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EO12866_Aircraft Engine Emission Standards 2060-AO70 NPRM Rulemaking 

Document_2011/03/25

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; Proposed Emission 

Standards and Test Procedures

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

SUMMARY: This action proposes several new NOx emission standards, compliance 

flexibilities, and other regulatory requirements for aircraft turbofan or turbojet engines 

with rated thrusts greater than 26.7 kilonewtons (kN). We also are proposing certain 

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

First, we are proposing to clarify 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 

proposing a new reporting requirement for manufacturers of gas turbine engines that are 
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subject to any exhaust emission standard to provide us with timely and consistent 

emission-related information. Third, and finally, we are proposing 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 proposed requirements were first developed. These proposed 

regulatory requirements have largely either been adopted or are actively under 

consideration by ICAO. Therefore, adopting the proposed requirements would bring the 

United States into alignment with international standards and recommended practices. 

DATES: Comments must be received on or before [insert date 60 days after 

publication in the Federal Register.] 

Hearing: The public hearing will be held [insert date no fewer than 15 days 

after publication and at least 30 days before end of comment period] at the 

Environmental Protection Agency, XXX Building, Room Number XXX, 1201 

Constitution Avenue, NW, Washington, DC 20004, Telephone: (202) 564-1682. See 

section VIII for more information about public hearings. 

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OAR2010-0687, by one of the following methods:

www.regulations.gov: Follow the on-line instructions for submitting comments.

 Email: A-and-R-Docket@epamail.epa.gov.
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 Fax: 202-566-9744

Mail: EPA Docket center, EPA West (Air Docket), Attention Docket ID No. 

EPA-HQ-OAR-2010-0687, Mailcode: Mail Code 2822T, 1200 Pennsylvania Ave., NW, 

Washington, DC 20460. Please include a total of two copies. In addition, please mail a 

copy of your comments to the contact person identified below (see FOR FURTHER 

INFORMATION CONTACT). Please mail a copy of your comments on the information 

collection provisions to the Office of Information and Regulatory Affairs, Office of 

Management and Budget (OMB), Attn: Desk Officer for EPA, 725 17th Street, NW, 

Washington, DC 20503.

Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-2010-

0687. EPA's policy is that all comments received will be included in the public docket 

without change and may be made available online at www.regulations.gov, including any

personal information provided, unless the comment includes information claimed to be 

Confidential Business Information (CBI) or other information whose disclosure is 

restricted by statute. Do not submit information that you consider to be CBI or otherwise 

protected through www.regulations.gov or e-mail. The www.regulations.gov website is

an “anonymous access” system, which means EPA will not know your identity or contact

information unless you provide it in the body of your comment. If you send an e-mail 

comment directly to EPA without going through www.regulations.gov your e-mail 

address will be automatically captured and included as part of the comment that is placed 
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in the public docket and made available on the Internet. If you submit an electronic 

comment, EPA recommends that you include your name and other contact information in 

the body of your comment and with any disk or CD-ROM you submit. If EPA cannot 

read your comment due to technical difficulties and cannot contact you for clarification, 

EPA may not be able to consider your comment. Electronic files should avoid the use of 

special characters, any form of encryption, and be free of any defects or viruses. 

Docket: All documents in the docket are listed in the www.regulations.gov index. 

Although listed in the index, some information is not publicly available, e.g., CBI or 

other information whose disclosure is restricted by statute. Certain other material, such 

as copyrighted material, will be publicly available only in hard copy. Publicly available 

docket materials are available either electronically in www.regulations.gov or in hard 

copy at 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 EPA Docket Center

is 202-566-1742

FOR FURTHER INFORMATION CONTACT: Bryan Manning, Office of 

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

Agency, 2000 Traverwood Drive, Ann Arbor, MI 48130; telephone number: (734) 214-

4832; fax number: (734) 214-4816; email address: manning.bryan@epa.gov. 
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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 CodesbExamples 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

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. Summary of the Proposal

B. EPA’s Responsibilities Under the Clean Air Act
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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. NOx Inventory Contribution

1. Landing and Takeoff (LTO) Emissions

2. Non-LTO Emissions

B. Health, Environmental and Air Quality Impacts

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 Proposed 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. Exemptions from the Tier 6 Production Cutoff

a. New Provisions for Spare Engines

b. New Provisions for Engines Installed in New Aircraft

i. Time-Frame and Scope

ii. Production Limit

iii. Exemption Requests

iv. Foreign Aircraft

c. Voluntary Emission Offsets

3. Potential Phase-In of New Tier 8 NOx Standards for NewlyManufactured Engines
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C. Application of Standards for Derivative Engines

D. Annual Reporting Requirement

E. Proposed 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

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 

B. Paperwork Reduction Act

C. Regulatory Flexibility Analysis

D. Unfunded Mandates Reform Act
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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

I. Overview and Background

This section summarizes the major provisions of the proposed rule for aircraft gas 

turbine engines. It also contains background on the EPA’s standard setting authority and 

responsibilities 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. Summary of the Proposal
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We are proposing 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 proposing two new tiers of more stringent emission 

standards for oxides of nitrogen (NOx). The proposed standards would apply differently 

to two classes of these engines, i.e., “newly-certified engines” and “newly-manufactured 

engines.” The newly-certified engine standards would 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 newly-manufactured engines 

would apply to aircraft engines that were previously certified and manufactured in 

compliance with preexisting standards, and would require manufacturers to either comply 

with the newer standards by a specified future date or cease production. Newlymanufactured engine standards are also sometimes referred to as “production cutoff”

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

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

not be able to comply with the first tier of the proposed NOx standards because of 

specific technical or economic reasons. 

 

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

convenience. 
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We are also proposing a number of additional changes that would apply to a wider 

range of aircraft gas turbine engines2than those that would be subject to the proposed 

new emission standards. First, we are proposing to clarify that when the emission 

characteristics of a new turbofan engine model have become different enough from its 

existing parent engine design, i.e., a derivative of an originally certified engine type, it 

must receive a new emissions approval showing conformance with the most current 

emission standards. Second, we are proposing new reporting requirements for 

manufacturers that produce gas turbine engines subject to any exhaust emission standard. 

This would provide us with timely and consistent emission data and other information 

that is necessary to conduct emission analyses and develop appropriate public policy for 

the aviation sector. Specifically, reports would be required for turbofan 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. Third, we are proposing amendments 

to the test and measurement procedures for aircraft engines. Finally, as described in 

section IV, we are proposing minor amendments to provisions addressing definitions, 

 

2 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). 
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acronyms and abbreviations, general applicability and requirements, exemptions, and 

incorporation by reference. 

Most of these proposed regulatory requirements have already been adopted or are 

actively under consideration by the United Nation’s International Civil Aviation 

Organization (ICAO). The proposed requirements would 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 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 
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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 insure 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 proposal further discusses our coordination with DOT through the 

FAA.

3

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

emission standards established by EPA.

C. Interaction with the International Community

 

3The 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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We began regulating the emissions from aircraft engines in 1973. Since that time, 

we have worked with the FAA and 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.”4 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 190 participating member States of ICAO. 5,6 

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. 

 

4

International Civil Aviation Organization (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.

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

are used interchangeably throughout this preamble.

6 There are currently 190 Contracting States according to ICAO website located at www.icao.int.
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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.7 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. 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 ICAO 

standards. 8,9 However, if a nation sets tighter standards than ICAO, air carriers not 

based in that nation (foreign-flagged carriers) would only be required to comply with 

ICAO standards or more stringent standards imposed by their own nations, if applicable.

ICAO Council’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 

 

7 Article 33 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.

8

ICAO, “Convention on International Civil Aviation,” Articles 87 and 88, Ninth Edition, Document 

7300/9, 2006. Copies of this document can be obtained from the ICAO website located at www.icao.int.

9

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

Copies of this document can be obtained from the ICAO website located at www.icao.int.. 
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Council that address the environmental impact of international civil aviation. CAEP is 

composed of various study groups, work groups, committees and other contributing 

memberships that include atmospheric, economic, aviation, environmental, and other 

professionals. At CAEP meetings, the United States is represented by the FAA, which 

plays an active role at these meetings. 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 for a new environmental standard, it 

then becomes part of ICAO standards and recommended practices (Annex 16 to the 

Chicago Convention).10

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 1973.11 Since that time, we have occasionally

revised those regulations. Two of these revisions are most pertinent to today’s proposal. 

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 

 

10 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.

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

1973.
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rated thrusts greater than 26.7kN.

12

 These ICAO requirements are generally referred to 

as CAEP/2 standards. (The numbering nomenclature for CAEP requirements is 

discussed in the next section.) This included new NOx emission standards for newlymanufactured commercial turbofan engines (those engines built after the effective date of 

the regulations that were already certified to pre-existing standards) 13 and for newlycertified 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.

14

 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 

 

12 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 at 25358. As 

explained later in today’s notice, we are proposing to expand the scope of that finding and of our standards 

to include such emissions from both commercial and non-commercial aircraft engines, in order to bring our 

standards into full alignment with ICAO’s.

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

existing in-use engines.

14 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.
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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.

15

 These standards limited aircraft 

engine emissions of 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.16 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 newly-manufactured engines unlike the CAEP/2 standards). In 2004, CAEP/6 

 

15 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.

16 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.
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recommended a 12 percent NOx reduction, which ICAO approved in 2005.

17 ,18 The 

CAEP/6 standards applied to newly-certified engine models beginning 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.19,20 The Committee also 

recommended that the CAEP/6 standards be applied to newly-manufactured engines. 

ICAO is currently considering the CAEP/8 recommendations. We expect final ICAO 

action regarding the CAEP/8 recommendations in 2011.

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 

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). 

 

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

18 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.

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

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

February 2010,” CAEP/8-WP/80, Agenda Item 2: Review of Technical Proposals Relating to Aircraft 

Emissions, April 2, 2010. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.
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One of the principal components of aircraft exhaust emissions is NOx. NOx is a 

precursor to the formation of ozone.21 Many commercial airports are located in urban 

areas and many of these areas have ambient pollutant levels above the National Ambient 

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

are in nonattainment for ozone and PM 2.5). 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 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 

 

21Ground-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.
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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.

The aircraft engine NOx emission inventories for the LTO and non-LTO flight 

regimes described above are discussed separately in the following sections.

1. Landing and Takeoff Emissions

In this section, we will discuss NOX emission inventories for commercial turbineengine aircraft, both nationally and for selected ozone nonattainment areas (NAAs). 

These inventories reflect emissions during the land 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).22 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 operations 

 

22

 “Historical Assessment of Aircraft Emissions (1986-2008),” Eastern Research Group, March XX, 2001. 

A copy of this document can be found in public docket EPA-HQ-OAR-2010-0687.
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contributed about 97 thousand tons to the national NOX inventory. A summary of the 

national inventory is shown in Table 1.

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

This historical analysis also included an assessment of selected ozone 

nonattainment areas (NAAs). The top 25 ozone NAAs were identified based first in 

terms of NAAs with airports which had high commercial traffic volumes and then those 

with the largest population. There was some overlap, and this led to a total of 41 NAAs 

for the study. These 41 NAAs collectively include 200 airports, accounting for about 70 

percent of commercial air traffic operations. Current (2008) NOX emissions for these 41 

NAAs are shown in Table 2. The relative contribution of aircraft in any given NAA 

would vary based on activity in other transportation and industrial sectors.
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Table 2: Current NOX Emissions in Selected Ozone Nonattainment Areas

Nonattainment Area 2008 Total NOX (tons)

Albuquerque, NM 382

Anchorage, AK 2562

Aspen 19

Atlanta, GA 5834

Baltimore, MD 1159

Boston-Lawrence-Worcester (eastern MA), MA 1907

Boston-Manchester-Portsmouth (southeast NH), NH 224

Charlotte-Gastonia-Rock Hill, NC-SC 2039

Chicago-Gary-Lake County, IL-IN 6024

Cincinnati-Hamilton, OH-KY-IN 1289

Cleveland-Akron-Lorain, OH 712

Dallas-Fort Worth, TX 3900

Denver-Boulder-Greeley-Fort Collins-Loveland, CO 2685

Detroit-Ann Arbor, MI 2328

El Paso, TX 224

Greater Connecticut, CT 413

Houston-Galveston-Brazoria, TX 3062

Indianapolis, IN 1093

Las Vegas, NV 2314

Los Angeles South Coast Air Basin, CA 6532

Louisville, KY-IN 1211

Memphis, TN-AR 2996

Milwaukee-Racine, WI 558

Minneapolis-St Paul, MN 2170

New York-N. New Jersey-Long Island, NY-NJ-CT 10319

Philadelphia-Wilmington-Atlantic City, PA-NY-MD-DE 2432

Phoenix-Mesa, AZ 2307

Pittsburgh-Beaver Valley, PA 508

Providence (entire State), RI 240

Raleigh-Durham-Chapel Hill, NC 593

Reno, NV 249

Riverside County (Coachella Valley), CA 75

Sacramento Metro, CA 608

Salt Lake City, UT 1250

San Diego, CA 1046

San Francisco Bay Area, CA 4447

San Joaquin Valley, CA 86

Seattle-Tacoma, WA 2242

St. Louis, MO-IL 813

Syracuse, NY 152

Washington, DC-MD-VA 3028

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

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

local NOX inventories and on ozone and PM levels will also increase.
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Table 3: Current and Projected Commercial Aircraft Operations

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

2. Non-LTO Emissions

Historically, emphasis has been placed on evaluating emissions during LTO 

operations given their obvious impact on local air quality. Less emphasis has been 

placed on evaluating emissions from non-LTO operations (emissions at altitudes greater 

than 3,000 feet above ground level) based on the assumption that such emissions have a 

lesser impact on local air quality. However, modeling by Barrett et al. (2010) finds that 

these upper atmosphere emissions may adversely affect public health more than was 

previously thought.23 Based on the data and methodology of the authors, this effect is 

caused primarily by two pathways:

 

23 Barrett, S. R. H., R. E. Britter and I. A. Waitz, 2010. Global mortality attributable to aircraft cruise 

emissions. Environmental Science & Technology 44 (19), pp. 7736-7742. DOI: 10.1021/es101325r.
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1. The formation of fine particulate matter, i.e., PM2.5, from emission of gaseous 

precursors of PM (NOx and SO2) in the upper atmosphere that are then 

transported to the lower atmosphere. (The formation of secondary PM2.5 from 

NOx is discussed further in section II.B.1.b). 

