Control of Air Pollution from Aircraft 

and Aircraft Engines; Final Emission 

Standards and Test Procedures 

Summary and Analysis of Comments 
Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency

Control of Air Pollution from Aircraft 

and Aircraft Engines; Final Emission 

Standards and Test Procedures 

Summary and Analysis of Comments

NOTICE 

This technical report does not necessarily represent final EPA decisions or 

positions. It is intended to present technical analysis of issues using data 

that are currently available. The purpose in the release of such reports is to 

facilitate the exchange of technical information and to inform the public of 

technical developments.

EPA-420-R-12-011 

May 2012 
 

 

 

 

 

 

Control of Air Pollution from Aircraft and Aircraft Engines; Final Emission Standards 

and Test Procedures 

Summary and Analysis of Comments 

Introduction 

In July of 2011, we proposed several new NOx emission standards, compliance flexibilities, and 

other regulatory requirements for aircraft turbofan and turbojet engines with rated thrusts greater 

than 26.7 kilonewtons (kN), as well as certain other requirements for gas turbine engines that are 

subject to exhaust emission standards. The proposed rule was published on July 27, 2011 (76 FR 

45012). A public hearing was held on August 11, 2011 in Chicago, IL. The public was invited 

to submit written comments on the proposal during the formal comment period, which ended on 

September 26, 2011. The following is a list of entities that provided relevant comments on the 

proposed rule: 

Aerospace Industries Association and General Aviation Manufacturers Association (joint 

comment) 

Air Transport Association 

Dassault Aviation 

General Electric Aviation 

Pratt & Whitney 

Rolls Royce1 

Williams International 

A transcript of the public hearing and all of the written comments are available in public 

docket EPA-HQ-OAR-2010-0687. This document contains summaries of the comments 

received and EPA responses to those comments. 

Issue: Leadtime Associated with the Production Cutoff 

Organization: General Electric Aviation (GE) 

Comment: The intent of the proposal was to provide one year between formal implementation of 

the Tier 6 standard (assuming a final rule by December 31, 2011) and the proposed January 1, 

2013 effective date of the Tier 6 production cutoff. Most of the engine models currently in 

1 Rolls Royce submitted comments under a claim of confidential business information (CBI). As such, they are

not available for public viewing. However, Rolls Royce did not raise any issues or present any new

information that was not addressed in other comments to which we are fully responding. 

1 
 

 

 

 

 

 

production that are certified to the Tier 4 standard have NOx emissions below the Tier 6 levels, 

as demonstrated in the original Tier 4 emissions certification reports that were submitted to FAA. 

In our estimate, the existing certification reports should be sufficient for FAA to formally certify 

these engines to the Tier 6 standard, thereby ensuring they will not be adversely affected by the 

Tier 6 production cutoff. However, if further interaction with the FAA is necessary, and other 

formal FAA action is required, we are concerned that production could be interrupted due to 

revisions of FAR Part 34 and review of existing certification reports. Therefore, rather than 

adopting January 1, 2013 as the effective date for the production cutoff, the final rule should 

specify that the requirement goes into effect 12 months after the final rule. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers 

Association (GAMA) 

Comment: There could be less than one year lead time between implementation of Tier 6 and the 

Tier 6 production cut-off if EPA’s final rule is not adopted before January 1, 2012. Such leadtime is not appropriate for manufacturers or regulators to make such changes. We suggest that if 

the final rule is delayed, the dates should then be adjusted to provide at least one year between 

formal implementation of the Tier 6 standard and the Tier 6 production cut-off. 

Response: We believe that our proposed dates for the Tier 6 requirements are appropriate and 

consistent with the Clean Air Act. Section 232(b) of the Act directly addresses our obligation 

relative to the effective date of regulations. Specifically, it says: “Any regulation prescribed 

under this section (and any revision thereof) shall take effect after such period as the 

Administrator finds necessary (after consultation with the Secretary of Transportation) to permit 

the development and application of the requisite technology, giving appropriate consideration to 

the cost of compliance within such period.” Based on the information provided by the 

commenter above, the aircraft engine models described by GE are already capable of complying 

with the EPA proposed Tier 6 NOx standards through the continued use of already developed 

and already applied requisite technology (the cost of applying with has already been borne), as 

the effective date of the corresponding ICAO CAEP/6 NOx standard has already passed. We do 

not believe there are any technical feasibility or economic implications arising from the 

continued application of the requisite technology for those engines to meet the proposed Tier 6 

