth Edition, Document 7300/9, 2006. 

Copies of this document can be obtained from the ICAO website located at 

www.icao.int/icaonet/arch/doc/7300/7300_9ed.pdf.
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ICAO standards. 13 However, if a nation sets tighter standards than ICAO, air carriers not based 

in that nation would only be required to comply with ICAO standards or more stringent 

standards imposed by their own nations, if applicable.

ICAO’s Committee on Aviation Environmental Protection (CAEP) undertakes ICAO’s 

technical work in the environmental field. The Committee is responsible for evaluating, 

researching, and recommending measures to the ICAO Council that address the environmental 

impact of international civil aviation. CAEP is composed of various task groups, work groups, 

and other committees whose contributing members include atmospheric, economic, aviation, 

environmental, and other professionals interested in aviation and environmental protection. At 

CAEP meetings, the United States is represented by the FAA, which plays an active role at these 

meetings.14 EPA has historically been a principal participant in the development of U.S. policy

in various ICAO/CAEP working groups and other international venues, assisting and advising 

FAA on aviation emissions, technology, and policy matters. If ICAO adopts a CAEP proposal 

 

13ICAO, “Convention on International Civil Aviation,” Articles 38, Ninth Edition, Document 7300/9, 2006. 

Copies of this document can be obtained from the ICAO website located at 

www.icao.int/icaonet/arch/doc/7300/7300_9ed.pdf.

14Pursuant to the President’s memorandum of August 11, 1960 (and related Executive Order No. 10883 

from 1960), the Interagency Group on International Aviation (IGIA) was established to facilitate coordinated 

recommendations to the Secretary of State on issues pertaining to international aviation. The DOT/FAA is the chair 

of IGIA, and as such, the FAA represents the U.S. on environmental matters at CAEP. 
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for a new environmental standard, it then becomes part of ICAO standards and recommended 

practices (Annex 16 to the Chicago Convention).15,16

D. Brief History of EPA’s Regulation of Aircraft Engine Emissions

As mentioned above, we initially regulated gaseous exhaust emissions, smoke, and fuel 

venting from aircraft engines in 1973.17 Since that time, we have occasionally revised those 

regulations. Two of these revisions are most pertinent to today’s final rule. First, in a 1997 

rulemaking, we made our emission standards and test procedures more consistent with those of 

ICAO for turbofan engines used in commercial aviation with rated thrusts greater than 26.7kN. 18 

These ICAO requirements are generally referred to as CAEP/2 standards. (The numbering 

nomenclature for CAEP requirements is discussed in the next section.) That action included new 

NOx emission standards for newly-manufactured commercial turbofan engines (those engines 

 

15 ICAO, “Aircraft Engine Emissions,” International Standards and Recommended Practices, 

Environmental Protection, Annex 16, Volume II, Second Edition, July 2008. A copy of this document is in docket 

number EPA-HQ-OAR-2010-0687.

16 CAEP develops new emission standards based on an assessment of the technical feasibility, cost, and 

environmental benefit of potential requirements.

17 U.S. EPA, “Emission Standards and Test Procedures for Aircraft;” Final Rule, 38 FR 19088, July 17, 

1973.

18 U.S. EPA, “Control of Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test 

Procedures;” Final Rule, 62 FR 25356, May 8, 1997. While ICAO’s standards were not limited to “commercial” 

aircraft engines, our 1997 standards were explicitly limited to commercial engines, as our finding that NOx and CO 

emissions from aircraft engines cause or contribute to air pollution which may reasonably be anticipated to endanger 

public health or welfare was so limited, See 62 FR 25358. As explained later in section IV.A.2. of today’s notice, 

we are expanding the scope of that finding and of our standards pursuant to section 231(a)(2)(A) of the Clean Air 

Act to include such emissions from both commercial and non-commercial aircraft engines based on the physical 

and operational similarities between commercial and noncommercial civilian aircraft andto bring our 

standards into full alignment with ICAO’s.
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built after the effective date of the regulations that were already certified to pre-existing 

standards) 19 and for newly-certified commercial turbofan engines (those engine models that 

received their initial type certificate after the effective date of the regulations). It also included a 

CO emission standard for newly-manufactured commercial turbofan engines. Second, in our 

most recent rulemaking in 2005, we promulgated more stringent NOx emission standards for 

newly-certified commercial turbofan engines.

20

 That final rule brought the U.S. standards closer 

to alignment with ICAO CAEP/4 requirements that were effective in 2004. In ruling on a

petition for judicial review of the 2005 rule filed by the National Association of Clean Air 

Agencies (NACAA), the U.S. Court of Appeals held that EPA’s approach of tracking the ICAO 

standards was reasonable and permissible under the CAA. NACAA v. EPA, 489 F.3d 1221, 

1230-32 (D.C. Cir. 2007). 

E. Brief History of ICAO Regulation of Aircraft Engine Emissions 

The first international standards and recommended practices for aircraft engine emissions

was recommended by CAEP’s predecessor, the Committee on Aircraft Engine Emissions 

(CAEE), and adopted by ICAO in 1981.

21

 These standards limited aircraft engine emissions of 

 

19 This does not mean that in 2005 we promulgated requirements for the re-certification or retrofit of 

existing in-use engines.

20 U.S. EPA, “Control of Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test 

Procedures;” Final Rule, 70 FR 2521, November 17, 2005.

21 ICAO, Foreword of “Aircraft Engine Emissions,” International Standards and Recommended Practices, 

Environmental Protection, Annex 16, Volume II, Third Edition, July 2008. Copies of this document can be obtained 

from the ICAO website at www.icao.int.
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HC, CO, and NOx. In 1994, ICAO adopted a CAEP/2 proposal to tighten the original NOx

standard by 20 percent and amend the test procedures.22 At the next CAEP meeting (CAEP/3) in 

1995, the Committee recommended a further tightening of 16 percent and additional test 

procedure amendments, but in 1997 the ICAO Council rejected this stringency proposal and 

approved only the test procedure amendments. At the CAEP/4 meeting in 1998, the Committee

adopted a similar 16 percent NOx reduction proposal, which ICAO approved on 1998. The 

CAEP/4 standards applied only to new engine designs certified after December 31, 2003 (i.e., the 

requirements did not also apply to previously certified, newly-manufactured engines unlike the 

CAEP/2 standards). In 2004, CAEP/6 recommended a 12 percent NOx reduction, which ICAO 

approved in 2005.

23 ,24 The CAEP/6 standards applied to new engine designs (newly-certified 

models) certified after December 31, 2007. At the most recent meeting, CAEP/8 recommended 

a further tightening of the NOx standards by 15 percent for newly-certified engines.25,26 The 

 

22 CAEP conducts its work over a period of years. Each work cycle is numbered sequentially and that 

identifier is used to differentiate the results from one CAEP to another by convention. The first technical meeting 

on aircraft emission standards was CAEP’s successor, i.e., CAEE. The first meeting of CAEP, therefore, is referred 

to as CAEP/2.

23 CAEP/5 did not address new aircraft engine emission standards.

24 ICAO, “Aircraft Engine Emissions,” Annex 16, Volume II, Third Edition, July 2008, Amendment 4 

effective on July 20, 2008. Copies of this document can be obtained from the ICAO website at www.icao.int.

25 CAEP/7 did not address new aircraft engine emission standards.

26 ICAO, “Committee on Aviation Environmental Protection (CAEP), Report of the Eighth Meeting, 

Montreal, February 1-12, 2010,” CAEP/8-WP/80. A copy of this document is in docket number EPA-HQ-OAR2010-0687.
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Committee also recommended that the CAEP/6 standards be applied to newly-manufactured 

engines. ICAO approved these recommendations in 2011.27

II. Why Is EPA Taking This Action?

As mentioned above, section 231(a)(2)(A) of the CAA authorizes the EPA Administrator 

to “from time to time, issue proposed emission standards applicable to the emission of any air 

pollution from any class or classes of aircraft or aircraft engines which in his judgment causes, or 

contributes to air pollution which may reasonably be anticipated to endanger public health or 

welfare.” 42 U.S.C. § 7571(a)(2)(A). 

One of the principal components of aircraft exhaust emissions is NOx, a precursor to the 

formation of tropospheric ozone and secondary PM.

28

 Most commercial airports are located in 

urbanized areas29 and many urbanized areas have ambient pollutant levels above the National 

Ambient Air Quality Standards (NAAQS) for ozone and fine particulate matter (PM 2.5) (i.e., 

 

27 27 ICAO, “Aircraft Engine Emissions,” Annex 16, Volume II, Third Edition, July 2008, Amendment 7 

effective on July 18, 2011. Copies of this document can be obtained from the ICAO website at www.icao.int.

28Ground-level ozone, the main ingredient in smog, is formed by complex chemical reactions of volatile 

organic compounds (VOC) and NOx in the presence of heat and sunlight. Standards that reduce NOx emissions will 

help address ambient ozone levels. They can also help reduce particulate matter (PM) levels as NOx emissions can 

also be part of the secondary formation of PM. See Section II.B below.

29 According to Airport Council International – North America and similar FAA databases, most 

commercial operations occur at airports that are in or near large cities or urbanized areas. There are about 130 

commercial airports in 78 ozone and fine particulate nonattainment areas (based on the nonattainment areas status of 

2008). There are about 325 commercial airports in the U.S. 
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they are in nonattainment for ozone and PM 2.5).

30

 This section discusses the contribution of 

aircraft engines used in commercial service with rated thrusts greater than 26.7kN to the national 

NOx emissions inventory and to NOx emission inventories in selected ozone and PM2.5

nonattainment areas, the potential effect of NOx emissions in the upper atmosphere on ground 

level PM 2.5 in addition to the health and welfare impacts of NOx and PM emissions.

A. Inventory Contribution

In contrast to all other mobile sources, whose emissions occur completely at ground 

level, the emissions from aircraft and aircraft engines can be divided into two flight regimes. 

The first regime includes the emissions that are released in the lower layer of the atmosphere and 

directly affect local and regional ambient air quality. These emissions generally occur at or 

below 3,000 feet above ground level, i.e., during the landing and takeoff (LTO) cycle. The 

aircraft operations that comprise an LTO cycle are: engine idle at the terminal gate (and 

sometimes during ground delays while holding for the active runway); taxiing between the 

terminal and the runway; take-off; climb-out; and approach to the airport. The second regime 

includes emissions that occur above 3,000 feet above ground level, known as non-LTO 

emissions. Collectively, the emissions associated with all ground and flight operations are 

generally referred to as full flight emissions.

 

30 For a current list of nonattainment areas see: http://www.epa.gov/oar/oaqps/greenbk/index.html
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In this section, we will discuss NOX emission inventories for commercial turbine-engine 

aircraft, both nationally and for selected ozone and PM2.5 nonattainment areas (NAAs). These 

inventories reflect emissions during the landing and takeoff cycle only. The most recent 

comprehensive analysis of historical and current LTO emissions from aircraft engines comes 

from a study undertaken for us by Eastern Research Group (ERG).31 The study analyzed the 

national emissions of commercial aircraft operations in the United States, and showed that in the 

most recent year studied (2008), such aircraft LTO operations contributed about 97 thousand 

tons to the national NOX inventory.

32

 A summary of the national inventory of LTO NOX

emissions is shown in Table 1. 

When these nationwide LTO emissions are compared to the total U.S. mobile source 

inventory for 2009, they account for less than one percent of the total. However, such a 

comparison may be a bit misleading, as it only includes those aircraft emissions that occur below 

3,000 feet altitude, while comparing them to the entirety of other mobile source emissions. In 

the U.S., LTO emissions account for only about ten percent of full flight NOX emissions. When 

considering full flight aircraft emissions (i.e., including both LTO and non-LTO emissions), the 

 

31

 “Historical Assessment of Aircraft Landing and Take-off Emissions (1986-2008),” Eastern Research 

Group, May 2011. A copy of this document can be found in public docket EPA-HQ-OAR-2010-0687.

32 The cumulative LTO NOx reduction associated with the new NOx standards is projected to be about 

100,000 tons from 2014 to 2030 (2014 is the implementation date of the CAEP/8 NOx standards). See “Historical 

Assessment of Aircraft Landing and Take-off Emissions (1986-2008),” Eastern Research Group, May 2011. A copy 

of this document can be found in public docket EPA-HQ-OAR-2010-0687.
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contribution of aircraft to the total mobile source NOX inventory is approximately 7.7 percent.33 

It is also worth noting that these LTO emissions are more localized in that they occur near 

airports, which are mostly within urban areas.

Table 1: Current National NOX Emissions from Commercial Aircraft

Aircraft Category 2008 Total NOX (thousand tons)

Air Carrier 86

Commuter/Air Taxi 11

Total Commercial 97

In addition, it is important to assess the contribution of commercial aircraft LTO NOX

emissions on a local level, especially in areas containing or adjacent to airports. The historical 

analysis conducted by ERG also included an assessment of selected ozone nonattainment areas 

(NAAs). The NAAs selected for study were chosen as follows. First, the 25 NAAs with 

airports which had high commercial traffic volumes were identified. Second, the 25 NAAs with 

the largest population were identified. These lists were combined. However, there was some 

overlap, and this led to a total of 40 NAAs being identified for the study.

34

 These NAAs 

 

33

 U.S. EPA, “Comparison of Aircraft LTO and Full Flight NOX Emissions to Total Mobile Source NOX

Emissions,” memorandum from John Mueller, Assessment and Standards Division, Office of Transportation and Air 

Quality, to docket EPA-HQ-OAR-2010-0687, May 10, 2011.

34 Although 41 NAAs were studied, the non-aircraft emissions data source that the aircraft emissions were 

compared to for this analysis did not distinguish between the Boston NAA in Massachusetts and the greater Boston 

NAA in New Hampshire. Thus, aircraft emissions from those two NAAs were combined into a single NAA for the 

purpose of this analysis, yielding 40 NAAs for study. 
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collectively include 200 airports, accounting for about 70 percent of commercial air traffic

operations.

Of the 40 NAAs originally studied by ERG as previously described, we identified the 30 

areas that were in nonattainment for ozone or PM2.5 as of March 30, 2012.35 Current (2008) and 

projected (2020) NOX emissions for these 30 ozone and PM2.5 NAAs, as well as the percent 

contribution of aircraft to total mobile source inventories (as compared to 2005 and 2020 mobile 

source inventories), are shown in Table 2.

36,37,38

 The relative contribution of aircraft in any given 

NAA varies based on activity in other transportation and industrial sectors. As can be seen from 

this table, expected growth in aircraft operations in many of these areas combined with 

anticipated reductions in NOX emissions from other mobile source categories results in the 

growth of the relative contribution of aircraft LTO emissions to mobile source NOX emissions in 

NAAs.

 

35 For a current list of nonattainment areas see: http://www.epa.gov/oar/oaqps/greenbk/index.html

36

 U.S. EPA, “Relative Contribution of Aircraft to Total Mobile Source NOX Emissions in Selected Ozone 

Nonattainment Areas,” memorandum from John Mueller, Assessment and Standards Division, Office of 

Transportation and Air Quality, to docket EPA-HQ-OAR-2010-0687, May 10, 2011.

37

 U.S. EPA, “Addendum to “Relative Contribution of Aircraft to Total Mobile Source NOX Emissions in 

Selected Ozone Nonattainment Areas,”” memorandum from John Mueller, Assessment and Standards Division, 

Office of Transportation and Air Quality, to docket EPA-HQ-OAR-2010-0687, May 17, 2011.

38

 U.S. EPA, “Update to “Relative Contribution of Aircraft to Total Mobile Source NOX Emissions in 

Selected Ozone Nonattainment Areas,”” memorandum from John Mueller, Assessment and Standards Division, 

Office of Transportation and Air Quality, to docket EPA-HQ-OAR-2010-0687, April 30, 2012.
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Table 2: NOX Emissions in Selected Ozone and PM2.5 Nonattainment Areas

Nonattainment Area 2008 Total NOX (tons)

2008 Aircraft Percent of 

Mobile Source NOX

2020 Aircraft Percent of 

Mobile Source NOX

Atlanta, GA 5,808 2.6 8.2

Baltimore, MD 1,148 1.3 4.4

Boston- including MA and NH 2,032 1.0 2.7
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NAAs

Charlotte-Gastonia-Rock Hill, 

NC-SC 1,917 2.6 10.0

Chicago-Gary-Lake County, 

IL-IN 6,007 1.8 5.0

Cleveland-Akron-Lorain, OH 680 0.5 1.3

Dallas-Fort Worth, TX 3,880 1.7 6.9

Denver-Boulder-Greeley-Fort 

Collins-Loveland, CO 2,649 2.5 7.1

Detroit-Ann Arbor, MI 2,312 1.1 3.0

Greater Connecticut, CT 405 0.8 2.4

Houston-Galveston-Brazoria, 

TX 3,045 1.3 3.4

Indianapolis, IN 1,089 1.4 3.0

Las Vegas, NV 2,308 6.0 15.8

Los Angeles South Coast Air 

Basin, CA 6,479 1.5 4.5

Louisville, KY-IN 1,211 1.9 6.2

Milwaukee-Racine, WI 557 0.9 3.2

New York-N. New JerseyLong Island, NY-NJ-CT 10,093 2.3 6.3

Philadelphia-WilmingtonAtlantic City, PA-NY-MD-DE 2,308 1.0 2.8

Phoenix-Mesa, AZ 2,298 1.4 3.3

Pittsburgh-Beaver Valley, PA 480 0.5 1.1

Providence (entire State), RI 232 1.0 2.3

Riverside County (Coachella 

Valley), CA 70 0.2 0.5

Sacramento Metro, CA 603 1.0 2.0

Salt Lake City, UT 1,235 4.4 14.1

San Diego, CA 1,035 1.4 3.4

San Francisco Bay Area, CA 4,405 2.7 6.7

San Joaquin Valley, CA 74 0.0 0.1

Seattle-Tacoma, WA 1,958 1.4 3.9

St. Louis, MO-IL 810 0.6 1.6

Washington, DC-MD-VA 2,983 2.0 6.2

Table 3 shows how commercial aircraft operations are projected to rise in the future on a 

nationwide basis. As operations increase, the inventory impact of these aircraft on national and 

local NOX inventories will also increase.

Table 3: Current and Projected Commercial Aircraft Operations
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Year Air Carrier 

Operations

(millions)

Commuter/

Air Taxi 

Operations

(millions)

Total 

Commercial 

Operations

(millions)

Total increase in 

commercial 

operations over 

2008 (percent)

2008 14.1 13.8 27.9 --

2020 16.5 14.1 30.5 9

2030 20.6 16.0 36.6 31

Source: December 2010 FAA TAF, which is located at http://aspm.faa.gov/main/taf.asp .

B. Health, Environmental and Air Quality Impacts

NOx emissions from aircraft and other mobile and stationary sources contribute to the 

formation of ozone. In addition, NOx emissions at low altitude also react in the atmosphere to 

form secondary fine particulate matter (PM2.5), particularly ammonium nitrate. In the following 

sections we discuss the adverse health and welfare effects associated with NOx emissions, in 

addition to the current and projected levels of ozone and PM across the country. The ICAO NOx

standards with which we are aligning will help reduce ambient ozone and secondary PM levels 

and thus will help areas with airports achieve or maintain attainment with the National Ambient 

Air Quality Standards (NAAQS).39

1. Background on Ozone, PM and NOX

 

39 The discussion of PM health and welfare effects throughout this notice relates exclusively to the effects 

of the NOx emission standards on the formation of secondary PM from nitrate formation in the atmosphere. 

Presently, there are no emission standards for PM emitted directly from aircraft turbine engines. The current and 

planned future work programs for CAEP/ICAO are developing PM test procedures and information to characterize 

the amount and type of these emissions from aircraft engines that are in production. Ultimately, this information 

will be used to assess the need for an aircraft turbine engine PM standard (i.e., whether PM emissions from aircraft 

cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare), with 

standard setting as appropriate. 
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a. What is Ozone?

Ground-level ozone pollution is typically formed through reactions involving VOC and 

NOX in the lower atmosphere in the presence of sunlight. These pollutants, often referred to as 

ozone precursors, are emitted by many types of pollution sources, such as highway and nonroad 

motor vehicles and engines, power plants, chemical plants, refineries, makers of consumer and 

commercial products, industrial facilities, and smaller area sources.

The science of ozone formation, transport, and accumulation is complex.40 Ground-level 

ozone is produced and destroyed in a cyclical set of chemical reactions, many of which are 

sensitive to temperature and sunlight. When ambient temperatures and sunlight levels remain 

high for several days and the air is relatively stagnant, ozone and its precursors can build up and 

result in more ozone than typically occurs on a single high-temperature day. Ozone and its 

precursors can be transported hundreds of miles downwind from precursor emissions, resulting 

in elevated ozone levels even in areas with low local VOC or NOX emissions.

b. What is Particulate Matter?

The discussion includes PM2.5 because the NOX emitted by aircraft engines can react in 

the atmosphere to form nitrate, a component of PM2.5. Particulate matter is a generic term for a 

 

40 U.S. EPA Air Quality Criteria for Ozone and Related Photochemical Oxidants (Final). U.S. 

Environmental Protection Agency, Washington, D.C., EPA 600/R-05/004aF-cF, 2006. This document is available 

in Docket EPA-HQ-OAR-2010-0687. This document may be accessed electronically at: 

http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_cr_cd.html.
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broad class of chemically and physically diverse substances. It can be principally characterized 

as discrete particles that exist in the condensed (liquid or solid) phase spanning several orders of 

magnitude in size. Since 1987, EPA has delineated that subset of inhalable particles small 

enough to penetrate to the thoracic region (including the tracheobronchial and alveolar regions) 

of the respiratory tract (referred to as thoracic particles). The current PM NAAQS uses PM2.5 as 

the indicator for fine particles (with PM2.5 generally referring to particles with a nominal mean 

aerodynamic diameter less than or equal to 2.5 micrometers (μm)), and use PM10 as the indicator 

for purposes of regulating the coarse fraction of PM10 (referred to as thoracic coarse particles or 

coarse-fraction particles; generally including particles with a nominal mean aerodynamic 

diameter greater than 2.5 μm and less than or equal to 10 μm, or PM10-2.5). Ultrafine particles are 

a subset of fine particles, generally less than 100 nanometers (0.1 μm) in diameter. 

Fine particles are produced primarily by combustion processes and by transformations of 

gaseous emissions (e.g., SOX, NOX and VOC) in the atmosphere. The chemical and physical 

properties of PM2.5 may vary greatly with time, region, meteorology, and source category. Thus, 

PM2.5 may include a complex mixture of different components including sulfates, nitrates, 

organic compounds, elemental carbon and metal compounds. These particles can remain in the 

atmosphere for days to weeks and travel hundreds to thousands of kilometers. 

c. What is NOX?
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Nitrogen dioxide (NO2) is a member of the NOX family of gases. Most NO2 is formed in 

the air from the oxidation of nitric oxide (NO) emitted when fuel is burned at a high temperature. 

NO2 and its gas phase oxidation products can dissolve in water droplets and further oxidize to 

form nitric acid which reacts with ammonia to form nitrates, an important component of ambient 

PM. NOX and VOC are the two major precursors of ozone. The health effects of ozone, ambient 

PM and NOX are covered in section II.B.2.

2. Health Effects Associated with Exposure to Ozone, PM and NOX

a. What are the Health Effects of Ozone?

The health and welfare effects of ozone are well documented and are assessed in EPA’s 2006 

Air Quality Criteria Document and 2007 Staff Paper.41, 42 People who are more susceptible to 

effects associated with exposure to ozone can include children, the elderly, and individuals with 

respiratory disease such as asthma. Those with greater exposures to ozone, for instance due to 

time spent outdoors (e.g., children and outdoor workers), are of particular concern. Ozone can 

irritate the respiratory system, causing coughing, throat irritation, and breathing discomfort. 

 

41 U.S. EPA Air Quality Criteria for Ozone and Related Photochemical Oxidants (Final). U.S. 

Environmental Protection Agency, Washington, D.C., EPA 600/R-05/004aF-cF, 2006. This document is available 

in Docket EPA-HQ-OAR-2010-0687. This document may be accessed electronically at: 

http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_cr_cd.html.

42 U.S. EPA (2007) Review of the National Ambient Air Quality Standards for Ozone, Policy Assessment 

of Scientific and Technical Information. OAQPS Staff Paper.EPA-452/R-07-003. This document is available in 

Docket EPA-HQ-OAR-2010-0687. This document is available electronically at: 

http:www.epa.gov/ttn/naaqs/standards/ozone/s_o3_cr_sp.html.
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Ozone can reduce lung function and cause pulmonary inflammation in healthy individuals. 

Ozone can also aggravate asthma, leading to more asthma attacks that require medical attention 

and/or the use of additional medication. Thus, ambient ozone may cause both healthy and 

asthmatic individuals to limit their outdoor activities. In addition, there is suggestive evidence of 

a contribution of ozone to cardiovascular-related morbidity and highly suggestive evidence that 

short-term ozone exposure directly or indirectly contributes to non-accidental and 

cardiopulmonary-related mortality, but additional research is needed to clarify the underlying 

mechanisms causing these effects. In a report on the estimation of ozone-related premature 

mortality published by the National Research Council (NRC), a panel of experts and reviewers 

concluded that short-term exposure to ambient ozone is likely to contribute to premature deaths 

and that ozone-related mortality should be included in estimates of the health benefits of 

reducing ozone exposure.43 Animal toxicological evidence indicates that with repeated 

exposure, ozone can inflame and damage the lining of the lungs, which may lead to permanent 

changes in lung tissue and irreversible reductions in lung function. The respiratory effects 

observed in controlled human exposure studies and animal studies are coherent with the evidence 

from epidemiologic studies supporting a causal relationship between acute ambient ozone 

exposures and increased respiratory-related emergency room visits and hospitalizations in the 

warm season. In addition, there is suggestive evidence of a contribution of ozone to 

cardiovascular-related morbidity and non-accidental and cardiopulmonary mortality.

 

43 National Research Council (NRC), 2008. Estimating Mortality Risk Reduction and Economic Benefits from 

Controlling Ozone Air Pollution. The National Academies Press: Washington, D.C. A copy of this document is in 

docket number EPA-HQ-OAR-2010-0687.
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b. What are the Health Effects of PM? 

Scientific studies show ambient PM is associated with a series of adverse health effects. 

These health effects are discussed in detail in EPA’s Integrated Science Assessment for 

Particulate Matter (ISA).

44

 The ISA summarizes health effects evidence associated with both 

short-term and long-term exposures to PM2.5, PM10-2.5, and ultrafine particles.

The ISA concludes that health effects associated with short-term exposures (hours to 

days) to ambient PM2.5 include mortality, cardiovascular effects, such as altered vasomotor 

function and myocardial ischemia, and hospital admissions and emergency department visits for 

ischemic heart disease and congestive heart failure, and respiratory effects, such as exacerbation 

of asthma symptoms in children and hospital admissions and emergency department visits for 

chronic obstructive pulmonary disease and respiratory infections.

45

 The ISA notes that longterm exposure (months to years) to PM2.5 is associated with the development/progression of 

cardiovascular disease, premature mortality, and respiratory effects, including reduced lung 

function growth in children, increased respiratory symptoms, and asthma development.46 The 

ISA concludes that the currently available scientific evidence from epidemiologic, controlled 

human exposure, and toxicological studies supports a causal association between short- and 

 

44 U.S. EPA (2009) Integrated Science Assessment for Particulate Matter, EPA 600/R-08/139F. A copy of this 

document is in docket number EPA-HQ-OAR-2010-0687. 

45 U.S. EPA (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. Environmental 

Protection Agency, Washington, DC, EPA/600/R-08/139F, 2009. Section 2.3.1.1.

46 U.S. EPA (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. Environmental 

Protection Agency, Washington, DC, EPA/600/R-08/139F, 2009. page 2-12, Sections 7.3.1.1 and 7.3.2.1.
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long-term exposures to PM2.5 and cardiovascular effects and premature mortality. Furthermore, 

the ISA concludes that the collective evidence supports likely causal associations between shortand long-term PM2.5 exposures and respiratory effects. The ISA also concludes that the scientific 

evidence is suggestive of a causal association for reproductive and developmental effects 

including respiratory-related infant mortality and cancer, mutagenicity, and genotoxicity and 

long-term exposure to PM2.5.