2. Aviation NOx emissions promote ozone formation throughout the troposphere and 

hence increase OH concentrations. This increases the oxidation of non-aviation 

SO2 (such as that emitted from power stations) in the gas phase relative to 

aqueous oxidation and dry deposition thereby increasing atmospheric sulfate (a 

type of PM2.5) concentrations.

The authors of this work estimated that full flight emissions cause almost 10,000 

premature mortalities (their central estimate) per year worldwide, with over 450 per year 

in the U.S. The pollutants emitted during cruise operations were estimated to be about 80 

percent of the population-weighed PM2.5 from aviation, with the remainder being 

associated with LTO operations (although they note the LTO portion may be underestimated). The study asserts that over 380 premature mortalities per year in the U.S. can 

be attributed to secondary PM2.5 associated with non-LTO operations. We request 

comments on the results of these studies, the existence of other research into this area, 

and the implications of these analyses on assessing the need for additional controls on 

aircraft engine emissions in the future.
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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 proposing to 

align will help reduce ambient ozone and secondary PM levels and thus will help areas 

with airports achieve and/or maintain compliance with the National Ambient Air Quality

Standards (NAAQS).24 

1. Background on Ozone, PM and NOX

 

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

of the proposed NOx emission standards on the formation 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 by the reaction of 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.25 

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 can be transported hundreds of miles downwind from the 

sources of precursor emissions, resulting in elevated ozone levels even in areas with low 

local VOC or NOX emissions.

 

25 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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b. What is Particulate Matter?

The discussion focuses on 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 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). Current NAAQS use PM2.5 as the indicator for fine particles (with PM2.5

referring to particles with a nominal mean aerodynamic diameter less than or equal to 2.5 

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 aerodynamic 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 
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Page 29 of 165

different pollutants 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?

Nitrogen dioxide (NO2) is a member of the NOX family of gases. Most NO2 is 

formed in the air through the oxidation of nitric oxide (NO) emitted when fuel is burned 

at a high temperature. NO2 can dissolve in water vapor and further oxidize to form nitric 

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

PM. NOX along with non-methane hydrocarbon (NMHC) 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?
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Page 30 of 165

The health and welfare effects of ozone are well documented and are assessed in 

EPA’s 2006 Air Quality Criteria Document (ozone AQCD) and 2007 Staff Paper.26, 27

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. 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 recent report on the 

 

26 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.

27 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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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.28 

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.

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 

 

28 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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Assessment for Particulate Matter (ISA).

29

 The ISA summarizes evidence associated 

with PM2.5, PM10-2.5, and ultrafine particles (UFPs), and concludes the following.

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 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 (COPD) and respiratory

infections.

30

 The ISA notes that long-term exposure to PM2.5 (months to years) is 

associated with the development/progression of cardiovascular disease, premature 

mortality, and respiratory effects, including reduced lung function growth, increased 

respiratory symptoms, and asthma development.31 The ISA concludes that the currently

available scientific evidence from epidemiologic, controlled human exposure, and 

toxicological studies supports a causal association between short- and long-term 

exposures to PM2.5 and cardiovascular effects and mortality. Furthermore, the ISA 

 

29 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 

30 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.

31 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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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 and cancer, mutagenicity, and genotoxicity and long-term 

exposure to PM2.5.

32

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

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

hospitalization for ischemic heart disease. There is also suggestive evidence of a causal 

relationship between short-term PM10-2.5 exposure and mortality and respiratory effects. 

Data are inadequate to draw conclusions regarding the health effects associated with 

long-term exposure to PM10-2.5. 

For UFPs, the ISA further 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 UFPs and respiratory effects. 

Data are inadequate to draw conclusions regarding the health effects associated with 

long-term exposure to UFP’s.

 

32 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.33 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. In addition, small but significant increases in non-specific airway hyperresponsiveness were reported following 1-hour exposures of asthmatics to 0.1 ppm NO2. 

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. Enhanced airway responsiveness could have important clinical 

 

33 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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Page 35 of 165

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 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 U.S. The sensitivity of terrestrial and aquatic ecosystems to 

acidification from nitrogen deposition is predominantly governed by geology. Prolonged 
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Page 36 of 165

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 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 and damage to forest 

productivity. Across the U.S. there are many terrestrial and aquatic ecosystems that have 

been identified as particularly sensitive to nitrogen deposition. The most extreme effects 

resulting from nitrogen deposition on aquatic ecosystems are due to nitrogen enrichment 
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Page 37 of 165

which contributes to “hypoxic” zones devoid of life. Three hypoxia zones of special 

concern in the U.S. are the zones located in the Gulf of Mexico, the Chesapeake Bay in 

the mid-Atlantic region, and Long Island Sound, in the northeast U.S.34

The deposition of airborne particles can reduce the aesthetic appeal of buildings 

and culturally important articles through soiling, and can contribute directly (or in 

conjunction with other pollutants) to structural damage by means of corrosion or 

erosion.35 Particles 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

 

34 U.S. EPA. (2008). Nitrogen Dioxide/Sulfur Dioxide Secondary NAAQS Review: Integrated Science 

Assessment (ISA). Washington, DC: U.S. Environmental Protection Agency. Retrieved on March 18, 2009 

from http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=180903.

35 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
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Page 38 of 165

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

formation of secondary PM2.5.

36

 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 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.37

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 

 

36 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.

37 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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Page 39 of 165

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 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 proposing would impact ambient 

concentrations of air pollutants. Nationally, levels of PM2.5, ozone, and NOX are 
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Page 40 of 165

declining.38 However as of 2008, approximately 127 million people lived in counties that 

exceeded any NAAQS.39 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 nonattainment areas are required to take action to bring those areas 

into compliance in the future. Based on the final rule designating and classifying 8-hour 

ozone nonattainment areas for the 1997 standard (69 FR 23951, April 30, 2004), most 8-

hour ozone nonattainment areas will be required to attain the ozone NAAQS in the 2007 

to 2013 time frame and then maintain the NAAQS thereafter. EPA is reconsidering the 

2008 ozone NAAQS. If EPA promulgates different ozone NAAQS as a result of the 

reconsideration, these standards would replace the 2008 ozone NAAQS and EPA would 

subsequently designate nonattainment areas for the revised primary ozone NAAQS. The 

attainment dates for areas designated nonattainment for a revised primary ozone NAAQS 

could range from 2015 to 2032, depending on the severity of the problem.40

 

38 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/. 

39 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/. 

40 U.S. EPA (2010), Fact Sheet Revisions to Ozone Standards. This document can be accessed 

electronically at: http://www.epa.gov/groundlevelozone/pdfs/fs20100106std.pdf
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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 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. The aircraft engine emission standards being proposed 

today were approved by ICAO/CAEP and would have an implementation date of 2013. 

Therefore, the aircraft engine emission reductions that are being proposed today should 

be useful to states in attaining or maintaining the PM2.5 NAAQS.

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 16 counties with a population of almost 35 million may not attain the 

2008 ozone standard of 0.075 ppm (75 ppb).41 In addition, our air quality modeling 

projects that in 2030 at least 9 counties with a population of almost 28 million may not 

attain the 1997 annual PM2.5 standard of 15 μg/m3and 26 counties with a population of 

 

41 U.S. EPA (2010). Regulatory Impact Analysis: Final Rulemaking to Establish Light-Duty Vehicle 

Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards. Chapter 7: 

Environmental and Health Impacts. EPA420-R-10-009.
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over 41 million may not attain the 2006 24-hour PM2.5 standard of 35 μg/m

3

.

42

 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.

There are currently no NO2 nonattainment areas. However, the NO2 standards 

were recently revised and a new 1-hour NO2 standard was promulgated.

43

 

Nonattainment area designations for the 1-hour NO2 standard are expected to be finalized 

in 2012. These proposed aircraft NOx reductions would be useful to states in attaining or 

maintaining the NO2 standards.

III. Details of the Proposed Rule

We are proposing 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).44 Each of the tiers would potentially apply to newly-certified 

 

42 U.S. EPA (2010). Regulatory Impact Analysis: Final Rulemaking to Establish Light-Duty Vehicle 

Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards. Chapter 7: 

Environmental and Health Impacts. EPA 420-R-10-009.

43 U.S. EPA, "Primary National Ambient Air Quality Standards for Nitrogen Dioxide;" Final Rule, 75 FR 

6474, February 9, 2010.

44 The proposed standards would 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. See section V.A.2. for more information 

regarding noncommercial applications.
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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.45 

We are also proposing to apply the first tier of the two tiers of standards to newlymanufactured engines. 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 newly-manufactured engines would need to comply with the same NOx limits as 

newly-certified engines, but at a later date or cease production.46 The end of this “phasein” period for the newly-manufactured engine standards is sometimes referred to a 

“production cutoff,” for obvious reasons. Again, we are proposing only the first of the 

 

45 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.

46 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, Amendment 4 effective on July 20, 2008. 

Copies of this document can be obtained from the ICAO website at www.icao.int. 
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Page 44 of 165

two new tiers of NOx standards for newly-manufactured engines. These provisions are 

described in detail below.

Five other regulatory features are being proposed in today’s action. First, we are 

proposing to revise provisions addressing certain time-limited flexibilities, i.e., potential 

exemptions, for newly-manufactured engines that may not be able to comply with the 

first tier of the proposed new NOx standards because of specific technical or economic 

reasons47. Second, we are proposing to clarify when the emission characteristics of a new 

engine model have become different enough from its existing parent engine design, i.e., a 

“derivative” of an originally certified engine type, that it must receive an emissions 

approval demonstrating conformance with the latest emission standard. Third, we are 

proposing 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. The proposed standards 

would meet our treaty obligation under the Convention on International Civil Aviation as 

previously described in section I.B. Fourth, we are proposing several amendments 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 by 

 

47 These apply only to the Tier 6 NOx standards as discussed below. We are not yet proposing a production 

cutoff for the Tier 8 NOx standard.
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reference. Finally, as described in Section IV, we are proposing amendments to current 

regulatory provisions addressing 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 discussed in section III.D., the proposed amendments reflect those changes 

that were previously adopted by ICAO or that CAEP has recommended for adoption by

ICAO in the near future. In this latter case, we are proposing these standards and 

recommended practices at this time rather than wait until ICAO takes final action to help 

ensure that our standards, and the FAA’s implementing regulations, are adopted in a 

timely manner once ICAO completes its process. We anticipate that our final standards 

would generally conform to ICAO’s final standards, once adopted. This would better 

enable the regulated industry to respond to new, globally harmonized requirements in an 

orderly manner, which is important given the international nature of the market for the 

aircraft engines that would be affected by today’s proposed rule. It would also avoid 

continuing the significant lag time that has sometimes occurred between ICAO’s 

adoption of international standards and our adoption of corresponding standards under 

U.S. law. To the extent ICAO adopts standards that differ from those recommended by
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Page 46 of 165

CAEP before we issue our final rule, we would then consider whether to make 

conforming amendments in our final standards, or to issue a supplemental proposal 

reflecting the amended ICAO standards, if appropriate.