NOx standards. Also, consistent with our most recent previous amendment to the NOx standards, 

which similarly promulgated the standard at a level that was already being met by aircraft engine 

manufacturers who were already applying the requisite technology, the proposed effective date 

does not need to build in additional lead time for the development and application of additional 

technology that would be needed to comply with the standards. See, e.g., 70 FR 69604, 69674-76 

(Nov. 17, 2005). As a result, the proposed dates provide more than adequate lead time under the 

statute. The AIA/GAMA comment does not present a specific example or information to 

illustrate the basis of the generalized assertion that one year of lead time is necessary for this 

standard. Therefore, because aircraft engine manufacturers are already able to comply with the 

proposed Tier 6 NOx standard through the continued use of already applied requisite technology, 

2 
 

 

 

 

 

 

 

 

and because the effective date of the corresponding ICAO CAEP/6 NOx standard has already 

passed, we do not believe that a basis has been established that a full year of lead time is needed 

between the Tier 6 NOx standard and the production cutoff. 

The production cutoff is actually an ICAO standard and we think it is important to stay aligned 

with the CAEP production cutoff date. We note that this is also being adopted by the European 

Aviation Safety Agency (EASA) and perhaps other aviation certification authorities. Our 

adoption of the proposed date insures international consistency regarding the production cutoff 

date. 

Regarding the need for engine models to be formally recognized by the FAA as complying with 

the proposed Tier 6 standard, this is completely within the purview of the FAA. In our previous 

most recent amendment to the NOx standard, we provided just a one-month lead time period 

before the revised standard became effective, and FAA did not adopt corresponding 

implementing regulations until significantly later, with no apparent disruption to the industry. 

See 70 FR 69664 (Nov. 17, 2005). The proposed Tier 6 standards are the same as the CAEP/6 

standards that were approved by ICAO in 2005 with an effective date of beginning after 

December 31, 2007. Therefore, just as for the 2005 revised NOx standard that we similarly 

promulgated significantly later than the effective date of the corresponding ICAO CAEP 

standard, we do not believe that it is necessary to delay the effective date based on a need for the 

FAA to revise its own implementation and enforcement regulations. 

Finally, section 232(a) of the Act directs the FAA to ensure compliance with our standards. In 

this regard, the FAA has developed a streamlined process to recognize compliance with Tier 6 

and/or Tier 8 as appropriate for currently type certified engine models which meet the emission 

standards and they have assured the regulated industry that they will dedicate the necessary 

resources to formally recognize conformance with the standards before the production cutoff 

date. Based on the FAA’s assurances and description of the streamlined process to formally 

recognize conformance with the new standards, engine manufacturers now support promulgating 

the production cutoff date as proposed.2 

For the reasons stated above, EPA is promulgating the production cutoff date as originally 

proposed. 

Issue: Exemptions/Exceptions from the Tier 6 Production Cutoff 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers 

Association (GAMA) 

2 Email and letter from Leslie Riegle, Aerospace Industries Association, to Lourdes Maurice, U.S. Federal Aviation 

Administration, February 23, 2012. 

3 
 

 

 

 

 

 

 

 

Comment: Requesting an increased amount of engine exemptions can take a significant amount 

of time. There may be insufficient time for a manufacturer to receive approval for additional 

engine exemptions if necessary to meet previously unknown market demands. It is important that 

when the NPRM refers to flexibility, it does not lose sight of the time required go through the 

exemption granting process. The FAA is the agency that holds jurisdiction in this process, and 

we ask that the EPA takes into account the existing role of the FAA in this process. 