47

For PM10-2.5, the ISA concludes that the current evidence is suggestive of a causal 

relationship between short-term exposures and premature mortality, cardiovascular effects, and 

respiratory effects. Data are inadequate to draw conclusions regarding the health effects 

associated with long-term exposure to PM10-2.5. 

For ultrafine particles, the ISA concludes that there is suggestive evidence of a causal 

relationship between short-term exposures and cardiovascular effects, such as changes in heart 

rhythm and blood vessel function. It also concludes that there is suggestive evidence of 

association between short-term exposure to ultrafine particles and respiratory effects. Data are 

inadequate to draw conclusions regarding the health effects associated with long-term exposure 

to ultrafine particles.

 

47 U.S. EPA (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. Environmental 

Protection Agency, Washington, DC, EPA/600/R-08/139F, 2009. Section 2.3.2.
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c. What are the Health Effects of NOX? 

Information on the health effects of NO2 can be found in the EPA Integrated Science 

Assessment (ISA) for Nitrogen Oxides.48 The EPA has concluded that the findings of 

epidemiologic, controlled human exposure, and animal toxicological studies provide evidence 

that is sufficient to infer a likely causal relationship between respiratory effects and short-term 

NO2 exposure. The ISA concludes that the strongest evidence for such a relationship comes from 

epidemiologic studies of respiratory effects including symptoms, emergency department visits, 

and hospital admissions. The ISA also draws two broad conclusions regarding airway

responsiveness following NO2 exposure. First, the ISA concludes that NO2 exposure may

enhance the sensitivity to allergen-induced decrements in lung function and increase the 

allergen-induced airway inflammatory response following 30-minute exposures of asthmatics to 

NO2 concentrations as low as 0.26 ppm. Second, exposure to NO2 has been found to enhance the 

inherent responsiveness of the airway to subsequent nonspecific challenges in controlled human 

exposure studies of asthmatic subjects. Small but significant increases in non-specific airway

hyperresponsiveness were reported following 1-hour exposures of asthmatics to 0.1 ppm NO2. 

Enhanced airway responsiveness could have important clinical implications for asthmatics since 

transient increases in airway responsiveness following NO2 exposure have the potential to 

increase symptoms and worsen asthma control. Together, the epidemiologic and experimental 

 

48 U.S. EPA (2008). Integrated Science Assessment for Oxides of Nitrogen – Health Criteria (Final Report).

EPA/600/R-08/071. Washington, DC: U.S.EPA. A copy of this document is in docket number EPA-HQ-OAR-2010-

0687.
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data sets form a plausible, consistent, and coherent description of a relationship between NO2

exposures and an array of adverse health effects that range from the onset of respiratory

symptoms to hospital admission. 

Although the weight of evidence supporting a causal relationship is somewhat less certain 

than that associated with respiratory morbidity, NO2 has also been linked to other health 

endpoints. These include all-cause (non-accidental) mortality, hospital admissions or emergency

department visits for cardiovascular disease, and decrements in lung function growth associated 

with chronic exposure.

3. Environmental Effects Associated with Exposure to Ozone, PM and NOX

a. Deposition of Nitrogen

Emissions of NOX from aircraft engines contribute to atmospheric deposition of nitrogen 

in the U.S. Atmospheric deposition of nitrogen contributes to acidification, altering 

biogeochemistry and affecting animal and plant life in terrestrial and aquatic ecosystems across 

the United States. The sensitivity of terrestrial and aquatic ecosystems to acidification from 

nitrogen deposition is predominantly governed by geology. Prolonged exposure to excess 

nitrogen deposition in sensitive areas acidifies lakes, rivers and soils. Increased acidity in 

surface waters creates inhospitable conditions for biota and affects the abundance and nutritional 

value of preferred prey species, threatening biodiversity and ecosystem function. Over time, 

acidifying deposition also removes essential nutrients from forest soils, depleting the capacity of 
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soils to neutralize future acid loadings and negatively affecting forest sustainability. Major 

effects include a decline in sensitive forest tree species, such as red spruce (Picea rubens) and 

sugar maple (Acer saccharum); and a loss of biodiversity of fishes, zooplankton, and macro 

invertebrates. 

In addition to the role nitrogen deposition plays in acidification, nitrogen deposition also 

leads to nutrient enrichment and altered biogeochemical cycling. In aquatic systems increased 

nitrogen can alter species assemblages and cause eutrophication. In terrestrial systems nitrogen 

loading can lead to loss of nitrogen sensitive lichen species, decreased biodiversity of grasslands, 

meadows and other sensitive habitats, and increased potential for invasive species. 

Adverse impacts on soil chemistry and plant life have been observed for areas heavily 

influenced by atmospheric deposition of nutrients, metals and acid species, resulting in species 

shifts, loss of biodiversity, forest decline damage to forest productivity and reductions in 

ecosystem services. Potential impacts also include adverse effects to human health through 

ingestion of contaminated vegetation or livestock (as in the case for dioxin deposition), reduction 

in crop yield, and limited use of land due to contamination. 

Atmospheric deposition of pollutants can reduce the aesthetic appeal of buildings and 

culturally important articles through soiling, and can contribute directly (or in conjunction with 
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other pollutants) to structural damage by means of corrosion or erosion.49 Atmospheric 

deposition may affect materials principally by promoting and accelerating the corrosion of 

metals, by degrading paints, and by deteriorating building materials such as concrete and 

limestone. Particles contribute to these effects because of their electrolytic, hygroscopic, and 

acidic properties, and their ability to adsorb corrosive gases (principally sulfur dioxide). 

b. Visibility Effects

NOx emissions contribute to visibility impairment in the U.S. through the formation of 

secondary PM2.5.

50

 Visibility impairment is caused by light scattering and absorption by

suspended particles and gases. Visibility is important because it has direct significance to 

people’s enjoyment of daily activities in all parts of the country. Individuals value good 

visibility for the well-being it provides them directly, where they live and work, and in places 

where they enjoy recreational opportunities. Visibility is also highly valued in significant natural 

 

49 U.S. EPA. (2005). Review of the National Ambient Air Quality Standards for Particulate Matter: Policy 

Assessment of Scientific and Technical Information, OAQPS Staff Paper. Retrieved on April 9, 2009 from 

http://www.epa.gov/ttn/naaqs/standards/pm/data/pmstaffpaper_20051221.pdf.

50 U.S. EPA. (2004). Air Quality Criteria for Particulate Matter (AQCD). Volume I Document No. 

EPA600/P-99/002aF and Volume II Document No. EPA600/P-99/002bF. Washington, DC: U.S. Environmental 

Protection Agency. Retrieved on March 18, 2009 from http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=87903.
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areas, such as national parks and wilderness areas, and special emphasis is given to protecting 

visibility in these areas. For more information on visibility see the final 2009 PM ISA.51

c. Plant and Ecosystem Effects of Ozone

Elevated ozone levels contribute to environmental effects, with impacts to plants and 

ecosystems being of most concern. Ozone can produce both acute and chronic injury in sensitive 

species depending on the concentration level and the duration of the exposure. Ozone effects 

also tend to accumulate over the growing season of the plant, so that even low concentrations 

experienced for a longer duration have the potential to create chronic stress on vegetation. 

Ozone damage to plants includes visible injury to leaves and impaired photosynthesis, both of 

which can lead to reduced plant growth and reproduction, resulting in reduced crop yields, 

forestry production, and use of sensitive ornamentals in landscaping. In addition, the impairment 

of photosynthesis, the process by which the plant makes carbohydrates (its source of energy and 

food), can lead to a subsequent reduction in root growth and carbohydrate storage below ground, 

resulting in other, more subtle plant and ecosystems impacts. These latter impacts include 

increased susceptibility of plants to insect attack, disease, harsh weather, interspecies 

competition and overall decreased plant vigor. The adverse effects of ozone on forest and other 

natural vegetation can potentially lead to species shifts and loss from the affected ecosystems, 

resulting in a loss or reduction in associated ecosystem goods and services. Lastly, visible ozone 

 

51 U.S. EPA (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. Environmental 

Protection Agency, Washington, DC, EPA/600/R-08/139F, 2009. A copy of this document is in docket number 

EPA-HQ-OAR-2010-0687. 
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injury to leaves can result in a loss of aesthetic value in areas of special scenic significance like 

national parks and wilderness areas. The final 2006 Ozone Air Quality Criteria Document 

presents more detailed information on ozone effects on vegetation and ecosystems.

4. Impacts on Ambient Air Quality

The aircraft NOx emission standards we are promulgating would affect ambient 

concentrations of air pollutants. Nationally, levels of PM2.5, ozone, and NOX are declining.52 

However as of March 30, 2012, over 15 million people live in areas designated nonattainment 

for one or more of the current NAAQS.53 These numbers do not include the people living in 

areas where there is a future risk of failing to maintain or attain the NAAQS. 

States with ozone nonattainment areas are required to take action to bring those areas into 

attainment. The attainment date assigned to an ozone nonattainment area is based on the area’s 

classification. Most ozone nonattainment areas are required to attain the 1997 8-hour ozone 

NAAQS in the 2007 to 2013 time frame and then to maintain it thereafter.55 We anticipate 

 

52 U. S. EPA (2010) Our Nation’s Air: Status and Trends through 2008. Office of Air Quality Planning and 

Standards, Research Triangle Park, NC. Publication No. EPA 454/R-09-002. This document can be accessed 

electronically at: http://www.epa.gov/airtrends/2010/. 

53 US EPA, 2012. http://www.epa.gov/oar/oaqps/greenbk/index.html 

55 The Los Angeles South Coast Air Basin 8-hour ozone nonattainment area and the San Joaquin Valley Air Basin 8-

hour ozone nonattainment area are designated as extreme and will have to attain before June 15, 2024. The 

Sacramento, Coachella Valley and Houston 8-hour ozone nonattainment areas are designated as severe and will 

have to attain by June 15, 2019. In addition, the Western Mojave 8-hour ozone nonattainment area has requested to 

be reclassified as severe. This request has not yet been acted on.
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designating areas for the 2008 ozone standards in late spring 2012; thus, the attainment dates for 

areas designated nonattainment for the 2008 8-hour ozone NAAQS would likely be in the 2015 

to 2032 timeframe, depending on the severity of the problem in each area.56 

Areas designated as not attaining the 1997 PM2.5 NAAQS will need to attain the 1997 

standards in the 2010 to 2015 time frame, and then maintain compliance with them thereafter. 

The 2006 24-hour PM2.5 nonattainment areas will be required to attain the 2006 24-hour PM2.5

NAAQS in the 2014 to 2019 time frame and then be required to maintain the 2006 24-hour PM2.5

NAAQS thereafter. 

EPA has already adopted many emission control programs that are expected to reduce 

ambient ozone and PM2.5 levels and which will assist in reducing the number of areas that fail to 

achieve the NAAQS. Even so, our air quality modeling projects that in 2030 as many as 10

counties with a population of over 30 million may not attain the 2008 ozone standard of 0.075 

ppm (75 ppb) without additional controls.58 In addition, our air quality modeling projects that in 

2030 at least four counties with a population of nearly 7 million may not attain the 1997 annual 

PM2.5 standard of 15 μg/m3and 22 counties with a population of over 33 million may not attain 

 

56 US EPA, 2012. Proposed Rule - Implementation of the 2008 National Ambient Air Quality Standards for Ozone: 

Nonattainment Area Classifications Approach, Attainment Deadlines and Revocation of the 1997 Ozone Standards 

for Transportation Conformity Purposes. (77 FR 8107, February 14, 2012).

58 U.S. EPA (2010). Regulatory Impact Analysis: Final Rulemaking to Establish Greenhouse Gas Emission 

Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles. Chapter 8: Health 

and Environmental Impacts. EPA 420-R-11-901.
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the 2006 24-hour PM2.5 standard of 35 μg/m

3 without additional controls.59,60

 These numbers do 

not account for those areas that are close to (e.g., within 10 percent of) the standards. These 

areas, although not violating the standards, would also benefit from any reductions in NOX

ensuring long-term maintenance of the NAAQS.

In summary, the aircraft NOx reductions resulting from these new aircraft engine 

emission standards will be useful to states in attaining or maintaining the ozone, PM2.5 , and NO2

NAAQS standards.

III. Details of the Final Rule

The following is a description of the regulations being adopted in this final rule, with any 

changes from the proposal also noted. The descriptions also include our response to the most 

significant comments received on the proposal. A full summary of the comments and our 

responses are contained in the response to comments document for the rule that is available in 

the public docket for this action.

62

 

59 U.S. EPA (2010). Regulatory Impact Analysis: Final Rulemaking to Establish Greenhouse Gas Emission 

Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles. Chapter 8: Health 

and Environmental Impacts. EPA 420-R-11-901.

60 These figures are based on the results of EPA computer modeling, which is not affected by the upcoming 

2008 ozone NAAQS nonattainment designations.

62 U.S. Environmental Protection Agency, “Summary and Analysis of Comments: Control of Air Pollution 

from Aircraft and Aircraft Engines,” Office of Transportation and Air Quality, EPA-420-R-12-011, May 2012. A 

copy of this document is in docket number EPA-HQ-OAR-2010-0687. 
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We are establishing two different levels or “tiers” of increasingly more stringent NOx 

emission standards for gas turbofan engines with maximum rated thrusts greater than 26.7 

kilonewtons (kN).63 Each of the tiers apply to newly-certified engines. Newly-certified aircraft 

engines are those that would receive a new type certificate after the effective date of the 

applicable standards. Such engine types or models would not have begun production prior to the 

effective date of the new requirement.64 

We are also requiring newly-manufactured engines to comply with the first tier of the two 

tiers of standards. Newly-manufactured aircraft engines are those that have been previously

certified and manufactured in compliance with preexisting standards, and will continue to be 

produced after the effective date of a new applicable standard. Normally, these newlymanufactured engines must comply with the same NOx limits as newly-certified engines, but at a 

later date or cease production.65 The end of this “phase-in” period for the newly-manufactured 

 

63 The standards will apply to engines used in commercial and noncommercial aviation for which the FAA 

issues airworthiness certificates, e.g., non-revenue, general aviation service. The vast majority of these engines are 

used in commercial applications. 

64 ICAO standards describe newly-certified engines as “...engines of a type or model for which the date of 

manufacture of the first individual production model was after....” the effective date of the emission standards. See 

ICAO, “Aircraft Engine Emissions,” Annex 16, Volume II, Third Edition, July 2008, Amendment 4 effective on 

July 20, 2008. Copies of this document can be obtained from the ICAO website at www.icao.int. The term “first 

individual production model” means the first engine ever produced of a unique model or type.

65 The standards for newly-manufactured engines are described in general regulatory terms as the date that 

the type or model was first certified and produced in conformance with specific emission standards, and the date 

beyond which an individual engine meeting those same requirements cannot be made. So ICAO standards describe 

newly-manufactured engines as “...engines of a type or model for which the date of manufacture of the first 

individual production model was after....” the effective date of the applicable standards, and “...for which the date 

of manufacture of the individual engine was on or before....” a specific date that is later than the first effective date 

of the standards. See ICAO, “Aircraft Engine Emissions,” Annex 16, Volume II, Third Edition, July 2008, 
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engine standards is sometimes referred to as a “production cutoff.”. Again, we are adopting 

only the first of the two new tiers of NOx standards for newly-manufactured engines. These 

provisions are described in detail below.

Five other regulatory features are being established in this final rule. First, we are 

revising provisions for certain time-limited flexibilities, i.e., potential exemptions, for newlymanufactured engines that may not be able to comply with the first tier of the new NOx 

standards because of specific technical or economic reasons.

66

 Second, we are defining 

“derivative engine” for emissions certification purposes. The intent of this definition is to 

distinguish when the emission characteristics of a new turbofan engine model vary substantially

from its existing parent engine design, and must show compliance with the emission standards 

for a newly-certificated engine. Third, we are establishing new CO and NOx standards for 

turbofan engines that are used to propel supersonic aircraft. These standards were adopted by 

ICAO in the 1980s, but were not previously added to our HC emission standard for these 

engines. Promulgating these standards meets our treaty obligation under the Convention on 

International Civil Aviation as previously described in section I.C. Fourth, we are making

several changes to the emission testing and measurement procedures in our regulations that are 

intended to implement ICAO’s Annex 16 and to incorporate the entire annex in our regulations 

 

Amendment 4 effective on July 20, 2008. Copies of this document can be obtained from the ICAO website at 

www.icao.int. 

66 These apply only to the first tier of NOx standards. We are not adopting a production cutoff for the 

second tier of standards.
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by reference. Finally, as described in section IV, we are amending the current regulatory

provisions that address definitions, acronyms and abbreviations, general applicability and 

requirements, exemptions, and incorporation by reference. These amendments are intended to 

clarify requirements, make them more consistent with other parts of the program, update the text 

to be consistent with current standard language conventions, or remove obsolete provisions.

As discussed further below, with the exception of the annual reporting requirement 

described in section III.D, the amendments reflect those changes that were previously adopted by

ICAO. 

This final rule also is consistent with our authority and obligations under the CAA as 

described in section I.B. More specifically, the technical feasibility and cost of the emission 

standards were well documented by our own analyses and CAEP as described later in this 

section and in section V, Technical Feasibility, Costs, and Emission Benefits. We think that the 

final rule provides adequate lead time for the development and application of the requisite 

technology with appropriate consideration to the cost of compliance. We have consulted with 

the Department of Transportation through the FAA regarding lead time, noise, safety, and the 

technical feasibility of the new standards. Today’s final rule is also consistent with U.S. treaty

obligations under the Chicago Convention as described in section I.C., because the requirements 

are consistent with current ICAO standards. 
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Except to the extent needed to make our standards conform to ICAO’s standards by

making them applicable to both commercial and non-commercial engines, we are not revising

exhaust emission standards for HC, CO, or smoke. All engines subject to the new NOx 

standards would also continue to be subject to the existing HC, CO, and smoke standards. It is 

worth emphasizing that although we are including these existing HC, CO, and smoke standards 

in a new section 87.23, which would also contain the new Tier 6 and Tier 8 NOx standards, we 

are not actually adopting new standards for these three pollutants, since under the current form of 

part 87 these HC, CO and smoke standards would already continue to apply to new engine types 

subject to future revised NOx standards. 

As discussed above, we are adopting a new naming convention in this preamble and the 

regulatory text to more easily distinguish between the tiers of increasingly more stringent NOx 

emission standards. This convention is also consistent with the numeric identifier that CAEP 

uses to differentiate the CAEP work cycle that produces new NOx standards. (The CAEP 

naming convention is described in section I.E.) As a result, the first tier of NOx standards, 

which correspond to CAEP/6, are referred to as Tier 6 in the remainder of today’s notice. The 

second tier of standards is referred to as Tier 8, which correspond to CAEP/8. We are also 

incorporating the new naming convention in the regulations for the existing NOx emission 

standards, i.e., Tier 0, Tier 2, and Tier 4. There is no material change to the existing NOx 

standards themselves, except to the extent that when today’s final rule becomes effective, the 

existing NOx standards would be superseded by Tier 6 standards. 
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We acknowledge that this new naming convention is a change from the past practice of 

not describing aircraft engine emission standards as tiers. However, we believe the new naming 

scheme is a valuable tool that makes referring to individual NOx standards much easier. It is 

also similar to the terminology we use for other mobile source sectors that are subject to 

environmental regulation and for which standards have become more stringent or have otherwise 

been amended over time. 

A. NOx Standards for Newly-Certified Engines

We are adopting two different tiers of increasingly stringent NOx standards. These 

standards would apply for all for newly-certified turbofan aircraft engines with maximum rated 

thrusts greater than 26.7 kN.

67

 (See section III.B for a discussion of how these standards apply 

for newly-manufactured engines that are not considered to be newly certified.) The numerical 

value of the applicable standard for an individual engine model is defined by the engine’s thrust 

level and pressure ratio. Simply stated, the pressure ratio is the numerical ratio of the air

pressure entering the engine to the air pressure at the entrance to the combustor, i.e., after the air 

has passed through the compressor section of the engine. 68 The new tiers are described 

separately below.

 

67 There are no gaseous emission standards, e.g., NOx, for gas turbine engines with maximum rated thrusts 

equal to or less than 26.7kN. These engines are, however, subject to smoke and fuel venting standards.

68 The combustor is a chamber where a mixture of fuel and air is burned to form very hot, expanding gases. 

As these gases move through the combustion chamber, the walls of the combustor are cooled with dilution air to 
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1. Tier 6 NOx Standards for Newly-Certified Engines

This first tier of new standards is equivalent to the CAEP/6 NOx limits that were adopted 

by ICAO and became internationally applicable after December 31, 2007. Given that aircraft 

turbofan engines are international commodities, engine manufacturers introduced engine models 

after that date that demonstrate compliance with these international standards, or are already 

planning to do so for upcoming engine designs. Based on this, our evaluation of the necessary

lead time, and the lack of any comments on this aspect of the proposal, this tier of standards 

takes effect immediately upon the effective date of this final rule. 

The basic form of the NOx standards for turbofan engines is different for higher- and 

lower-rated thrust engines. Higher output engines are defined as having rated thrusts equal to or 

greater than 89 kN, while lower output engines are defined as having rated thrusts less than 89

kN but greater than 26.7 kN. The new Tier 6 NOx standards for each of these power grouping 

are described separately below.

a. Numerical Emission Limits for Higher Thrust Engines

The Tier 6 NOx standards for newly-certified gas turbine engines with rated thrusts more 

than 89 kN are differentiated by pressure ratio as shown below.

 

prevent thermal damage. Dilution air is also used to tailor the gas’ temperature profile as it exits the combustor so 

that the final temperatures will not exceed the allowable limit at the turbine inlet.
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• For engines with a pressure ratio of 30 or less:

g/kN rated output = 16.72 + (1.4080 * engine pressure ratio)

• For engines with a pressure ratio of more than 30 but less than 82.6:

g/kN rated output = -1.04 + (2.0 * engine pressure ratio)

• For engines with a pressure ratio of 82.6 or more:

g/kN rated output = 32 + (1.6 * engine pressure ratio)

The new Tier 6 NOx standards for these higher thrust engines are presented in Figure 1 

along with the previous EPA NOx standards, which were based on CAEP/4, for comparison. 
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As a matter of convention, the relative stringency from one CAEP standard to another is 

expressed relative to a pressure ratio of 30, because the percentage reduction is usually

inconsistent across all of the possible pressure ratios, which otherwise makes a simple 

comparison difficult. Using that convention, the Tier 6 standards (CAEP/6) are referred to as 

being 12 percent more stringent than the existing EPA NOx Tier 4 standards (CAEP/4). The 

relative stringency can also be illustrated at other pressure ratios. At pressure ratios less than 30 

the reductions are also 12 percent. At pressure ratios above 30, however, the percent reduction 

decreases as the pressure ratio is increased. Based on the figure, the percent reduction for current 

technology engines ranges from about 8 to 12 percent. 

0

20

40

60

80

100

120

140

160

180

10 30 50 70 90

g/k

N

T

hru

st

Pressure Ratio (PR)

Figure 1: Tier 6 NOx Standards for Higher

Thrust Engines

Existing Tier 4 Standard

Tier 6

8% Reduction

Current Engine PRs

12% Reduction
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b. Numerical Emission Limits for Lower Thrust Engines

The new Tier 6 NOx standards for newly-certified gas turbine engines with rated thrusts 

between 26.7 and equal to or less than 89.0 kN are differentiated by both pressure ratio and rated 

thrust as shown below.

• For engines with a pressure ratio of 30 or less: 

g/kN rated output = 38.5486 + (1.6823 * engine pressure ratio) - (0.2453 * kN rated 

thrust) - (0.00308 * engine pressure ratio * kN rated thrust)

• For engines with a pressure ratio of more than 30 but less than 82.6:

g/kN rated output = 46.1600 + (1.4286 * engine pressure ratio) - (0.5303 * kN rated 

thrust) + (0.00642 * engine pressure ratio * kN rated thrust)

In developing the corresponding NOx standards for lower thrust engines, CAEP 

recognized the technical challenges that physically smaller-sized engines sometimes present 

relative to incorporating some of the lowest NOx technology approaches, which are otherwise 

available to their larger counterparts. These technical difficulties are well documented and 

increase progressively as size is reduced (from around 89 kN).69 For example, the relatively 

small combustor space and section height of these engines creates constraints on the use of low 

 

69 ICAO/CAEP, “Report of Third Meeting, Montreal, Quebec, December 5-15, 1995,” Document 9675, 

CAEP/3. A copy of this paper can be found in Docket EPA-HQ-OAR-2010-0687.
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NOx fuel-staged combustor concepts which inherently require the availability of greater flow 

path cross-sectional area than conventional combustors. Also, fuel-staged combustors need more 

fuel injectors, and this need is not compatible with the relatively smaller total fuel flows of lower 

thrust engines. (Reductions in fuel flow per nozzle are difficult to attain without having clogging 

problems due to the small sizes of the fuel metering ports.) In addition, lower thrust engine 

combustors have an inherently greater liner surface-to-combustion volume ratio, and this 

requires increased wall cooling air flow. Thus, less air will be available to obtain acceptable 

turbine inlet temperature distribution and for emissions control.70 With these technological 

constraints in mind, CAEP fashioned the CAEP/6 NOx standards across the range of thrusts 

represented by low-thrust engines to become comparatively less stringent, i.e., CAEP/6 relative 

to CAEP/4, as the rated output and physical size of the engines decrease. We agree with this 

approach.

As mentioned, the new Tier 6 standards depend on an individual engine’s rated thrust and 

pressure ratio. With two variables in the calculation, the standards cannot be represented in a 

simple figure, i.e., no single line graph showing the standards for all engines within the thrust 

range is possible as it was for higher thrust engines. Regardless of this complexity, however, 

some general observations are useful to characterize the Tier 6 NOx standards for lower thrust 

 

70 ICAO, “Combined Report of the Certification and Technology Subgroups,” section 2.3.6.1, CAEP 

Working Group 3 (Emissions). Presented by the Chairman of the Technology Subgroup, Third Meeting, Bonn, 

Germany, June 1995. A copy of this paper can be found in Docket EPA-HQ-OAR-2010-0687.
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engines based on the engine size versus technological challenge described in the previous 

paragraph. 

Comparing the new lower and higher thrust standards at 89 kN, which is the demarcation 

point between the two sets of standards, shows that the standards for lower thrust engines are

numerically equivalent to the limit for higher thrust engines at each pressure ratio. This is as 

expected because the engine sizes and ability to incorporate low-NOx technologies are the same 

at 89.0 kN delineation point. 

Again focusing only on 89 kN engines, the new Tier 6 standards represent a 12 percent 

reduction from the existing EPA Tier 4 (CAEP/4 based standards) for pressure ratios of 30 or 

less as shown below in Figure 2. This includes the region represented by almost all current 

engine designs. At higher pressure ratios, the relative numerical reduction is progressively less 

because the slope of the two standards is essentially the same. 
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At other thrust ratings the percent reduction between the new Tier 6 and existing EPA 

NOx standards at any pressure ratio becomes progressively smaller as thrust decreases. This is 

illustrated in Figure 3 for a pressure ratio of 30. This pressure ratio was chosen for the example 

because, as before, the relative stringency of CAEP NOx standards is generally compared at this 

point as a matter of convention. As shown in the figure for current engines, the reduction ranges 

from 12 percent at the upper end of the thrust range to 0 percent at the lower end of the range. 

The pattern is similar for the other pressure ratios. Only the actual numerical value for 

percentage reduction at 89 kN, as shown on the far right of the figure, may vary by pressure 

ratio, as described at the beginning of this paragraph. However, in the region of pressure ratios 

0

20

40

60

80

100

120

140

160

180

10 20 30 40 50 60

g/k

N

T

hru

st

Pressure Ratio (PR)

Figure 2: Tier 6 NOx Standards for Lower

Thrust Engines Rated at 89.0 kN

Existing Standard

Proposed Tier 6

12% Reduction

Current Engine PRs
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represented by today’s engines, the results are identical to those shown in the figure, i.e., a 12 

percent reduction at 89 kN decreasing to 0 percent at 26.7 kN.