This proposal 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 

proposed emission standards were well documented by our own analyses and CAEP as 

described later in this section and in section V., Regulatory Impacts. We think that the 

proposal would provide 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 leadtime,

noise, safety, and the technical feasibility of the proposed standards. Today’s proposal is 

also consistent with U.S. treaty obligations under the Chicago Convention as described in 

section I.C., because the proposed requirements are consistent with current ICAO 

standards or those that we expect ICAO to adopt prior to the promulgation of any final 

rule. 

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 

proposing revised exhaust emission standards for HC, CO, or smoke, which would 

remain in effect as currently promulgated. All engines subject to the proposed new NOx 

standards would also continue to be subject to the existing HC, CO, and smoke standards. 
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It is worth emphasizing that although we are proposing to include these existing HC, CO, 

and smoke standards in a new section 87.23, which would also contain the proposed Tier 

6 and Tier 8 NOx standards, we are not actually proposing new standards, 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. 

We are proposing to adopt a new naming convention in this preamble and the 

regulatory text to more easily distinguish between the proposed 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 proposed NOx standards, which are consistent with CAEP/6, will be referred 

to as Tier 6 in the remainder of today’s notice. The second tier of proposed standards 

will be referred to as Tier 8, which is consistent with 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 upon the effectiveness of a final rule reflecting 

today’s proposal the existing NOx standards would be superseded by Tier 6 standards. 

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 
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Page 48 of 165

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 proposing 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.

48

 (See section III.B for a discussion of how 

these standards would 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 a 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. Each of the proposed tiers is described separately below.

1. Tier 6 NOx Standards for Newly-Certified Engines

This first tier of proposed standards is equivalent to the CAEP/6 NOx limits that 

were already adopted by ICAO and became internationally effective after December 31, 

 

48 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.
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Page 49 of 165

2007. Given that aircraft turbofan engines are international commodities, engine 

manufacturers have already 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, and on our evaluation of the necessary

leadtime, we are proposing that this tier of standards take effect immediately upon the 

effective date of our final regulations. 

The basic form of the NOx standards for turbofan engines is different for higherand 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 proposed Tier 6 NOx standards for 

each of these power grouping are described separately below.

a. Numerical Emission Limits for Higher Thrust Engines

The proposed Tier 6 NOx standards for newly-certified gas turbine engines with 

rated thrusts of 89 kN or more are differentiated by pressure ratio as shown below.

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

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

The corresponding CAEP/6 standards were derived by CAEP using the following 

methodology:

• Make the CAEP/6 standard 12 percent more stringent than the CAEP/4 requirement at 

a pressure ratio of 30;

• Retain the same percent reduction, i.e., 12 percent, for pressure ratios below 30;

• Retain the slope of the CAEP/4 standard for pressure ratios of 30 to 62.5 for the 

CAEP/6 pressure ratios of 30 to 82.6;

• Retain the slope of the CAEP/4 standard for pressure ratios equal to or greater than

62.5 for the CAEP/6 pressure ratios at or above 82.6.49

 

49 Reverting to the CAEP/4 slope at a pressure ratio of 82.6 prevents the CAEP/6 standard from otherwise 

intersecting the older CAEP/2 standard at this point and thereby actually making CAEP/6 less stringent 

than CAEP/2. It has no practical value because current engines or anticipated engine designs do not utilize 

such high pressure ratios. Presently, there are no current engines with pressure ratios above approximately 

42.
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The resulting proposed Tier 6 NOx standards for these higher thrust engines are 

presented in Figure 1 along with the most recently adopted existing EPA NOx standards, 

which were based on CAEP/4, for comparison. 

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 proposed 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

Figure 1: Proposed Tier 6 NOx Standards for 

Higher Thrust Engines

0

20

40

60

80

100

120

140

160

180

10 30 50 70 90

Pressure Ratio (PR)

g/kN Thrust

Existing Standard

Proposed Tier 6

8% Reduction

Current Engine PRs

12% Reduction
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Page 52 of 165

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. 

b. Numerical Emission Limits for Lower Thrust Engines

The proposed Tier 6 NOx standards for newly-certified gas turbine engines with 

rated thrusts between 26.7 and 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 = 46.1504 + (1.4285 * engine pressure ratio) - (0.5298 * kN rated 

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

In developing the corresponding 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 
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Page 53 of 165

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

and increase progressively as size is reduced (from around 89 kN).50 For example, the 

relatively small combustor51 space and section height of these engines creates constraints 

on the use of low 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.52 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 

 

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

CAEP/3.

51 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 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.

52 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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Page 54 of 165

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

this approach.

As mentioned, the proposed 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 proposed Tier 6 NOx standards for lower thrust engines based on the 

engine size versus technological challenge described in the previous paragraph. 

Comparing the proposed 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 proposed Tier 6 standards represent a 

12 percent reduction from the existing EPA CAEP/4-based standards (Tier 4) 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 
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Page 55 of 165

reduction is progressively less because the slope of the two standards is essentially the 

same. 

At other thrust ratings the percent reduction between the proposed 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 

Figure 2: Proposed Tier 6 NOx Standards for 

Lower Thrust Engines Rated at 89.0 kN

0

20

40

60

80

100

120

140

160

180

10 20 30 40 50 60

Pressure Ratio (PR)

g/kN Thrust

Existing Standard

Proposed Tier 6

12% Reduction

Current Engine PRs
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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 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 proposed 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 

Figure 3: Proposed Tier 6 NOx Standards for 

Lower Thrust Engines At Pressure Ratio 30

40

50

60

70

80

90

100

20 40 60 80 100

Thrust (kN)

g/kN Thrust

Existing Standard

Proposed Tier 6

0% Reduction

at 26.7kN

12% Reduction

at 89kN

Current Engine Thrusts
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ICAO.53 The CAEP/8 recommended standards have a recommended effective date after

December 31, 2013. As discussed further in section V. of today’s notice, we agree with 

CAEP that this provides engine manufacturers with adequate leadtime to respond to these 

more stringent NOx standards considering the technical feasibility and cost associated 

with the requirements. Therefore, we are proposing that this tier of proposed standards 

would take effect on January 1, 2014, provided ICAO adopts CAEP/8’s recommended 

standards and effective date. If ICAO adopts different standards or a different effective 

date, we would evaluate whether to similarly adopt correspondingly different standards

and effective dates, or seek further public comment before doing so. 

As with the Tier 6 NOx standards, the basic form of the Tier 8 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 longer-term standards for each of these power grouping are described separately 

below.

a. Numerical Emission Limits for Higher Thrust Engines

 

53 CAEP/7 did not adopt new aircraft engine NOx standards.
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The proposed 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.

• 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 corresponding CAEP/8 standards were derived by CAEP using the following 

methodology: 

• Make the CAEP/8 standard 15 percent more stringent than the CAEP/6 requirement at 

a pressure ratio of 30;

• Retain the slope of the CAEP/6 standard for pressure ratios below 30;

• Retain the slope of the CAEP/6 standard for pressure ratios of 30 to 82.6 for the 

CAEP/8 pressure ratios of 30 to 104.7;
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• Retain the slope of the CAEP/6 standard for pressure ratios above 82.6 for the CAEP/8 

pressure ratios equal to or greater than 104.7.54

The resulting proposed Tier 8 NOx standards for these higher thrust engines are 

presented in Figure 4 along with the proposed Tier 6 standards for comparison. 

 

54 Reverting to the CAEP/6 slope at a pressure ratio of 104.7 prevents the CAEP/8 standard from otherwise 

intersecting the older CAEP/2 standard at this point and thereby actually making CAEP/8 less stringent 

than CAEP/2. It has no practical value because current engines or anticipated engine designs do not utilize 

such high pressure ratios. Presently, there are no current engines with pressure ratios above approximately 

42.

Figure 4: Proposed Tier 8 NOx Standards for 

Higher Thrust Engines

0

20

40

60

80

100

120

140

160

180

10 30 50 70 90

Pressure Ratio (PR)

g/kN Thrust

Proposed Tier 6

Proposed Tier 8

Current Engine PRs

19% Reduction

15% Reduction

11% Reduction
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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 proposed Tier 8 standards (CAEP/8 ) are referred to as being 15 

percent more stringent than the proposed 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 technology engines 

ranges from about 11 to 19 percent. 

b. Numerical Emission Limits for Lower Thrust Engines

The proposed Tier 8 NOx standards for newly-certified gas turbine engines with 

rated thrusts between 26.7 but 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 = 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)
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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 proposed 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 proposed Tier 8 NOx standards for lower thrust engines based on the 

engine size versus technological challenge described in the previous paragraph. First, the 

proposed 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 proposed Tier 6 standards. Second, as 

shown below in Figure 5 for 89 kN engines, at this thrust rating the proposed Tier 8 

standards represents a 15 percent reduction from the proposed 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. 
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 Third, at other thrust ratings the percent reduction between the proposed 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 5: Proposed Tier 8 NOx Standards for 

Lower Thrust Engines Rated at 89.0 kN

0

20

40

60

80

100

120

140

160

180

10 20 30 40 50 60

Pressure Ratio

g/kN Thrust

Proposed Tier 6

Proposed Tier 8

Current Engine PRs

15% Reduction

23% Reduction

19% Reduction
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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.

 

B. Application of the Tier 6 NOx Standards to Newly-Manufactured Engines

This section describes our proposal to apply the proposed Tier 6 NOx standards to 

newly-manufactured engines, and our proposed amended temporary flexibilities for 

newly-manufactured engines that may have significant problems complying with these 

requirements. Also, consistent with CAEP/8, we are not proposing to apply the Tier 8 

Figure 6: Proposed Tier 8 NOx Standards for 

Lower Thrust Engines at Pressure Ratio 30

40

50

60

70

80

90

20 40 60 80 100

Thrust (kN)

g/kN Thrust

Proposed Tier 6

Proposed Tier 8

Current Engine Thrusts

15% Reduction at

89 kN

5% Reduction 

at 26.7 kN
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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

As described above, the proposed Tier 6 NOx standards would apply to all engine 

types or models that receive a new type certificate after the effective date of the final rule. 

We are also proposing to phase-in these same NOx limits for newly-manufactured 

engines for engine models (and their derivatives) 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.

55

 As a result, 

manufacturers would need to bring newly-manufactured 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.56 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 foundational to its basic design and 

purpose and helps to ensure that the full benefits of newer, more stringent requirements 

 

55 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.b. for more information about new and spare engines.

56 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. 
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will be achieved in a reasonable time.57 We are, however, proposing certain limited 

flexibilities for engines that cannot be made compliant because of specific technical or 

economic reasons, as discussed later in this section.

The proposed effective date of January 1, 2013

58 for the newly-manufactured 

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 200959,60,61

 

57 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.

58 The proposed 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 proposed standards for new-manufactured engines is effectively January 1, 2013.

59 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. 

60 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.

61

 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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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 2011 time frame, and 3) 

any noncompliant models will be phased out of production because of low market 

demand. 

We think that the proposed five-year phase-in period from ICAO’s effective date 

of the CAEP/6 standards (corresponding to our proposed Tier 6 NOx standards) for 

newly-certified engines is adequate for manufacturers and their customers to respond to 

the new requirements without significantly disrupting their future planning and 

purchasing decisions.62,63 This phase-in period for applying the Tier 6 NOx standards to 

newly-manufactured engines is identical to the date for this same requirement that 

CAEP/8 has recommended to ICAO for adoption.64 Therefore, we are proposing that all 

engines newly-manufactured after December 31, 2012 must comply with the Tier 6 NOx 

standards. Again, if ICAO ultimately adopts a production cutoff date that differs from 

 

62 The ICAO CAEP/6 NOx standards became effective after December 31, 2007.

63 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.

64 We expect that ICAO will formally adopt the CAEP/8 recommendations in early 2011, which is well 

before the projected effective date of our final rule.
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this proposed date, we would evaluate whether to adopt a correspondingly different date 

in the final rule or to seek further public comment on the change.

2. Exemption from the Tier 6 Production Cutoff

In conjunction with the implementation of the proposed Tier 6 NOx standards, we 

are proposing provisions which would allow engine manufacturers to request exemption 

from meeting the Tier 6 NOx standards. These proposed provisions would replace 

existing provisions addressing exemptions, currently promulgated in section 87.7 of our 

aircraft engine regulations. (Any exemptions previously issued under section 87.7 would 

not be affected by the proposed revisions.) This section of the preamble describes these 

proposed exemption provisions which have largely been crafted to be consistent with 

exemption provisions in the ICAO Environmental Technical Manual (ETM).65,66 The 

provisions of the ETM guidance were crafted in the context of the CAEP/6 NOx 

production cutoff deliberations leading up to the CAEP/8 meeting in February 2010.