Response: The comment does not provide a specific example or other information that may 

illustrate this concern. As a general matter, given the long lead time between the initiation of 

discussions among aircraft purchasers and aircraft manufacturers, and actual orders and final 

deliveries, we expect that manufacturers will have enough time to request additional engine 

exemptions, and if appropriate, for the FAA and EPA to approve such a request. We expect that 

amending an already approved exemption would take less time to act upon than the original 

petition. Also, engine manufacturers may request an expedited review from the FAA, and by 

association the EPA, if circumstances warrant. Finally, to the extent that an engine manufacturer 

has specific concerns in this area, they could be ameliorated by improving the lines of 

communication with air frame manufacturers to increase the manufacturer’s awareness of market 

interest in potential new orders. Accordingly, we are not revising our proposal based on this 

comment. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers 

Association (GAMA) 

Comment: The term “excepted” for spare engines that do not comply with the Tier 6 NOx 

standards, but may continue to be sold after the Tier 6 production cut-off requirements takes 

effect, is inconsistent with current engine name plate labeling practice. Currently engines are 

either marked “COMPLY” or “EXEMPT” for emissions. It might be concerning to the operators 

holding an engine with a plate reading “EXCEPTED.” Therefore, for the purpose of the name 

plate we believe “exempt” should be utilized instead of “excepted.” 

Organization: Air Transport Association (ATA) 

Comment: The EPA proposes a different means – that spares be considered “exceptions” for 

which case-by-case approval is not required, subjecting them only to a labeling requirement. 

ATA supports this change of approach, which follows CAEP’s judgment but provides separate 

treatment of spares in a slightly differing way and simplifies administration for FAA without 

compromising the structure of the exemptions program set forth in the ETM. 

Response: The Tier 6 production cutoff does not apply to the continued production of engines 

that are designated spares. Spare engines are produced to replace a similar engine already in 

service that was removed from service for maintenance purposes. Accordingly, the production of 

a spare engine is not restricted by the production cutoff, and the regulation does not apply to 

these engines. The non-applicability of the cutoff eliminates the need to process an exemption 

for continued production of these engines beyond December 31, 2012. 

4 
 

 

 

 

 

 

 

 

 

 

Conversely, engines that are intended to be produced for new installations (i.e. not replacing an 

engine already in service) are subject to the production cutoff regulation and the continued 

production of such engines beyond the cutoff date would require a grant of exemption. Since the 

production of spare engines is not subject to the new cutoff regulations, the FAA proposed and 

the EPA accepted the idea that referring to these engines as exceptions to the regulation was 

more appropriate than requiring case-by-case consideration of exemptions when the regulation 

did not apply. 

Moreover, the word “exemption” is a meaningful regulatory term. It is used by the FAA in 14 

CFR Part 11 to mean that an applicant is subject to a particular regulation and is requesting timelimited relief under a specific set of criteria. It is a specialized form of rulemaking. When an 

entity or its product is specifically left out of a regulatory provision, it is considered ‘excepted’. 

Organization: Pratt and Whitney (PW) 

Comment: Once the final rule is enacted there might be a delay before EPA and FAA can 

establish and undertake procedures to review exemption requests. This could be very disruptive 

to engine manufacturers that have already contracted to deliver engines or parts of engines 

during that period, and also be harmful to airplane manufacturers and airlines. To avoid this type 

of economic disruption, the final rule “...should grant a one-time, interim block of, perhaps, 

twenty (20) exemptions to each engine manufacturer.” This is well within EPA’s standardsetting authority under section 231 of the Clean Air Act. Such an approach would both head off 

uncertainty for the aviation industry, as well as give the FAA and EPA the time to establish 

exemption request review procedures and lighten their administrative burden while doing so. 

Response: Based on supplemental information we received from Pratt &Whitney,3 we find their 

concerns center on six engines for which they have contract commitments to build and deliver 

within several months of this final rule. These six engines belong to two engine models, with 

four engines in one model and two engines in the other. The first model consisting of four 

engines is scheduled to begin shipping in January 2013, shortly after the January 1, 2013 Tier 6 

production cutoff. These engines are currently certificated to the Tier 4 NOx standards. Pratt & 

Whitney have stated, however, that the design of this engine model has been technically 

modified to achieve the Tier 6 standards. Unfortunately, compliance testing of this model to 

meet the Tier 6 standards cannot be performed until December of 2012 when the first production 

version is built. Assuming that this testing is successful, inadequate time remains for the FAA to 

formally recognize Tier 6 compliance based on those tests before the production cutoff becomes 

effective.4 The two new aircraft using these engines are being built and will be delivered to a 

foreign airline. 

The second model is comprised of two engines with a contracted deliver date in May 2013. 