2. Tier 8 NOx Standards for Newly-Certified Engines

The second tier of new standards, i.e., Tier 8, are equivalent to the NOx limits that were 

most recently recommended at CAEP/8 in February 2010 for adoption by ICAO.71 The CAEP/8 

recommended standards have a recommended applicable date after December 31, 2013. As 

discussed further in section V of today’s notice, we agree with CAEP that this provides engine 

 

71 CAEP/7 did not adopt new aircraft engine NOx standards.

40

50

60

70

80

90

100

20 40 60 80 100

g/k

N

T

hru

st

Thrust (kN)

Figure 3: Tier 6 NOx Standards for Lower Thrust 

Engines At Pressure Ratio 30

Existing Tier 4 Standard

Tier 6

0% Reduction

at 26.7kN 12% Reduction

at 89kN

Current Engine Thrusts
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manufacturers with adequate lead time to respond to these more stringent NOx standards 

considering the technical feasibility and cost associated with the requirements.72 Therefore, this 

tier of standards takes effect on January 1, 2014. As with the new Tier 6 NOx standards, the 

basic form of the new Tier 8 standards for turbofan engines is different for higher- and lowerrated thrust engines. Higher output engines are defined as having rated thrusts equal to or greater 

than 89 kN, while lower output engines are defined as having rated thrusts less than 89 kN but 

greater than 26.7 kN. The longer-term standards for each of these power grouping are described 

separately below.

a. Numerical Emission Limits for Higher Thrust Engines

The new Tier 8 NOx standards for newly-certified turbofan engines with rated thrusts of 

89 N or more are differentiated by pressure ratio as shown below.

 

72 Leadtime in this context refers to the time between CAEP adoption of a new emission standard and the 

effective date of the requirement. ICAO emission standards are global in nature and designed to provide engine 

manufacturers with adequate time to develop and deploy the requisite technology. Manufacturers produce engines 

that comply with new ICAO standards to ensure their products can be sold and used worldwide even in the absence 

of specific U.S. regulations. Based on this response to the ICAO standard, we find that there is also adequate 

leadtime between EPA’s promulgation of the new requirement and the associated effective date. No public 

comments pertaining to leadtime were received.
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• For engines with a pressure ratio of 30 or less:

g/kN rated output = 7.88 + (1.4080 * engine pressure ratio)

• For engines with a pressure ratio of more than 30 but less than 104.7:

g/kN rated output = -9.88+ (2.0 * engine pressure ratio)

• For engines with a pressure ratio of 104.7 or more:

g/kN rated output = 32 + (1.6 * engine pressure ratio)

The new Tier 8 NOx standards for these higher thrust engines are presented in Figure 4 

along with the new Tier 6 standards for comparison. 
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As noted previously, as a matter of convention the relative stringency from one CAEP 

standard to another is generally expressed relative to a pressure ratio of 30. Using that 

convention, the new Tier 8 standards (CAEP/8) are referred to as being 15 percent more stringent 

than the new Tier 6 NOx standards (CAEP/6). The relative stringency can also be illustrated at 

other pressure ratios. At pressure ratios less than 30 the reductions increase. At pressure ratios 

above 30, however, the percent reduction decreases. Based on the figure, the percent reduction 

for current engine designs range from about 11 to 19 percent. 

b. Numerical Emission Limits for Lower Thrust Engines

0

20

40

60

80

100

120

140

160

180

10 30 50 70 90

g/k

N

T

hru

st

Pressure Ratio (PR)

Figure 4: Tier 8 NOx Standards for Higher

Thrust Engines

Tier 6

Tier 8

Current Engine PRs

19% Reduction

15% Reduction

11% Reduction
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The new Tier 8 NOx standards for newly-certified gas turbine engines with rated thrusts 

between 26.7 but less than or equal to 89.0 kN are differentiated by both pressure ratio and rated 

thrust as shown below.

• For engines with a pressure ratio of 30 or less: 

g/kN rated output = 40.052 + (1.5681 * engine pressure ratio) - (0.3615 * kN rated 

thrust) - (0.0018 * engine pressure ratio * kN rated thrust)

• For engines with a pressure ratio of more than 30 but less than 104.7:

g/kN rated output = 41.9435 + (1.505 * engine pressure ratio) - (0.55823 * kN rated 

thrust) + (0.005562 * engine pressure ratio * kN rated thrust)

In developing the corresponding CAEP/8 NOx standards for low thrust engines, CAEP 

recognized the technical challenges that physically smaller-sized engines represent relative to 

incorporating some of the lowest NOx technology, which is otherwise available to their larger 

counterparts. These technical difficulties were described in the previous section for the Tier 6 

low-thrust engine standards.

Also as previously described, no single line graph showing the standards for all engines 

within the thrust range is possible as it was for higher thrust engines, because the equations have 

two variables. However, some general observations are useful to characterize the new Tier 8 

NOx standards for lower thrust engines based on the engine size versus technological challenge 
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described in the previous paragraph. First, the new Tier 8 NOx standards for lower thrust 

engines are numerically equivalent to the limit for higher thrust engines across all pressure ratios 

at the highest rating of 89 kN, where the engine sizes and ability to incorporated low-NOx 

technologies are comparable. This same characteristic was observed for the Tier 6 standards. 

Second, as shown below in Figure 5 for 89 kN engines, at this thrust rating the new Tier 8 

standards represents a 15 percent reduction from the Tier 6 standards for a pressure ratio of 30. 

However, within the region of pressure ratios for all current engine designs, the reductions range 

from 19 to 23 percent. 

0

20

40

60

80

100

120

140

160

180

10 20 30 40 50 60

g/k

N

T

hru

st

Pressure Ratio

Figure 5: Tier 8 NOx Standards for Lower

Thrust Engines Rated at 89.0 kN

Tier 6

Tier 8

Current Engine PRs

15% Reduction

23% Reduction

19% Reduction
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 Third, at other thrust ratings the percent reduction between the new Tier 6 and Tier 8 

standards at any pressure ratio becomes progressively smaller as thrust decreases. This is 

illustrated in Figure 6 for a pressure ratio of 30, following the convention described above. Also 

as shown in the figure for current engines, the reduction ranges from 15 percent at the upper end 

of the thrust range to 5 percent at the lower end of the range. While not depicted in a figure, the 

pattern is similar for the other pressure ratios. However, the actual numerical values for 

percentage reductions at both ends of the thrust range, i.e., 26.7 to 89 kN, may vary by pressure 

ratio. In the region of pressure ratios represented by today’s engines, the results are identical to 

those shown in Figure 6 at 26.7 kN, i.e., a 5 percent reduction at all pressure ratios for that thrust 

rating. However, percent reductions increase linearly up to a maximum 23 percent reduction for 

89 kN engines with pressure ratios of about 15.
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B. Application of the Tier 6 NOx Standards to Newly-Manufactured Engines

This section describes the application of the new Tier 6 NOx standards to newlymanufactured engines, and our amended temporary flexibilities for newly-manufactured engines 

that show significant problems complying with these requirements. Also, consistent with 

CAEP/8, we are not applying the new Tier 8 NOx standards to newly-manufactured engines at 

this time. This section concludes with a description of future efforts to examine such a 

possibility. 

1. Phase-In of the Tier 6 NOx Standards for Newly-Manufactured Engines

40

50

60

70

80

90

20 40 60 80 100

g/k

N

T

hru

st

Thrust (kN)

Figure 6: Tier 8 NOx Standards for Lower Thrust 

Engines at Pressure Ratio 30

Tier 6

Tier 8

Current Engine Thrusts

15% Reduction at 

89 kN

5% Reduction 

at 26.7 kN
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As described above, the new Tier 6 NOx standards apply to all engine types or models 

that receive a new type certificate after the effective date of the final rule. We are also phasing in 

these same NOx limits for newly-manufactured engines for engine models (and their derivatives

for emissions certification purposes) that were originally certified to less stringent requirements 

(i.e., Tier 2 or Tier 4) and were already being produced for installation on new aircraft prior to 

the effective date of the final rule.

73

 As a result, manufacturers need to bring newlymanufactured engines of these previously certified models into compliance with the applicable 

Tier 6 standards by a future date or cease production of those engine models.74 As we discussed 

and described in our analysis of the need for a CAEP/6 production cutoff during the CAEP 

process, establishing a date certain for compliance with any emission standard is necessary to 

ensure that the full benefits of newer, more stringent requirements will be achieved in a 

reasonable time.75 We are, however, adopting certain limited flexibilities for engines that cannot 

be made compliant because of specific technical or economic reasons, as discussed later in this 

section. 

 

73 The requirement that newly-manufactured engines must meet the CAEP 6 NOx standard by a date certain 

applies only to engines that are intended to be installed on all new airframes. It would not apply to engines 

produced as “spares,” which are intended to be installed on existing airframes as replacements for maintenance or 

other reasons. See section III.B.2 for more information about new and spare engines.

74 After this date the production of any noncompliant engines would cease because the FAA would 

discontinue issuing an airworthiness approval tag (FAA Form 8130-3) to these engines. 

75 ICAO, Committee on Aviation Environmental Protection (CAEP), Eight Meeting, Montreal, 1 to 12 

February 2010, Agenda 2: Review of Technical Proposals Relating to Aircraft Engine Emissions, Adoption of 

Production Cutoff for Emission Standards, WP/56, Presented by the United States, December 12, 2009. A copy of 

this document is in docket number EPA-HQ-OAR-2010-0687.
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As described in the proposal, the effective date of January 1, 201376 for the newlymanufactured engine standards is consistent with the expected market demand for these 

previously certified engine types. Historically, engine manufacturers have often responded to the 

adoption of more stringent NOx standards by bringing older engine types into compliance with 

the newer requirements well before the required date in anticipation of the likely market demand, 

or planning for the orderly withdrawal of these engines from the marketplace. Information 

developed during the ICAO process in 2008 and 200977,78,79 and our more recent discussions 

with manufacturers indicate that: 1) all but a few models are already compliant with CAEP/6 

standards, 2) nearly without exception, all current production models will meet the CAEP/6 

requirements by the 2012 time frame, and 3) any noncompliant models will be phased out of 

production because of low market demand. 

 

76 The regulatory text specifies that engine models certified at or below the Tier 4 NOx standards may be 

produced through December 31, 2012 without meeting the Tier 6 NOx standards. Therefore, the effective date of 

the standards for newly-manufactured engines is effectively January 1, 2013.

77 ICAO, Committee on Aviation Environmental Protection (CAEP), Steering Group Meeting, 

Salvador, Brazil, 22 to 26 June 2009, Agenda 6: Emissions Technical-WG3, Production Cutoffs and Associated 

Flexibilities for ICAO Engine Emission Standards, WP/39, Presented by U.S. Representative, August 6, 2009. A 

copy of this document is in docket number EPA-HQ-OAR-2010-0687. 

78 ICAO, Committee on Aviation Environmental Protection (CAEP), Steering Group Meeting, 

Salvador, Brazil, 22 to 26 June 2009, Agenda Item 3: Forecasting and Economic Analysis Support Group (FESG), 

CAEP/6 NOx Production Cutoff Cost Analysis, WP/39, Presented by the FESG NOx Stringency Task Group, 

February 6, 2009. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.

79

 ICAO, Committee on Aviation Environmental Protection (CAEP), Steering Group Meeting, 

Seattle, 22 to 26 September 2008, Agenda Item 3: Forecasting and Economic Analysis Support Group (FESG), 

Production Cutoff for NOx Standards, WP/6, Presented by the FESG Rapporteurs, April 9, 2008. A copy of this 

document is in docket number EPA-HQ-OAR-2010-0687.
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We think that the five-year phase-in period from ICAO’s effective date of the CAEP/6 

standards (corresponding to our new Tier 6 NOx standards) for newly-manufactured engines is 

adequate for manufacturers and their customers to respond to the new requirements without 

disrupting their future planning and purchasing decisions.80,81 This phase-in period for applying 

the Tier 6 NOx standards to newly-manufactured engines is also identical to the date for this 

same requirement that was adopted by ICAO. No comments were received expressing concern 

with this phase-in period for newly-manufactured engines. 

We did, however, receive two comments expressing the view that the time between the 

date of our final rule and the January 1, 2013 effective date of the production cutoff would be too

short if it is less than one year. General Electric Aviation (GE) was the most detailed and began 

by noting that most of the engine models currently in production were certified to the Tier 4 

standards and had demonstrated NOx emissions below the Tier 6 at that time. They continued 

that if the original certification reports are sufficient for the FAA to formally certify these 

engines to the Tier 6 standards, then none of these engines would be adversely affected by the 

production cutoff. However, GE expressed the concern that if additional interactions or formal 

action by the FAA were needed, or revisions to the FAA’s FAR Part 34 were required, then 

 

80 The ICAO CAEP/6 NOx standards became effective after December 31, 2007.

81 This period of time is also consistent with the phase-in period associated with previous ICAO standards. 

CAEP’s predecessor, the Committee on Aircraft Engines Emissions, established the first international emission 

standards with an effective date four years after adoption, i.e., effectively a four year phase-in. CAEP2 included a 

phase-in period of 4 years for newly-manufactured engines.
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having less than one year between EPA’s final rule and the production cutoff could disrupt 

current engine production. As a result, GE asked that the date of the production cutoff be 

delayed to take effect 12 months after the final rule, i.e., 2013. The other joint comment from 

the Aerospace Industries Association (AIA) and the General Aviation Manufacturers Association 

(GAMA) was similar in nature, but without supporting details.

The commenters’ concerns do not relate to the technical or economic feasibility of 

newly-manufactured engines achieving emission levels in compliance with the new Tier 6 

standards by the date of the production cutoff as proposed. The concerns expressed do not argue 

that additional time is necessary “to permit the development and application of the requisite 

technology” to comply with the standards under CAA section 231(b). Therefore, the date of the 

Tier 6 production cutoff is appropriate and consistent with the Clean Air Act. 

Section 232(b) of the Act directly addresses our obligation relative to the effective date of 

the regulation. Specifically, it says: “Any regulation prescribed under this section (and any 

revision thereof) shall take effect after such period as the Administrator finds necessary (after 

consultation with the Secretary of Transportation) to permit the development and application of 

the requisite technology, giving appropriate consideration to the cost of compliance within such 

period.” Based on the information provided above, the aircraft engine models described by GE 

are already capable of complying with the EPA Tier 6 NOx standards using already applied 

requisite technology, i.e., the cost of applying with has already been borne, as the effective date 
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of the corresponding ICAO CAEP/6 NOx standard has already passed. We do not believe there 

are any technical feasibility or economic implications arising from the continued application of 

the requisite technology for those engines to meet the Tier 6 NOx standards. Also, consistent 

with our most recent previous amendment to the NOx standards, which similarly promulgated 

the standard at a level that was already being met by aircraft engine manufacturers who were 

already applying the requisite technology, the effective date does not need to include additional 

lead time for the development and application of additional technology that would be needed to 

comply with the standards. See, e.g., 70 FR 69604, 69674-76 (Nov. 17, 2005). As a result, the 

implementation dates provide more than adequate lead time under the statute. Therefore, 

because aircraft engine manufacturers are already able to comply with the Tier 6 NOx standard 

through the continued use of already applied requisite technology, and because the effective date 

of the corresponding ICAO CAEP/6 NOx standard has already passed (and also based on the 

assessment described in section V. Technical Feasibility, Cost, and Emission Benefits), we find 

that the dates provide more than adequate lead time under the statute for application of requisite 

technology.

We also want to stress that the production cutoff is actually an ICAO standard and we 

think it is important to stay aligned with the CAEP production cutoff date. We note that this is 

also being adopted by the European Aviation Safety Agency (EASA) and perhaps other aviation 

certification authorities. Our adoption of the proposed date insures international consistency
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regarding the production cutoff date and avoids contradicting our international bilateral 

agreements with other governments, e.g., the European Union. 

Regarding the need for engine models to be formally recognized by the FAA as 

complying with the new Tier 6 standard, this is completely within the purview of the FAA. In 

our previous most recent amendment to the NOx standard, we provided just a one-month lead 

time period before the revised standard became effective, and FAA did not adopt corresponding 

implementing regulations until one year later, with no apparent disruption to the industry. (See 

70 FR 69664, Nov. 17, 2005.) The new Tier 6 standards are the same as the CAEP/6 standards 

that were approved by ICAO in 2005 with an effective date of beginning after December 31, 

2007. Therefore, just as for the 2005 revised NOx standard that we similarly promulgated 

significantly later than the effective date of the corresponding ICAO CAEP standard, we do not 

believe that it is necessary to delay the effective date based on a need for the FAA to revise its 

own implementation and enforcement regulations.

Finally, section 232(a) of the Act directs the FAA to ensure compliance with our 

standards. In this regard, the FAA has developed a streamlined process to recognize compliance 

with Tier 6 and or Tier 8 as appropriate for currently type certified engine models which meet 

the emission standards and they have assured the regulated industry that they will dedicate the 

necessary resources to formally recognize conformance with the standards before the production 

cutoff date. 
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For the reasons stated above, EPA is promulgating the Tier 6 production cutoff with the 

originally proposed effective date of January 1, 2013.

2. 2. Carryover of Previously Generated Emission Test Data

Aircraft engine models normally receive type certificates, which include a determination 

that the model meets the emission standards in force at the time the type certificate is granted. 

EPA has not updated its aircraft emission standards or test procedure regulations since 2005. In 

this action we are adopting Tier 6 and Tier 8 NOx emission standards and are adopting either in 

40 CFR part 87 directly or through incorporation by reference of Annex 16, Volume II a number 

of minor changes to test procedures and related requirements. These changes will become 

effective on the date when the rule becomes effective.

This leaves open a question regarding the future validity and acceptability for amended 

type certificates of emission tests and emission test data generated under previously specified test 

procedures and related requirements. For example, there may be an engine model tested in 2004

that demonstrated HC, CO, and NOx emission levels below the exhaust emission standards in 

effect at that time and also below the Tier 6 or perhaps even the Tier 8 standards that are being 

promulgated in this final rule. We want to be clear that we do not intend minor changes to test 

procedures or related provisions and requirements to trigger the need for additional testing. 

Thus, in cases where a manufacturer has a valid current type certificate based on emissions 

information generated under the test procedures in force at the time the type certificate was 
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granted, we consider that data to be valid for any formal FAA recognition of compliance, e.g., an 

amended type certificate, with the Tier 6 or Tier 8 NOx emission requirements if the original test 

data demonstrate such compliance. The same is true for the HC and CO emission standards. 

This clarification should greatly facilitate compliance determinations by the FAA and eliminate 

any uncertainty regarding the potential for otherwise minor test procedure changes to trigger new 

emissions testing for previously certificated engines with emission levels below the new NOx 

standards.

3. Exemptions and Exceptions from the Tier 6 Production Cutoff

In conjunction with the implementation of the new Tier 6 NOx standards, we are 

establishing provisions which allow engine manufacturers to request an exemption or exception 

from meeting the Tier 6 NOx standards for newly-manufactured engines. These provisions 

replace existing provisions addressing exemptions that were promulgated in section 87.7 of our 

aircraft engine regulations. (Any exemptions previously issued under section 87.7 would not be 

affected by the revisions.) This section of the preamble describes these exemption and 

exception provisions, i.e., exemptions for engines installed in new aircraft and exceptions for 

spare engines used in existing aircraft for maintenance purposes. It also includes a description of 

a short-term exception program (termed the low-volume, time-limited transitional exemption 

program). These provisions have largely been crafted to be consistent with exemption provisions 
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in the ICAO Environmental Technical Manual (ETM).84,85 The provisions of the ETM guidance 

were developed in the context of the CAEP/6 NOx production cutoff deliberations leading up to 

the CAEP/8 meeting in February 2010.

While we are revising our regulations, the process for evaluating any request for an 

exemption, i.e., petition, and any final decision on its disposition would be unchanged. In this 

regard, the FAA is the process owner under its enforcement authority contained in section 232 of

the Clean Air Act.

86

 The FAA must consult with EPA in evaluating the merits of the request, 

and the EPA must formally concur with any decision regarding the granting or denial of the 

request. 

We are deleting from our regulations the requirement in §87.7(e) that the FAA publish a 

notice of the exemption in the Federal Register. The FAA has an established process in place for 

publishing requests for exemption that are filed in accordance with 14 CFR part 11. Under 

§87.7(b) of the existing regulations, the FAA, with EPA concurrence, may also exempt low-

 

84 ICAO, “Committee on Aviation Environmental Protection (CAEP), Report of the Eighth Meeting, 

Montreal, February 1-12, 2010,” CAEP/8-WP/80. A copy of this document is in docket number EPA-HQ-OAR2010-0687.

85 Note that EPA has submitted a paper to amend the exemption provisions included in this ETM to be 

consistent with this rule. See ICAO, “Newly Produced Engine Exemptions for CAEP/6 NOx Production Cutoff,”

CAEP9_WG3-CTG-2_IP01, September 23, 2010. A copy of this document is in docket number EPA-HQ-OAR2010-0687.

86 EPA formally transferred the responsibility and authority for the evaluation of requests for exemptions 

from the emission standards to the Secretary of Transportation (DOT). See “Control of Air Pollution from Aircraft 

and Aircraft Engines; Emission Standards and Test Procedures;” Final Rule, 47 FR 58462, December 30, 1982.
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production volume engines from being fully compliant with the emission standards. Several 

such short-term exemptions were granted in the 1980s when emission standards were first 

applied. These exemptions have since expired, and requests for new exemptions under those 

provisions have not been submitted. We have determined that these provisions, which were 

adopted in conjunction with revised emission standards in 1982, are no longer of any utility.

87

Therefore, we are deleting these provisions to avoid confusion. 

We are also deleting the time-limited exemption provision for in-use engines that is 

contained in section 87.7(d) of the existing regulations. This provision applies to fuel venting 

and smoke emission standards, which were new when the exemption was adopted in 1973. The 

exemption allowance was limited to in-use engines that were unable to comply with the 

requirements when the regulation became effective in 1974. The in-use fleet of engines was 

fully retrofitted to comply with the standards later in the 1970s. Therefore, this provision is now 

obsolete and we are deleting it to avoid confusion. We proposed to delete the existing provisions 

for temporary exemptions based on flights for short durations and infrequent intervals. This 

proposal was based on the EPA’s and FAA’s belief that the provisions were unnecessary because 

our standards apply to aircraft certificated by the FAA, and the FAA does not address in the 

certification process whether an aircraft will be used for short durations or infrequent intervals. 

Hence, the provisions appeared to have no utility. 

 

87 U.S.EPA, “Control of Air Pollution from Aircraft and Aircraft Engines; Emission Standards and Test 

Procedures,” Final Rule, 47 FR 58462, December 30, 1982.
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We received two comments from the Aerospace Industries Association (AIA) and the 

General Aviation Manufacturers Association (GAMA) requesting that the provision be retained. 

First, they argued that as in the past, a new aircraft may be produced at a commercial facility that 

is destined for immediate conversion to a military only application at a separate facility. These 

aircraft may require a small number of airworthiness flight tests before being delivered to the 

conversion facility and conceivably would be subject to EPA standards during flight testing. 

While these aircraft would generally utilize compliant engines, it may be possible that noncompliant engines could be used (our standards do not apply to engines used on military aircraft 

as discussed later) and temporary exemptions would be necessary. Second, AIA and GAMA 

commented that it would be helpful if the provision also allowed for granting a discrete number 

of exemptions over a specified time period, rather than having to request the exemption prior to 

each flight as currently required. 

In considering the commenters’ suggestion to retain the exemption provision, we note 

that allowing such operations will not have any significant adverse affect on the environment 

because of the infrequent nature and short duration of such flights. Retaining the exemption is

also consistent with exempting military aircraft from emission control requirements as discussed 

later. Therefore, we have retained the provision with one change, made in response to the 

comments, as described below. 
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The current provision calls for the Secretary of Transportation to consult with the EPA 

Administrator when considering any exemption request for infrequent interval and short duration 

flights not explicitly allowed by the regulations. Given the inconsequential nature of such flights 

on the environment, we believe that the Secretary should be able to consider and act on these 

petitions unilaterally to streamline the process. Therefore, we are deleting that portion of the 

previous exemption provision. Of course, we will consult with the Secretary if asked to do so. 

As for requesting a discrete number of temporary exemptions, we believe this is an issue that the 

Secretary of Transportation may address under its enforcement role as described in section 232 

of the CAA. 

The current regulations also provide for permanent exemptions for newly-manufactured 

engines based on consideration of the certain factors specified in section 87.7(c). We are 

replacing these provisions with new regulatory text generally consistent with the ETM that 

would provide for permanent exemptions or exceptions88 for newly manufactured engines used 

on new aircraft and spare engines used for maintenance or replacement purposes. These are 

summarized below. (See §87.50 of the regulations for additional details on these 

exemptions/exceptions.) 

 a. New Provisions for Spare Engines

 

88

 As used in 40 CFR part 87, as a practical matter the meanings of “exception” and “exemption” are 

essentially equivalent. However, under FAA regulations, the meanings of these terms are distinct, especially with 

respect to the manner in which they are administered. 
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We are revising the regulations to allow the sale of a newly-manufactured engine for 

installation on an in-service aircraft, i.e., a spare engine that does not conform to the applicable 

emissions standards at the time it was produced. It does not allow for installing such an engine 

on a new aircraft. Spare engines are produced from time to time in order to keep an aircraft in 

revenue service when the existing in-service engine must be removed for maintenance or 

replacement purposes as needed. Otherwise removing these aircraft from active service would 

be very expensive and logistically difficult. 

As we explained in the proposal, explicitly allowing for the production of spare engines 

is not addressed in the existing regulations because there is no production cutoff for the current 

Tier 4 NOx standards. Thus manufacturers have been allowed to continue production of older 

engine designs under type certificates first issued before the Tier 4 standards took effect (e.g., 

Tier 2). However, final regulations now apply a Tier 6 NOx production cutoff to all newlymanufactured engines. This means that if we did not also adopt a provision for the continued 

production of spare engines, manufacturers would be prohibited from producing Tier 4 engines 

under the existing type certificates for this purpose. We see no reason to change our policy of 

allowing manufacturers to produce new engines for use as spares. Therefore, the final regulatory

provisions allow this practice to continue.

To ensure there would be no adverse environmental effect from allowing the use of a 

spare engine as a direct replacement for an existing engine, we proposed that the spare could be 
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used only when the emissions for all pollutants of that engine were equal to or lower than those 

of the engine it replaced. This proposed requirement was consistent with the ETM, which also 

contains this allowance. We received a joint comment from AIA and GAMA stating that this is 

impractical because, while unlikely, a spare engine might have a different emissions profile for 

some pollutants than the engine it would replace. As an example, they stated that the two 

engines could have somewhat different combustion systems that might make one engine lower in 

NOx but higher in CO. They also suggested that EPA should consider the totality of the 

emissions in the decision, or delete the requirement in the final rule.

These comments are surprising because this ETM provision, as well as the exception 

provisions, was subject to significant discussions within CAEP that included the engine 

manufacturers as well as a representative from AIA. Nonetheless, in this instance we believe the 

proposed provision should be modified to accommodate the potential for unusual circumstances 

as explained by the commenter.

As noted above, AIA and GAMA suggested that EPA consider of the totality of 

emissions relative to their environmental effects as the basis for evaluating spare engine 

exemptions. This would entail understanding and comparing the environmental consequences of 

the different pollutants. We find that could be very complicated because different pollutants 

have different health and welfare end points and consequences. For example, in the illustration 

offered by the commenters, the effects of LTO NOx and CO are largely unrelated to one another. 
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We think a preferred option to evaluating total environmental effects, or even dropping 

the provision entirely, is to incorporate an anti-backsliding requirement which ensures that at a 

minimum the excepted spare engine at least meets the same emission standards that are 

applicable to the engine it is replacing. For this reason, in response to the AIA and GAMA 

comment, we are modifying this provision in the final rule to allow an excepted spare engine to 

have different emission levels compared to the engine it replaces as long as it remains compliant 

with each of the applicable emission standards and any other requirements of its type certificate. 

Given the limited number of spare engines in the fleet, we expect allowing these engines to have 

somewhat different emissions profile from engines they are replacing will have no significant

adverse environmental effect. This is especially true given that we expect the emissions of an 

excepted spare engine will be equal or better than the engine it is replacing in most cases in 

accordance with the basic tenant of the ETM. 