 

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

February 2010,” CAEP/8-WP/80, Agenda Item 2: Review of Technical Proposals Relating to Aircraft 

Emissions, April 2, 2010. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.

66 Note that EPA has submitted a paper to amend the exemption provisions included in this ETM to be 

consistent with this proposed 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-OAR-2010-0687. 
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While we are proposing to revise our regulations, the process for evaluating any

request for an exemption 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. 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. 

Under the existing regulations, the FAA, with EPA concurrence, may exempt 

low-production volume engines from being fully compliant with the emission 

standards.67 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; therefore, we 

believe that the provisions allowing for such exemptions are no longer of any utility, and 

are proposing to delete these provisions. We are also proposing to delete the existing 

provisions for temporary exemptions based on flights for short durations and infrequent 

intervals. These provisions are not necessary because our standards apply to aircraft 

certificated by the FAA, and the FAA does not address in the certification process 

 

67 An exemption allows an engine manufacturer to produce an engine that does not meet current NOx 

emission standards, even though the current NOx standard would otherwise apply. Such engines would 

need to meet the current emission standards for other pollutants. Exempted engines must also meet a less 

stringent NOx emission standard. Exempted engines must therefore still get FAA certification. 
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Page 69 of 165

whether an aircraft will be used for short durations or infrequent intervals. Hence, the 

provisions are of no utility. 

The current regulations also provide for permanent exemptions based on 

consideration of the certain factors specified in §87.7(c). We are proposing to replace 

these provisions with new regulatory text consistent with the ETM that would provide for 

two separate types of permanent exemptions: exemptions for spare engines and 

exemptions for engines on new aircraft. These are summarized below. (See §87.50 of 

the proposed regulations for additional details on these exemptions.) 

Finally, we are deleting the exemption provisions in §87.7(d). These provisions, 

which were intended for when the standards of §§87.11(a), 87.31(a), and 87.31(c) took 

effect, are now obsolete.

 a. New Provisions for Spare Engines

This proposed exemption is intended to allow production and sale of a newlymanufactured engine for installation on an in-service aircraft (i.e., a “spare engine”). It

would 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 purposes. Otherwise 

removing these aircraft from active service would be very expensive and logistically 

difficult. Also, under our proposed regulations, there would be no adverse environmental 
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Page 70 of 165

effect from allowing the use of a spare engine as a direct replacement for an existing 

engine, because a spare could be used only when the emissions of the spare engine are

equal to or lower than those of the engine it is replacing, for all pollutants. While 

manufacturers would not be required to obtain FAA or EPA approval before producing or 

shipping spare engines, they would have to submit an annual report to the EPA with 

information about spare engines. The permanent record for each engine exempted under 

this provision would need to indicate that the engine is an exempted spare engine and the 

engine itself would need to be labeled as “EXEMPT SPARE.” in accordance with FAA 

marking requirements of 14 CFR.

Exemptions for spare engines are not addressed in the existing regulations 

because there is not a 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, our proposal to apply a Tier 6 NOx production cutoff to all newlymanufactured engines means that if we did not also propose this exemption process, 

manufacturers would be prohibited from producing Tier 4 spare engines under the 

existing type certificates. We see no reason to change our policy of allowing 

manufacturers to produce new engines for use as spares. The proposed regulatory

provisions would allow this practice to continue.
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Under the proposed regulations, engines meeting the requirements for spare 

engines could be produced and enter into commerce without prior approval from EPA. 

(The FAA intends to adopt its own separate provisions for overseeing production of spare 

engines.) It is important to note that while engines would be exempt from the Tier 6 NOx

standards being proposed today, they would still need to be produced under an FAA type 

certificate. (This FAA oversight would essentially serve as the same role as the 

exemption approval step envisioned by ICAO in its ETM language for spare engines.) 

We would expect little or no additional burden for manufacturers, since we are not 

proposing new restrictions, monitoring, recordkeeping, or reporting requirements other 

than the end of year report. When combined with the proposed prohibition against using 

spare engines to replace lower emitting engines, this program will ensure that using a 

spare engine would not increase emissions, but would at the same time allow the 

availability of spares for maintenance or replacement as needed.

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 
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Page 72 of 165

adopted in the middle of a production cycle to take effect a few years later, manufacturers 

generally devote technical resources to bringing 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 

needed if a manufacturer does not complete the production cycle before the production 

cutoff date and projected production volumes are not adequate to justify resource 

investment to reduce emissions or there are other technological issues. 

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 sections 87.7(c) and 

(d), entitled, respectively, “Exemptions for New Engines in Other Categories,” and 

“Time Limited Exemptions for In Use Engines.” Today’s proposed amendments would 

replace these provisions with a new set of provisions addressing exemptions for new 
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engines. We invite public comment on any other ways to address the need for 

flexibilities in the above circumstances.

i. Time Frame and Scope

The proposed regulations would allow manufacturers to request an exemption for 

engines not meeting the Tier 6 NOx standards to be installed in new aircraft. If granted, 

the exemption would allow manufacturers to produce a limited number of newlymanufactured engines, in a time period beginning after December 31, 2012 and going 

through December 31, 2016. The time period for any given approved exemption could 

be shorter depending on the specifics of the application but could not be longer. This 

exemption would be limited to NOx emissions from engines that are covered by a valid 

type certificate issued by FAA. The engines would be required to meet all other 

applicable requirements. More specifically, an engine exempted from the Tier 6 NOx 

standards would need to be covered by a previously issued type certificate showing 

compliance with the Tier 4 NOx standards,68 as well as the current HC, CO, fuel venting, 

and smoke standards.

ii. Production Limit 

 

68 Engines certified only for compliance with earlier 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 NOx they may be recertified to the Tier 4 standards, but only before the 

effective date of the proposed regulations.
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We are proposing that the number of engines eligible for exemptions would 

generally not be allowed to exceed 75 engines per manufacturer – or more precisely per 

type certificate holder.69,70 Any specific approved exemption would include a specific 

limit based in part on the information presented in the manufacturer’s exemption request. 

We acknowledge that this proposed limit differs from the current ICAO ETM exemption 

guidance, which would generally allow up to 75 engines per type certificate. 71 While 

our proposal is different than the current ETM guidance (assuming under the ETM 

guidance any manufacturer might seek multiple exemptions for more than a total of 75), 

it would have practical significance only to the extent that any manufacturer seeks

exemptions for more than one engine type and could separately justify exempting 

sufficient numbers of each type to exceed the 75 total. We do not expect this situation to 

occur for the Tier 6 NOx standards for the reasons discussed below. 

 

69 Under normal circumstances, the number may not exceed 75 engines per type certificate holder. 

However, in unusual circumstances, a type certificate holder may ask that this limit be waived. 

70 While in most cases the type certificate holder and the production organization are the same, there are 

cases where more than one production organization exists for a given type certificate. This is especially 

likely to be the case in joint ventures. In such cases, we would expect that the type certificate holder and its 

production organizations would need to coordinate in the development of exemption application requests, 

and that the type certificate holder would ultimately need to take responsibility for coordinating requests --

in order to avoid a situation where the cumulative exemption requests exceeded 75 for a given type 

certificate holder. Note that this preamble discussion generally uses the term manufacturer for simplicity.

71 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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Prior to the CAEP/8 meeting in February 2010, ICAO had no specific provisions 

regarding exemptions. The only language regarding exemptions was contained in Annex 

16 Volume II section 2.1.1 which rather generically stated that:

In considering exemptions, certificating authorities should take into account the 

probable number of such engines that will be produced and their impact on the 

environment. When such an exemption is granted, the certificating authority

should consider imposing a time limit on the production of such engines for 

installation on new aircraft or on existing aircraft as spares.

When ICAO/CAEP began considering a production cut-off for the CAEP/6 NOx 

standard, there was a consensus among the participants in the technical working group 

that more specific provisions were needed with respect to potential exemptions from that 

requirement.72 The provisions would help support an orderly transition in the 

implementation of the production cut-off. Toward that end, the group consulted 

periodically over several months to craft provisions addressing number, time limit, and 

emission levels (impact on the environment). The deliberations were complicated by the 

 

72 ICAO, “Committee on Aviation Environmental Protection (CAEP), Report of the 6th Meeting,” CAEP/8-

WG3-WP7-03, Presented by the Rapporteurs, London, UK, April 1-3, 2009. A copy of this document is in 

docket number EPA-HQ-OAR-2010-0687.
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fact that the language in Annex 16 simultaneously addressed both engines for new 

production aircraft and spare engines for existing aircraft.73

For both new production and spare engines agreement was reached relatively

quickly that the time period for exemptions to be available should be four years after the 

production cut-off becomes effective and that any engine model for which an exemption 

was requested should meet at least the emission standards being affected by the cut-off. 

In this case engines would have to meet at least CAEP/4 NOx requirements. Similarly, it 

was readily agreed in the technical working group that there would be no limit on the 

number of spare engines during the four-year period since these would essentially be 

replacing in use engines removed for maintenance or other reasons.74

However, discussions and deliberations were more difficult with regard to the 

number of potential exemptions for engines for new production aircraft. This difficulty

stemmed from the fact that the ICAO Emissions Data Bank identified 20 unique engine 

models/sub models that could have been affected by the production cutoff. Those models 

 

73 ICAO, “Committee on Aviation Environmental Protection (CAEP), Draft Minutes of ETM/Annex 16 

Ad-Hoc Group Telecon,” May 26, 2009. A copy of this document is in docket number EPA-HQ-OAR2010-0687.

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

February 2010,” CAEP/8-WP/80, Appendix B, April 2, 2010. A copy of this document is in docket 

number EPA-HQ-OAR-2010-0687.
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had valid type certificates and therefore were considered to be “in production.”75 During 

further discussions the engine manufacturers clarified that most of these 20 were not in 

active production because the airlines normally purchase new aircraft with engines 

meeting the latest emission standards. However, it was stated that if the demand existed, 

14 of these 20 models could be produced under the exemption provisions since they had 

valid type certificates and met the previously mentioned exemption emission 

requirements.

76,77,78,79

 After much deliberation, the technical working group settled on a 

value of 75 engines per type certificate over the four years for the ICAO ETM 

guidance.80

 

75 U.S. EPA, “Simplified Working Copy of ICAO EDB, Issue 16A,” Glenn Passavant, Assessment and 

Standards Division, March 25, 2010. A copy of this document is in docket number EPA-HQ-OAR-2010-

0687.

76 ICAO, “Committee on Aviation Environmental Protection (CAEP), Response to EPA Paper 14 and 16,” 

WG-3 Flimsy 6-2, ICCAIA, London, UK, April 13, 2009. A copy of this document is in docket number

EPA-HQ-OAR-2010-0687.

77 ICAO, “Committee on Aviation Environmental Protection (CAEP), Production Cut-Off for Engine NOx 

Standards,” CAEP-SG/20082-WP/6, Presented by FESG, September 4, 2008. A copy of this document is 

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

78 ICAO, “Committee on Aviation Environmental Protection (CAEP), CAEP/6 NOx Productin Cut-Off 

Analysis,” CAEP-SB/20093-IP/19, Presented by FESG NOx Stringency Task Group, June 2, 2009. A copy 

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

79 ICAO, “Committee on Aviation Environmental Protection (CAEP), Production Cut-Off and Associated 

Flexibilities for ICAO Engine Emission Standards,” CAEP-SB/20093-WP/39, U.S.EPA, June 8, 2009. A 

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

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

February 2010,” CAEP/8-WP/80, Appendix B, April 2, 2010. A copy of this document is in docket 

number EPA-HQ-OAR-2010-0687.
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Page 78 of 165

This value was of concern to EPA. First, in the worst case, it represented the 

potential for over 1000 exempt engines (500 aircraft) to enter the fleet over this time 

period based on the information above. Assuming two engines per aircraft, this is 

essentially equivalent to the number of civil aircraft shipped in a single year.81 Second, 

from a broader perspective, while EPA regulations normally include hardship type 

provisions, it is not normal for EPA to include transitional exemptions of this magnitude 

in our regulations. Instead, we provide for other means such as emission credit programs 

to provide the flexibility necessary to transition into or out of emission control 

requirements. Such an emission credit-related provision was recognized in the ETM 

guidance as being a potentially useful adjunct that may be required “...in vew of the 

number of engines for which exemptions are sought (e.g., greater than 30), duration 

and/or exceedance described in an application.” However, such provisions are helpful 

when considerating exemptions from the CAEP/6 production cutoff because there are no 

NOx credits available today.