They are also certificated to the Tier 4 NOx standards. These engines are at the end of their 

production life, i.e., no additional future deliveries for civilian uses are anticipated beyond these 

two contracted engines. For this reason, Pratt & Whitney has stated that it is not economically 

3 Memoranda documenting this supplemental information are located in docket number EPA-HQ-OAR-2010-0687. 4 The FAA has stated to EPA that inadequate time exists for the required formal compliance determination before 

the production cutoff takes effect. 

5 
 

 

 

 

 

 

feasible to redesign this model to conform with the Tier 6 standards, even if it were technically 

feasible. The single new aircraft using these engines is also being built for delivery to a foreign 

airline. 

In assessing Pratt &Whitney’s concern, we find that a considerable amount of time will indeed 

be required between the time this final rule becomes effective and completing any formal FAA 

action using the normal exemption process as previously described in this notice. Specifically, 

time is needed for: 1) the FAA to amend 14 CFR part 34 through rulemaking to incorporate the 

production cutoff and procedures for granting exemption from the new standards; 2) the 

manufacturer to develop the information needed to support a request; 3) submitting the request 

for review by FAA and EPA; 4) coordination with other certificating authorities; and 5) EPA and 

FAA review and final action on the request, i.e., approval or disapproval. Regarding this review 

and final action, we note that FAA staff involved in reviewing the manufacturer’s request may 

also be engaged in conducting the processes to adopt this rule in 14 CFR part 34 and to review 

emission information on current type certificates to confirm that they meet either Tier 6 or Tier 8 

requirements, as previously described. Therefore, we conclude that inadequate time exists to act 

on an exemption request with certainty for these six engines before their contract deliver dates. 

Consequently, we conclude that a limited modification to the otherwise universal effective date 

of the final Tier 6 compliance deadline is appropriate to accommodate Pratt & Whitney’s unique 

situation, and that for these six specific engines additional lead time is needed due to cost and 

technical feasibility factors. 

We also believe that disrupting the scheduled delivery dates of these engines could risk 

subjecting Pratt & Whitney to possible financial penalties for late delivery, with possible followon effects for the aircraft manufacturer and airlines. We also find that there is no significant 

adverse effect on the environment in allowing these six engines to be produced and sold as 

compliant with Tier 4 standards, especially if four of the engines ultimately comply with the Tier 

6 standards. 

For the above reasons, and in response to the comments and under our authority under sections 

231(a)(3) and (b) to issue final regulations with such modifications to the proposal as the 

Administrator deems appropriate and to make revised standards effective after such period as the 

Administrator finds necessary to permit the development and application of requisite technology, 

giving appropriate consideration to the cost of compliance within such period, we are including 

an exception provision in the regulations that permits Pratt & Whitney to produce and enter into 

commerce up to six newly manufactured engines with a date of manufacture, as defined in the 

regulations, prior to August 31, 2013 that are not certificated to meet Tier 6 emission 

requirements. These engines would be required to have a type certificate which indicates that 

they meet the 40 CFR 87 requirements last updated on October 30, 2009 (i.e., Tier 4). No formal 

exemption request or approval would be required for these six engines. 

We know of no other engine manufacturer that is in this situation today, (i.e., contracted

deliveries of engines not meeting the production cut-off within several months of the 

production cut-off date). However, as a matter of equity and to address situations which 

6 
 

 

 

 

we may not be informed of at this time, we are extending the availability of this transitional

flexibility to any manufacturers that may be in similar circumstances. 

Organization: General Electric Aviation (GE) 

Comment: The proposed EPA exemption deviates from the current ICAO ETM guidance. 

Maintaining harmonization with the international community is not only required by the Chicago 

Convention, but also provides streamlined processes and procedures within the regulated 

industry. Any purported benefits to EPA’s proposed unique exemption scheme are outweighed 

by setting up a conflict with the remainder of the world. If EPA wants a different approach to 

evaluating exemptions, it would be more appropriate to work inside the ICAO/CAEP process 

toward that end. 