We are not requiring engine manufacturers to obtain FAA or EPA approval before 

producing spare engines. However, they must submit information about the production of spare 

engines in an annual report to EPA (see section III. D for more on the annual report). We 

proposed that because manufacturers are not required to seek or obtain formal approval to 

produce spare engines, this allowance was referred to as an “exception” rather than an 

“exemption”. This terminology would be consistent with current FAA regulations. 

Furthermore, we proposed that the permanent record for each engine excepted under this 

provision would need to indicate that the engine is an excepted spare engine and the engine itself 
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would need to be labeled as “EXCEPTED SPARE.” in accordance with FAA marking 

requirements of 14 CFR.

We received comments relating to allowing spare engines to be produced without 

requiring prior approval and the use of the terms “exceptions” or “excepted.” The Air Transport 

Association (ATA)89 appreciated that there would be no case-by-case approval, noting that it 

simplifies administering the provision for FAA without compromising the structure of the 

exemptions program set forth in the ETM. Regarding the terminology, AIA and GAMA noted 

that the terminology was inconsistent with current engine name plate labeling practices. They

stated that engines are currently either marked “COMPLY” or “EXEMPT” for emissions. Both 

organizations generally felt the change in terminology for spare engines might be concerning to 

the operators holding an engine with a plate reading “EXCEPTED.” They concluded that the 

name plate for spare engines should continue to use “exempt.” The ATA appeared to give at 

least tacit approval to the new terminology by acknowledging without objection that spare 

engines would be labeled accordingly. 

First, we are puzzled that operators with a spare engine labeled as “excepted spare” rather 

than “exempt” may have a concern, because AIA and GAMA did not elaborate on just what the 

concern might be. Without at least an example, we are unable to discern the nature of the 

concern and respond directly to it. We also find it puzzling that the two organizations that 

 

89 The Air Transport Association has changed its name to Airlines for America (A4A).
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represent aerospace manufacturers expressed a concern regarding operators of aircraft and 

aircraft engines when the actual organization representing those companies, ATA, did not 

express such a concern.

Second, regarding the terminology, the Tier 6 production cutoff does not apply to the 

continued production of engines that are designated spares. Spare engines are produced to 

replace a similar engine already in service that was removed from service for maintenance 

purposes. Accordingly, the production of a spare engine is not restricted by the production 

cutoff, and the regulation does not apply to these engines. The non-applicability of the cutoff 

eliminates the need to process an exemption for continued production of these engines beyond 

December 31, 2012. 

Conversely, engines that are intended to be produced for new installations (i.e. not 

replacing an engine already in service) are subject to the production cutoff regulation and the 

continued production of such engines beyond the cutoff date would require a grant of exemption. 

Since the production of spare engines is not subject to the new cutoff regulations, the FAA 

proposed and the EPA accepted the idea that referring to these engines as exceptions to the 

regulation was more appropriate than requiring case-by-case consideration of exemptions when 

the regulation did not apply.

Moreover, the word “exemption” is a meaningful regulatory term. It is used by the FAA

in 14 CFR Part 11 to mean that an applicant is subject to a particular regulation and is requesting 
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time-limited relief under a specific set of criteria. It is a specialized form of rulemaking. When 

an entity or its product is specifically left out of a regulatory provision, it is considered 

“excepted”. Any regulation adopted by the FAA would use these terms consistently. 

As already mentioned, assuming incorporation of these provisions by the FAA, engines 

meeting the requirements for spare engines could be produced and entered into commerce

without prior approval from EPA or FAA. It is important to note that while spare engines would 

be excepted from the Tier 6 NOx standards being promulgated today, they still need to be 

produced under an FAA type certificate. (This FAA oversight would serve the same role as the 

exemption approval step envisioned by ICAO in its ETM language for spare engines.) We also 

expect minimal additional burden for manufacturers, since we are not establishing new 

restrictions, monitoring, recordkeeping, or reporting requirements other than the end of year 

report. 

b. New Provisions for Engines Installed in New Aircraft

The primary purpose of allowing limited continued production of Tier 4 engines is to 

provide for an orderly implementation of the Tier 6 NOx production cutoff. It addresses engines 

reaching the end of their production cycles in the time frame when new emission standards take 

effect. The typical production cycle would have annual production volumes ramp up quickly, 

remain at relatively large volumes for several or many years, and then fall off over a few more 

years. When new emission standards are adopted in the middle of a production cycle to take 
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effect a few years later, manufacturers generally devote technical resources to bring into 

compliance those engine models expected to be produced in large numbers in the time frame 

when the new standards are in effect. In contrast, they may plan not to invest in upgrading the 

emissions of engine models that would be very near the end of their normal production cycles 

when compliance with the new standards becomes required. The actual length and shape of this 

tail of production volumes can be affected by factors not fully within the engine manufacturers’ 

control, e.g., unexpected market demand. Thus, exemptions may be justified if a manufacturer 

does not complete the production cycle before the production cutoff date and projected 

production volumes are not adequate to justify investing the necessary resources to reduce 

emissions or there are other technological issues. 

Furthermore, in certain exceptional circumstances exemptions may also be appropriate. 

These are “hardship” situations that may arise as a result of unforeseen technical or economic 

circumstances or events beyond control of the manufacturer. For example, this could vary from 

unexpected problems with technology upgrade programs to labor disruptions or natural events 

disrupting production or parts availability. 

Our regulations currently address these kinds of situations in section 87.7(c), entitled,

“Exemptions for New Engines in Other Categories.” We are replacing this provision with a new 

set of provisions addressing exemptions for new engines. 

i. Time Frame and Scope
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The final regulations allow engine manufacturers to request an exemption for newlymanufactured engines not meeting the Tier 6 NOx standards so they may be installed in new 

aircraft. If granted, manufacturers may produce a limited number of these newly-manufactured 

engines in a four year time period beginning after December 31, 2012 and going through 

December 31, 2016. This four-year time period is consistent with the ETM. The period for any 

given approved exemption could be shorter depending on the specifics of the application, but it 

could not be longer. This exemption limits NOx emissions from engines that are covered by a 

valid type certificate issued by FAA. The engines must meet all other applicable requirements. 

More specifically, an engine exempted from the Tier 6 NOx standards must be covered by a 

previously issued type certificate showing compliance with the Tier 4 NOx standards,90 as well 

as the current HC, CO, fuel venting, and smoke standards.

As explained above, the scope of the exemption provisions are limited to newlymanufactured engines that do not comply with the Tier 6 NOx standards. No need has been 

identified to apply such exemption language to the other regulated exhaust pollutants, i.e., 

smoke, hydrocarbons and carbon monoxide. The emission standards for those pollutant species 

have remained unchanged for nearly three decades and present no technical issues for modern 

 

90 Engines certified only for compliance with earlier Tier 2 NOx standards would not be eligible for 

exemptions. This is also consistent with the exemption language in the ICAO ETM. Note that where such engines 

have emissions actually meeting the Tier 4 NOx standard, they may be recertified to the Tier 4 standards, but only 

before the effective date of the regulations.
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turbofan engines.91 If new emission standards for these pollutants are considered in the future, 

the potential need for exemption provisions will also be assessed at that time. 

We received comments requesting that exemptions be available for newly-certified 

engines in addition to newly-manufactured engines. General Electric Aviation (GE) stated that 

unforeseen circumstances may arise during the lengthy aircraft engine development process that 

necessitates a change in design, and that may affect the ability of that engine model to meet the 

prevailing Tier emission standard at certification. For that reason, GE concluded that 

exemptions for newly-certified engine would be beneficial. The AIA and GAMA jointly stated 

that the existing 40 CFR section 87.7(c) not only provides the flexibility to exempt newlymanufactured engines from a production cutoff, but also for newly-certificated engine models 

subject to any emission standards, e.g., the Tier 8 NOx standards. They requested that this 

flexibility should be retained. 

Regarding the availability of exemptions for newly-certified engine models, the proposed 

regulatory text made clear that the exemption provisions would only apply to newlymanufactured engines. Specifically, the intent was to establish provisions for newlymanufactured engines to address the potential technology and economic adversities that may

arise as part of adopting the Tier 6 production cutoff. The ICAO ETM provisions are clearly 

intended for that same purpose. Also, the original intent of EPA’s current exemption provisions 

 

91 For example, the hydrocarbon exhaust emission standards were adopted on December 30, 1982. See 47 

FR 58462.
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in section 87.7(c), which we are modifying in this rulemaking, is clear from the proposed 

rulemaking and final rulemaking that resulted in those provisions. The March 24, 1978 proposal 

described the concern as “...engines which are nearly [at] the end of their production life would 

be terminated prematurely because there would be insufficient future sales to justify

incorporating emission controls.” (See 43 FR 12619, March 24, 1978.) The December 30, 1982 

final rule referenced “...the removal of an engine model from the market because of its failure to 

comply.” (See 47 FR 58468, December 30, 1982.) Obviously, the intent of the existing 

exemption provision cited by AIA and GAMA was to make it apply only to newly-manufactured 

engines.

As a general matter, we believe an exemption from the Tier 6 standard, or any other 

standard, for newly-certified engine models is speculative at this time and would undermine the 

goal of regulatory compliance by new engine designs. In any event, neither the current ICAO 

Annex 16, Volume II provisions nor the ETM provide for newly-certified engine exemptions. 

We believe that such would be a fundamental shift from Annex 16 and the ETM should be 

explored within the framework of ICAO/CAEP. Furthermore, engine manufacturers already 

have significant leadtime between the date CAEP adopts a new emission standard and the 

standard’s effective date, e.g., usually 3-5 years. Finally, engine manufacturers historically 

design new engine models to comply with the most stringent future standard that also provides 

for a longer development time horizon. Therefore, we are promulgating the exemption provisions 

for newly-manufactured engines as proposed. 
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ii. Production Limit 

As proposed, section 87.5 of the final regulations reflect the essence of the general 

exemption language for exhaust emission standards regarding how to determine the number of 

allowable exemptions that is embodied in existing section 87.7(c) of the regulations. That 

provision generally that the FAA, with EPA’s concurrence, may grant exemptions to exhaust 

emission standards based on factors such as adverse economic impact on the engine 

manufacturer, aircraft manufacturer, or airline industry; in addition to the effects on public health 

and welfare. 

As a result, section 87.5 does not specify a nominal number of exemptions. Rather, each 

request for exemption would be evaluated on a case-by-case basis, using the information 

provided by the applicant and any other relevant information that is available to FAA and EPA at 

the time. Any approved exemption would include a specific limit on the number of such engines 

based on that information and is not defined on a basis such as type certificate. (See section 

III.B.b.iii for a description of what the request must contain.) The intent, of course, would be to 

exempt the minimum number of engines that can be clearly justified, including a consideration 

of the public health and welfare effect associated with the exemptions. 

In the proposal, we acknowledged that our approach to determining limits on the number 

of exempt engines differs from the language contained in the current ICAO ETM guidance. The 

ETM states that “[t]he number of engines exempted would normally not exceed 75 per engine 
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type....” 92 We chose not to propose adopting this language on the nominal number of engines 

based on a single type certificate. Our reasons for this deviation were detailed in the. The 

interested reader is referred to the proposed rule for more detail. (See 76 FR 45012. July 27. 

2011.) We also want to emphasize that the exemption provisions as proposed and promulgated 

in this notice are not necessarily limited to the Tier 6 NOx production cut-off, but could in fact 

be applied to future aircraft engine emission standards if a similar production cut-off was 

adopted. Therefore, we believe our approach is preferable because it more clearly leaves the 

number of exemptions that might be granted open, not limited to either more or less than 75 per 

engine type, and subject to the justification supplied by the engine manufacturer, both for the 

Tier 6 production cut-off and the future.

We received several comments focusing primarily on the number of exemptions and the 

underlying process that is embodied in the ETM and our proposal. General Electric Aviation

(GE) maintained that harmonization with the international community is not only required by the 

Chicago Convention, but also provides streamlined processes and procedures within the 

regulated industry. They contended that any purported benefits to EPA’s unique exemption 

scheme were outweighed by setting up a conflict with the remainder of the world. They also 

suggested that if EPA wants a different approach for evaluating exemptions, it would be more 

appropriate to work inside the ICAO/CAEP process toward that end.

 

92 CAEP/8 – WP/18, Environmental Technical Manual (ETM), Vol II on the Use of Procedures in the 

Emission Certification of Aircraft Engines, Appendix ”ICAO Emissions Environmental Technical Manual”.
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The ATA commented that EPA’s case-by-case approach to determining the number of 

engines is a rejection of the ICAO/ETM provisions that limit “...the number of exemptions ... to 

75 engines per type certificate....” They argued that this would create a serious discontinuity

between the U.S. and the rest of the world, undermining ICAO’s objective of international 

uniformity. The ATA also argued that the ICAO exemption limits are intended to be coordinated 

among international aviation authorities, and that differing rules would make this impracticable. 

As evidence of this problem, ATA cited the European Aviation Safety Agency’s (EASA) 

proposed rulemaking, which they noted was based on the assumption that the ICAO proposals 

will be adopted unaltered by other aviation authorities of the world. The ATA also stated that 

the ICAO ETM guidance document supplements the official standards of Annex 16, Vol. II and, 

therefore, the ETM provides technical elaboration on the implementation of Annex 16. From 

this ATA concluded that differing practices in this regard are counter to the Chicago Convention.

Regarding consistency with the Chicago Convention, our proposal thoroughly explained 

that the ETM is guidance material; not an ICAO standard or regulation of any type. While

consistency is desireable, it is not compelled when a deviation is justified. Therefore, we 

disagree with the commenters on this point, and specifically with ATA’s comment that the ICAO 

guidance is effectively the equivalent of an ICAO Annex 16 standard. 

Turning to ATA’s comment regarding the ETM cap of 75 engines per type certificate, we 

first want to point out that this is not a maximum limit on the number of potential exemptions per 
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type certificate nor is it an implied entitlement. Rather the ETM provision is an expectation that 

“[T]he number of engines exempted would normally not exceed 75 per engine type certificate 

....” as stated in the document. With this perspective both the ETM and our approach are similar 

in that the maximum number of exempted engines is based on a consideration of the petitioner’s 

justification for such exemptions. 

Finally, we disagree with the comment that the differences with the ETM make 

international coordination unworkable. In fact, one of the proposed justification elements, i.e., 

how many affected aircraft will be registered in the U.S. and other countries (estimate allowed), 

was described in the preamble for the proposal as being aimed at helping to facilitate 

consultation and coordination. Also, as noted above, the ETM’s expectation and our approach 

are similar in that the maximum number of exempted engines under both approaches is based on 

a consideration of the petitioner’s justification for such exemptions. We do not think 

coordination with foreign aviation authorities, with these few differences, should pose any 

problems. After considering the above comments on the number of exemptions and the 

underlying process embodied in the ETM and our approach, we are promulgating the provisions 

relating to the comments as originally proposed.

iii. Exemption Requests

We are establishing a process for requesting exemptions (for engines used on new 

aircraft) that would be more formal and structured than the current process. We are requiring
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manufacturers submit their request to the FAA, as currently required. The FAA will then share 

the submittal with EPA and execute the consultation process. 

To ensure that we have the information necessary to evaluate exemption requests in this 

specific manner, the requests need to include the following details to describe the specific engine

model for which the manufacturer is requesting the exemption. The final provisions contained in 

§87.50, which are summarized below, are consistent with and in some areas expand on the 

provisions in the ETM:

General Information

• Corporate name and an authorized representative’s contact information (including a 

signed statement verifying the information);

• Description of the engines for which you are requesting the exemption, including the 

engine model and sub-model names;

• The number of engines that you would produce under the exemption and the period 

during which you would produce them;

• Identify the authorizing type certificate (type certificate number and date); 

• Information about the aircraft in which the engines will be installed, including the 

airframe models and expected first purchasers/users of the aircraft, and the countries in 
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which you expect the aircraft to be registered (including an estimate of how many will be 

registered in the U.S.); and 

• List of other certificating authorities from which you have requested (or expect to 

request) exemptions, and a summary of each request.

Justification and Impacts Assessment

• A detailed description and assessment of the environmental impact of granting the 

exemption;

• Technical issues, from an environmental and airworthiness perspective, which may

have caused a delay in compliance with a production cutoff, if any;

• Any economic impacts on the manufacturer, operator(s), and aviation industry at large; 

and

• Projected future production volumes and plans for producing a compliant version of the 

engine model in question.

Other Factors

• Hardship: Impact of unforeseen technical circumstances, business events, or other 

natural or manmade calamities beyond your control, and
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• Equity issues in administering the production cutoff among economically competing 

parties.

It is important that any action on a potential exemption request be in the public interest; 

the fairly comprehensive list of application information in the regulations is intended to gather 

the information needed for this assessment. We would expect to take a broad perspective in 

evaluating what is or is not in the public interest. This is why a manufacturer’s justification 

needs to include a quantified description of the environmental effects of granting the exemption, 

as well as discussion of economic and technical issues related to bringing the engine into 

compliance. The analysis of environmental impacts needs to specify by how much the exempted 

engines would exceed the standards, the in-use effects in terms of lifetime tons of NOx, and 

estimate the emissions rates of engines/aircraft that could potentially be used if the exemption 

was not granted. Since exemptions granted under the regulations apply only to NOx emissions, 

the analysis could also include possible benefits regarding noise levels or reduced emissions of 

pollutants other than NOx. Relevant economic impacts could include effects on the engine 

manufacturer, airframe manufacturer, airline(s), and the general public.

As we detailed in the proposal, some manufacturers have requested exemptions in the 

past based on the largest number of engines they hoped to continue manufacturing without 

knowing how many they would actually be able to produce or who would purchase them. The 

new exemption language calls for manufacturers to target their requests more specifically based 
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on likely production needs and time periods. While we expect a manufacturer to have this 

specific information when they submit a request, the final regulations allow us to process 

exemption requests with somewhat less specific information. However, we expect this to apply

only for unusual circumstances. Manufacturers also are being required to notify the FAA if they

determine after submitting a request that the information is not accurate, either from an error or 

from changing circumstances. 

The final regulations also allow manufacturers to revise their requests to justify covering

additional engines at any time before approval. We would then review the revised request. 

Similarly, for exemptions that are already approved, manufacturers could request that additional 

engines be added after providing the justification for the increase. 

We received comments on the level of detail required in a request for exemption and the 

time needed to add more engines to such a request or an already approved exemption. First, 

ATA was concerned that requesting an increased amount of engine exemptions can take a 

significant amount of time. They stated that there may be insufficient time for a manufacturer to 

receive approval for additional engine exemptions if necessary to meet previously unknown 

market demands.

In response, we find it unfortunate that the comment does not provide a specific example 

or other information that may illustrate this concern. As a general response, given the long 

leadtime between the initiation of discussions among aircraft purchasers and aircraft 
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manufacturers, and actual orders and final deliveries, we expect that manufacturers will have 

enough time to request additional engine exemptions, and if appropriate, for the FAA and EPA 

to approve such a request. We expect that amending an already approved exemption would take 

less time to act upon than the original petition. Also, engine manufacturers may request an 

expedited review from the FAA, and by association the EPA, if circumstances warrant. Finally, 

to the extent that an engine manufacturer has specific concerns in this area, they could be 

ameliorated by improving the lines of communication with air frame manufacturers to increase 

the manufacturer’s awareness of market interest in potential new orders. Accordingly, we are 

promulgating the exemption provision relating to this comment as proposed.

Second, ATA commented negatively that the exemption request for each individual 

engine be justified, “...including the exact number, initial purchasers/users, countries of registry

and plans for bringing the product into compliance.” They claimed that this knowledge may not 

be known at the time of the exemption request because of market leadtime. As an example, 

ATA cited the 1998 Rolls Royce (RR) exemption request from the CAEP/2 cutoff for 150 

engines that was not based on that type of certainty, but was a prospective exemption for two 

years as protection against the uncertainties of technical development. They stated that RR did 

not know when the development process would be completed, and hence did not know the exact 

number of non-compliant engines that airlines would purchase. The ATA also added that the 

three affected airlines worked with RR to provide documentation of the financial and operational 

hardship that they would suffer based on their aircraft delivery schedules. 
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In response to ATA’s second comment, we simply want to note that the information we 

would normally expect to be contained in the exemption application is actually not much 

different than the justification envisioned by the ETM. That guidance document explains that 

the petitioner should, to the extent possible, provide quantitative support to justify the 

exemptions. Specifically, the ETM states that it “...provides guidelines on the process and 

criteria for issuing exemptions....” These include some of the same elements as contained in our 

proposal and referenced above, i.e., the exact number of exemptions being requested, to whom 

the engines will be originally delivered, and plans for producing a compliant product. Therefore, 

the ETM envisions a consideration of specific information as part of the exemption request, in a 

similar fashion as EPA’s approach, in order to decide on the exact number of exemptions to 

grant. We are simply being more explicit in some areas concerning the type of information that

should be included in any exemption request. We also note ATA’s comment that “[T]he airlines 

worked with Rolls Royce to provide documentation of the financial and operational hardship that 

they would suffer if there were an interruption in the supply of ICAO-compliant engines during 

their aircraft delivery schedules.” 

Given the long lead times generally associated with new aircraft orders and deliveries, we 

expect aircraft operators will work closely with aircraft manufacturers as their new aircraft needs 

are identified. Engine manufacturers should in turn work with aircraft manufacturers to stay

aware of market interest in potential new orders. This appears to be reflected in the commenter’s 

example regarding the cooperation between airlines and RR in fashioning the exemption 
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justification. Also, as explained in the proposed regulatory text, the petitioner should include 

information on the “expected” first purchasers/users of the aircraft. It also asked for information 

on the number of aircraft that will be registered in the U.S. versus other countries and that this

may be estimated if not known. Therefore, precise knowledge is not needed for certain elements 

of the justification. The preamble to the proposed requirements also stated that the regulations 

would allow us to process exemption requests with somewhat less specific information, although 

we expected that to apply only for unusual circumstances. We have made this clearer in the final 

regulations.

In order to allow us to oversee these exempted engines, manufacturers are being required 

to also provide an annual report to EPA on exempt engines similar to the information about spare 

excepted engines. The permanent record for each engine exempted under this provision must

indicate that the engine is an exempted engine and the engine itself must be labeled as 

“EXEMPT NEW.”

iv. Coordination of Exemption Requests

The limit on the number of potentially exempt engines as described in the ETM is 

intended to apply to overall worldwide production. Toward that end, the ETM envisions that

certificating authorities and member states should coordinate whenever any authority receives an 

exemption request. 
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Working with the FAA, we expect to consult with other aviation authorities whenever we 

receive an exemption request. This would include a consultation with other certificating 

authorities as well as coordination with the appropriate civil aviation authority of any country

where the aircraft with the exempted engines will be registered. 

To facilitate this coordination we are asking that manufacturers also include in their 

requests, a list of countries in which the aircraft are expected to be registered. While not 

specifically listed in the ETM, we believe that this information is consistent with the ETM as it 

would be necessary to ensure proper coordination. The ETM appears to presume that each 

member country will recognize exemptions granted by other countries. This presumption seems 

reasonable assuming that the exemption being granted is generally consistent with the guidelines 

of the ETM and that the consultation and coordination called for in the ETM was conducted in

good faith. However, there should be no presumption that EPA would agree to an exemption for 

an engine model if the aforementioned collaboration, consultation, and coordination were not 

conducted. The Clean Air Act (which provides EPA with its authority to establish emission 

standards) includes no provisions that would allow any foreign country or other certificating 

authority to exempt subject aircraft engines, over the objection of FAA and EPA, from the 

applicable standards EPA promulgates.104 Nevertheless, because our final exemptions provisions 

 

104 It is possible that applications for exemptions by foreign entities may be filed with their national 

certificating authorities for engines manufactured after December 31, 2012 and could be operated in the United 

States. The FAA has several international bilateral agreements in place that include provisions and obligations for 

technical assistance on environmental certification matters. The FAA plans to continue to coordinate with those 
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are generally consistent with the procedures called for in the ETM, assuming appropriate 

consultation and coordination in accordance with the ETM and absent unforeseen complications, 

it is reasonable to believe that FAA and EPA would not object to exemptions for engines 

properly exempted by other countries under those procedures. The FAA would still need to take 

the certification action as called out in 14 CFR 91.203 and 14 CFR 21.183. 

This, however, raises the question as to how we would respond to an exemption request 

when another certificating authority did not consult or coordinate on a previous request for the 

same engine model. A related concern arises if an FAA type certificate is sought under a 

reciprocity agreement for an engine which was previously certificated under an exemption by a 

foreign certificating authority, and the original exemption was not coordinated with the United 

States. Such requests would likely be viewed as new exemption requests if the anticipated 

collaboration, consultation, and coordination had not occurred. 

Thus to avoid these issues, in most cases, manufacturers may want to work with all 

relevant certificating authorities at the same time as well as the civil aviation authority of 

nation(s) where the aircraft will be initially registered or operated if that nation requires a type 

certificate issued under its own regulations to operate in its air space consistent with international 

agreements.

 

foreign certificating authorities in their considering and granting petitions for exemptions and, likewise, those that 

are filed with the FAA and in consultation with EPA. 
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v. Low-volume, time-limited transitional exemption program

We received a comment from one manufacturer expressing concern that once the final 

rule becomes effective additional time may be required for EPA and FAA to establish and 

undertake procedures to review and act upon exemption requests. They stated that the time 

needed for this process could be very disruptive for engine manufacturers that have already 

contracted to deliver engines during the period which FAA/EPA would need to consider 

exemption requests. They also claimed it would be harmful to airplane manufacturers and 

airlines. To avoid such an undesirable outcome, the commenter suggested that EPA should grant 

a one-time, interim block of perhaps 20 exemptions.

Based on supplemental information we received from the commenter,

105 we find the 

concerns center on six engines for which they have contract commitments to build and deliver 

within several months of this final rule. These six engines belong to two engine models, with

four engines in one model and two engines in the other. The first model consisting of four 

engines is scheduled to begin shipping in January 2013, shortly after the January 1, 2013 Tier 6 

production cut off. These engines are currently certificated to the Tier 4 NOx standards. The 

commenter has stated, however, that the design of this engine model has been technically

modified to achieve the Tier 6 standards. Unfortunately, compliance testing of this model to 

 

105 Memoranda documenting this supplemental information are located in docket number EPA-HQ-OAR2010-0687.
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meet the Tier 6 standards cannot be performed until December of 2012 when the first production 

version is built. Assuming that this testing is successful, inadequate time remains for the FAA to 

formally recognize Tier 6 compliance based on those tests before the production cutoff becomes 

effective.106 The two new aircraft using these engines are being built and will be delivered to a 

foreign airline. 

The second model is comprised of two engines with a contracted deliver date in May

2013. They are also certificated to the Tier 4 NOx standards. These engines are at the end of 

their production life, i.e., no additional future deliveries for civilian uses are anticipated beyond 

these two contracted engines. For this reason, the commenter has stated that it is not 

economically feasible to redesign this model to conform with the Tier 6 NOx standards, even if it 

were technically feasible. The single new aircraft using these engines is also being built for 

delivery to a foreign airline.

After assessing this concern, we are including an exception provision in the regulations

that permits any aircraft engine manufacturer to produce and enter into commerce up to six 

newly-manufactured engines with a date of manufacture, as defined in the regulations, prior to 

August 31, 2013 that are not certificated to meet Tier 6 emission requirements. We find that a 

considerable amount of time will indeed be required between the time this final rule becomes 

 

106 The FAA has stated to EPA that inadequate time exists for the required formal compliance 

determination before the production cutoff takes effect.
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effective and completing any formal FAA action using the normal exemption process as 

previously described in this notice. Specifically, time is needed for: 1) the FAA to amend 14 

CFR part 34 through rulemaking to incorporate the production cutoff and procedures for granting 

exemption from the new standards; 2) the manufacturer to develop the information needed s to 

support a request; 3) submitting the request for review by FAA and EPA; 4) coordination with 

other certificating authorities; and 5) EPA and FAA review and final action on the request, i.e., 

approval or disapproval. Regarding this review and final action, we note that FAA staff involved 

in reviewing the manufacturers request may also be engaged in conducting the processes to adopt 

this rule in 14 CFR part 34 and to review emission information on current type certificates to 

confirm that they meet either Tier 6 or Tier 8 requirements, as previously described. Therefore, 

we conclude that inadequate time exists to act on an exemption request with certainty for these 

six engines before their contract deliver dates. Consequently, we conclude that a limited 

modification to the otherwise universal effective date of the final Tier 6 compliance deadline is 

appropriate to accommodate the commenter’s situation and that for these six specific engines 

additional lead time is needed due to cost and technical feasibility factors.