We began our assessment of a reasonable limit for potential exemptions from the 

CAEP/6 standards by noting the underlying conditions that may support the need for such

provisions. In this regard, it is often the case that the engine modifications needed to 

 

81 See Table 5 of the most recent AIA statistical report available at http://www.aiaaerospace.org/assets/Table 5.pdf.
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Page 79 of 165

meet more stringent standards and subsequent recertification are often an expensive 

undertaking. When future sales are projected to be larger in number, manufacturers have 

argued that economics favor a return on investment and that market forces dictate that 

they make the investment to so that they have fully compliant engines to meet customer 

demands.82,83 In these cases exemptions would probably not be necessary. However, 

when an engine model has low expected future sales, i.e., near the end of its production 

life, then the economics involved in transitioning to a new emission standard are less 

attractive and the market forces argument is less compelling. In such cases, limited 

exemptions may be appropriate. 

To help inform us regarding situations such as those described above, we looked 

at past production histories and projected future orders of engine models, focusing on the 

years associated with the production cutoff wherever possible.84 We utilized the 

ASCEND Database85 to conduct this analysis. ASCEND contains information on past 

 

82 ICAO, “Committee on Aviation Environmental Protection (CAEP), Response to U.S. EPA Papers 14 and 

16” WP3 Flimsy 6-2, ICCAIA, April 1-3, 2009. A copy of this document is in docket number EPA-HQOAR-2010-0687.

83 ICAO, “Committee on Aviation Environmental Protection (CAEP), NOx Production Cut-Off 

Considerations,” ICCAIA, January 9, 2009. A copy of this document is in docket number EPA-HQ-OAR2010-0687.

84 U.S. EPA, “Engine Exemption Allowable Limit Assessment,” Memorandum from Brad Nordman to 

Glenn Passavant, Assessment and Standards Division, Office of Transportation and Air Quality, April 

2011. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.

85 ASCEND Online (www.ascendworldwide.com) is a database that includes comprehensive transaction 

data, orders and deliveries, and airline fleet histories
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Page 80 of 165

production volumes and projected production volumes for future years based on either 

actual orders for aircraft or potential new orders. The results of this analysis were 

supportive of a limit for potential exemptions from the CAEP/6 standards that was much 

less than the ETM guidance of 75 engines per type certificate. Rather it appeared a 

number of approximately 100 engines per type certificate holder was more likely to be 

adequate. 

In addition, two new pieces of information became available during the 

development of this proposed rule that were unavailable during the deliberations leading 

up to the ICAO decision for the ETM guidance. First, a review of previously unavailable 

information on past exemption requests to FAA under the previous less specific ICAO 

language indicated that of the eight requests granted since 1983, only three involved 

exemptions during standards transition (two related to smoke for turboprop engines and 

one related to NOx for a turbofan engine). These three exemption petitions in 

combination ultimately affected less than 50 engines.86 Second, engine manufacturers 

indicated individually that the potential need for exemptions was not as large as EPA 

understood during the technical working group deliberations, and that absent unforeseen 

 

86 U.S. FAA, "Historical Exemptions from Gas Turbine Aircraft Engine Emission Standards," Electronic 

spreadsheet from Edward McQueen, Office of Environment and Energy, September 22, 2010. An extract 

from this spreadsheet addressing the pertinent issue is in docket number EPA-HQ-OAR-2010-0687.
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events, a much smaller value was workable on a per manufacturer basis as opposed to a 

per type certificate basis.87,88,89

Our subsequent discussions with engine manufacturers affected by the proposed 

Tier 6 NOx standards, i.e., CAEP/6 standards, resulted in a consensus that a numerical 

limit of 75 exempt engines per manufacturer, or more specifically type certificate holder, 

with some flexibility for additional exemptions to allow for very unusual circumstances, 

was reasonable for the proposed Tier 6 NOx standards. It was also agreed that if a 

newly-manufactured engine requirement is considered in the future for the proposed Tier 

8 NOx standards i.e., CAEP/8 standards, than any numerical limit associated with those 

standards would need to be evaluated based on information available at the time. 

Therefore, based on the above and after consultation with FAA, EPA is proposing 

to keep the 75 engines from the ETM guidance, but apply it on a per type certificate 

holder basis with some flexibility to increase the limit in very unusual circumstances. 

 

87 ICAO, “Committee on Aviation Environmental Protection (CAEP), Response to EPA Paper 14 and 16,” 

WG-3 Flimsy 6-2, ICCAIA, London, UK, April 13, 2009. A copy of this document is in docket number

EPA-HQ-OAR-2010-0687.

88 ICAO, “Committee on Aviation Environmental Protection (CAEP), Production Cut-Off for Engine NOx 

Standards,” CAEP-SG/20082-WP/6, Presented by FESG, September 4, 2008. A copy of this document is 

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

89 ICAO, “Committee on Aviation Environmental Protection (CAEP), CAEP/6 NOx Production Cut-Off 

Analysis,” CAEP-SB/20093-IP/19, Presented by FESG NOx Stringency Task Group, June 2, 2009. A copy 

of this document is in docket number EPA-HQ-OAR-2010-0687.
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We believe this approach addresses the intent of the ICAO guidance and the potential 

need of the manufacturers, while minimizing the potential for adverse environmental 

impacts from exemptions and aligning with EPA’s general approach with regard to 

exemptions and hardship provisions. We have also submitted a paper through the 

ICAO/CAEP process seeking to align the ETM guidance with the provisions in this 

proposal.90 

While it is not possible to know precisely how many engines (if any at all) might 

qualify for exemptions during the four-year period, we can estimate a worst-case 

scenario. For example, previous CAEP analysis indicated that there are four engine 

manufacturers with product that did not yet meet the proposed Tier 6 NOx standard. If 

each of these type certificate holders applied for and were granted the maximum 

allowable 75 exemptions over the four-year period, the total of 300 exempted engines 

worldwide would only be 2-3 percent of the newly produced fleet.91 More recent 

information from engine manufacturers suggests, however, that only one or two 

manufacturers may each request an exemption for a single engine model (i.e., a total two 

exemptions for two type certificate holders). In this case, and assuming each type 

 

90 ICAO, “Newly Produced Engine Exemptions for CAEP/6 NOx Production Cutoff,” CAEP9_WG3-CTG2_IP01, September 23, 2010. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.

91 ICAO, “Committee on Aviation Environmental Protection (CAEP), Production Cut-Off and Associated 

Flexibilities for ICAO Engine Emission Standards,” CAEP-SB/20093-WP/39, U.S.EPA, June 8, 2009. A 

copy of this document is in docket number EPA-HQ-OAR-2010-0687.
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certificate holder requested 75 exemptions, then the exempted engines would represent 

only 1-2 percent of sales over the four-year exemption period.

iii. Exemption Requests

We are proposing a process for requesting exemptions (for engines used on new 

aircraft) that would be more formal and structured than the current process. We are 

proposing that manufacturers be required to submit their request to the FAA, as currently 

required. The FAA will then inform and share the submittal with EPA. 

To ensure that we have the information necessary to evaluate exemption requests 

in this specific manner, the requests would need to include the following details to 

describe the specific engine model for which the manufacturer is requesting the 

exemption. The proposed 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;
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• 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 

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.
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Other Factors

• Hardship: Impact of unforeseen technical circumstances, business events. Or other 

natural or manmade calamities beyond your control, and

• 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 proposed 

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 the manufacturer justifications would need 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 would need 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 proposed regulations would apply only for 

NOx emissions, the analysis could also include possible benefits regarding noise levels or 

reduced emissions of pollutants other than NOx. Relevant economic impacts could 
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include effects on the engine manufacturer, airframe manufacturer, airline(s), and the 

general public.

In the past, some manufacturers have requested exemptions based on the largest 

number of engines they hoped to continue producing 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 on likely

production needs and time periods. At any time before approval, manufacturers could 

revise their requests to justify covering additional engines up to the allowable limit. We 

would then review the revised request. For exemptions that have already been approved, 

manufacturers could also ask for additional engines, again subject to the limit. If they 

were able to justify it, we would then amend the exemption. For example, in the past, a 

manufacturer with a potential customer interested in purchasing 10 engines might have 

requested an exemption to cover up to 100 engines in case they subsequently find 

additional customers. Under the proposed regulations, the manufacturer would request 

an exemption for the first 10 engines. If additional engines are needed after approval of 

the exemption, including cases where they are needed by a different customer, the 

manufacturer could ask to amend their approved exemption to cover a higher number of 

engines. Manufacturers also would be 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. 
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While we expect a manufacturer to have this specific information when they 

submit a request, the regulations would allow us to process exemption requests with 

somewhat less specific information. However, we would expect this to apply only for 

unusual circumstances.

If, after consulting with FAA, we determine that the exemption request is fully

documented and approval would be in the public interest, we would concur with 

approving the request if the FAA also concluded that the request should be granted. Note 

that we could approve the exemption for a smaller number of engines than the 

manufacturer requested, or we could include certain other conditions. 

In order to allow us to oversee these exempted engines, manufacturers would also 

be required to provide an annual report to EPA on exempt engines similar to the 

information about spare exempt engines. The permanent record for each engine 

exempted under this provision would need to indicate that the engine is an exempted 

engine and the engine itself would need to be labeled as “EXEMPT NEW” in accordance 

with FAA marking requirements of 14 CFR.

iv. Foreign Aircraft

We are proposing that manufacturers also include in their requests a list of 

countries in which the aircraft are expected to be registered (i.e., “flagged”), as 

previously noted. While not specifically listed in the ETM, we believe that this 
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information is consistent with the ETM as it would be necessary to ensure proper 

coordination with other countries in which these aircraft are expected to be registered. 

This coordination is necessary because many countries require FAA certification even for 

aircraft that will never operate in the U.S. Normally, we would not expect that we would 

approve an exemption for engines used on aircraft that would be registered in countries 

opposing the exemption.

It is worth emphasizing that the proposed requirement for EPA concurrence with 

any FAA approval would apply equally for engines that were exempted by foreign 

authorities if any of them would be used on aircraft subject to U.S. regulations. The 

ETM appears to presume that each member country will recognize exemptions granted 

by other countries. However, this presumption is conditioned upon the exemption being 

granted consistent with the guidelines of the ETM. Significantly, the ETM requires 

thorough coordination when exempted engines will be used in multiple countries. It 

states:

Exemptions for new engines should be processed and approved by the competent 

authorities for both the manufacture of the exempted engines and the initial 

operator of the aircraft to which they are to be fitted. Given the international 

nature of the aviation enterprise, civil aviation authorities of member states should 

attempt to collaborate and consult on the details of exemptions. In the case where 

engine type certification is done through a reciprocity agreement between or 
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among member states, the states involved should coordinate on the processing of 

exemptions and concur before approval is granted. 92

Thus in most cases, manufacturers should be getting approval from all relevant 

authorities at the same time, e.g., FAA, European Aviation Safety Agency (EASA), and 

Foreign Civil Aviation Authority (FCAA). However, whether they seek approval at the 

same time or in sequence, requiring EPA concurrence with any FAA approval of

exemptions for foreign aircraft subject to U.S. regulations is consistent with our 

international agreements. The Clean Air Act (which provides EPA with its authority to 

establish emission standards) includes no provisions that would allow any foreign 

country to exempt aircraft engines from the applicable standards promulgated thereunder. 

Nevertheless, since our proposed exemptions provisions are consistent with the 

procedures called for in the ETM, assuming appropriate coordination, we would not

expect to object to exemptions to engines properly exempted by other countries under 

those procedures.

Finally, the proposed production limit would apply to worldwide sales of the 

exempted engines. More specifically, we would not grant an exemption that would 

 

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

February 2010,” CAEP/8-WP/80, Agenda Item 2: Review of Technical Proposals Relating to Aircraft 

Emissions, April 2, 2010. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.
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violate the ETM specifications with respect to worldwide sales. For example, where a 

manufacturer requesting an exemption already has an exemption for that same engine 

model that was issued by a foreign competent authority for 20 engines not subject to EPA 

emission standards, the maximum number of engines that we would exempt would be an 

additional 55. We believe that to approve more than 55 would be inconsistent with the 

ETM. We would also likely include as a condition of our exemption approvals that 

manufacturers could not obtain exemptions for more than 75 engines worldwide. 

c. Voluntary Emission Offsets

We are requesting 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 is summarized in a memorandum to the docket93, and a basic overview of how 

credits might be generated is presented in the following paragraph. The types of 

programs being considered would be administered solely by EPA. Therefore, the FAA 

would have no direct responsibility for a voluntary emission offset program, although 

such a program would be considered by both agencies when evaluating the merits of any

exemption request. We would expect manufacturers to be interested in generating offsets 

 

93 U.S. EPA, “Draft Regulatory Text for Voluntary Offset Program,” Memorandum from Charles Moulis, 

Assessment and Standards Division, to Docket EPA-HQ-OAR-2010-0687, November XX, 2010.
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for one of three purposes. First, manufacturers might choose to generate offsets as part of 

their justifications for exemptions. For example, where we determine that an exemption 

would not be in the public interest because it would have an undue adverse effect on air 

quality, a manufacturer might use offsets so that the combination of the exemption and 

offsets would be more emission neutral. Second, manufacturers might choose to generate 

offsets as part of a justification for being allowed to exceed the limit of 75 exempted 

engines per manufacturer. Note that since this is not specifically allowed in the proposed 

regulations, we would need to amend the proposed regulations as part of the final rule to 

allow this option. We are asking for comment on this option, and could include it in the 

final rule based on the comments and our assessment of the inputs and issues. Third, 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. This would also require a change to the 

proposed regulations.