Organization: Air Transport Association (ATA) 

Comment: The EPA proposed case-by-case approach to determining the number of engines that 

may be exempt for installation on new aircraft is a rejection of the ICAO/ETM provisions that 

limit “...the number of exemptions ... to 75 engines per type certificate...”. This would create a 

serious discontinuity between the U.S. and the rest of the world, undermining ICAO’s objective 

of international uniformity. The ICAO exemption limits are intended to be applied globally 

through the coordinated efforts of international aviation authorities. Differing rules would make 

this impracticable. That this would make coordination unworkable is evidenced by EASA’s 

assumption in its proposal that “the ICAO proposals will be adopted unaltered by other aviation 

authorities of the world.” It is also “... immaterial that the variance is from the ETM, an ICAO 

guidance document supplementing the official standards of Annex 16, Vol. II, rather than the 

Annex itself. The ETM provides technical elaboration on the implementation of Annex 16, and 

differing practices have the same disruptive effect.” 

Rather than accepting the ETM cap of 75 engines per type certificate, EPA proposes to require 

that the exemption request for each individual engine be justified, “...including the exact 

number, initial purchasers/users, countries of registry and plans for bringing the product into 

compliance.” This knowledge may not be known at the time of the exemption request because of 

market lead times. For example, the 1998 RR exemption request from the CAEP2 cutoff for 150 

engines was not based on this type of certainty, but was a prospective exemption for two years as 

protection against the uncertainties of technical development. RR did not know when the 

development process would be completed, and hence did not know the exact number of noncompliant engines that airlines would purchase. The three affected airlines worked with RR to 

provide documentation of the financial and operational hardship that they would suffer based on 

their aircraft delivery schedules. 

Also, the uncertainties regarding total production make it impossible to make an accurate 

estimate of the total environmental impact under the exemption. The ICAO cap of 75 engines 

per type certificate allows ready calculation of the global impact that CAEP has determined to be 

environmentally acceptable. 

7 
 

 

 

 

 

Response: The commenters’ concerns appear to be primarily focused on the number of 

exemptions and the underlying process that is embodied in the ETM and our proposal. We 

proposed to continue using the general exemption language for exhaust emission standards 

contained in part 87.7(c) of our current regulations. More specifically, we proposed to evaluate 

each request for exemption on a case-by-case basis using the information provided by the 

applicant and any other relevant information that is available to FAA and EPA at the time. Any 

approved exemption would include a specific limit on the number of such engines based on that 

information and is not defined on a basis such as type certificate. An engine manufacturer could 

also request that an exemption be expanded to include additional engines after providing 

additional information to justify such an increase. The intent, of course, would be to exempt the 

minimum number of engines that can be justified, including a consideration of the public health 

and welfare effects associated with the exemptions. We acknowledged that our proposed 

language differed from the ETM allowance that “...would normally not exceed 75 per engine 

type certificate....” However, the outcome in terms of number could be similar, if justified. 

Regarding consistency with the Chicago Convention, our proposal thoroughly explained that the 

ETM is guidance material; not an ICAO standard or regulation of any type. Moreover, even if 

the ETM were a standard, consistency is not compelled when a deviation is justified, and we 

were comfortable with our proposed exemption provision for those reasons. We disagree with 

ATA’s comment that the ICAO guidance is effectively the equivalent of an ICAO Annex 16 

standard. It is interesting to note that elsewhere in their comments, ATA supported a deviation 

from the ETM language for labeling spare engines as “except” rather than “exempt.” Finally, as 

noted in the proposal, we intend to work within CAEP to align the ETM with our approach. 

Turning to ATA’s comment regarding the ETM cap of 75 engines per type certificate, we first 

want to point out that this is not a maximum limit on the number of potential exemptions per 

type certificate. Rather the ETM provision is an expectation that “[T]he number of engines 

exempted would normally not exceed 75 per engine type certificate ....” With this perspective 

both the ETM and our proposed approach are similar in that the maximum number of exempted 

engines is based on a consideration of the petitioner’s justification for such exemptions. 

The commenter is correct that our proposed approach “...requires an applicant to provide 

detailed justification for each individual engine, including exact number, initial purchasers/users, 

countries of registry, and plans for bringing the product into compliance.” This is actually not 

much different than the justification envisioned by the ETM. That guidance document explains 

that the petitioner should, to the extent possible, provide quantitative support to justify the 

exemptions. Specifically, the ETM “...provides guidelines on the process and criteria for issuing 

exemptions....” These include some of the same elements as contained in our proposal and 

referenced above, i.e., the exact number of exemptions being requested, to whom the engines 

will be originally delivered, and plans for producing a compliant product. Therefore, the ETM 

envisions a consideration of specific information as part of the exemption request, in a similar 

fashion as EPA’s approach, in order to decide on the exact number of exemptions to grant. We 

are simply being more explicit in some areas concerning the type of information that should be 

included in any exemption request. 