We also believe that disrupting the scheduled delivery dates of these engines could risk

subjecting the commenter to possible financial penalties for late delivery, with possible followon effects for the aircraft manufacturer and airlines. We also find that there is no significant 

adverse effect on the environment in allowing these six engines to be produced and sold as 
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compliant with Tier 4 standards, especially if four of the engines ultimately comply with the Tier 

6 standards. 

For the above reasons, and in response to the comments and under our authority under 

sections 231(a)(3) and (b) to issue final regulations with such modifications to the proposal as 

the Administrator deems appropriate and to make revised standards effective after such period as 

the Administrator finds necessary to permit the development and application or requisite 

technology, giving appropriate consideration to the cost of compliance within such period, we 

are including an exception provision in the regulations that permits any aircraft engine 

manufacturer to produce and enter into commerce up to six newly manufactured engines with a 

date of manufacture, as defined in the regulations, prior to August 31, 2013 that are not 

certificated to meet Tier 6 emission requirements. These engines must have a type certificate 

which indicates that they meet the 40 CFR 87 requirements last updated on October 30, 2009

(i.e., Tier 4). No formal exemption request or approval will be required for these six engines. 

These engines will be reported to EPA as part of the annual reporting requirement as described 

above for exempt engines.

We know of no other engine manufacturer that is in this situation today, (i.e., contracted 

deliveries of engines not meeting the production cut-off within several months of the production 

cut-off date). However, as a matter of equity and to address situations which we may not be 

informed of at this time, we are extending this transitional flexibility to all manufacturers. 
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c. Voluntary Emission Offsets

We requested comment on establishing a voluntary EPA program by which 

manufacturers could receive emission credits for producing cleaner engines, which they could 

use to offset higher emissions from exempted engines. An example of such a program was

summarized in a memorandum to the docket.

107

 The types of programs we were considering 

would be developed, promulgated, and administered by EPA. 

As described in the proposal and summarized here, we expected manufacturers to be 

interested in generating offsets for one of three purposes. First, manufacturers might choose to 

generate offsets as part of their justifications for exemptions. Second, manufacturers might 

choose to generate offsets as part of a justification for being allowed to exceed the numerical 

limit that FAA and EPA are willing to approve in an exemption request. Third, provided a 

provision was promulgated to allow this, a manufacturer might also be interested in generating

offsets to bank for use for exemptions of engines to be produced after the credit generating 

engines are produced, or possibly against a future production cutoff. 

Under the proposed approach, generation of offsets would be voluntary and would be 

open to all certifying engine manufacturers. One concept was to allow credits to be generated 

only from engine models that are introduced after this rule and that had characteristic levels 

 

107 U.S. EPA, “Draft Regulatory Text for Voluntary Offset Program,” Memorandum from Charles Moulis, 

Assessment and Standards Division, Office of Air Quality and Transportation, June 2011. A copy of this document 

is in docket number EPA-HQ-OAR-2010-0687.
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significantly below the otherwise applicable standard (e.g., at least 10 percent below). There was 

a separate question, however, regarding how to calculate the credit. If we adopted, for example, 

a 10 percent threshold for eligibility, we would probably also allow credits only to the degree 

which the NOx characteristic level was more than 10 percent below the standard. This would 

ensure a net improvement in emissions. Also, we could reserve the right to restrict the use of 

credits so that they were used in a manner that ensured there was no net adverse impact on air 

quality. Such a program would need to ensure that emission benefits from one aircraft model 

truly offset the higher emissions from another model. Equivalency factors could be developed to 

account for differences in the number of LTOs per year and the lifetime of the aircraft. 

We received a number of comments on the possibility of implementing a voluntary credit 

offset program. The ATA expressed significant doubt that EPA had the legal authority to adopt 

a voluntary emissions offset program. They argued that the standard setting authority under 

section 231 of the CAA does not appear to provide such authority. ATA further stated that 

where offsets or emissions trading schemes exist for other source categories, the authority is 

express. Examples cited were the CAA authority for the trading program under the acid rain 

program, and the Energy Independence and Security Act authorization for the offset program 

used under the Corporate Average Fuel Efficiency Standards. Pratt & Whitney provided 

comments very similar to ATA relative to the lack of EPA’s legal authority to create such a 

program.
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The ATA also commented that the voluntary offset program embodied in the proposal 

would be unworkable in the context of aviation. They noted that unlike cars or trucks, aircraft 

engine manufacturers have relatively low production volumes and few frequently updated 

models for generating credits. Also, some manufacturers have more models than others and this 

could possibly lead to competitive distortions in the market. The AIA and GAMA also raised 

concerns regarding potential market disruptions. Further, ATA argued that opportunities for 

generating offsets would be limited by the proposal’s high thresholds for generating those 

credits. In the context of using emission credits for exemptions ATA added that each situation 

would be unique and it would not be possible to match exemptions to credits, or to assess the 

further complexities of the “equivalency factors” described in the proposal. Finally, they stated 

that an airline’s delivery schedule would be held hostage to the manufacturer’s ability to justify

credits based on some other engine that the airline is not buying. For these reasons, ATA asked 

that no offset program be adopted. 

Pratt & Whitney stated that the EPA proposal assumes that an offset program would 

create an incentive for manufacturers to build lower-emissions engines. On the contrary they

argued, manufacturers already have that incentive because using the lowest-emitting technology

that is available maximizes the life of the engine. Such a program would simply create a 

windfall to manufacturers whose product lines are already capable of generating credits. The 

AIA, GAMA, and GE jointly commented that the proposed emission offset program goes 

beyond the borders of CAEP, and any emissions offset program should be developed within 
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ICAO. General Electric was interested in exploring a potential emission offset program, 

particularly if the program would be applicable to new engine designs and derivatives that are 

subject to the proposed Tier 8 standards, and if it created the incentive to adopt new technologies 

earlier than would otherwise be the case in the absence of such incentives.

We appreciate the concerns raised by the commenters regarding the proposed voluntary 

offset emission program. We are also encouraged by GE’s interest in further discussions about 

how this program may be useful in the context of the Tier 8 standards and a possible future Tier 

8 production cutoff. EPA agrees that the proposal needs to be further developed to address 

certain aspects of the offset program. We have determined that the time it would take to 

sufficiently develop the program is incompatible with the need to promptly promulgate the Tier 6 

production cutoff standard with a near-term effective date of January 1, 2013. Therefore we are 

not including the voluntary emission offset program in the final rule at this time. Nonetheless, we 

continue to see value in such a program for the aviation industry and recommend continuing to 

consider such a regulatory flexibility in the future.

Although we are deferring action on the proposed voluntary emission offset program for 

the time being, we believe that such programs are envisioned within the ETM language related to 

exemptions. Furthermore, we do not agree with the commenters who questioned the EPA's legal 

authority for adopting a voluntary emissions offset program as part of the aircraft engine 

emission standards. We are somewhat surprised by the industry commenters who questioned the 
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authority for averaging, banking, and trading (ABT) programs outside of the narrow examples 

cited in their comments, and we are not yet persuaded by their claims. Note that the U.S. Court 

of Appeals for the D.C. Circuit has clearly stated that EPA has substantial discretion under the 

CAA section 231 to adopt final aircraft emission standards as the agency deems appropriate

(National Ass’n of Clean Air Agencies v. EPA 489 F.3d 1221 (D.C. Cir. 2007)). We also 

wonder to what extent their view represents the industry as a whole, including any aircraft engine 

manufacturers who also manufacture engines that are subject to other EPA regulations that 

provide for ABT without the “express” statutory authority the commenters claim is necessary. If 

in future actions we seek additional comments on the legality of ABT programs under our 

aircraft standards, we will be interested in receiving comments from other stakeholders in the 

mobile source arena who might have views regarding the arguments presented by the industry

commenters above. 

In the meantime, we note that several of our mobile source regulations, in addition to the 

rule cited by industry commenters, have long provided regulated industry with the flexibilities 

inherent in an ABT program, under the authority of, for example CAA section 213, and none of 

those subject industries have opposed the creation of such programs or questioned their legal 

basis. (See, e.g., 40 C.F.R. part 89, subpart C (averaging, banking and trading provisions for 

nonroad compression-ignition engines); 40 C.F.R. part 90, subpart C (certification averaging, 

banking and trading provisions for nonroad spark-ignition engines at or below 19 kilowatts); 40 

C.F.R. part 91, subpart C (averaging, banking and trading provisions for marine spark-ignition 
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engines); 40 C.F.R. part 92, subpart D (certification averaging, banking and trading provisions 

for locomotives and locomotive engines); 40 C.F.R. part 94, subpart D (certification averaging, 

banking and trading provisions for marine compression-ignition engines).) EPA continues to 

believe that the legal basis of these ABT programs is sound.

4. Potential Phase-In of New Tier 8 NOx Standards for Newly-Manufactured Engines

We did not propose a production cutoff for the Tier 8 NOx standards for newlymanufactured engines. This means that engine manufacturers may continue to produce Tier 6 

compliant engines of previously certified models after the Tier 8 standards become effective for 

newly-certified engine models. As noted elsewhere, EPA is working within the ICAO/CAEP 

framework to develop harmonized international standards for aircraft turbine engines. At the 

February 2010 meeting of CAEP, where the CAEP/8 NOx standards were approved for 

recommendation to ICAO, the committee decided that further consideration could be given to a 

related newly-manufactured engine standard pending new information on technology and market 

responses, although no formal action was taken at the time to explicitly make this a future work 

item for CAEP.

108

 

Assuming a CAEP/8 production cutoff is adopted at some time in the future, we will reexamine the permanent exemption provisions to ensure a timely and orderly phase-out of engine 

 

108 ICAO, “Committee on Aviation Environmental Protection (CAEP), Report of the Eighth Meeting, 

Montreal, February 1-12, 2010,” CAEP/8-WP-80. A copy of this document is in docket number EPA-HQ-OAR2010-0687.
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models that do not meet the CAEP/8 NOx standards. We would expect this to be done through a 

notice and comment rulemaking process to amend our own regulations.

C. Application of Standards for Derivative Engines

It is very common for a manufacturer to make changes to an originally type certificated 

engine model that is in production while keeping the same basic engine core and combustor 

design. In some cases these modifications may affect emissions. As a result, the certificating 

authority (in our case the FAA) must decide whether the emission characteristics of the modified 

design were significant enough from the parent engine’s certification basis that a demonstration 

of compliance with more recent emission standards is necessary, or if the changes were minor 

relative to the parent engine’s emission certification basis so that it is considered a derivative 

version of the original model with no emissions changes. This may be further complicated 

because of the common practice of making iterative changes over time raises the question as to 

when the cumulative changes reach a point where a new demonstration of compliance is 

warranted. 

In the past, these determinations were made for turbofan engines by an engineering 

evaluation that was performed by the engine manufacturer and then reviewed by the FAA. As 

part of the ICAO/CAEP deliberations leading up to the February 2010 CAEP/8 meeting, a new 

standardized guidance was agreed upon as described in the ETM. The guidance, which the U.S. 

fully supported, includes specific criteria that can be used to determine when a design 
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modification requires a new demonstration of compliance with newer emission standards, or 

when a modification was simple enough to be considered a no emissions change. 

We are including the ETM requirements in our regulations to address the longstanding 

need to provide consistent standards for the decision process regarding derivative engines and 

applicable emission standards. The definition of “derivative engines for emissions certification

purposes,” along with the criteria for making this determination, will provide engine 

manufacturers and the regulators with more certainty regarding emission standard requirements 

for future modifications made to certificated models. To ensure that the numerical decision 

criteria can be administered to allow for the consideration of unusual circumstances or special 

information, we are also providing the FAA with some flexibility to make adjustments to the 

specific criteria based on good engineering judgment. In summary, if the FAA determines that 

an engine model is sufficiently similar to its parent engine so as to meet the criteria established in 

part 87.48, the manufacturer may demonstrate certification compliance and continue production 

of the engine model to the same extent as allowed for the original engine model. However, if the 

FAA determines that an engine model is not a derivative for emission certification purposes, the 

manufacturer would be required to demonstrate compliance with the most recent emissions 

standards. This determination will be made using numerical criteria consistent with ICAO 

provisions, and a modified engine model can be considered a “derivative” only if it is: 1)

derived from an original engine that had received a U.S. certification, 2) the original engine was 

certified under title 14 of the CFR, and 3) one of the following conditions is met:
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(1) The FAA determined that a safety issue exists that requires an engine modification; or

(2) Emissions from the derivative engines are equivalent to or lower than the original 

engine.

The proposed rule provided that the engine manufacturer could show emissions 

equivalency by demonstrating that the difference between emission rates of a derivative engine 

and the original engine are within the following allowable ranges, unless otherwise adjusted 

using good engineering judgment as determined by the FAA:

± 3.0 g/kN for NOx.

± 1.0 g/kN for HC.

± 5.0 g/kN for CO.

± 2.0 SN for smoke.

The proposed rule also provided that engine models represented by characteristic levels at 

least five percent below all applicable standards would be allowed to demonstrate equivalency

by engineering analysis. In all other cases, the manufacturer would be required to test the new 

engine model to show that its emissions met the equivalency criteria. 

We received three significant comments on the proposed derivative provisions. First, 

ATA, PW, and Dassault-Aviation (DA) pointed out that the proposed criteria contained a 
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substantial deviation from the expressed intent of the proposal and the ETM guidance. 

Specifically, they noted that the ETM provides that “If a modified engine remains on the existing 

type certificate, it may retain the existing certification basis of the parent engine if the

modification(s) ...results in a decrease of the absolute emissions levels....” They pointed out, 

however, that the proposed rule provided that the certificate holder must demonstrate “...the 

proposed derivative engine model’s emissions meet the applicable standards and differ from the 

original model’s emission rates only within...” specified ranges for each pollutant. For example, 

the specified range is + or – 3 g/kN for NOx. The commenters stated that this is more stringent 

than the ETM, and could discourage cleaner engines that are not clean enough to meet the next 

tier of standards. They asked that the final rule be consistent with the ETM to prevent this 

untoward effect.

We agree that the regulations should allow for such engines to be considered derivatives, 

even if the difference was outside the “no emission change” range. This allowance is clearly 

consistent with the ETM and was inadvertently left out of our proposed language. Therefore, the 

final regulations contain this allowance.

Second, AIA and GAMA jointly commented that the term “new model” was 

inappropriate when used to determine which engine models could demonstrate equivalency by

engineering analysis, and when the manufacturer would be required to test the new engine model 

to demonstrate compliance with the equivalency criteria. They argued that because this 
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provision applies to changes made to an existing engine, it could cause an engine manufacturer 

to conduct an additional emissions test in cases where a very small change was made to the 

engine due to a performance or engine weight change. The commenters recommended that this 

be altered to allow a manufacturer to consider “...such emissions changes by analysis prior to 

this point, and only if such analysis revealed a deterioration that pushed the engine very close to 

the emission limits that the manufacturer be requested to complete an engine emissions test.”

The AIA and GAMA also jointly commented on the proposed regulatory text that states 

if the characteristic level of the original certificated engine model before modification is at or 

above 95 percent of the applicable standard for any pollutant, you must measure the proposed 

derivative engine model’s emissions for all pollutants to demonstrate the derivative engine’s 

resulting characteristic levels will not exceed the applicable emission standards. They claimed 

that the use of the term “you must measure” also implies further engine testing when additional 

analysis may likely prove sufficient.

We agree that the term “new model” should be modified and have instead used the term 

“new engine configuration” in the final regulations. We want to clarify, however, that the

regulations do explicitly require engine testing when an original engine’s emissions are within 5

percent of any emission standard. This text does not allow engineering analysis in such cases.

We continue to believe this to be the appropriate policy. Given the greater uncertainty of 

engineering analysis relative to actual testing, we cannot rely on it for engines very close to the 
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standard. This provision is also consistent with the ETM. Therefore, we are promulgating this 

requirement as proposed.

Third, AIA, GAMA, and GE commented that as a general matter, EPA should not codify

the ETM’s derivative engine decision criteria because the ETM guidance will evolve over time 

and the Agency’s rigid regulations will not, even allowing for the FAA flexibility to use good 

engineering judgment if necessary when deciding what is or is not a derivative engine. They

concluded it was simply better to let the FAA rely on the ETM guidance in its decision making. 

As noted by the commenters, the ICAO ETM itself is a guidance document for use by aviation 

authorities. It does not represent a standard or any other enforceable regulatory requirement. In 

the particular case cited by the commenters, they appear to ask that FAA be given unlimited 

discretion to determine which engines are subject to each new tier of standards. 

In response to the comment, we also note that the Clean Air Act directs EPA to establish 

air pollution emission standards for aircraft engines. (See 42 U.S.C. 7551 (a)(2)(A).) 

Implementation of this statutory directive mandates that we specify enforceable air pollution 

emission standards and control requirements for aircraft engines in regulatory form. We believe 

that it is reasonable for us to also establish other associated requirements in regulatory form. Our 

final rule achieves an appropriate balance between providing FAA discretion to implement the 

standards, and the need to establish aircraft engine emission regulations that ensure consistency

in application. 
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We also disagree with the suggestion that the ETM will evolve over time, but that our 

regulations will not. As a working member of ICAO’s Committee on Aviation Environmental 

Protection, we will participate in developing any relevant revisions to the ETM and will make 

appropriate adjustments to our regulations as needed. 

We continue to believe that the ETM specifications for “no emissions change” are 

appropriate objective criteria for derivative engines. Thus, because we are codifying regulatory

provisions to objectively specify when engines are considered to be “derivative engines”, we are 

promulgating regulatory provisions consistent with the ICAO ETM guidance.

D. Annual Reporting Requirements

In May of 1980, ICAO’s Committee on Aircraft Engine Emissions (CAEE) recognized 

that certain information relating to environmental aspects of aviation should be organized into 

one document. This document became ICAO’s “Annex 16 to the Convention on International 

Civil Aviation, International Standards and Recommended Practices, Environmental Protection”

and was split into two volumes – Volume I addressing Aircraft Noise topics and Volume II

addressing Aircraft Engine Emissions. Annex 16 has continued to grow and today Annex 16,

Volume II includes a list of mandatory requirements to be satisfied in order for an aircraft engine 

to meet the ICAO emission standards.

109 These requirements include information relating to 

 

109 ICAO, “Annex 16 to the Convention on International Civil Aviation, Environmental Protection, Volume 

II, Aircraft Engine Emissions,” Part III, Chapter 2, Section 2.4. A copy of this document is in docket number EPAHQ-OAR-2010-0687.
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engine identification and characteristics, fuel usage, data from engine testing, data analysis, and 

the results derived from the test data. Additionally, this list of aircraft engine requirements is 

supplemented with voluntarily reported information which has been assembled into an electronic 

spreadsheet entitled “Emissions Databank” (EDB)110 for turbofan engines with maximum thrust 

ratings greater than 26.7 kN in order to aid with emission calculations and analysis as well as 

help inform the general public. 

In order to understand how current gaseous emission standards are affecting the current 

fleet, we need to have access to timely, representative emissions data of the engine fleet at the 

requisite model level. The EDB is a useful tool for providing a general overview of the aircraft 

fleet, as it contains information on engine exhaust emissions and performance tests. However, it 

is not updated on a consistent basis, it contains a varying amount of voluntarily reported data 

from each manufacturer, and it does not specifically list every engine sub-model.

111

 It also does 

not contain information on smaller thrust category turbofans or turboprops, and contains no 

information on past or recent engine production volumes. We need this data to conduct accurate

emission inventories and develop appropriate policy. Accordingly, we do not consider the EDB 

to be a sufficient tool upon which to base policy decisions or adopt future standards.

 

110 United Kingdom, Civil Aviation Authority, “ICAO Emissions Databank.” Available at the Civil 

Aviation Authority website www.caa.co.uk/default.aspx?catid=702. 

111 Under today’s regulations, a grouping of engines with an essentially identical emission-related design

are defined to be an “engine sub-model”. Engines with slightly different designs are defined to be an “engine 

model”.
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Furthermore, in the context of EPA’s standards-setting role under the Clean Air Act with regard 

to aircraft engine emissions, it is consistent with our policy and practice to ask for timely and 

reasonable reporting of emission certification testing and other information that is relevant to our 

mission. Under the Clean Air Act, we are authorized to require manufacturers to establish and 

maintain necessary records, make reports, and provide such other information as we may

reasonably require to discharge our functions under the Act. (See 42 U.S.C. § 7414(a)(1).)

Therefore, we proposed to require that each aircraft engine manufacturer submit a 

production report directly to EPA112 with specific information for each individual engine submodel that: 1) is designed to propel subsonic aircraft, 2) is subject to our exhaust emission 

standards, and 3) has received a U.S. type certificate. More specifically, the scope of the 

proposed production report would include turbofan engines as described above with maximum 

rated thrusts greater than 26.7 kN, i.e., those subject to gaseous emission and smoke standards. 

In addition, it would include turbofans with maximum rated thrusts less than or equal to 26.7 kN 

and all turboprop engines, i.e., those only subject to smoke standards. We also proposed that this 

specific exhaust emission related information be reported to us in a timely manner, which will 

allow us to conduct proper emissions inventory analyses of the existing fleet and to ensure that 

any public policy we create based on this information will be well informed. All of the specific 

reporting items we proposed were the same as requested for the EDB, with the exception of total 

 

112 The report would be submitted only to EPA. No separate submission or communication of any kind is 

required for the FAA. 
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annual engine production volumes, information on type certificates, and the emission standards 

to which the engine sub-model was certified. We anticipated that the new emissions database 

would be a significant improvement over the current EDB because the data reporting is 

mandatory, it will be comprehensive in that it covers all engine models, and it must be updated 

annually.

In addition to some minor comments which are addressed in the analysis of comments 

document, we received comments from engine manufacturers addressing two specific areas of 

the proposed production reporting provision. First, the Aerospace Industries Association (AIA), 

General Aviation Manufacturers Association (GAMA) and Pratt & Whitney (PW) commented 

that annual production volume data is considered confidential business information (CBI) and as 

such, it should be exempt from Freedom of Information Act (FOIA) requests or other methods of 

public disclosure. Second, AIA, GAMA, PW and Williams International pointed out that for 

those engines which are only subject to smoke standards (turbofans with maximum thrust ratings 

less than or equal to 26.7 kN, and turboprops), manufacturers are not required under current 

regulations to measure gaseous emissions (HC, CO, NOx, CO2). As such, data on these gaseous 

emissions, as well as information used to measure gaseous emissions (reference pressure ratio 

and fuel flow data) are not readily available for these engines. Further, smoke data by mode of 

the LTO cycle may not be available for these older engines. These manufacturers pointed out 

that new testing of such engines would be required to generate these data, and that appropriate 

test procedures for these engines do not currently exist.
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We understand and respect the needs of manufacturers to maintain the confidentiality of 

their legitimately proprietary data. However, we do not include in our regulations an up-front

blanket CBI determination for any of the other mobile source sectors, and do not believe it is 

necessary here. As such, in response to the comments, we are including regulatory language 

patterned after existing regulations for several other mobile source categories which sets forth 

how we would treat – on a case by case basis – submitted data which is covered by a CBI claim 

from the manufacturer as provided by 40 CFR part 2. The addition of this provision will ensure 

that no information that is legitimately protected CBI gets inadvertently released to the public.

We do not believe it is appropriate to require additional testing for turbofans with 

maximum thrust ratings less than or equal to 26.7 kN and turboprops specifically for production 

reporting purposes. Thus, for these engines, we will not be requiring the submission of HC, CO, 

NOx, CO2, reference pressure ratio or fuel rate data. Further, we will not require additional 

testing of older engines for which smoke data by specific LTO cycle segment is not currently

available.

We also noted in the proposal that the reported information would be used in conjunction 

with the NOx and CO2 emission data already required to be submitted to us under section 87.64

for purposes of greenhouse gas (GHG) reporting to establish. This would effectively provide us 

with a complete and comprehensive engine exhaust emissions database. We noted our

expectation that most manufacturers would likely add the proposed information items to the 
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annual GHG report. No comments were received on combining the two reports. After further 

deliberation, we have decided to require a single, integrated report in this final rule to eliminate 

any possible confusion regarding the two separate reports and make reporting more efficient. 

 The incremental reporting elements for each affected gas turbine engine sub-model are 

listed below. Although not proposed, we have added engine type to the list for completeness. 

The reporting elements of the existing GHG report are also identified for completeness. 

• Company corporate name as listed on the engine type certificate (GHG);

• Engine Type (turbofan, mixed turbofan, or turboprop)

• Calendar year for which reporting (GHG);

• Complete sub-model name (This will generally include the model name and the submodel identifier, but may also include an engine type certificate family identifier) (GHG);

• The type certificate number, as issued by the FAA (Specify if the sub-model also has a 

type certificate issued by a certificating authority other than the FAA) (GHG);

• Date of issue of type certificate and/or exemption, i.e. month and year (GHG);

• Emission standards to which the engine is certified, i.e., the specific Annex 16, Volume 

II, edition number and publication date in which the numerical standards first appeared.
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• If this is a derivative engine for emissions certification purposes, identify the original 

certificated engine model.

• Engine sub-model that received the original type certificate for the engine type 

certificate family;

• Production volume of the sub-model for the previous calendar year (even if zero). If an 

engine sub-model is no longer being produced, state that the engine sub-model is not in 

production and list the date of manufacture (month and year) of the last engine produced;

• Regarding the above production volume report, specify (if known) the number of 

engines that are intended for use on new aircraft and the number intended for use as certified 

(non-exempt) spare engines on in-use aircraft;

• Reference pressure ratio (GHG) (not applicable to turbofans with maximum thrust 

ratings less than or equal to 26.7 kN, and turboprops);

• Combustor description (type of combustor where more than one type available on an 

engine);

• Engine maximum rated thrust output, in kilonewtons (kN) ) or kilowatts (kW) 

(depending on engine type) (GHG);
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• Unburned hydrocarbon (HC) mass (g) total (weighted) and over each segment of the 

Landing and Take-off Cycle (LTO), i.e. Take-off, Climb, Approach, Taxi/Ground Idle (not 

applicable to turbofans with maximum thrust ratings less than or equal to 26.7 kN, and 

turboprops);113

• Unburned hydrocarbon (HC) characteristic level (i.e. mass of hydrocarbons over LTO 

cycle/Rated Thrust (Dp/Foo)) (not applicable to turbofans with maximum thrust ratings less than 

or equal to 26.7 kN, and turboprops); 114

• Carbon monoxide (CO) mass (g) total (weighted) and over each segment of the entire 

Landing and Take-off Cycle (LTO) (i.e. Take-off, Climb, Approach, Taxi/Ground Idle) (not 

applicable to turbofans with maximum thrust ratings less than or equal to 26.7 kN, and 

turboprops);

• Carbon monoxide (CO) characteristic level (i.e. mass of CO over LTO cycle/Rated 

Thrust (Dp/Foo)) (not applicable to turbofans with maximum thrust ratings less than or equal to 

26.7 kN, and turboprops);

• Nitrogen oxides (NOx) mass (g) total (weighted) and over each segment of the entire 

Landing and Take-off Cycle (LTO) (i.e. Take-off, Climb, Approach, Taxi/Ground Idle) (GHG) 

 

113 See Regulation Part 87-Control of Air Pollution from Aircraft and Aircraft Engines, Subpart E, §87.42 

Production report to EPA for definitions.