Under this approach, generation of offsets would be voluntary and would be open 

to all certifying engine manufacturers. One concept would be to allow credits to be 

generated only from engine models that are introduced after this rule and that had 

characteristic levels significantly below the otherwise applicable standard (e.g., at least 

10 percent below). It is a separate question, however, how to calculate the credit. If we 

adopted a 10 percent threshold for eligibility, we would probably also allow credits only 
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to the degree which the NOx characteristic level was more than 10 percent below the 

standard. For example, an engine that was 15 percent below the standard would generate 

credits equivalent to 5 percent of the standard. This would ensure a net improvement in 

emissions. If we were to finalize such a program, 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. 

For example, emissions from regional aircraft may not be directly equivalent to emissions 

from aircraft designed for longer cross-country or international flights. Equivalency

factors could be developed to account for differences in the number of LTOs per years, 

the lifetime of the aircraft, and the number of LTOs per mile, These factors could be 

developed based on the operation characteristics from existing sources of information and 

would not require the collection new operational data. Commenters are encouraged to 

review additional information contained in the memorandum to the public docket and 

provide input on the ideas, concepts, and options presented therein.

3. Potential Phase-In of New Tier 8 NOx Standards for Newly-Manufactured 

Engines

We are not proposing to phase-in the proposed Tier 8 NOx standards for newlymanufactured engines at this time, since such a feature is not included in the CAEP/8 

recommendation to ICAO. This means that engine manufacturers may continue to 
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produce Tier 6 compliant engines within already certified models after the proposed 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 to continue considering a related newly-manufactured engine standard as a future 

work item at CAEP, pending new information on technology and market responses. 

We will continue our efforts to evaluate a newly-manufactured engine standard as 

a complement to the Tier 8 NOx standards as part of the future CAEP work programs. 

We believe that such a requirement is a necessary component of any effective NOx 

control strategy for aircraft turbine engines. It provides an orderly, stable transition 

between emission requirements that is helpful for product planning by engine and 

airframe manufacturers, and in making purchasing decisions by their customers. It also 

ensures compliance with any new emission standard in a reasonable period of time, 

thereby providing the public with all the environmental benefits that a new emission

standard can provide. However, in order to maximize consistency with the CAEP/8 NOx

standard as currently recommended to ICAO, our proposed Tier 8 standard does not 

contain a production cutoff.

Assuming a CAEP/8 production cutoff is adopted at some time in the future, we 

will re-examine the permanent exemption provisions to ensure a timely and orderly 
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phase-out of engine models that do not meet the CAEP/8 NOx standards. We would 

expect this to be done as part of future CAEP deliberations and 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 must decide if the emission characteristics of the 

modified design were significant enough from the parent engine’s certification basis that 

a demonstration of compliance with newer 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 “no emissions change” derivative version of the original model. This may

be further complicated because of the common practice of making iterative changes over 

time, that leaves open 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 approved 

by the FAA’s certificating office. 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 
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criteria that can be used to determine when a design modification required 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 proposing to include the ETM language in our regulations. This addresses 

a longstanding need to make the decision process regarding derivative engines and 

applicable emission standards more transparent and consistent. It will provide engine 

manufacturers with more certainty regarding emission standard requirements as they

contempt future engine modifications. Finally, it will make the decision criteria 

enforceable. To ensure that the numerical decision criteria described below can be 

administered in a way that allows for the consideration of unusual circumstances or 

special information, we are also proposing that the FAA have some flexibility to make 

adjustments to the specific criteria based on good engineering judgment. In summary, if 

the FAA determines an engine model to be sufficiently similar to be considered a 

derivative engine, then the manufacturer could continue production of engine model to 

the same extent as allowed for the original engine model. However, if the FAA 

determines that an engine model is not an emissions-related derivative of a previously

certificated engine model, then the manufacturer would be required to demonstrate 

conformance with the most recent emissions standards. Consistent with ICAO provisions, 

we would consider a modified engine to be a derivative engine for emissions purposes if 
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the modified engine model had been derived from an original engine that was certified to 

the requirements of this part, and one of the following conditions is met:

(1) All modifications from the original engine were necessary for improved safety 

and continued airworthiness, as determined by FAA; and

(2) Emissions from the derivative engines must be equivalent to or lower than the 

original engine.

The proposed regulations specify that to show emissions equivalency, the engine 

manufacturer must demonstrate that the difference between emission rates of a derivative 

engine and the original engine are within the following allowable ranges, unless 

otherwise adjusted by the FAA using good engineering judgment:

± 3.0 g/kN for NOx.

± 1.0 g/kN for HC.

± 5.0 g/kN for CO.

± 2.0 SN for smoke.

Engine models represented by characteristic levels at least five percent below all 

applicable standards would be allowed to demonstrate equivalency by engineering 
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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. 

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.

94 These requirements include information relating to 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 

 

94 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 EPA-HQ-OAR-2010-0687
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assembled into an electronic spreadsheet entitled “Emissions Databank” (EDB)95 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.

96

 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 EBD to be a sufficient 

tool upon which to base policy decisions or adopt future standards. 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 

 

95 United Kingdom, Civil Aviation Authority, “ICAO Emissions Databank.” Available at the Civil 

Aviation Authority website www.caa.co.uk/default.aspx?catid=702. 

96 Under the proposed regulations, a grouping of engines with an essentially identical emission-related 

design would defined to be an “engine sub-model”. Engines with slightly different designs would be 

defined to be an “engine model”.
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reasonable reporting of emission certification testing and other information that is 

relevant to our mission.

97

 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 discharge our functions under the 

Act. (See 42 U.S.C. § 7414(a)(1).)

Therefore, we are proposing to require that any engine manufacturer submit a 

production report directly to EPA98 with specific information for each individual engine 

sub-model 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 are also proposing that this specific exhaust emission 

related information be reported to us in a timely manner, which will allow us to conduct 

 

97 The FAA already requires much of the information EPA is seeking through the certification process, but 

is unable to share it because of confidentiality agreements with engine manufacturers. Also, that 

information is part of a much larger submission, making it difficult to extract the specific reporting 

elements for EPA. 

98 The proposed report would be submitted only to EPA. No separate submission or communication of any 

kind is required for the FAA. 
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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. 

We are proposing to have each affected engine manufacturer report a reduced 

number of specific data elements to us as compared to those already reported voluntarily

and periodically by most engine manufacturers to the EDB. We feel that this minimizes 

the reporting burden for each manufacturer while still providing us with sufficient

information to perform our job. All of the specific reporting items we are proposing are 

same as requested for the EDB, with the exception of total annual engine production 

volumes, information on type certificates, and the emission standards to which the engine 

sub-model was certified. 

This information will be used in conjunction with the NOx and CO2 emission data 

already required to be submitted to us under part 87.64 for purposes of greenhouse gas 

(GHG) reporting to establish our own independent engine exhaust emissions database. 

We would expect most manufacturers generally to add the proposed information items to 

the annual GHG report. We want to clarify, however, that comments are invited only on 

the proposed incremental data reporting elements that comprise the production report. 

No changes are being proposed to the contents of the GHG report.
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The proposed incremental reporting elements for each affected gas turbine 

engine sub-model are listed below. The reporting elements of the existing GHG report 

are also identified for completeness.

• Company corporate name as listed on the engine type certificate (GHG);

• 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.

• If this is a derivative engine, 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, or if zero, state that 

the engine model is not in production and list the date of manufacture (month and year) 

of the last engine produced;
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• 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);

• 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);

• 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;

99

• Unburned hydrocarbon characteristic level (i.e. mass of hydrocarbons over LTO cycle / 

Rated Thrust (Dp/Foo);

100

• 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);

• Carbon monoxide (CO) characteristic level (i.e. mass of CO over LTO cycle / Rated 

Thrust (Dp/Foo));

 

99 See Regulation Part 87-Control of Air Pollution from Aircraft and Aircraft Engines, Subpart E, §87.42 

Certification report to EPA for definitions.

100 Dp/Foo : total gross emission of each gaseous pollutant (mass) / rated thrust (g/kN).
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• 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);

• Nitrogen oxides (NOx) characteristic level (i.e. mass of NOx over LTO cycle / Rated 

Thrust (Dp/Foo)) (GHG);

• 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);

• 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);

• 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); and

• Any additional remarks to the EPA.

The proposed annual report would be submitted for each calendar year in which a 

manufacturer produces any turbofan engine subject to emission standards as previously 

described. These reports would be due by February 28 of each year, starting with the 

2014 calendar year, and cover the previous calendar year. This report would be sent to 
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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 proposed reports to help inform 

any further public policy approaches regarding aircraft engine emissions that we 

consider, including possible future emissions standards, as well as help provide 

transparency to the general public. 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 would be 

updated annually. By collecting and publically posting this information on EPA’s 

website, we will be able to calculate turbine exhaust emission rates and demonstrate to 

the public how the fleet meets the current emission requirements. We believe that this 

information will also be useful to the general public to help inform public knowledge 

regarding aircraft exhaust emissions. We ask for comment on our proposed plan to post 

this information on our website and whether any of it should be omitted as confidential 

business information. Such confidential information would be retained by EPA. For 

guidance on how to preserve a claim of confidentiality and on how EPA would treat 

submitted information covered by such a claim, please see our earlier discussion in 
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section VII. of this notice regarding how a public commenter on the proposed rule should 

submit information that the submitter considers to be confidential business information.

We have assessed the potential reporting burden associated with the proposed 

annual reporting requirement. That assessment is presented in sections V. and IX.A. of 

this notice.E. Proposed Standards for Supersonic Aircraft Turbine Engines

We are proposing 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 proposed 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. (See section III.G. for a brief discussion of potential revised 

emission standards for future engine designs that may be used on supersonic aircraft.) 

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 
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appropriate to propose these conforming standards. Therefore, the proposed standard 

simply aligns EPA standards with the rest of the world.

F. Amendments to Test and Measurement Procedures

We are proposing to incorporate 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. These amendments to Annex 16, 

Volume II are mainly intended to ensure that the provisions reflect current certification 

practices. The amendments make clarifications or add flexibilities for engine 

manufacturers. They are described separately below for the amendments that have 

already been adopted by ICAO101,102 and those that have been recommended by CAEP 

for adoption by ICAO. 103

The amendments that have already been adopted by ICAO are:

 

101 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.

102 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.

103 ICAO, “Agenda Item 2,” Committee on Aviation Environmental Protection (CAEP), Montreal, 1 to 

February 2010, CAEP/8-WP/80. A copy of this document is in docket number EPA-HQ-OAR-2010-0687.
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• Standardizing of the terminology relating to engine thrust/power;

• 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; and 

• Clarifying the appropriate value of fuel flow to be used at each LTO test point.

The amendments that have been recommended for adoption by ICAO are:

• Clarifying exhaust nozzle terminology for exhaust emissions sampling; and

• Allowing an equivalent procedure for gaseous emission and smoke measurement if 

approved by the certificating authority. 

The test procedure amendments that ICAO has already adopted became 

applicable on November 20, 2008. The amendments that have been recommended to

ICAO are expected to be adopted prior to the date of the final action on today’s proposed 

rule. 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 

are, therefore, unlikely require new action by manufacturers beyond what they are 

already undertaking to meet ICAO’s adopted and recommended amendments. 
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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 kNs, 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 2018 timeframe.

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. This might affect 
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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. 104 Our recent 

 

104 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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discussions with engine manufacturers indicate that no substantive work is being 

undertaken at this time, however. We will continue to work within CAEP on this issue 

and undertake rulemaking to revise the regulations for supersonic aircraft engines as 

appropriate. 

We request comments on the status and timing of open rotor and future engine

designs for supersonic aircraft, and how the aircraft engine emission standards and test 

procedures may need to be modified to accommodate these types of engines.