8 
 

 

 

 

The commenter appears to contradict its position that a significant amount of information may 

not be available regarding expected purchases at the time of the exemption request, while also 

stating that “[T]he airlines worked with Rolls Royce to provide documentation of the financial 

and operational hardship that they would suffer if there were an interruption in the supply of 

ICAO-compliant engines during their aircraft delivery schedules.” Given the long lead times 

generally associated with new aircraft orders and deliveries, we expect aircraft operators will 

work closely with aircraft manufacturers as their new aircraft needs are identified. Engine 

manufacturers should in turn work with aircraft manufacturers to stay aware of market interest in 

potential new orders. This appears to be reflected in the commenter’s example regarding the 

cooperation between airlines and RR in fashioning the exemption justification. Also, the 

proposed regulatory text notes that the petitioner should include information on ”expected” first 

purchasers/users of the aircraft. It also asks for information on the number of aircraft that will be 

registered in the U.S. versus other countries that may be estimated if not known. Therefore, 

precise knowledge is not needed for certain elements of the justification. The preamble to the 

proposed requirements also states that the regulations would allow us to process exemption 

requests with somewhat less specific information, although we expected that to apply only for 

unusual circumstances. We have made this clearer in the final regulations. 

We disagree with the comment that the proposed differences with the ETM make international 

coordination unworkable. In fact, one of the proposed justification elements, i.e., how many 

affected aircraft will be registered in the U.S. and other countries (estimate allowed), was 

described in the preamble for the proposal as being aimed at helping to facilitate consultation and 

coordination. Also, as noted above, the ETM’s expectation that exemptions would normally not 

exceed 75 per type certificate and our proposal are similar in that the maximum number of 

exempted engines under both approaches is based on a consideration of the petitioner’s 

justification for such exemptions. Finally, as described in the proposal, it now appears that only 

one or two engine models may be candidates for exemptions, and that the potential number of 

justifiable exemptions would be less than 75 in total. We do not think coordination with foreign 

aviation authorities, most likely EASA, with these few exemptions should pose any problems. 

Therefore, we find nothing in the justification elements that should impinge upon the ability to 

internationally collaborate and consult on exemptions. 

Finally, regarding the estimate of total environmental impact, the engine manufacturer must base 

this estimate on the number of exemptions requested, and the differences in pollutant levels 

between the non-compliant engine and an alternative that would meet the applicable standards. 

As noted above, this estimate would simply be based on the manufacturer’s ability to determine 

this information as accurately as possible, just as for the ETM. We are also unaware of any 

explicit CAEP analysis that characterized the “environmental acceptability” of the suggested 

ETM limit of 75 engines per type certificate, as implied by the Air Transport Association. 

Issue: Exemptions for Newly-certified Engine Models 

Organization: General Electric (GE) 

Comment: The development timeline for a new aircraft engine can span 6 or more years from 

concept to certification. As a result, unforeseen circumstances may arise during aircraft engine 

9 
 

 

 

 

 

 

 

 

 

 

 

development that necessitates a change in design that may impact the ability of that engine to 

meet the prevailing Tier emission standard at certification. Therefore, exemptions should be 

available for newly-certified engines in addition to newly-manufactured engines. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers 

Association (GAMA) 

Comment: The existing 40 CFR section 87.7(c) not only provides the flexibility to exempt 

newly-manufactured engines from a production cutoff, but also for newly-certificated engine 

models subject to any emission standards, e.g., the Tier 8 NOx standards. This flexibility should 

be retained. 

Throughout the NPRM the Agency suggests it will pursue a production cut-off for the proposed 

Tier 8 NOx standards at a later date. CAEP indicated that such a cut-off would need to take into 

account future work and the manufacturers’ response to the CAEP/8 regulations. Not adhering to 

the same principles is concerning. 