114 Dp/Foo : total gross emissions of each gaseous pollutant (mass) / rated thrust (g/kN).
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(not applicable to turbofans with maximum thrust ratings less than or equal to 26.7 kN, and 

turboprops);

• Nitrogen oxides (NOx) characteristic level (i.e. mass of NOx over LTO cycle/Rated 

Thrust (Dp/Foo)) (GHG) (not applicable to turbofans with maximum thrust ratings less than or 

equal to 26.7 kN, and turboprops);

• Smoke number total and over each segment of the entire Landing and Take-off Cycle 

(LTO) (i.e. Take-off, Climb, Approach, Taxi/Ground Idle), if available;

• Smoke number characteristic level;

• Carbon dioxide (CO2) mass (g) total (weighted) and over each segment of the entire 

Landing and Take-off Cycle (LTO), (i.e. Take-off, Climb, Approach, Taxi/Ground Idle (GHG)) 

(not applicable to turbofans with maximum thrust ratings less than or equal to 26.7 kN, and 

turboprops);

• Number of tests run per sub-model (GHG);

• Number of engines tested per sub-model (GHG);

• Fuel flow (grams / second) total (weighted) and over each segment of the Landing and 

Take-off Cycle (LTO) (i.e. Take-off, Climb, Approach, Taxi/Ground Idle) (GHG) (not 
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applicable to turbofans with maximum thrust ratings less than or equal to 26.7 kN, and 

turboprops); and

• Any additional remarks to the EPA.

The annual report is required to be submitted for each calendar year in which a 

manufacturer produces any engine subject to emission standards as previously described. These 

reports will be due by February 28 of each year, starting with the 2014 calendar year, and cover 

the previous calendar year. This report shall be sent to the Designated EPA Program Officer. 

Where information provided for any previous year remains valid and complete, the engine 

manufacturer may report the production figures and state that there are no changes instead of 

resubmitting the original information. To facilitate and standardize reporting, we expect to

specify a particular format for this reporting in the form of a spreadsheet or database template 

that we provide to each manufacturer. As noted previously, we intend to use the reports to help 

inform any policy approaches regarding aircraft engine emissions that we consider, including 

possible future emissions standards. The information will also enhance the general public’s 

understanding of the emission characteristics of aviation gas turbine engines and allow 

independent development of emission inventories and assessments of local environmental 

effects. Subject to the applicable requirements of 42 U.S.C. 7414(c), 18 U.S.C. 1905, and 40 

CFR part 2, all data received by the Administrator that is not confidential business information 

may be posted on our website and will be updated annually. We have assessed the potential 
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reporting burden associated with this annual reporting requirement. That assessment is presented 

in sections V. and IX.B of this notice.

E. Standards for Supersonic Aircraft Turbine Engines

We proposed CO and NOx emission standards for turbine engines that are used to propel 

aircraft at sustained supersonic speeds, i.e., supersonic aircraft to complement our existing HC 

standard for these engines. These standards were originally adopted by ICAO in the 1980s, and 

our adoption of NOx and CO standards for commercial engines in 1997 omitted coverage of 

these pollutants for supersonic commercial engines that were then in use. The lack of EPA CO 

and NOx standards for engines used by supersonic aircraft has had no practical effect, because 

no such engines have been certified by the FAA. Also, none of the engines used on these aircraft

are currently in production. 

The Aerospace Industries Association (AIA) and the General Aviation Manufacturers 

Association (GAMA) commented that within CAEP it was agreed that these standards are “not 

appropriate for future products” and should not be adopted by EPA.115 However, to meet U.S.

treaty obligations under the Convention on International Civil Aviation as previously described 

in section I.C, we believe it is necessary and appropriate to adopt these conforming standards. 

 

115 The CAEP position referred to by AIA and GAMA is based on the expectation that future designs for 

supersonic aircraft will be significantly different from past designs. The agreement was reached at CAEP/8 to 

evaluate emission standards for these engines as a future work item.
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Therefore, we are promulgating the standards for supersonic aircraft as proposed. As previously 

noted, this action has no practical effect, and simply aligns EPA standards with the rest of the 

world. (See section III.G for a brief discussion of potential revised emission standards for future 

engine designs that may be used on supersonic aircraft.) 

F. Amendments to Test and Measurement Procedures

We are incorporating by reference into the 40 CFR §87.60 regulatory text, amendments 

to ICAO’s International Standards and Recommended Practices for aircraft engine emissions 

testing and certification. 116,117,118 These amendments to Annex 16, Volume II are primarily

intended to ensure that the provisions reflect current certification practices. The amendments 

make clarifications or add flexibilities for engine manufacturers. They are described below.

• Standardizing the terminology relating to engine thrust/power

 

116 A strikeout and highlighted version of the amendments is contained in Attachment A to ICAO state 

letter AN 1/61.2, AN 1/62.2 - 07/32 entitled, “Proposed Amendment to International Standards and Recommended 

Practices, Environmental Protection, Annex 16 to the Convention on International Civil Aviation, Volume II 

Aircraft Engine Emissions, May 27, 2007. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.

117 ICAO, “International Standards and Recommended Practices, Annex 16 to the Convention on 

International Civil Aviation, Environmental Protection, Volume II Aircraft Engine Emissions,” Third Edition, July 

2008, International Civil Aviation Organization. This document contains the full text of ICAO standards and 

practices and is in docket number EPA-HQ-OAR-2010-0687.

118 ICAO, “International Standards and Recommended Practices, Annex 16 to the Convention on 

International Civil Aviation, Environmental Protection, Volume II Aircraft Engine Emissions, Amendment 7, 

effective July 18, 2011” Third. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.
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• Clarifying the need to correct measured results to standard reference day and

reference engine conditions

• Allowing a certificating authority to approve the use of test fuels other than those 

specified during certification testing

• Allowing materials other than stainless steel in the sample collection equipment

• Clarifying the appropriate value of fuel flow to be used at each LTO test point

• Clarifying exhaust nozzle terminology for exhaust emissions sampling

• Allowing an equivalent procedure for gaseous emission and smoke measurement if 

approved by the certificating authority

Manufacturers are either already voluntarily complying with these changes or will be 

even in the absence of a final rule. Our adoption of these test procedure amendments is,

therefore, unlikely to require new action by manufacturers beyond what they have already done

to meet ICAO’s adopted and recommended amendments. 

Our incorporation by reference of the ICAO test procedure makes most of the existing 

subpart G and all of subpart H of part 87 obsolete. Therefore, we are removing these sections 

from the regulation, as proposed.
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G. Possible Future Revisions to Emission Standards for New Technology Turbine 

Engines and Supersonic Aircraft Turbine Engines

As a general matter, emission standards not only apply to all conventional turbofan 

aircraft engines greater than 26.7 kN, but also to all aircraft engines designed for applications 

that otherwise would have been fulfilled by turbofan aircraft engines. The high price of jet fuel, 

current emphasis on fuel economy, and need to reduce emissions have renewed interest in open 

rotor propulsion designs for future aircraft gas turbine engines. Essentially, the fan of an open 

rotor engine is not contained within an engine nacelle as it is with a conventional turbofan

engine. This design has also been referred to as an unducted fan, propfan, or ultra-high bypass 

engine. At least two engine manufacturers are actively pursuing such designs for certification in 

the later part of this decade.

It now appears that certain aspects of EPA’s gas turbine engine emission standards may

be incompatible with these new designs. For example, the current landing and takeoff cycle for 

emissions certification is based on conventional engine designs where a significant amount of 

thrust is generated by an idling engine. Specifically, idle emissions are measured and calculated 

at seven percent of the engine’s rated thrust. However, the fan/prop blades of an open rotor 

engine may be variable in pitch and this may allow the blades to be “feathered” at idle. In that 

position, the blades are rotated so very little thrust is generated as the engine idles and generates 

emissions. Also, future aircraft using these engine designs may fly at somewhat slower speeds. 
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This might affect the time these aircraft spend during the climbout mode of the landing and 

takeoff cycle. Therefore, the traditional landing and takeoff cycle used in turbofan engine 

emissions certification may need to be revised in the future to accommodate open rotor engines. 

We will be working within CAEP to evaluate the differences between conventional 

turbine engine and open rotor engine technologies, and to revise the emission standards and test 

procedures as appropriate for these latter engines. If any changes are required, EPA will 

undertake rulemaking to revise our regulations accordingly.

There may also be changes in the emission standards and test procedures for engines used 

to power future supersonic transport aircraft designs. The emission standards for these engines 

were originally developed in the early 1970s in response to the Aerospatiale-BAC Concorde. 

Since that time, there have been varying levels of interest in developing a new generation of 

supersonic transport. As a result, the current CAEP work program is evaluating the status of 

supersonic aircraft engine development and the potential need for new emission standards and 

test procedures. 119 Our recent discussions with engine manufacturers indicate that no 

substantive work is being undertaken at this time, however. We will continue to work within 

 

119 The CAEP Working Group 3 has taken the position that engine development programs for future 

supersonic aircraft applications should be focused on achieving the emission standards that are applicable to 

subsonic aircraft engines. Past supersonic aircraft engines required the use of afterburner technology to achieve 

supersonic speeds. Future supersonic aircraft are expected to use engines without that technology, making them 

more similar to their subsonic counterparts.
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CAEP on this issue and undertake rulemaking to revise the regulations for supersonic aircraft 

engines as appropriate. 

IV. Description of Other Revisions to the Regulatory Text

In addition to the changes discussed above, we are including a number of other changes 

to the regulatory program. Most of these changes are designed to bring the program into 

conformity with current technology and current technical or policy practice. Each of these is 

discussed below. 

A. Applicability Issues

This section discusses how this final rule relates to engines used in military and 

noncommercial civilian aircraft. We do not believe these changes will have practical 

significance for current engine models because the changes align with manufacturers’ current 

practice in certifying their engines. 

1. Military Engines

We do not intend today’s action to have any impact on engines installed on military

aircraft, or new aircraft that are destined to be converted for military use. Military aircraft are 

not required to have FAA standard airworthiness certificates, and our 1997 endangerment 

finding for NOx and CO emissions and resulting standards did not cover military aircraft (see 62 

FR at 25359). As such, engines used in military aircraft are not required to meet EPA emission 
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standards, since our current regulations define “aircraft” subject to our rules as any airplane for 

which a U.S. standard airworthiness certificate (or foreign equivalent) is issued. (See 40 C.F.R. 

§ 87.1(a) of the existing regulations.) Currently, manufacturers certificate some engine models 

used in military aircraft with the FAA (with respect to emissions), because these engine models 

also have commercial applications and have to be certificated for such use. Our new standards 

and requirements will continue to apply only to engines used in aircraft for which standard 

airworthiness certificates are required, and thus are not applicable to engines used in military

aircraft. It is not our intent to interfere with current practice with regard to engine models with 

joint commercial/military applications to the extent such engines are used in military aircraft. 

Although civilian aircraft applications of all such engines would be subject to the new standards 

and production cutoff, in the NPRM we proposed to include a statement in the regulations to 

clarify that the proposed production cutoff would not apply for previously certificated engines 

that are installed and used in military aircraft. One manufacturer commented that the definition 

of “military aircraft” we proposed should extend to sales of military aircraft outside of the U.S. 

While we believe the regulations as written do not apply to foreign sales of military aircraft, we 

are nonetheless revising our proposed definition of “military aircraft” to clarify that foreign 

aircraft considered military under international laws and agreements are not covered by 40 CFR 

part 87.

2. Noncommercial Engines
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Prior to this action, section 87.21(d) specified that gaseous emission standards applied to 

engines used in commercial applications with rated thrusts greater than 26.7 kN. These are 

engines intended for use by an air carrier or a commercial operator as defined in the Chapter I, 

Title 49 of the United States Code and Title 14 of the Code of Federal Regulations. Therefore, 

engines of equivalent thrust ratings that are used in aircraft certificated by the FAA that are used

in non-revenue, general aviation service were not required to comply with our current HC, CO, 

and NOx exhaust emission standards in §87.21(d). They were and are subject, however, to the 

current standards for smoke and fuel venting.

In today’s action we are applying the gaseous emission standards for commercial engines 

to their noncommercial civilian counterparts that are required to obtain standard airworthiness 

certificates. There are a couple of reasons for this action. First, the ICAO Annex 16, Volume II

standards and recommended practices apply equally to commercial and noncommercial engines, 

and our rules’ previous failure to reflect this meant that our requirements did not fully conform to 

ICAO’s standards. Second, manufacturers already emissions certify engines that are used in 

non-revenue, general aviation service to these standards. Therefore, this provision simply

incorporates the status quo.

In order to make EPA standards conform to ICAO’s, we needed to, in addition to 

promulgating the necessary regulatory amendments, update the underlying finding regarding the 

need to limit gaseous emissions from commercial and non-commercial civilian aircraft, pursuant 
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to CAA section 231(a)(2)(A). In 1997, our analysis and finding, and hence our regulations, were 

limited to commercial aircraft emissions. (See 62 FR at 25358.) In conjunction with the NPRM 

for this final rule, we proposed to expand that analysis and finding to include gaseous emissions 

from both commercial and non-commercial civilian aircraft engines with rated thrusts greater 

than 26.7 kN. We received no comments on that proposed finding, and are therefore finalizing 

our emissions assessment supporting this finding, which is contained in the docket for this 

rulemaking.120

B. Non-substantive Revisions

We are also taking the opportunity to revisit the clarity of other regulatory provisions in 

part 87. Many of these provisions were first written 30 or 40 years ago with little or no change 

since then. We are revising the text related to some of these provisions to better organize, 

clarify, and update the regulations. Our goal is to revise the regulations in part 87 to properly 

organize the content of the regulation, use clearer language to describe the applicable 

requirements, clarify some definitions, and clear up a variety of terms and current practices that 

have not been adequately addressed. 

 

120 U.S. EPA, “Final Finding for Commercial and Noncommercial Turbofan and Turbojet Aircraft 

Emissions,” memorandum from John Mueller, Assessment and Standards Division, Office of Transportation and Air 

Quality, March 2012. A copy of this document is in docket EPA-HQ-OAR-2010-0687
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Except as discussed in previous sections, the changes to part 87 are not intended to 

significantly change the certification and compliance program. We did not reopen for comment 

the substance of any part of the program that remains unchanged substantively. 

This rule includes the following definitions and other minor changes in addition to those 

changes described earlier in this section or in section III.

The definition of the term “aircraft” is being revised to be consistent with its meaning 

under FAA regulations in 14 CFR 1.1. The existing part 87 definition limits “aircraft” to be only 

those aircraft issued an airworthiness certificate. This was done as a way to specify the 

applicability of the standards. However, this can cause confusion in a variety of ways. For 

example, this departs from the plain meaning of “aircraft,” as well as from the meaning given 

under the Clean Air Act and Title 49 of the United States Code. The revised definition aligns 

with these statutory definitions. The changed wording is intended to clarify the existing policy

without changing it.

Text specifying general applicability is being added to part 87.3 to be consistent with the 

new definition of “aircraft” and maintain the effective applicability of the existing regulations, 

which uses narrow definitions to limit applicability. For example, the existing regulations limit 

the applicability of the standards by defining “aircraft” to only include fixed-wing airplanes with 

airworthiness certificates. They exclude non-propulsion engines from the definition of “aircraft 

engine” and turboshaft engines from the definition of “aircraft gas turbine engine.” We believe it 
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is more appropriate to explicitly exclude these engines in an applicability section than to rely on 

readers finding these exclusions in the definitions section. We are also renaming part 87.3 as 

“General applicability and requirements” and reorganizing the content for clarity. Finally, we 

are replacing the existing regulatory text related to federal preemption for exempted engines in 

part 87.7(f) with a codification of the statutory preemption language in part 87.3 and an 

explanatory note that the statutory preemption applies to exempted engines because they are 

certified to prior-tier standards.

ICAO Annex 16, Volume II is being incorporated by reference for test procedures. This

involves a broader reference to Annex 16, with less content repeated in part 87. However, this 

does not substantively change the test procedures that apply since the existing procedures are 

based directly on Annex 16, Volume II. As part of this change, we are adding the ICAO

definition of “characteristic level” to properly describe how manufacturers demonstrate that they

meet applicable standards.

Definitions are being added for “date of introduction,” “date of manufacture,” and 

“derivative engine for emissions certification purposes,” and the definition of “engine model” is 

being revised, to more carefully describe when new emission standards apply to specific aircraft 

engines. These definitions are generally consistent with the most common understandings of 

these terms by industry and FAA, and with the CAEP/8 recommendation for adoption by ICAO. 

Except for engines subject to exemptions, there will be no more engines required to be certified 
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to the standards specified in part 87.21, so changing the definition of “engine model” will not 

change the requirements for engines certified to the Tier 4 or earlier standards. For the benefit of 

the reader, we are also reprinting the following definitions that remain unchanged: 

• Aircraft engine 

• Aircraft gas turbine engine 

• Class TP 

• Class TF 

• Class T3 

• Class T8 

• Class TSS 

• Commercial aircraft gas turbine engine

• Fuel venting emissions

Specific provisions are being added to define and require the use of “good engineering 

judgment.” This applies for instances where the regulation cannot spell out every technical 

detail of how a manufacturer should comply with the regulation. For example, the regulations 

rely on good engineering judgment being used on the engineering analysis of emissions 

equivalency for derivative engines (part 87.48(b)(2)), and for applying the turbofan test 

procedures to turboprop engines (part 87.60(a)). The general approach for implementing good

engineering judgment is to allow manufacturers to exercise well substantiated and explained 

technical judgment subject to potential EPA and FAA review (as appropriate). The 
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consequences of disagreements with a manufacturer’s decision would depend on whether we 

believe the manufacturer made the decision in good faith. Where the manufacturer makes its 

decision in good faith, EPA or FAA could require a different approach for future work if we

believe it would represent better engineering judgment. We believe these provisions reflect the 

spirit of the approach being used today to interpret the applicable regulations.

Provisions are being added specifying rounding practices for rated output, rated pressure 

ratio, and calculated emission standards; generally specifying that they be expressed to at least 

three significant figures. The primary exception to this is the specification that smoke numbers 

be expressed to one decimal place. These specifications are consistent with how manufacturers 

are generally certifying engines today. Defining how to round these values would prevent 

manufacturers in the future from effecting small changes in the level of the emission standards to 

which they certify their engines. This is because standards are calculated using the numerical 

values of the rated output and rated pressure ratio. Without these specifications, manufacturers 

could subject themselves to a slightly less stringent standard by selectively rounding or 

truncating an engine model’s rated output to be low and its rated pressure ratio to be high, or by 

strategically rounding the calculated standard itself. While this has not been an issue in the past, 

it is important to maintain a level playing field for all manufacturers as standards become more 

stringent. We do not expect any more engines type-certificated to the standards specified in part 

87.21, so the specified procedures for rounding these values will not change the requirements for 

engines certified to the Tier 4 or earlier standards
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Definitions are being added for “turbofan engine,” “turbojet engine,” “turboprop engine,” 

“turboshaft engine,” “supersonic,” and “subsonic” to avoid any uncertainty about how the 

standards apply to different types of engines. The definitions are intended to reflect the plain 

meaning of these terms. 

The regulations include the following additional amendments:

Regulation

cite

Description of 

Amendment

Notes

87.1 Add definition of 

“characteristic level”.

The characteristic level is established by ICAO 

Annex 16 as a means of calculating a statistical 

adjustment to measured emission results to take 

into account the level of uncertainty 

corresponding to the number of tests run for a 

given pollutant.

87.1 Remove definitions for 

“emission measurement 

system”, “power 

setting”, “sample 

system”, “shaft power”, 

“taxi/idle (in)”, and 

“taxi/idle (out).”

These terms will no longer be used in part 87. 

There will be no more engines certified to the 

standards specified in §87.21, so removing these 

definitions will not change the requirements for 

engines certified to the Tier 4 or earlier 

standards.
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87.1 Revise definition of 

“exhaust emissions” 

and “smoke”.

The new language references the emission 

testing procedures, since that is the practical 

meaning of these terms in part 87. This 

clarifies, for example, that emissions from the 

nozzle of an aircraft or aircraft engine count as 

exhaust emissions only if they are measured 

using the specified test procedures. There will 

be no more engines certified to the standards 

specified in §87.21, so revising these definitions 

will not change the requirements for engines 

certified to the Tier 4 or earlier standards.

87.1 Define “new” instead of 

defining “new aircraft 

turbine engine”.

The regulations also refer to new turboprop 

engines and new engines used for supersonic 

aircraft, so it is appropriate to define the 

adjective as it relates to these different kinds of 

engines. This approach does not change the 

meaning of the applicable terms and therefore 

has no bearing on the requirements that applied 

under the standards specified in §87.21.

87.1 Revise the definition of 

“standard day 

condition”: (1) remove 

the reference to the 

1976 U.S. Standard 

Atmosphere, (2) correct 

a typographical error in 

the humidity 

specification, and (3) 

change the atmospheric 

pressure units from Pa 

to kPa.

The editorial changes do not involve any 

substantive change in the specified conditions.

87.2 Remove FAA from the 

list of acronyms in 

§87.2 and add it to the 

set of defined terms in 

§87.1.

This is intended to not involve a change in 

emission standards or implementation.
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87.3 Add provisions 

describing the scope of 

applicability of part 87. 

The broad statement in §87.3 is not intended to 

conflict with the applicability statements in 

individual subparts, since those additional 

statements indicate that certain requirements in 

part 87 apply more narrowly. All applicability 

statements in the rule are intended to be 

consistent with current policy.

87.3 Remove the provision 

related to preemption of 

state standards for 

exempted aircraft and 

replace it with the 

preemption provision in 

the Clean Air Act.

This change more carefully tracks the statutory 

provisions related to preemption.

87.5 Move the provisions 

related to special test 

procedures to §87.60.

This provision, and the similar provision from 

§87.3(a), should be described together in the 

context of the testing requirements in subpart G.

87.21 Identify the specific 

date when the smoke 

standard started to 

apply for turbofan 

engines with rated 

output less than 26.7 

kilonewtons.

This corrects a typographical error from the 

Federal Register.

87.21 Revise paragraph (f) to 

correctly reference the 

regulatory sections that 

describe the applicable 

test procedures.

This change is strictly editorial.

87.60 Revise the description 

of test procedures to 

rely broadly on the 

procedures specified in 

There will be no more engines certified to the 

standards specified in §87.21, so any changes to 

the test procedures will not change the 

requirements for engines certified to the Tier 4 
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ICAO Annex 16. This 

includes a variety of 

recent changes to the 

Annex 16 procedures.

or earlier standards. Moreover, engine 

manufacturers are expected to perform all their 

testing based on the current test procedures from 

ICAO Annex 16, regardless of the standards that 

apply.

C. Clarifying Language for Regulatory Text

The regulations incorporate the changes described in this preamble. The following table 

highlights and clarifies several provisions that may not be obvious to the reader.

Regulation cite Note

87.1, Definition of 

“aircraft”

This definition would revert to the normal FAA definition 

of aircraft, rather than the much narrower current definition in part 

87. To understand this change, the definition needs to be considered 

along with the changes to applicability in 87.3(a).

87.1, Definition of “date 

of manufacture”

This is generally the same definition as given in ICAO 

Annex 16. However, our definition addresses certain specific 

circumstances that could possibly occur, but that are not addressed 

by the Annex. For example, our definition would provide a date of 

manufacture for an engine not previously documented by a 

manufacturer.

87.1, Definition of 

“derivative engine for emissions 

certification purposes”

It is important to consider this definition in combination 

with the definition of “engine type certificate family”.
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87.1 Definition of 

“engine model”

A manufacturer or FAA may further divide an engine model 

into sub-models. Engines from an engine model must be contained 

within a single engine type certificate family. Where FAA 

determines that engines are not sufficiently similar to be included 

under a single type certificate, they will not be considered to be the 

same engine model for purposes of part 87.

87.1, Definition of 

“military aircraft” and 87.23(d).

In §87.23(d) we clarify that the production cutoff does not 

apply for military aircraft engines (even if they have been 

certificated). In §87.1, we define military aircraft to primarily mean 

“aircraft owned by, operated by, or produced for sale to the armed 

forces or other agency of the federal government responsible for 

national security (including but not limited to the Department of 

Defense).” For example, aircraft owned by the U.S. Coast Guard 

would be military aircraft. In response to comments, we added a 

clarification that military aircraft also include “other aircraft 

considered to be military aircraft under international law and 

conventions.”

87.1, Definition of 

“production cutoff date”

The production cutoff date for the Tier 6 NOx standards is 

December 31, 2012.

87.1, Definition of “spare 

engine”

Newly manufactured spare engines may be excepted under 

§87.50.

87.1, Definitions of tiers As specified in the definitions of “Tier 0” through “Tier 8”, 

tiers apply only for NOx standards. Tiers do not apply for HC, CO, 

and smoke standards because these continue to apply, independent 

of the NOx standards. 

87.23(d)(2) The allowance to continue production of Tier 6 engines 

after the Tier 8 standards start to apply is not necessary for engines 

with rated pressure ratio at or above 104.7 because the Tier 6 and 

Tier 8 standards are numerically identical at these thrust levels.

87.42(c)(1) §87.42 requires that a manufacturer report the engines it 

produces by sub-model. The manufacturer must specify the 
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manufacturer’s unique sub-model name, which will generally 

include a model name and a sub-model name. It may also include a 

family name.

87.50 This provision specifies that EPA must provide written 

concurrence for exemptions. 

87.50(a)(1)(iv)(F) This provision states that manufacturers requesting 

exemptions should describe equity issues. As an example of equity 

issues related to an exemption request, a manufacturer might 

provide a rationale for granting the exemption when another 

manufacturer has a compliant engine and does not need an 

exemption, taking into account the implications for operator fleet 

composition, commonality, and related issues in the absence of the 

engine model in question.

87.50(a)(6) This provision requires manufacturers to promptly notify 

the FAA if new or changed information could have affected 

approval of an exemption. For corrections to an exemption request 

that would not affect the approval of the exemption, manufacturers 

may include the updated information in the annual report described 

in §87.50(e). 

V. Technical Feasibility, Cost Impacts, Emission Benefits

During the CAEP process, the technical feasibility and cost of compliance of the CAEP/6 

and CAEP/8 NOx standards were thoroughly assessed and documented.121,122 EPA participated 

 

121 CAEP/6 NOx standards: CAEP Forecasting and Economic Analysis Support Group, Economic Analysis 

of NOx Emissions Stringency Options, CAEP/6-IP/13 (Information Paper 13), January 15, 2004. A copy of this 

document is in docket number EPA-HQ-OAR-2010-0687. 

122 CAEP/8 NOx standards: CAEP Working Group 3, NOx Stringency Technology Response Assessment, 

CAEP-SG/20082-WP/18 (Working Paper 18), September 25, 2008. CAEP Forecasting and Economic Analysis 
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in these analyses and supported the results. Generally, CAEP considered certain factors as 

pertinent to the cost estimates of a technology level for engine changes, and these factors or 

technology levels are described below. The first technology level was regarded as a minor 

change, and it could include modeling work, minor design changes, and additional testing and recertification of emissions. The second technology level was considered a scaled proven 

technology. At this level an engine manufacturer applies its best-proven, combustion technology

that was already certified in at least one other engine type to another engine type. This second 

technology level would include substantial modeling, design, combustion rig testing, 

modification and testing of development engines, and flight testing. The third technology level 

was regarded as new technology or current industry best practice, and it was considered where a 

manufacturer has no proven technology that can be scaled to provide a solution and some 

technology acquisition activity is required. (One or more manufacturers have demonstrated the

necessary technology, while the remaining manufacturers would need to acquire the technology

to catch up.) Since the effective date for the CAEP/6 NOx standard was January 1, 2008 and 

nearly all in-production engines currently meet this standard, we believe this clearly 

demonstrates the technical feasibility of those standards. Therefore, we will limit our discussion 

 

Support Group, Economic Assessment of the NOx Stringency Scenarios, CAEP/8-IP/14, November 30, 2009. 

Modeling Task Force, MODTF NOx Stringency Assessment, CAEP/8-IP/13, December 11, 2009. United States, 

Aviation Environmental Portfolio Management Tool for Economics (APMT-Economics) and Its Application in the 

CAEP/8 NOx Stringency Analysis, CAEP/8-IP/29, January 6, 2010. A copy of these documents are in docket 

number EPA-HQ-OAR-2010-0687.
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below to applying these technology levels to engines that need to comply with the CAEP/8 NOx 

standard. 

At the time of the CAEP reports, the CAEP/8 NOx standard for higher thrust engines, 

i.e., 89.0 kN or more would apply to a total of 15 engine types. For these types the following 

technology level response was anticipated: six types would require no change, one type would 

need the first technology level change, five would require the second technology level, and three

would need the third technology level. For lower thrust engines, i.e., greater that 26.7 but less 

than 89.0 kN, CAEP listed a total of 13 engine types in their analysis of the CAEP/8 NOx 

standard. The following technology level response was estimated for these types: 11 types

would require no change, 1 type would need the first technology level change, and 1 type would 

require a second technology. Based on these analyses, CAEP concluded that the CAEP/8 NOx 

standards were technically feasible within the lead time and time frame identified in the action.