IV. Description of Other Revisions to the Regulatory Text

In addition to the proposed changes discussed above, we are proposing 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 the proposed rule relates to engines used in military

and noncommercial civilian aircraft. We do not believe the proposed changes would 

have practical significance for current engine models because the changes align with 

manufacturers’ current practice in certifying their engines. 
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1. Military Engines

We do not intend our proposal to have any impact on engines installed on military 

aircraft. 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 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 proposed 

new standards and requirements would continue to apply only to engines for which 

standard airworthiness certificates are issued, and 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, we are proposing 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.

cutoff2. Noncommercial Engines
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The current section 87.21(d) specifies that gaseous emission standards apply 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 

Federal Aviation Act 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 are not required to comply with our current HC, 

CO, and NOx exhaust emission standards in §87.21(d). They are subject, however, to 

the current standards for smoke and fuel venting. 

We are proposing to apply the proposed 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 doing this. 

First, the ICAO Annex 16 standards and recommended practices apply equally to 

commercial and noncommercial engines, and our rules’ current failure to reflect this 

means that our requirements do 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 proposal simply incorporates the 

status quo.

In order to make EPA standards conform to ICAO’s, we need 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
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civilian aircraft, pursuant 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.) Today, we are proposing 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. 

These noncommercial and commercial engines have a great deal in common. 

First, they each use the same thermodynamic engine cycle (i.e., a gas (air) compressor, 

fuel combustor, and expansion turbine), engine design, and technology. That means they

emit the same pollutants, i.e., HC, CO, and NOx. Second, they are each used in the same 

manner, i.e., landing and takeoff operations from airports in the U.S., including 

commercial airports in ozone and CO nonattainment areas. That means their emissions 

are geographically, spatially, and temporally similar, and that they collectively contribute 

to ozone and CO nonattainment concentrations and are projected to continue to do so. 

Third, noncommercial engines are usually the same engine model and sometimes submodel as engines used in commercial operations, which makes distinguishing between 

commercial and noncommercial engines somewhat artificial. These attributes, taken 

together, demonstrate that engines used in commercial and noncommercial service have 

the same effect on the environment as their commercial counterparts. Therefore, the 

Administrator is proposing to find that commercial and noncommercial applications for 

turbofan and turbojet engines with rated thrusts greater than 26.7 kN collectively cause or 
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contribute to the same air pollution as their commercial counterparts. Our emissions 

assessment supporting this conclusion is contained in the docket for this proposed 

rulemaking.105

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 proposing changes to 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. 

Except as discussed in previous sections, the proposed changes to part 87 are not 

intended to significantly change the certification and compliance program. We are not 

reopening for comment the substance of any part of the program that remains unchanged 

substantively. Specifically, for those instances where we propose to move a provision to 

a different section or reword a provision in clearer language, we do not consider those 

 

105 U.S. EPA, “Assessment of Turbofan and Turbojet Aircraft Emissions,” memorandum from John 

Mueller, Assessment and Standards Division, to docket EPA-HQ-OAR-2010-0687, December XX, 2010.
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changes to be substantive. It is also important to note that the changes to the regulation 

apply starting with the date that the final rule takes effect. 

In particular, it is worth emphasizing that while we are restating the HC, CO, and 

smoke standards, as they would apply to Tier 6 and later NOx standard-subject engines,

in a new part 87.23, we are not proposing them as new standards or otherwise reopening 

them for comment. The HC, CO, and smoke standards in the proposed part 87.23 are 

identical to the existing standards of part87.21 and are being copied into the new section 

merely for clarity to readers.

The proposed 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 craft 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 the Federal Aviation Act. The 

proposed definition aligns with these statutory definitions. The changed wording is 

intended to clarify the existing policy without changing it.
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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 nonpropulsion engines from the definition of “aircraft engine” and turboshaft engines from 

the definition of “aircraft gas turbine engine.” We believe it 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 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. 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.
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Definitions are being added for “date of introduction,” “date of manufacture,” and 

“derivative engine” , 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 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, without requesting comment on those definitions: 

• Aircraft engine 

• Aircraft gas turbine engine 

• Class TP 

• Class TF 

• Class T3 

• Class T8 

• Class TSS 

• Commercial aircraft gas turbine engine

• Fuel venting emissions
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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 proposed regulations would rely on a good engineering judgment standard 

for showing emissions equivalence of derivative engines by engineering analysis (part 

87.48(b)(2)), and for applying the turbofan test procedures to turboprop engines (part 

87.60(a)). The good engineering judgment standard is somewhat analogous to the 

common law concept of a “reasonable person” standard. The general approach for 

implementing the good-engineering-judgment standard is allow manufacturers to exercise 

some judgment subject to potential EPA and FAA review (as appropriate). The 

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 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. These specifications are consistent with 

how manufacturers are generally certifying engines today. Defining how to round these 
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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

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 proposed definitions are 

intended to reflect the plain meaning of these terms. 

The proposed regulations include the following additional amendments:

Regulation 

cite

Description of Amendment Notes

87.1 Add definition of The characteristic level is established by ICAO 
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“characteristic level”. 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.

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 

The editorial changes do not involve any 

substantive change in the specified conditions.
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humidity specification, and 

(3) change the atmospheric 

pressure units from Pa to kPa.

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.

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 proposed 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 

This change is strictly editorial.
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procedures.

87.60 Revise the description of test 

procedures to rely broadly on 

the procedures specified in 

ICAO Annex 16. This 

includes a variety of recent 

changes to the Annex 16 

procedures.

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 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 proposed 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 proposed definition 

needs to be considered along with the proposed 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”

It is important to consider this definition in combination with 

the definition of “engine type certificate family”.

87.1 Definition of “engine A manufacturer or FAA may further divide an engine model 
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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 

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.

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 exempt 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 manufacturer report the engines it 

produces by sub-model. The manufacturer must specify

the 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, 
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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.

106,107 

EPA participated 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 re-certification of emissions. The 

 

106 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. 

107 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 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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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 will limit our discussion below of applying these technology levels to 

engines that needed 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: 6 types would require no 

change, 1 type would need the first technology level change, 5 would require the second 

technology level, and 3 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 
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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. 

Regarding the costs of this specific proposal, aircraft turbofan engines are 

designed and build 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 or are already developing 

improved technology in response to ICAO standards that match the standards proposed 

here. Also, the proposed 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 a final rule. Therefore, EPA believes 

that today’s proposed 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)). 
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In fact, engine manufacturers have suggested that certain benefits accrue 

for compliant products when the U.S. adoptions 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 proposed annual reporting requirement for emission 

related information. (See section III.D. for a description of the proposed 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

reported to the ICAO-related Emissions Databank (EDB). 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 
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manufacturers we believe that the reporting burden will be small because all of the 

information we are proposing to require 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 six hours and $365 per 

manufacturer. With 10 manufacturers submitting a reports, the total burden of this 

reporting requirement is estimated to be 60 hours, for a total cost of $3,646. 

Turning to emission benefits, CAEP’s assessments indicated that the CAEP/8 

NOx standards would provide global NOx reductions, which would translate to emission 

reductions in the U.S. The global LTO NOx reductions were estimated to be about 5.5

percent in 2026 and 7 percent in 2036 relative to the baseline. According to an analysis 

we had conducted for the U.S., it was estimated that this would translate to LTO NOx 

reductions in the U.S. of about 0.7 percent in 2020 and 1.1 percent in 2030,108 and the 

cumulative LTO NOx reductions from 2014 to 2030 (2014 is the implementation date of 

the CAEP/8 NOx standards) were projected to be about 17,000 NOx tons. 

VI. Coordination with FAA

 

108 U.S. EPA, Historical Assessment of Aircraft Emissions, Prepared by Eastern Research Group under 

Contract to E.H. Pechan and Associates, Inc., November XX, 2010. A copy of this document is in docket 

number EPA-HQ-OAR-2010-0687.
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The requirements contained in this action are being proposed after 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 231.109 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.

 

109The 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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Moreover, FAA is the official U.S. delegate to ICAO. FAA agreed to the 

amendments at ICAO's Sixth and Fourth Meetings of the Committee on Aviation 

Environmental Protection (CAEP/6) after advisement from EPA.110 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 subsequently recommended to ICAO for adoption. 

In addition, as discussed above, FAA will have the duty to enforce today's 

requirements. As a part of these duties, FAA conducts the emission tests or delegates 

that responsibility to the engine manufacturer, which is then monitored by the FAA. 

Since the FAA does not have the resources or the funding to test engines, FAA generally

selects engineers at each plant to serve as representatives (called designated engineering 

representatives (DERs)) for the FAA while the manufacturer performs the test 

procedures. DERs' responsibilities include evaluating the test plan, the test engine, the 

 

110 The Sixth Meeting of CAEP (CAEP/6) occurred in Montreal, Quebec from February 2 through 12 in 

2004.
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test equipment, and the final testing report sent to FAA. DERs' responsibilities are 

determined by the FAA and today's rulemaking will not affect their duties.

Finally, the FAA takes the lead in processing a manufacturer’s petition for 

exemptions to the aircraft emission standards. As part of that process, the FAA consults 

with EPA, and both Agencies must concur on any decision regarding such requests.

VII. Public Participation 

We request comment on this proposal, however, we are not reopening for 

comment the substance of any part of the program that remains substantially unchanged 

as described in section IV.B. The remainder of this section describes how you can 

participate in this process.

How Do I Submit Comments?

We are opening a formal comment period by publishing this document. We will 

accept comments during the period indicated in the DATES section at the beginning of 

this document. If you have an interest in the proposed emission control program 

described in this document, we encourage you to comment on any aspect of this 

rulemaking. 

Your comments will be most useful if you include appropriate and detailed 

supporting rationale, data, and analysis. Commenters are especially encouraged to 
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provide specific suggestions for any changes to any aspect of the regulations that they

believe need to be modified or improved. You should send all comments, except those 

containing proprietary information, to our Air Docket (see ADDRESSES located at the 

beginning of this document) before the end of the comment period.

You may submit comments electronically, by mail, or through hand 

delivery/courier. To ensure proper receipt by EPA, identify the appropriate docket 

identification number in the subject line on the first page of your comment. Please ensure

that your comments are submitted within the specified comment period. Comments 

received after the close of the comment period will be marked “late.” EPA is not 

required to consider these late comments. If you wish to submit Confidential Business 

Information (CBI) or information that is otherwise protected by statute, please follow the 

instructions in section VIII.B. 

How Should I Submit CBI to the Agency?

Do not submit information that you consider to be CBI electronically through the 

electronic public docket, www.regulations.gov, or by e-mail. Send or deliver information 

identified as CBI only to the following address: U.S. Environmental Protection Agency, 

Assessment and Standards Division, 2000 Traverwood Drive, Ann Arbor, MI, 48105, 

Attention Docket ID EPA-HQ-OAR-2010-0687. You may claim information that you 

submit to EPA as CBI by marking any part or all of that information as CBI (if you 
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submit CBI on disk or CD ROM, mark the outside of the disk or CD ROM as CBI and 

then identify electronically within the disk or CD ROM the specific information that is 

CBI). Information so marked will not be disclosed except in accordance with procedures 

set forth in 40 CFR part 2.

In addition to one complete version of the comment that includes any information 

claimed as CBI, a copy of the comment that does not contain the information claimed as 

CBI must be submitted for inclusion in the public docket. If you submit the copy that 

does not contain CBI on disk or CD ROM, mark the outside of the disk or CD ROM 

clearly that it does not contain CBI. Information not marked as CBI will be included in 

the public docket without prior notice. If you have any questions about CBI or the 

procedures for claiming CBI, please consult the person identified in the FOR 

FURTHER INFORMATION CONTACT section at the beginning of this document.

Will There Be a Public Hearing?

We will hold a public hearing on [Insert date no fewer than 15 days before and 

at least 30 days before end of comment period] at the Environmental Protection 

Agency, XXX Building, Room Number XXX, 1201 Constitution Avenue, NW., 

Washington, DC 20004, Telephone: (202) 564-1682. The hearing will start at XX:XX

local time and continue until everyone has had a chance to speak. 
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If you would like to present testimony at the public hearing, we ask that you 

notify the contact person listed under FOR FURTHER INFORMATION CONTACT

at least ten days before the hearing. You should estimate the time you will need for your 

presentation and identify any needed audio/visual equipment. We suggest that you bring 

copies of your statement or other material for the EPA panel and the audience. It would 

also be helpful if you send us a copy of your statement or other materials before the 

hearing. 

We will make a tentative schedule for the order of testimony based on the 

notifications we receive. This schedule will be available on the morning of the hearing. 

In addition, we will reserve a block of time for anyone else in the audience who wants to 

give testimony. 

We will conduct the hearing informally, and technical rules of evidence won’t 

apply. We will arrange for a written transcript of the hearing and keep the official record 

of the hearing open for 30 days to allow you to submit supplementary information. You 

may make arrangements for copies of the transcript directly with the court reporter.

Comment Period
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The comment period for this rule will end on [Insert date 60 days after date 

publication].

What Should I Consider as I Prepare My Comments for EPA?

You may find the following suggestions helpful for preparing your comments:

Explain your views as clearly as possible.