Response: Regarding the availability of exemptions for newly-certified engine models, the 

proposed regulatory text makes clear that the exemption provisions would only apply to newlymanufactured engines. Specifically, the intent was to establish provisions for newlymanufactured engines to address the potential technology and economic adversities that may 

arise as part of adopting the Tier 6 production cutoff. The ICAO ETM provisions are clearly 

intended for that same purpose. Also, the original intent of EPA’s current exemption provisions 

in section 87.7(c), which we are modifying in this rulemaking, is clear from the proposed 

rulemaking and final rulemaking that resulted in those provisions. The March 24, 1978 proposal 

described the concern as “...engines which are nearly [at] the end of their production life would 

be terminated prematurely because there would be insufficient future sales to justify 

incorporating emission controls.” (See 43 FR 12619, March 24, 1978.) The December 30, 1982 

final rule referenced “...the removal of an engine model from the market because of its failure to 

comply.” (See 47 FR 58468, December 30, 1982.) Clearly, the intent of the existing exemption 

provision cited by AIA/GAMA was to make it apply to newly-manufactured engines. 

As a general matter, we believe an exemption from the Tier 6 standard, or any other standard, for 

newly-certified engine models is speculative at this time and would undermine the goal of 

regulatory compliance by new engine designs. In any event, neither the current ICAO Annex 16 

nor the ETM provide for newly-certified engine exemptions. We believe that such would be a 

fundamental shift from Annex 16 and the ETM should be explored within the framework of 

ICAO/CAEP. Furthermore, engine manufacturers already have significant leadtime between the 

date CAEP adopts a new emission standard and the standard’s effective date, e.g., usually 3-5 

years. Finally, engine manufacturers historically design new engine models to comply with the 

most stringent future standard that also provides for a longer development time horizon. 

Therefore, we are promulgating the exemption provisions for newly-manufactured engines as 

proposed. 

We do not understand the AIA and GAMA concern with our stated goal of pursuing a potential 

phase-in of the proposed Tier 8 standard, i.e., a production cut-off. The preamble clearly 

10 
 

 

 

 

 

 

described our intent to work within the ICAO/CAEP framework to develop harmonized 

international standards for any such requirement. We also generally described that CAEP had 

decided to consider a Tier 8 production cut-off “...as a future work item, pending new 

information on technology and market responses.” So we believe we are adhering to the same 

principles as CAEP. 

Issue: Limits on Pollutants from Excepted Spare Engines 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers 

Association (GAMA) 

Comment: The proposal would require that the emissions of an excepted spare engine be equal to 

or lower than the engine it is replacing. This is impractical because, while unlikely, a spare 

engine might have a different emissions profile for some pollutants than the engine it would 

replace. For example, the engines could have somewhat different combustion systems that might 

make one engine lower in NOx but higher in carbon monoxide (CO). The EPA needs to consider 

the totality of the emissions in decision, or delete this requirement in the final rule. (AIA) 

Response: The proposed language to limit the emissions from an excepted spare engine is 

consistent with the ICAO/CAEP ETM. This provision, as well as the exemption provisions, was 

subject to significant discussions that included the engine manufacturers as well as a 

representative from AIA. Nonetheless, in this instance we believe the proposed provision should 

be modified to accommodate the potential for unusual circumstances as explained by the 

commenter. 

The AIA and GAMA suggest that EPA consider of the totality of emissions relative to their 

environmental effects as the basis for evaluating spare engine exemptions. This would entail 

understanding and comparing the environmental consequences of the different pollutants. We 

find that could be very complicated because different pollutants have different health and welfare 

end points and consequences. For example in the illustration offered by the commenter, the 

effects of LTO NOx and CO are largely unrelated to one another. 

We think a preferred option to evaluating total environmental effects, or even dropping the 

provision entirely, is to incorporate an anti-backsliding requirement which ensures that at a 

minimum the excepted spare engine meets specific emission limits. For this reason, and in 

response to the AIA and GAMA comments, we have modified this provision in the final rule to 

allow an excepted spare engine to have different emission levels compared to the engine it 

replaces as long as it remains compliant with the emission standards and other requirements of 

its type certificate. Given the limited number of spare engines in the fleet, we expect that 

allowing these engines to have somewhat different emission profiles from the engines they are 

replacing will have no significant adverse environmental effect. We do expect, however, that in 

most cases the emissions of an excepted spare engine will be equal or better than the engine it is 

replacing in accordance with the basic tenant of the ETM. 