Regarding the costs of this final rule, aircraft turbofan engines are designed and built for 

use on aircraft that are sold and operated throughout the world. As a result, engine 

manufacturers respond to this market reality by designing and building engines that conform to 

ICAO international standards and practices. This normal business practice means that engine 

manufacturers are compelled to make the necessary business decisions and investments to 

maximize their international markets even in the absence of U.S. regulations that would 

otherwise codify ICAO standards and practices. Indeed, engine manufacturers have developed 
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or are already developing improved technology in response to ICAO standards that match the 

standards being promulgated in this final rule. Also, the recommended practices, e.g., test 

procedures, needed to demonstrate compliance are being adhered to by manufacturers during 

current engine certification tests, or will be even in the absence this final rule. Therefore, EPA 

believes that today’s standards and practices that conform with ICAO standards and practices 

will impose no real additional burden on engine manufacturers. This finding regarding no 

incremental burden, is also consistent with past EPA rulemakings that adopted ICAO 

requirements. ((See 62 FR 25356 (May 8, 1997) and 70 FR 69664 (November 11, 2005)). 

In fact, engine manufacturers have suggested that certain benefits accrue for compliant 

products when the U.S. adopts ICAO standards and practices, but have not provided detailed 

information regarding these benefits. Primarily, such action makes FAA certification more 

straightforward and transparent. That in turn is advantageous when marketing their products to 

potential customers, because compliance with ICAO standards is an important consideration in 

purchasing decisions. It simply removes any question that their engines comply with 

international requirements. There will be some cost, however, associated with our annual 

reporting requirement for emission related information. (See section III.D for a description of 

the reports.) There are a total of 10 engine manufacturers that would be affected. Eight of these 

produce turbofan engines with rated thrusts greater than 26.7 kN, which are already voluntarily
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reported to the ICAO-related Emissions Databank (EDB).

123

 We expect the incremental 

reporting burden for these manufacturers to be very small because we: 1) have significantly 

reduced the number of reporting elements from those requested in the EDB, and 2) are adding 

only three basic reporting categories to those already requested by the EDB. Also, four of the 

eight manufacturers make smaller turbofan and turboprop engines that will be reporting for the 

first time. This will add a small incremental burden for these four manufacturers that otherwise 

already voluntarily report to the EDB. There are also two engine manufacturers that only 

produce turbofan engines with rated thrusts less than or equal to 26.7 kN and they will be 

reporting for the first time. For these two manufacturers we believe that the reporting burden 

will be small because all of the information we are requiring should be readily available, and 

these manufacturers have a very limited number of engine models. 

We have estimated the annual burden and cost to be about six hours and $365 per 

manufacturer. With 10 manufacturers submitting reports, the total burden of this reporting 

requirement is estimated to be 60 hours, for a total cost of $3,646. 

VI. Coordination with FAA

 

123 As discussed in section III. D, we are requiring a single report that integrates the new reporting 

requirement contained in this final rule with the existing mandatory greenhouse gas (GHG) reporting of NOx and 

CO2 as already required under §87.64. Combining the existing GHG report with the new reporting requirement will 

not increase an engine manufacturer’s reporting burden. A single, integrated report may actually reduce a 

manufacturers total reporting burden somewhat because of the efficiency inherent in reporting to EPA once instead 

of twice.
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The requirements contained in this action were developed in consultation with the 

Federal Aviation Administration (FAA). Section 231(a)(2)(B)(i) of the CAA requires EPA to 

“consult with the Administrator of the [FAA] on aircraft engine emission standards” 42 U.S.C. 

7571(a)(2)(B)(i), and section 231(a)(2)(B)(ii) indicates that EPA “shall not change the aircraft 

engine emission standards if such change would significantly increase noise....” 42 U.S.C. 

7571(a)(2)(B)(ii). Section 231(b) of the CAA states that “[a]ny regulation prescribed under this 

section (and any revision thereof) shall take effect after such period as the Administrator finds 

necessary (after consultation with the Secretary of Transportation) to permit the development and 

application of the requisite technology, giving appropriate consideration to the cost of 

compliance within such period.” 42 U.S.C. 7571(b). Section 231(c) provides that any regulation 

under section 231 “shall not apply if disapproved by the President...on the basis of a finding by

the Secretary of Transportation that any such regulation would create a hazard to aircraft safety.” 

42 U.S.C. 7571(c). Under section 232 of the CAA, the Department of Transportation (DOT) has 

the responsibility to enforce the aircraft emission standards established by EPA under section 

231.126 As in past rulemakings and pursuant to the above referenced sections of the CAA, EPA 

has coordinated with the FAA, i.e., DOT, with respect to today's action.

Moreover, FAA is the official U.S. delegate to ICAO. FAA agreed to the amendments at 

ICAO's Sixth and Eighth Meetings of the Committee on Aviation Environmental Protection 

 

126The functions of the Secretary of Transportation under part B of title II of the Clean Air Act (§§ 231-234, 

42 U.S.C. 7571-7574) have been delegated to the Administrator of the FAA. 49 CFR 1.47(g).
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(CAEP/6) after advisement from EPA.127 FAA and EPA were both members of the CAEP’s 

Working Group 3 (among others), whose objective was to evaluate emissions technical issues 

and develop recommendations on such issues for CAEP/6 and CAEP/8. After assessing 

emissions test procedure amendments and new NOx standards, Working Group 3 made 

recommendations to CAEP on these elements. These recommendations were approved by

CAEP/6 meetings prior to their adoption by ICAO in 2004. Similarly, the more recent Working 

Group 3 recommendations were approved by CAEP/8 and have been adopted ICAO. 

In addition, as discussed above, FAA will have the duty to enforce today's requirements. 

As a part of these duties, the FAA witnesses the emission tests or delegates aspects of that 

responsibility to the engine manufacturer, which is then monitored by the FAA. 

VII. Public Participation 

We proposed this regulation on July 27, 2011 (76 FR 45012). A public hearing was held 

on August 11, 2011 in Chicago, IL. The public was invited to submit written comments on the 

proposal during the formal comment period, which ended on September 26, 2011. We received 

eight public comments from aircraft and aircraft engine manufacturers, airline operators and an 

individual.

 

127 The Sixth Meeting of CAEP (CAEP/6) occurred in Montreal, Quebec from February 2 through 12 in 

2004.
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The vast majority of commenters supported the central tenets of the proposed regulations. 

That is, there was broad support for the adoption of these standards and the alignment of U.S. 

and international emissions regulations. We received specific comments on several aspects of 

the proposal.

Throughout this notice, we discussed the key issues arising from the public comment and 

our responses. In addition, we have addressed all of the public comments in the analysis of 

comments document associated with this final action and located in the docket (Docket ID EPAHQ-OAR-2010-0687).

VIII. Statutory Provisions and Legal Authority

The statutory authority for today's proposal is provided by sections 114, 231-234 and 

301(a) of the Clean Air Act, as amended, 42 U.S.C. §§ 7414, 7571-7574 and 7601(a). See 

section II of today's rule for discussion of how EPA meets the CAA's statutory requirements.

IX. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review, and Executive 

Order13563: Improving Regulation and Regulatory Review

Under Executive Order (EO) 12866 (58 FR 51735, October 4, 1993), this action is a 

"significant regulatory action.” This action promulgates new aircraft engine emissions 

regulations and as such, requires consultation and coordination with the Federal Aviation 
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Administration (FAA). OMB has determined that this action raises “... novel legal or policy

issues arising out of legal mandates, the President’s priorities, or the principles set forth in the 

EO.” Accordingly, EPA submitted this action to the Office of Management and Budget (OMB) 

for review under EO 12866 and 13563 (76 FR 3821, January 21, 2011) and any changes made in 

response to OMB recommendations have been documented in the docket for this action.

As discussed further in section V, we do not attribute any costs to the compliance with 

today’s regulations that conform to ICAO standards and recommended practices. Aircraft 

turbofan engines are international commodities. As a result, engine manufacturers respond to 

this market reality by designing and building engines that conform to ICAO international 

standards and practices. Therefore, engine manufacturers are compelled to make the necessary

business decisions and investments to maximize their international markets even in the absence 

of U.S. action. Indeed, engine manufacturers have or are already responding, or will in the 

future, to ICAO requirements that match the standards and practices adopted here. Therefore, 

EPA believes that today’s requirements that conform with ICAO standards and practices will 

impose no real additional burden on engine manufacturers. This finding is also consistent with 

past EPA rulemakings that adopted ICAO requirements.

There is, nonetheless, a small burden associated with the reporting requirements, as 

discussed in section IX.B.

B. Paperwork Reduction Act
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The information collection requirements in this rule have been submitted for approval to 

the Office of Management and Budget (OMB) under the Paperwork Reduction Act, 44 U.S.C. 

3501 et seq. The information collection requirements are not enforceable until OMB approves 

them.

Manufacturers keep substantial records to document their compliance with emission 

standards. We need to be able to access this data to conduct accurate emission inventories, 

understand how emission standards affect the current fleet, and develop appropriate policy in the 

form of future emission standards. Most manufacturers are already accustomed to reporting 

much of this information to ICAO. However, these reports are voluntary and aperiodic. As part 

of this action, we are requiring that engine manufacturers send this information to EPA on an 

annual basis. We are also requiring manufacturers to send us their annual production volumes, 

which we would treat as confidential business information. Under the Clean Air Act, we are 

authorized to require manufacturers to establish and maintain necessary records, make reports, 

and provide such other information as we may reasonably require to execute our functions under 

the Act. See 42 U.S.C. 7414(a)(1). We will simply require manufacturers to add the required 

information items to the annual report they are already required to submit with information about 

NOx and CO2 emission levels. See section III.D for a more complete description of the annual 

reporting requirement.
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We have estimated the total annual burden of the reporting requirement to be 60 hours, 

and the total cost to be $3,646. The annual burden and cost per respondent is estimated to be 6 

hours and $365. Burden is defined at 5 CFR 1320.3(b). 

An agency may not conduct or sponsor, and a person is not required to respond to, a 

collection of information unless it displays a currently valid OMB control number. The OMB 

control numbers for EPA's regulations in 40 CFR are listed in 40 CFR part 9. When this ICR is 

approved by OMB, the Agency will publish a technical amendment to 40 CFR part 9 in the 

Federal Register to display the OMB control number for the approved information collection 

requirements contained in this final rule.

C. Regulatory Flexibility Analysis

The Regulatory Flexibility Act (RFA) generally requires an agency to prepare a 

regulatory flexibility analysis of any rule subject to notice and comment rulemaking 

requirements under the Administrative Procedure Act or any other statute unless the agency

certifies that the rule will not have a significant economic impact on a substantial number of 

small entities. Small entities include small businesses, small organizations, and small 

governmental jurisdictions.

For purposes of assessing the impacts of today's rule on small entities, small entity is 

defined as: (1) a small business as defined by SBA size standards; (2) a small governmental 

jurisdiction that is a government of a city, county, town, school district or special district with a 
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population of less than 50,000; and (3) a small organization that is any not-for-profit enterprise 

which is independently owned and operated and is not dominant in its field. The following 

Table 4 provides an overview of the primary SBA small business categories potentially affected 

by this regulation.

Table 4: Primary Potentially Affected SBA Small Business Categories

Industry NAICS

a

Codes

Defined by SBA as a small 

business if:b

Manufacturers of new aircraft engines 336412 < 1,000 employees

Manufacturers of new aircraft 336411 < 1,500 employees

a

North American Industry Classification System (NAICS)

b

According to SBA's regulations (13 CFR part 121), businesses with no more than the listed number of employees 

or dollars in annual receipts are considered “small entities” for purposes of a regulatory flexibility analysis.

After considering the economic impacts of today’s rule on small entities, I certify that 

this action will not have a significant economic impact on a substantial number of small entities. 

Small governmental jurisdictions and small organizations as described above will not be 

impacted. We have determined that the estimated effect of the rule’s reporting requirement is to 

affect one small entity turbofan engine manufacturer with costs less than one percent of 

revenues. This one company represents all of the small businesses affected by the regulations. 

An analysis of the impacts of the proposed rule on small businesses has been prepared and 
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placed in the docket for this rulemaking.128 Since this final rule is largely unchanged from the 

proposal, that analysis remains valid for the final rule.

D. Unfunded Mandates Reform Act

This rule does not contain a Federal mandate that may result in expenditures of $100 

million or more for State, local, and tribal governments, in the aggregate, or the private sector in 

any one year. As discussed in section III, today’s action will establish consistency between U.S. 

and existing international emission standards. The engine manufacturers are already developing 

the technology to meet the existing ICAO standards, and we do not believe it is appropriate to 

attribute the costs of that technology to this action. Thus, this rule is not subject to the 

requirements of sections 202 or 205 of UMRA.

This rule is also not subject to the requirements of section 203 of UMRA because it 

contains no regulatory requirements that might significantly or uniquely affect small 

governments. The provisions of this rule apply to the manufacturers of aircraft and aircraft 

engines, and as such would not affect small governments.

E. Executive Order 13132: Federalism

 

128 “Small Business Impact Memo, Proposed Aircraft Engine Emission Standards – Determination of No 

SISNOSE,” EPA memo from Solveig Irvine to Alexander Cristofaro, November, 2010. 
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This action does not have federalism implications. It will not have substantial direct 

effects on the States, on the relationship between the national government and the States, or on 

the distribution of power and responsibilities among the various levels of government, as 

specified in Executive Order 13132. As discussed earlier, section 233 of the CAA preempts 

states from adopting or enforcing aircraft engine emission standards that are not identical to our 

standards. This rule revises the Code of Federal Regulations to more accurately reflect the 

statutory preemption established by the Clean Air Act. This rule does not impose any new 

preemption of State and local law. Thus, Executive Order 13132 does not apply to this action.

F. Executive Order 13175: Consultation and Coordination with Indian Tribal 

Governments

These rules regulate aircraft manufacturers and aircraft engine manufacturers. We do not 

believe that Tribes own any of these businesses nor are there other implications for Tribes. Thus, 

Executive Order 13175 does not apply to this action.

G. Executive Order 13045: Protection of Children from Environmental Health & Safety 

Risks

This rule is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because

it is not economically significant as defined in EO 12866 and the Agency does not believe the 

environmental health risks or safety risks addressed by this action present a disproportionate risk 

to children. See section II.B.2 for a discussion of the health impacts of NOX emissions.
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H. Executive Order 13211: Actions that Significantly Affect Energy Supply, 

Distribution, or Use

This action is not a “significant energy action” as defined in Executive Order 13211 (66 

FR 28355 (May 22, 2001)), because it is not likely to have a significant adverse effect on the 

supply, distribution, or use of energy. These aircraft engine emissions regulations are not 

expected to result in any changes to aircraft fuel consumption.

I. National Technology Transfer Advancement Act

Section 12(d) of the National Technology Transfer and Advancement Act of 1995 

(“NTTAA”), Public Law No. 104-113 (15 U.S.C. 272 note) directs EPA to use voluntary

consensus standards in its regulatory activities unless to do so would be inconsistent with 

applicable law or otherwise impractical. Voluntary consensus standards are technical standards 

(e.g., materials specifications, test methods, sampling procedures, and business practices) that are 

developed or adopted by voluntary consensus standards bodies. NTTAA directs EPA to provide 

Congress, through OMB, explanations when the Agency decides not to use available and 

applicable voluntary consensus standards.

This rulemaking involves technical standards for testing emissions for aircraft gas turbine

engines. EPA is using test procedures contained in ICAO’s International Standards and 

Recommended Practices Environmental Protection, Annex 16, Volume II along with the 
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modifications contained in this rulemaking.129 These procedures are currently used by all 

manufacturers of aircraft gas turbine engines (with thrust greater than 26.7 kN) to demonstrate 

compliance with ICAO emissions standards.

J. EO 12898: Federal Actions to Address Environmental Justice in Minority

Populations and Low-Income Populations

Executive Order (EO) 12898 (59 FR 7629 (Feb. 16, 1994)) establishes federal executive 

policy on environmental justice. Its main provision directs federal agencies, to the greatest 

extent practicable and permitted by law, to make environmental justice part of their mission by

identifying and addressing, as appropriate, disproportionately high and adverse human health or 

environmental effects of their programs, policies, and activities on minority populations and lowincome populations in the United States. 

EPA has determined that this rule will not have disproportionately high and adverse 

human health or environmental effects on minority or low-income populations because it 

increases the level of environmental protection for all affected populations without having any 

disproportionately high and adverse human health or environmental effects on any population, 

including any minority or low-income population.

 

129ICAO International Standards and Recommended Practices Environmental Protection, Annex 16, 

Volume II, “Aircraft Engine Emissions,” Second Edition, July 1993 -- Amendment 3, March 20, 1997. Copies of 

this document can be obtained from ICAO (www.icao.int).
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K. Congressional Review Act

The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the Small Business 

Regulatory Enforcement Fairness Act of 1996, generally provides that before a rule may take 

effect, the agency promulgating the rule must submit a rule report, which includes a copy of the 

rule, to each House of the Congress and to the Comptroller General of the United States. EPA 

will submit a report containing this rule and other required information to the U.S. Senate, the 

U.S. House of Representatives, and the Comptroller General of the United States prior to 

publication of the rule in the Federal Register. A major rule cannot take effect until 60 days after 

it is published in the Federal Register. This action is not a “major rule” as defined by 5 U.S.C. 

804(2). This rule will be effective [insert date 30 days after publication in the Federal Register].

List of Subjects 

40 CFR Part 87

Environmental protection, Air pollution control, Aircraft, Incorporation by reference.

40 CFR Part 1068

Environmental protection, Administrative practice and procedure, Confidential business 

information, Imports, Incorporation by reference, Motor vehicle pollution, Penalties, Reporting 

and recordkeeping requirements, Warranties.
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 Dated: _______________________________

_______________________________________

Lisa P. Jackson,

Administrator
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PART 87-CONTROL OF AIR POLLUTION FROM AIRCRAFT AND AIRCRAFT 

ENGINES

1. The authority citation for part 87 is revised to read as follows:

Authority: 42 U.S.C. 7401 et seq.

Subpart A-[Amended]

2. Revise §87.1 to read as follows:

§87.1 Definitions.

The definitions in this section apply to this part. The definitions apply to all subparts. 

Any terms not defined in this section have the meaning given in the Clean Air Act. The 

definitions follow:

Act means the Clean Air Act, as amended (42 U.S.C. 7401 et seq).
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Administrator means the Administrator of the Environmental Protection Agency and any

other officer or employee of the Environmental Protection Agency to whom authority involved 

may be delegated.

Aircraft has the meaning given in 14 CFR 1.1, which defines aircraft to mean a device used 

or intended to be used for flight in the air. Note that under §87.3, the requirements of this part 

generally apply only to propulsion engines used on certain airplanes for which U.S. 

airworthiness certificates are required.

Aircraft engine means a propulsion engine which is installed in or which is manufactured for 

installation in an aircraft.

Aircraft gas turbine engine means a turboprop, turbofan, or turbojet aircraft engine.

Characteristic level has the meaning given in Appendix 6 of ICAO Annex 16 (as of July

2008). The characteristic level is a calculated emission level for each pollutant based on a 

statistical assessment of measured emissions from multiple tests. 

Class TP means all aircraft turboprop engines.

Class TF means all turbofan or turbojet aircraft engines or aircraft engines designed for 

applications that otherwise would have been fulfilled by turbojet and turbofan engines except 

engines of class T3, T8, and TSS.
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Class T3 means all aircraft gas turbine engines of the JT3D model family.

Class T8 means all aircraft gas turbine engines of the JT8D model family.

Class TSS means all aircraft gas turbine engines employed for propulsion of aircraft designed 

to operate at supersonic flight speeds.

Commercial aircraft engine means any aircraft engine used or intended for use by an “air 

carrier,” (including those engaged in “intrastate air transportation”) or a “commercial operator” 

(including those engaged in “intrastate air transportation”) as these terms are defined in subtitle 7 

of title 49 of the United States Code and title 14 of the Code of Federal Regulations.

Commercial aircraft gas turbine engine means a turboprop, turbofan, or turbojet commercial 

aircraft engine.

Date of introduction or introduction date means the date of manufacture of the first individual 

production engine of a given engine model or engine type certificate family to be certificated. 

This does not include test engines or other engines not placed into service.

Date of manufacture means the date on which a manufacturer is issued documentation by

FAA (or other competent authority for engines certificated outside the United States) attesting 

that the given engine conforms to all applicable requirements. This date may not be earlier that 

the date on which assembly of the engine is complete. Where the manufacturer does not obtain 
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such documentation from FAA (or other competent authority for engines certificated outside the 

United States), date of manufacture means the date of final assembly of the engine. 

Derivative engine for emissions certification purposes means an engine that has the same or 

similar emissions characteristics as an engine covered by a U.S. type certificate issued under 14 

CFR part 33. These characteristics are specified in §87.48.

 Designated EPA Program Officer means the Director of the Assessment and Standards 

Division, 2000 Traverwood Drive, Ann Arbor, Michigan 48105.

DOT Secretary means the Secretary of the Transportation and any other officer or employee 

of the Department of Transportation to whom the authority involved may be delegated.

Engine means an individual engine. A group of identical engines together make up an engine 

model or sub-model.

Engine model means an engine manufacturer’s designation for an engine grouping of engines 

and/or engine sub-models within a single engine type certificate family, where such engines have

similar design, including being similar with respect to the core engine and combustor designs. 

Engine sub-model means a designation for a grouping of engines with essentially identical 

design, especially with respect to the core engine and combustor designs and other emissionrelated features. Engines from an engine sub-model must be contained within a single engine 

model. For purposes of this part, an original engine model configuration is considered a sub-
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model. For example, if a manufacturer initially produces an engine model designated ABC and 

later introduces a new sub-model ABC-1, the engine model consists of two sub-models: ABC 

and ABC-1.

Engine type certificate family means a group of engines (comprising one or more engine 

models, including sub-models and derivative engines for emissions certification purposes of 

those engine models) determined by FAA to have a sufficiently common design to be grouped 

together under a type certificate.

EPA means the U.S. Environmental Protection Agency.

Except means to routinely allow engines to be produced and sold that do not meet (or do not 

fully meet) otherwise applicable standards. (Note that this definition applies only with respect to 

spare engines and that the term “except” has its plain meaning in other contexts.) Excepted 

engines must conform to regulatory conditions specified for an exception in this part and other 

applicable regulations. Excepted engines are deemed to be “subject to” the standards of this part 

even though they are not required to comply with the otherwise applicable requirements. Engines 

excepted with respect to certain standards must comply with other standards from which they are 

not excepted.

Exempt means to allow (through a formal case-by-case process) engines to be produced and 

sold that do not meet (or do not fully meet) otherwise applicable standards. Exempted engines 

must conform to regulatory conditions specified for an exemption in this part and other 
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applicable regulations. Exempted engines are deemed to be “subject to” the standards of this part 

even though they are not required to comply with the otherwise applicable requirements. Engines 

exempted with respect to certain standards must comply with other standards as a condition of 

the exemption. 

Exhaust emissions means substances emitted to the atmosphere from exhaust discharge 

nozzles, as measured by the test procedures specified in subpart G of this part.

FAA means the U.S. Department of Transportation, Federal Aviation Administration.

Fuel venting emissions means raw fuel, exclusive of hydrocarbons in the exhaust emissions, 

discharged from aircraft gas turbine engines during all normal ground and flight operations.

Good engineering judgment involves making decisions consistent with generally accepted 

scientific and engineering principles and all relevant information, subject to the provisions of 40 

CFR 1068.5. 

ICAO Annex 16 means Volume II of Annex 16 to the Convention on International Civil 

Aviation (incorporated by reference in §87.8).

In-use aircraft gas turbine engine means an aircraft gas turbine engine which is in 

service.
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Military aircraft means aircraft owned by, operated by, or produced for sale to the armed 

forces or other agency of the federal government responsible for national security (including but 

not limited to the Department of Defense) and other aircraft considered to be military aircraft 

under international law and conventions.

New means relating to an aircraft or aircraft engine that has never been placed into service. 

Operator means any person or company that owns or operates an aircraft. 

Production cutoff date or date of the production cutoff means the date on which interim 

phase-out allowances end. 

Rated output (rO) means the maximum power/thrust available for takeoff at standard day

conditions as approved for the engine by FAA, including reheat contribution where applicable, 

but excluding any contribution due to water injection, expressed in kilowatts or kilonewtons (as 

applicable) and rounded to at least three significant figures.

Rated pressure ratio (rPR) means the ratio between the combustor inlet pressure and the 

engine inlet pressure achieved by an engine operating at rated output, rounded to at least three 

significant figures.

Round means to round numbers according to NIST SP 811 (March 2008), unless otherwise 

specified.
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Smoke means the matter in exhaust emissions that obscures the transmission of light, as 

measured by the test procedures specified in subpart G of this part.

Smoke number means a dimensionless value quantifying smoke emissions calculated in 

accordance with ICAO Annex 16.

Spare engine means an engine installed (or intended to be installed) on an in-service aircraft 

to replace an existing engine and that is excepted as described in §87.50(c).. 

Standard day conditions means the following ambient conditions: temperature =15 °C, 

specific humidity = 0.00634 kg H2O/kg dry air, and pressure =101.325 kPa.

Subsonic means relating to aircraft that are not supersonic aircraft. 

Supersonic means relating to aircraft that are certificated to fly faster than the speed of sound.

Tier 0 means relating to an engine that is subject to the Tier 0 NOx standards specified in 

§87.21.

Tier 2 means relating to an engine that is subject to the Tier 2 NOx standards specified in 

§87.21.

Tier 4 means relating to an engine that is subject to the Tier 4 NOx standards specified in 

§87.21.
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Tier 6 means relating to an engine that is subject to the Tier 6 NOx standards specified in 

§87.23.

Tier 8 means relating to an engine that is subject to the Tier 8 NOx standards specified in 

§87.23.

Turbofan engine means a gas turbine engine designed to create its propulsion from exhaust 

gases and from air that bypasses the combustion process and is accelerated in a ducted space 

between the inner (core) engine case and the outer engine fan casing.

Turbojet engine means a gas turbine engine that is designed to create all of its propulsion 

from exhaust gases. 

Turboprop engine means a gas turbine engine that is designed to create most of its propulsion 

from a propeller driven by a turbine, usually through a gearbox.

Turboshaft engine means a gas turbine engine that is designed to drive a rotor transmission 

system or a gas turbine engine not used for propulsion.

U.S.-registered aircraft means an aircraft that is on the U.S. Registry.

We (us, our) means the Administrator of the Environmental Protection Agency and any

authorized representatives.
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3. Revise §87.2 to read as follows:

§87.2 Abbreviations.

The abbreviations used in this part have the following meanings:

% percent

° degree

CO carbon monoxide

CO2 carbon dioxide

g gram

HC hydrocarbon(s)

kN kilonewton

kW kilowatt

LTO landing and takeoff

NOx oxides of nitrogen

rO rated output

rPR rated pressure ratio

SN smoke number

4. Revise §87.3 to read as follows:

§87.3 General applicability and requirements.

(a) The regulations of this part apply to engines on all aircraft that are required to be 

certificated by FAA under 14 CFR part 33 except as specified in this paragraph (a). These 

regulations do not apply to the following aircraft engines:

(1) Reciprocating engines (including engines used in ultralight aircraft).
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(2) Turboshaft engines such as those used in helicopters.

(3) Engines used only in aircraft that are not airplanes. For purposes of this paragraph 

(a)(3), “airplane” means a fixed-wing aircraft that is heavier than air. 

(4) Engines not used for propulsion.

(b) Under section 232 of the Act, the Secretary of Transportation issues regulations to 

ensure compliance with the standards and related requirements of this part (42 U.S.C. 7572).

(c) The Secretary of Transportation shall apply these regulations to aircraft of foreign 

registry in a manner consistent with obligations assumed by the United States in any treaty, 

convention or agreement between the United States and any foreign country or foreign countries. 

(d) No State or political subdivision of a State may adopt or attempt to enforce any 

aircraft or aircraft engine standard respecting emissions unless the standard is identical to a 

standard applicable to such aircraft under this part (including prior-tier standards applicable to 

exempt engines). 