Describe any assumptions that you used.

Provide any technical information and/or data you used that support your views.

If you estimate potential burden or costs, explain how you arrived at your 

estimate.

Provide specific examples to illustrate your concerns.

Offer alternatives.

Make sure to submit your comments by the comment period deadline identified.

To ensure proper receipt by EPA, identify the appropriate docket identification 

number in the subject line on the first page of your response. It would also be helpful if 

you provided the name, date, and Federal Register citation related to your comments.

VIII. Statutory Provisions and Legal Authority
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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 

Under Executive Order (EO) 12866 (58 FR 51735, October 4, 1993), this action is 

a "significant regulatory action.” This action proposes the adoption of new aircraft 

engine emissions regulations and as such, requires consultation and coordination with the 

Federal Aviation 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 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 proposed regulations that conform with 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 
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are compelled to make the necessary business decisions and investments to maximize 

their international markets even in the absence of U.S. Indeed, engine manufacturers 

have or are already responding, or will in the future, to ICAO requirements that match the 

standards and practices proposed here. Therefore, EPA believes that today’s proposed 

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 proposed reporting 

requirements, as discussed in section IX.B.

B. Paperwork Reduction Act

The information collection requirements in this proposed 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 Request 

(ICR) document prepared by EPA has been assigned EPA ICR Number 2427.01.

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. We are, therefore,
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proposing to require that engine manufacturers send this information to EPA on an 

annual basis. We also propose to require manufacturers to send us their annual 

production volumes, which is the only item 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 would expect most manufacturers generally to add the proposed 

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 proposed annual reporting requirement.

We have estimated the total annual burden of the proposed 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. 

To comment on the Agency's need for this information, the accuracy of the provided 

burden estimates, and any suggested methods for minimizing respondent burden, EPA 

has established a public docket for this rule, which includes this ICR, under Docket ID 

EPA–HQ–OAR–2010-0687. Submit any comments related to the ICR to EPA and OMB. 
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See the ADDRESSES section at the beginning of this notice for where to submit 

comments to EPA. Send comments to OMB at the Office of Information and Regulatory

Affairs, Office of Management and Budget, 725 17th Street, NW, Washington, DC 

20503, Attention: Desk Office for EPA. Since OMB is required to make a decision 

concerning the ICR between 30 and 60 days after [Insert date of publication in the 

Federal Register], a comment to OMB is best assured of having its full effect if OMB 

receives it by [Insert date 30 days after publication in the Federal Register]. The 

final rule will respond to any OMB or public comments on the information collection 

requirements contained in this proposal.

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 
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governmental jurisdiction that is a government of a city, county, town, school district or 

special district with a 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 SBA Small Business Categories Potentially Affected by This 

Regulation

Industry NAICSa

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 proposed 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 proposed 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 impacted by the proposed regulations. An 
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analysis of the impacts of the proposed rule on small businesses has been prepared and 

placed in the docket for this rulemaking.111

We continue to be interested in the potential impacts of the proposed rule on small 

entities and welcome comments on issues related to such impacts.

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 IV, today’s proposed 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 proposed 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 

 

111 “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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governments. The provisions of this proposal apply to the manufacturers of aircraft and 

aircraft engines, and as such would not affect small governments.

E. Executive Order 13132: Federalism

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 proposes to revise 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.

In the spirit of Executive Order 13132, and consistent with EPA policy to promote 

communications between EPA and State and local governments, EPA specifically solicits 

comment on this proposed action from State and local officials.

F. Executive Order 13175: Consultation and Coordination with Indian Tribal 

Governments
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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. 

EPA specifically solicits additional comment on this proposed action from tribal 

officials.

G. Executive Order 13045: Protection of Children from Environmental Health & 

Safety Risks

This rule is not subject to Executive Order 13045 because it is not a significant 

regulatory action under E.O. 12866. Furthermore, the Agency does not have reason to 

believe the environmental health risks or safety risks addressed by this action present a 

disproportionate risk to children. EPA believes that the NOx emission reductions (NOx is 

a precursor to the formation of ozone and PM) from this rulemaking will further improve 

air quality and will further improve children’s health. See Section II.B.2. for a discussion 

of the health impacts of NOX emissions.

The public is invited to submit comments or identify peer-reviewed studies and 

data that assess effects of early life exposure to aircraft emissions.

H. Executive Order 13211: Actions that Significantly Affect Energy Supply, 

Distribution, or Use
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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 proposed 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 proposed rulemaking involves technical standards for testing emissions for 

aircraft gas turbine engines. EPA proposes to use test procedures contained in ICAO’s 

International Standards and Recommended Practices Environmental Protection, Annex
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16, along with the modifications contained in this rulemaking.112 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.

EPA welcomes comments on this aspect of the proposed rulemaking and, 

specifically, invites the public to identify potentially-applicable voluntary consensus 

standards and to explain why such standards should be used in this regulation.

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 low-income populations in the United States. 

EPA has determined that this proposed rule will not have disproportionately high 

and adverse human health or environmental effects on minority or low-income 

 

112ICAO 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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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.

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.

 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).

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 §87.1, 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.

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 
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operator” (including those engaged in “intrastate air transportation”) as these terms are 

defined in the Federal Aviation Act 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 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 means an engine of the same generic family as an engine model 

already covered by a type certificate issued by FAA under 14 CFR part 33as 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 emission-related 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-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 derivatives 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.
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Exempt means to allow 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 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 means judgments made 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.

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). 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.

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.
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Spare engine means an engine installed (or intended to be installed) on a used (inservice) aircraft to replace an existing engine for maintenance purposes. 

Standard day conditions means the following ambient conditions: temperature =15 

°C, specific humidity = 0.00 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.

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.

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)
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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).

(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)(4), “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.

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]
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7. Remove §87.7.

8. Revise §87.8 to read as follows:

§87.8 Incorporation by reference.

Documents listed in this section have been incorporated by reference into this part. The 

Director of the Federal Register approved the incorporation by reference as prescribed in 

5 U.S.C. 552(a) and 1 CFR part 51. Anyone may inspect copies at the U.S. EPA, Air and 

Radiation Docket and Information Center, 1301 Constitution Ave., NW., Room B102, 

EPA West Building, Washington, DC 20460 or at the National Archives and Records 

Administration (NARA). For information on the availability of this material at NARA, 

call 202-741-6030, or go to: 

http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.

(a) ICAO material. This paragraph (a) lists material from the International Civil Aviation 

Organization that is incorporated by reference. Anyone may purchase copies of these 

materials from the International Civil Aviation Organization, Document Sales Unit, 999 

University Street, Montreal, Quebec, Canada H3C 5H7. Table 1 follows:

(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]

(b) NIST material. This paragraph (b) lists material from the National Institute of 

Standards and Technology that we have incorporated by reference. Anyone may purchase 

copies of these materials from the Government Printing Office, Washington, DC 20402 

or download them free from the Internet at www.nist.gov. 

(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]

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.
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This section describes the emission standards that apply for Tier 4 and earlier engines that 

apply for aircraft engines manufactured before [INSERT EFFECTIVE DATE OF FINAL 

RULE] 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) * * *

(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:

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 EFFECTIVE DATE OF FINAL RULE], 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 the 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). Engines comply with an applicable standard 
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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 

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, 

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:

(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, 

whichever is smaller

— —

rO > 26.7 kN 83.6•rO-0.274 or 50, 

whichever is smaller

19.6 118
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(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 the associated derivative engines).

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 

introduced before January 1, 2014 (and the associated derivative engines).

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 EFFECTIVE DATE OF FINAL 

RULE] 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 derivative 

engines covered by the same type certificate. 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 derivative 

engines covered by the same type certificate. 

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.

87.42 Certification report to EPA.

87.44 Reporting CO2 emissions.

87.46 Recordkeeping.

87.48 Derivative engines.

§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. If you produce exempted engines, you may submit a single 

report with information on both certificated and exempted engines.
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(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 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).

(v) Whether or not this is a derivative engine. 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) The calendar-year production volume of engines from the sub-model that are 

covered by an FAA type certificate, 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 certificated (non-exempt) spare 

engines on in-use aircraft. 

(4) The number of engines tested and the number of test runs for the applicable type 

certificate. 

(5) 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. Include the percent of standard for the applicable standard, and for 

NOx include percent of standard for all the NOx standards specified in §§87.21 and 

87.23. 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) [Reserved]
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(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. 

§87.48 Derivative engines.

[The FAA to provide appropriate terminology regarding the established rules for 

describing the certification process relative to distinguishing derivative from nonderivative engines and how this distinction is made in the engine type certificate. Both 

here and in the definitions as needed]

(a) General. A manufacturer may ask for a determination that an engine model is a 

derivative of a previously certificated engine having substantially the same engine core 

design. To be considered a derivative engine under this part, it must have been derived 

from an original engine that was certificated to the requirements of this part, and one of 

the following conditions must be met:

(1) All modifications from the original engine were necessary for improved safety 

and continued airworthiness, as determined by FAA.

(2) Emissions from the derivative engines are determined to be equivalent. 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.

(b) Emissions equivalency. The engine manufacturer must demonstrate that the modified

engine’s emission rates meet the applicable standards and are sufficiently similar to the 

emission rates of the original model in the engine type certificate family, as follows: 

(1) The difference between emission rates of a derivative engine and the original 

engine should be within the following allowable ranges:
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(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 parent engine before modification is at or above 

95% of the applicable standard for any pollutant, you generally must measure 

emissions for all pollutants to demonstrate that the derivative engine’s resulting 

characteristic levels will not exceed the applicable emission standards. You may

otherwise use an engineering analysis to demonstrate that the derivative engine will 

not exceed the applicable emission standards, consistent with good engineering 

judgment. 

(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. Where FAA determines that an engine model is not a 

derivative of a previously certificated engine model, you must have an emission approval 

from the FAA.

12. Add a new subpart F containing §87.50 to part 87 to read as follows:

Subpart F —Exemptions 

§87.50 Exemptions.

This section specifies provisions related to exempting engines from some or all of the 

standards and requirements of this part 87. Exempted engines must conform to regulatory 

conditions specified for an exemption in this section and other 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. Exemption requests under this section must be approved by

FAA under 14 CFR part 34. EPA will participate in this approval process by engaging in 

consultations with FAA and providing written concurrence for engines that qualify for an 

exemption under the provisions of this section. 

(a) Engines installed in new aircraft. Engine manufacturers may request an exemption to 

produce and sell 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 
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by FAA. Under normal circumstances, this number may not exceed 75 engines per type 

certificate holder. However, in unusual circumstances, you may ask us to waive this 

limit. 

(1) Submit your request for an exemption before producing the engines to be 

exempted to the FAA who will provide a copy to the Designated EPA Program 

Officer. This requirement applies equally for engine models that have already been 

exempted by a competent authority outside the United States. All requests must 

include the following:

(i) Your corporate name and an authorized representative’s contact information.

(ii) A description of the engines for which you are requesting the exemption. 

Include in your description the engine model and sub-model names and the types 

of aircraft in which the engines will be installed. Specify the number of engines 

that you would produce under the exemption and the period during which you 

would produce them. Also identify the authorizing type certificate (type 

certificate number and date). 

(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.

(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.
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(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).

(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”.

(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) [Reserved]

(c) Spare engines. Newly manufactured engines meeting the definition of “spare engine” 

are exempt as follows: 

(1) This exemption allows production and sale of a newly manufactured engine for 

installation on an in-service aircraft. It does not allow for installing a new 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 exempted under this paragraph (c) may be used only where the 

emissions of the spare engines are equal to or lower than those of the engines they are 

replacing, for all pollutants.
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(4) Manufacturers are not required to obtain approval before producing or shipping 

spare engines. However, engine manufacturers must submit the annual report 

specified in paragraph (d) of this section with information about spare engines.

(5) The permanent record for each engine exempted under this paragraph (c) must 

indicate that the engine is an exempted spare engine.

(6) Engines exempted under this paragraph (c) must be labeled with the following 

statement: “EXEMPT SPARE”.

(d) Annual reports. If you produce engines with an exemption 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 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 exemptions separate from other new engine 

exemptions. Include the following for each exemption 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.

(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 

determine 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 
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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 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. 

(2) The alternate procedure is shown to be equivalent to or better 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)

Percent 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

(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.

16. Amend §87.64 by revising paragraph (a) to read as follows:

§87.64 Sampling and analytical procedures for measuring gaseous exhaust 

emissions.

(a) [Reserved.]

* * * * *

§§87.65-87.71—[Removed]

17. Remove §§87.65-87.71.

Subpart H—[Removed]

18. Remove subpart H.

PART 1068--GENERAL COMPLIANCE PROVISIONS FOR ENGINE 

PROGRAMS
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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).

(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.

* * * * *