§87.5—[Removed]

5. Remove §87.5.
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6. Revise §87.6 to read as follows:

§87.6 Aircraft safety.

The provisions of this part will be revised if at any time the DOT Secretary determines 

that an emission standard cannot be met within the specified time without creating a hazard to 

aircraft safety.

§87.7—[Removed]

7. Remove §87.7.

8. Revise §87.8 to read as follows:

§87.8 Incorporation by reference.

(a) Certain material is incorporated by reference into this part with the approval of the 

Director of the Federal Register under 5 U.S.C. 552(a) and 1 CFR part 51. To enforce any 

edition other than that specified in this section, the Environmental Protection Agency must 

publish notice of change in the Federal Register and the material must be available to the public. 
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All approved material is available for inspection at U.S. EPA, Air and Radiation Docket and 

Information Center, 1301 Constitution Ave., NW., Room B102, EPA West Building, 

Washington, DC 20460, (202) 202-1744, and is available from the sources listed below. It is also 

available for inspection at the National Archives and Records Administration (NARA). For 

information on the availability of this material at NARA, call 202-741-6030 or go 

tohttp://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.

(b) International Civil Aviation Organization, Document Sales Unit, 999 University

Street, Montreal, Quebec, Canada H3C 5H7, (514) 954-8022, www.icao.int, or sales@icao.int. 

(1) Annex 16 to the Convention on International Civil Aviation, Environmental 

Protection, Volume II – Aircraft Engine Emissions, Third Edition, July 2008. [Update for 

CAEP8 changes]; IBR approved for §§87.2, 87.40, 87.42(d) and (f), and 87.60(a) and (b).

(2) [Reserved]

(c) National Institute of Standards and Technology, 100 Bureau Drive, Stop 1070, 

Gaithersburg, MD 20899-1070, (301) 975-6478, www.nist.gov, or inquiries@nist.gov. Anyone 

may also purchase copies of these materials from the Government Printing Office, Washington, 

DC 20402, (202) 512-0916, www.gpo.gov, or prntproc@gpo.gov. 
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(1) NIST Special Publication 811, 1995 Edition, Guide for the Use of the 

International System of Units (SI), Barry N. Taylor, Physics Laboratory; IBR approved for 

§87.2.

(2) [Reserved]
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Subpart C—[Amended]

9. Amend §87.21 as follows:

a. By revising the section heading.

b. By adding introductory text.

c. By revising paragraphs (d)(1)(iii), (d)(1)(iv), (d)(1)(vi) introductory text, (e)(1), and 

(f).

§87.21 Exhaust emission standards for Tier 4 and earlier engines.

This section describes the emission standards that apply for Tier 4 and earlier engines that 

apply for aircraft engines manufactured before [INSERT DATE 30 DAYS AFTER 

PUBLICATION IN THE FEDERAL REGISTER] and certain engines exempted under §87.50. 

Note that the tier of standards identified for an engine relates to NOx emissions and that the 

specified standards for HC, CO, and smoke emissions apply independent of the changes to the 

NOx emission standards. 

(d) * * *

(1) * * *
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(iii) The following Tier 0 emission standard applies for engines of a type or model 

of which the date of manufacture of the first individual production model was on or 

before December 31, 1995 and for which the date of manufacture of the individual engine 

was on or before December 31, 1999.

Oxides of Nitrogen: (40 + 2(rPR)) grams/kilonewton rO.

(iv) The following Tier 2 emission standard applies for engines of a type or model 

of which the date of manufacture of the first individual production model was after 

December 31, 1995 or for which the date of manufacture of the individual engine was 

after December 31, 1999:

Oxides of Nitrogen: (32 + 1.6(rPR)) grams/kilonewton rO.

* * * * *

(vi) The following Tier 4 emission standards apply for engines of a type or model 

of which the date of manufacture of the first individual production model was after 

December 31, 2003:

(e) * * *

(1) Class TF of rated output less than 26.7 kilonewtons manufactured on or after 

August 9, 1985:
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SN=83.6(rO)-0.274 (rO is in kilonewtons) not to exceed a maximum of SN=50.

* * * * *

(f) The standards in this section refer to a composite emission sample measured and 

calculated in accordance with the procedures described in subpart G of this part.

10. Add a new §87.23 to read as follows:

§87.23 Exhaust emission standards for Tier 6 and Tier 8 engines.

This section describes the emission standards that apply for Tier 6 and Tier 8 engines. 

The standards of this section apply for aircraft engines manufactured on or after [INSERT DATE 

30 DAYS AFTER PUBLICATION IN THE FEDERAL REGISTER], except where we specify

that they apply differently by year, or where the engine is exempt from one or more standards of 

this section. Except as specified in paragraph (d) of this section, these standards apply based on 

the date the engine is manufactured. Where a gaseous emission standard is specified by a 

formula, calculate and round the standard to three significant figures or to the nearest 0.1 g/kN 

(for standards at or above 100 g/kN). Where a smoke standard is specified by a formula, 

calculate and round the standard to the nearest 0.1 SN. Engines comply with an applicable 

standard if the testing results show that the engine type certificate family’s characteristic level 

does not exceed the numerical level of that standard, as described in §87.60. The tier of 
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standards identified for an engine relates to NOx emissions and that the specified standards for 

HC, CO, and smoke emissions apply independent of the changes to the NOx emission standards.

(a) New turboprop aircraft engines with rated output at or above 1,000 kilowatts must 

comply with a smoke standard of 187•rO-0.168.

(b) New supersonic engines must comply with the standards shown in the following 

table:

Table 1 to §87.23– Smoke and Gaseous Emission Standards for New Supersonic Engines

Rated

Output

Smoke

Number

HC

(g/kN rated output)

NOx

(g/kN rated output)

CO

(g/kN rated output)

rO < 26.7 kN

—

140•0.92rPR 36+2.42•rPR 4550•rPR-1.03

rO > 26.7 kN 83.6•rO-0.274 or 50.0, 

whichever is smaller 140•0.92rPR 36+2.42•rPR 4550•rPR-1.03

(c) New turbofan or turbojet aircraft engines that are installed in subsonic aircraft must 

comply with the following standards:
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(1) The applicable smoke, HC, and CO standards are shown in the following table:

Table 2 to §87.23 – Smoke, HC, and CO Standards 

for New Subsonic Turbofan or Turbojet Engines

Rated Output 

(kN)

Smoke 

Standard

Gaseous Emission Standards 

(g/kN rated output)

HC CO

rO < 26.7 kN 83.6•rO-0.274 or 50.0, 

whichever is smaller

— —

rO > 26.7 kN 83.6•rO-0.274 or 50.0, 

whichever is smaller

19.6 118

(2) The Tier 6 NOx standards apply as described in this paragraph (c)(2). See 

paragraph (d) of this section for provisions related to models introduced before these 

standards started to apply and engines determined to be derivative engines for emissions 

certification purposes under the requirements of this part.
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Table 3 to §87.23– Tier 6 NOx Standards for New 

Subsonic Turbofan or Turbojet Engines with Rated Output Above 26.7 kN

If the rated pressure 

ratio is...

and the rated output 

(in kN) is...

The NOx emission standard (in g/kN rated output) is....

rPR < 30 26.7 < rO < 89 38.5486 + 1.6823•rPR - 0.2453•rO - 0.00308•rPR•rO 

rO > 89 16.72 + 1.4080•rPR 

30 < rPR < 82.6 26.7 < rO < 89 46.1600 + 1.4286•rPR - 0.5303•rO + 0.00642•rPR•rO 

rO > 89 –1.04 + 2.0•rPR 

rPR > 82.6 all 32 + 1.6•rPR 

(3) The Tier 8 NOx standards apply as described in this paragraph (c)(3) beginning 

January 1, 2014. See paragraph (d) of this section for provisions related to models 
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introduced before January 1, 2014 apply and engines determined to be derivative engines for 

emissions certification purposes under the requirements of this part.

Table 4 to §87.23– Tier 8 NOx Standards for New 

Subsonic Turbofan or Turbojet Engines with Rated Output Above 26.7 kN

If the rated pressure 

ratio is...

and the rated output 

(in kN) is...

The NOx emission standard (in g/kN rated output) is....

rPR < 30 26.7 < rO < 89

40.052 + 1.5681•rPR - 0.3615•rO - 0.0018•rPR•rO

rO > 89

7.88 + 1.4080•rPR

30 < rPR < 104.7 26.7 < rO < 89

41.9435 + 1.505•rPR - 0.5823•rO + 0.005562•rPR•rO

rO > 89

–9.88 + 2.0•rPR

rPR > 104.7 all

32 + 1.6•rPR
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(d) This paragraph specifies phase-in provisions that allow continued production of 

certain engines after the Tier 6 and Tier 8 standards begin to apply.

(1) Engine type certificate families certificated with characteristic levels at or below 

the Tier 4 NOx standards of §87.21 (as applicable based on rated output and rated pressure 

ratio) and introduced before [INSERT DATE 30 DAYS AFTER PUBLICATION IN THE 

FEDERAL REGISTER] may be produced through December 31, 2012 without meeting the 

Tier 6 NOx standards of paragraph (c)(2) of this section. This also applies for engines that 

are covered by the same type certificate and are determined to be derivative engines for 

emissions certification purposes under the requirements of this part. Note that after this 

production cutoff date for the Tier 6 NOx standards, such engines may be produced only if 

they are covered by an exemption under §87.50. This production cutoff does not apply to 

engines installed (or delivered for installation) on military aircraft.

(2) Engine type certificate families certificated with characteristic levels at or below 

the Tier 6 NOx standards of paragraph (c)(2) of this section with an introduction date before 

January 1, 2014 may continue to be produced. This also applies for engines that are covered 

by the same type certificate and are determined to be derivative engines for emissions 

certification purposes under the requirements of this part. 
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(3) An engine manufacturer may produce up to six newly manufactured Tier 4 

engines on or after [INSERT DATE 30 DAYS AFTER PUBLICATION IN THE FEDERAL 

REGISTER], subject to the provisions of this paragraph (d)(3). Tier 4 engines meeting the 

criteria of this paragraph (d)(3) are excepted without request from the otherwise applicable 

Tier 6 NOx emission standard. To be eligible for this exception the engines must have a date 

of manufacture prior to August 31, 2013 and be fully compliant with all requirements 

applicable to Tier 4 engines. The manufacturer must include these engines in the report 

required by §87.50. This exception is void for any manufacturer that produces more than six 

excepted engines under this paragraph.

11. Add a new subpart E containing §§87.40, 87.42, 87.44, 87.46, and 87.48 to part 87 to read as 

follows:

Subpart E —Certification Provisions

Sec.

87.40 General certification requirement.
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87.42 Certification report to EPA.

87.44 Reporting CO2 emissions.

87.46 Recordkeeping.

87.48 Derivative engines for emissions certification purposes.

§87.40 General certification requirement.

Manufacturers of engines subject to this part must meet the requirements of title 14 of the 

Code of Federal Regulations as applicable. 

§87.42 Production report to EPA.

Engine manufacturers must submit an annual production report as specified in this 

section. This requirement applies for engines produced on or after January 1, 2013. 

(a) You must submit the report for each calendar year in which you produce any engines 

subject to emission standards under this part. The report is due by February 28 of the following 

calendar year. Note that §87.64 requires you to report CO2 emission rates to EPA in addition to 

NOx. Include these data in the report required by this section. If you produce exempted or 
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excepted engines, you may submit a single report with information on exempted/excepted and 

normally certificated engines.

(b) Send the report to the Designated EPA Program Officer. 

(c) In the report, specify your corporate name and the year for which you are reporting. 

Include information as described in this section for each engine sub-model subject to emission 

standards under this part. List each engine sub-model produced or certificated during the 

calendar year, including the following information for each sub-model:

(1) The type of engine (turbofan, turboprop, etc.) and complete sub-model name, 

including any applicable model name, sub-model identifier, and engine type certificate 

family identifier.

(2) The certificate under which it was produced. Identify all the following:

(i) The type certificate number. Specify if the sub-model also has a type 

certificate issued by a certificating authority other than FAA.

(ii) Your corporate name as listed in the certificate.

(iii) Emission standards to which the engine is certificated.

(iv) Date of issue of type certificate (month and year).
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(v) Whether or not this is a derivative engine for emissions certification purposes. 

If so, identify the original certificated engine model. 

(vi) The engine sub-model that received the original type certificate for an engine 

type certificate family.

(3) Identify the combustor of the sub-model, where more than one type of combustor 

is available. 

(4) The calendar-year production volume of engines from the sub-model that are 

covered by an FAA type certificate. Record zero for sub-models with no engines produced 

during the calendar year, or state that the engine model is no longer in production and list the 

date of manufacture (month and year) of the last engine produced. Specify the number of 

these engines that are intended for use on new aircraft and the number that are intended for 

use as non-exempt engines on in-use aircraft. For engines delivered without a final submodel status and for which the manufacturer has not ascertained the engine’s sub-model 

when installed before submitting its production report, the manufacturer may do any of the 

following in its initial report, and amend it later:

(i) List the sub-model that was shipped or the most probable sub-model.

(ii) List all potential sub-models.

(iii) State “Unknown Sub-Model”.
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(5) The number of engines tested and the number of test runs for the applicable type 

certificate. 

(6) The applicable test data and related information specified in Part III, Section 2.4 

of ICAO Annex 16 (incorporated by reference in §87.8), except as otherwise allowed by this 

paragraph. For purposes of this paragraph (c)(6), applicable test data means data required to 

certify the engine sub-model, which would typically include NOx, HC, CO and smoke 

number. However, applicable test data would not include NOx, HC, or CO emissions for 

engines subject to only smoke standards. Note that §87.64 also requires you to report CO2

emissions. Specify thrust in kW for turboprop engines. You may omit the following items 

specified in Part III, Section 2.4 of ICAO Annex 16:

(i) Fuel specifications including fuel specification reference and hydrogen/carbon 

ratio.

(ii) Methods used for data acquisition, correcting for ambient conditions, and data 

analysis.

(iii) Intermediate emission indices and rates, however you may not omit the final 

characteristic level for each regulated pollutant in units of g/kN or g/kW.

(d) Clearly show what information you consider confidential by marking, circling, 

bracketing, stamping, or some other method. We will store your confidential information as 
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described in 40 CFR part 2. Also, we will disclose it only as specified in 40 CFR part 2. If you 

send us information without claiming it is confidential, we may make it available to the public 

without further notice to you, as described in 40 CFR 2.204.

(e) Include the following signed statement and endorsement by an authorized 

representative of your company: “We submit this report under 40 CFR 87.42. All the 

information in this report is true and accurate to the best of my knowledge.”

(f) Where information provided for the previous year remains valid and complete, you 

may report your production volumes and state that there are no changes, without resubmitting the 

other information specified in this section.

§87.46 Recordkeeping.

(a) You must keep a copy of any reports or other information you submit to us for at least 

three years.

(b) Store these records in any format and on any media, as long as you can promptly send 

us organized, written records in English if we ask for them. You must keep these records readily

available. We may review them at any time. 
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§87.48 Derivative engines for emissions certification purposes.

(a) General. A type certificate holder may request from the FAA a determination that an 

engine configuration is considered a derivative engine for emissions certification purposes. This 

would mean that the engine configuration is determined to be similar in design to a previously

certificated engine(the “original” engine) for purposes of compliance with exhaust emission 

standards (gaseous and smoke). In order for the engine configuration to be considered a 

derivative engine for emission purposes under this part, it must have been derived from an 

original engine that was certificated to the requirements of 14 CFR part 33, and one of the 

following conditions must be met:

(1) The FAA determined that a safety issue exists that requires an engine 

modification.

(2) Emissions from the derivative engines are determined to be similar. In general, 

this means the emissions must meet the criteria specified in paragraph (b) of this section. 

FAA may adjust these criteria in unusual circumstances, consistent with good engineering 

judgment.

(3) All of the regulated emissions from the derivative engine are lower than the 

original engine.
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(b) Emissions similarity. (1) The type certificate holder must demonstrate that the 

proposed derivative engine model’s emissions meet the applicable standards and differ from the 

original model’s emission rates 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. 

(2) If the characteristic level of the original certificated engine model (or any other 

sub-models within the emission type certificate family tested for certification) before 

modification is at or above 95% of the applicable standard for any pollutant, you must 

measure the proposed derivative engine model’s emissions for all pollutants to demonstrate 

that the derivative engine’s resulting characteristic levels will not exceed the applicable 

emission standards. If the characteristic levels of the originally certificated engine model 

(and all other sub-models within the emission type certificate family tested for certification)

are below 95% of the applicable standard for each pollutant, then, you may use engineering 

analysis to demonstrate that the derivative engine will not exceed the applicable emission 

standards, consistent with good engineering judgment. The engineering analysis must 
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address all modifications from the original engine, including those approved for previous 

derivative engines.

(c) Continued production allowance. Where we allow continued production of an engine 

model after new standards begin to apply, you may also produce engine derivatives if they 

conform to the specifications of this section.

(d) Non-derivative engines. If the FAA determines that an engine model does not meet 

the requirements for a derivative engine for emissions certification purposes, the type certificate 

holder is required to demonstrate that the engine complies with the emissions standards 

applicable to a new engine type.

12. Add a new subpart F containing §87.50 to part 87 to read as follows:

Subpart F —Exemptions and exceptions

§87.50 Exemptions and exceptions.
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This section specifies provisions related to exempting/excepting engines from some or all 

of the standards and requirements of this part 87. Exempted/excepted engines must conform to 

regulatory conditions specified for an exemption in this section and other applicable regulations. 

Exempted/excepted engines are deemed to be “subject to” the standards of this part even though 

they are not required to comply with the otherwise applicable requirements. Engines 

exempted/excepted with respect to certain standards must comply with other standards. 

Exemption requests under paragraph (a) of this section must be approved by the FAA, with the 

written concurrence of EPA, to be effective. Exemption requests under paragraph (b) of this 

section must be approved only by the FAA to be effective. Exceptions do not require a case-bycase FAA approval. 

(a) Engines installed in new aircraft. Type certificate holders may request an exemption 

to produce a limited number of newly manufactured engines through December 31, 2016, to be 

installed in new aircraft as specified in this paragraph (a). This exemption is limited to NOx 

emissions from engines that are covered by a valid type certificate issued by FAA. 

(1) Submit your request for an exemption to the FAA before producing the engines to 

be exempted, who will provide a copy to the Designated EPA Program Officer. Exemption 

by an authority outside the United States does not satisfy this requirement. Unless EPA and 

FAA allow otherwise, all requests must include the following:

(i) Your corporate name and an authorized representative’s contact information.
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(ii) A description of the engines for which you are requesting the exemption

including the type certificate number and date it was issued by the FAA. Include in your 

description the engine model and sub-model names and the types of aircraft in which the 

engines are expected to be installed. Specify the number of engines that you would 

produce under the exemption and the period during which you would produce them. 

(iii) Information about the aircraft in which the engines will be installed. Specify

the airframe models and expected first purchasers/users of the aircraft. Identify all 

countries in which you expect the aircraft to be registered. Specify how many aircraft 

will be registered in the United States and how many will be registered in other countries; 

you may estimate this if it is not known. 

(iv) A justification of why the exemption is appropriate. Justifications must 

include a description of the environmental impact of granting the exemption. Include 

other relevant information such as the following. 

(A) Technical issues, from an environmental and airworthiness perspective, 

which may have caused a delay in compliance with a production cutoff.

(B) Economic impacts on the manufacturer, operator(s), and aviation 

industry at large.
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(C) Environmental effects. This should consider the amount of additional air 

pollutant emissions that will result from the exemption. This could include 

consideration of items such as:

(1) The amount that the engine model exceeds the standard, taking into 

account any other engine models in the engine type certificate family covered 

by the same type certificate and their relation to the standard.

(2) The amount of the applicable air pollutant that would be emitted by

an alternative engine for the same application.

(3) The impact of changes to reduce the applicable air pollutant on other 

environmental factors, including emission rates of other air pollutants, 

community noise, and fuel consumption.

(4) The degree to which the adverse impact would be offset by cleaner 

engines produced in the same time period (unless we decide to consider earlier 

engines).

(D) Impact of unforeseen circumstances and hardship due to business 

circumstances beyond your control (such as an employee strike, supplier disruption, 

or calamitous events).
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(E) Projected future production volumes and plans for producing a compliant 

version of the engine model in question.

(F) Equity issues in administering the production cutoff among economically

competing parties.

(G) List of other certificating authorities from which you have requested (or 

expect to request) exemptions, and a summary of the request.

(H) Any other relevant factors.

(v) A statement signed by your authorized representative attesting that all 

information included in the request is accurate.

(2) In consultation with the EPA, the FAA may specify additional conditions for the 

exemption. 

(3) You must submit the annual report specified in paragraph (d) of this section. 

(4) The permanent record for each engine exempted under this paragraph (a) must 

indicate that the engine is an exempted new engine.

(5) Engines exempted under this paragraph (a) must be labeled with the following 

statement: “EXEMPT NEW”.
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(6) You must notify the FAA if you determine after submitting your request that the 

information is not accurate, either from an error or from changing circumstances. If you 

believe the new or changed information could have affected approval of your exemption

(including information that could have affected the number of engines we exempt), you must 

notify the FAA promptly. The FAA will consult with EPA as needed to address any 

concerns related to this new or corrected information.

(b) Temporary exemptions based on flights for short durations at infrequent intervals.

The emission standards of this part do not apply to engines which power aircraft operated in the 

United States for short durations at infrequent intervals. Such operations are limited to:

(1) Flights of an aircraft for the purpose of export to a foreign country, including 

any flights essential to demonstrate the integrity of an aircraft prior to its flight to a point 

outside the United States.

(2) Flights to a base where repairs, alterations or maintenance are to be 

performed, or to a point of storage, and flights for the purpose of returning an aircraft to 

service.

(3) Official visits by representatives of foreign governments.

(4) Other flights the Secretary determines to be for short durations at infrequent 

intervals. A request for such a determination shall be made before the flight takes place. 
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(c) Spare engines. Newly manufactured engines meeting the definition of “spare engine” 

are excepted as follows: 

(1) This exception allows production of a newly manufactured engine for installation 

on an in-service aircraft. It does not allow for installation of a spare engine on a new aircraft.

(2) Each spare engine must be identical to a sub-model previously certificated to meet 

all requirements applicable to Tier 4 engines or later requirements.

(3) Spare engines excepted under this paragraph (c) may be used only where the 

emissions of the spare engines are certificated to equal to or lower emission standards than 

those of the engines they are replacing, for all regulated pollutants.

(4) No prior approval is required to produce spare engines. Engine manufacturers 

must include information about their production of spare engines in the annual report 

specified in paragraph (d) of this section

(5) The permanent record for each engine excepted under this paragraph (c) must 

indicate that the engine was produced as an excepted spare engine.

(6) Engines excepted under this paragraph (c) must be labeled with the following 

statement: “EXCEPTED SPARE”.
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(d) Annual reports. If you produce engines with an exemption/exception under this 

section, you must submit an annual report with respect to such engines.

(1) You must send the Designated EPA Program Officer a report describing your 

production of exempted/excepted engines for each calendar year in which you produce such 

engines by February 28 of the following calendar year. You may include this information in 

the certification report described in §87.42. Confirm that the information in your initial 

request is still accurate, or describe any relevant changes.

(2) Provide the information specified in this paragraph (d)(2). For purposes of this 

paragraph (d), treat spare engine exceptions separate from other new engine exemptions. 

Include the following for each exemption/exception and each engine model and sub-model: 

(i) Engine model and sub-model names.

(ii) Serial number of each engine.

(iii) Use of each engine (for example, spare or new installation).

(iv) Types of aircraft in which the engines were installed (or are intended to be 

installed for spare engines).

(v) Serial number of the new aircraft in which engines are installed (if known) , or 

the name of the air carriers (or other operators) using spare engines.
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(3) Include information in the report only for engines having a date of manufacture 

within the specific calendar year.

Subpart G—Test Procedures 

13. The heading for subpart G is revised as set forth above.

14. Revise §87.60 to read as follows:

§87.60 Testing engines.

(a) Use the equipment and procedures specified in Appendix 3, Appendix 5, and 

Appendix 6 of ICAO Annex 16 (incorporated by reference in §87.8), as applicable, to 

demonstrate whether engines meet the gaseous emission standards specified in subpart C of this 

part. Measure the emissions of all regulated gaseous pollutants. Similarly, use the equipment 

and procedures specified in Appendix 2 and Appendix 6 of ICAO Annex 16 to determine 

whether engines meet the smoke standard specified in subpart C of this part. The compliance 

demonstration consists of establishing a mean value from testing some number of engines, then 

calculating a “characteristic level” by applying a set of statistical factors that take into account 

the number of engines tested. Round each characteristic level to the same number of decimal 
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places as the corresponding emission standard. For turboprop engines, use the procedures 

specified for turbofan engines, consistent with good engineering judgment.

(b) Use a test fuel meeting the specifications described in Appendix 4 of ICAO Annex 16 

(incorporated by reference in §87.8). The test fuel must not have additives whose purpose is to 

suppress smoke, such as organometallic compounds.

(c) Prepare test engines by including accessories that are available with production 

engines if they can reasonably be expected to influence emissions. The test engine may not 

extract shaft power or bleed service air to provide power to auxiliary gearbox-mounted 

components required to drive aircraft systems.

(d) Test engines must reach a steady operating temperature before the start of emission 

measurements.

(e) In consultation with the EPA, the FAA may approve alternate procedures for 

measuring emissions as specified in this paragraph (e). This might include testing and sampling 

methods, analytical techniques, and equipment specifications that differ from those specified in 

this part. Manufacturers and operators may request this approval by sending a written request 

with supporting justification to the FAA and to the Designated EPA Program Officer. Such a 

request may be approved only if one of the following conditions is met:

(1) The engine cannot be tested using the specified procedures. 
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(2) The alternate procedure is shown to be equivalent to or better (e.g., more accurate 

or precise) than the specified procedure.
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(f) The following landing and take-off (LTO) cycles apply for emission testing and 

calculating weighted LTO values:

Table 1 to §87.60 – LTO Test Cycles

Mode Turboprop Subsonic Turbofan Supersonic Turbofan

Percent of 

Rated Output

Time in 

Mode 

(minutes) Perc

ent of Rated 

Output

Time in 

Mode 

(minutes)

Percent of 

Rated Output

Time in 

Mode 

(minutes)

Take-off 100 0.5 100 0.7 100 1.2

Climb 90 2.5 85 2.2 65 2.0

Descent — — — — 15 1.2

Approach 30 4.5 30 4.0 34 2.3

Taxi/ground idle 7 26.0 7 26.0 5.8 26.0
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(g) Engines comply with an applicable standard if the testing results show that the engine 

type certificate family’s characteristic level does not exceed the numerical level of that standard, 

as described in §87.60.

§§87.61-87.63—[Removed]

15. Remove §§87.61-87.63.

§87.64—[Revised]

16. Remove and reserve paragraph (a). 

§§87.65-87.71—[Removed]

17. Remove §§87.65-87.71.

Subpart H—[Removed]
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18. Remove subpart H.

PART 1068--GENERAL COMPLIANCE PROVISIONS FOR ENGINE 

PROGRAMS

19. The authority citation for part 1068 continues to read as follows:

Authority: 42 U.S.C. 7401-7671q.

Subpart A—[Amended]

20. Amend §1068.1 by revising paragraph (b) to read as follows:

§1068.1 Does this part apply to me? 

* * * * *

(b) This part does not apply to any of the following engine or vehicle categories:

(1) Light-duty motor vehicles (see 40 CFR part 86).
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(2) Heavy-duty motor vehicles and motor vehicle engines, except as specified in 40 

CFR part 86.

(3) Aircraft engines, except as specified in 40 CFR part 87.

(4) Land-based nonroad compression-ignition engines we regulate under 40 CFR part 

89.

(5) Small nonroad spark-ignition engines we regulate under 40 CFR part 90.

(6) Marine spark-ignition engines we regulate under 40 CFR part 91.

(7) Locomotive engines we regulate under 40 CFR part 92.

(8) Marine compression-ignition engines we regulate under 40 CFR parts 89 or 94.

* * * * *