Issue: Exemptions for Short Duration Flights 

11 
 

 

 

 

 

 

 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers 

Association (GAMA) 

Comment: The existing provision that allows temporary exemptions for flights of short duration 

and infrequent intervals should be retained. As in the past, a new aircraft may be produced at a 

commercial facility that is destined for immediate conversion to a military-only application at a 

separate facility. These aircraft may require a small number of airworthiness flight tests before 

being ferried to the conversion facility. While these military-only aircraft would generally utilize 

compliant engines, it may be possible that non-compliant engines could be used in 2017 and 

temporary exemptions would be necessary. Additionally, it would be helpful if the provision also 

allowed for the granting of a discrete number of exemptions over a specified time period, rather 

than having to request the exemption prior to each flight as currently required. 

Response: The proposal to delete the exemption allowance for infrequent interval and short 

duration flights that is contained in section 87.7(a)(4) was developed in consultation with the 

FAA. Unfortunately, the need for temporary exemptions for the specific scenario described by 

the commenters was not identified. In considering the commenters’ suggestion to retain the 

exemption, we note that allowing such operations will not have any significant adverse affect on 

the environment because of the infrequent and short duration of such flights. Retaining the 

exemption is also consistent with the intent of the separate proposal to exempt military aircraft 

from emission control requirements. Therefore, EPA is retaining the provision in the final rule 

with one change, made in response to the comments, as described below. 

The current provision calls for the Secretary of Transportation to consult with the EPA 

Administrator when considering any exemption request for infrequent interval and short duration 

flights. Given the inconsequential nature of such flights on the environment, we believe that the 

Secretary should be able to consider and act on these petitions unilaterally to streamline the 

process. Therefore, we have deleted that portion of the current exemption. Of course, we will 

consult with the Secretary if asked. 

As for requesting a discrete number of temporary exemptions, we believe this is an issue that the 

Secretary of Transportation may determine under its enforcement role as described in section 

232 of the CAA. 

Issue: Military Exclusion 

Organization: Pratt & Whitney (PW) 

Comment: We support the recognition that the proposed standards should not apply to aircraft 

produced for military use, noting that this is consistent with the ICAO Convention, which does 

not apply to state aircraft, including military aircraft. However, the proposed definition of 

“military aircraft” covers only aircraft “owned by, operated by, or produced for sale to the armed 

forces or other agency of the Federal government responsible for national security.” The 

military exception should extend to sales outside of the U.S. for four reasons. First, “There is no 

basis to distinguish between military-use engines used by the United States and other nations, 

and it furthers the interest of harmonization to allow engines intended for both domestic and 

12 
 

 

 

 

 

 

 

 

 

 

 

foreign military use to utilize the same exception to EPA’s emissions standards.” Second, 

“extending the military exception to international sales does not implicate the United States’ 

national security, because the State Department oversees such sales.” Third, “engines sold for 

foreign military use will rarely, if ever, enter American airspace, and thus will not affect air 

quality in the United States.” Finally, “a global military-use exception is in keeping with the 

international parity implicit in the ICAO’s Chicago Convention. “ 

Response: We agree with the commenter that foreign military aircraft should not be subject to 

our emission standards. However, we disagree with the commenter that the proposed regulations 

would do so. Section 87.3 of the proposed regulations, which addresses the general applicability 

of the entire part 87, limits the applicability to only those aircraft subject to FAA regulation. 

Since FAA does not regulate foreign military aircraft, such aircraft are not subject to our 

emission standards. Nevertheless, to avoid any potential confusion we are including in the final 

rule a revised definition of “military aircraft” which clarifies that foreign aircraft considered 

military under international laws or agreements are not covered by 40 CFR part 87. 

Issue: Voluntary Emissions Offsets (Credits) 

Organization: Air Transport Association (ATA) 

Comment: There are significant doubts that EPA has the legal authority to adopt a voluntary 

emissions offset program. The standard setting authority under section 231 of the CAA does not 

appear to provide such authority. Where offsets or emissions trading schemes exist for other 

source categories, the authority is express. Examples of this are the CAA authority for the 

trading program under the acid rain program, and the Energy Independence and Security Act 

authorization for the offset program used under the Corporate Average Fuel Efficiency 

Standards. A voluntary offset program embodied in the proposal would be unworkable in the 

context of aviation. Unlike car or trucks, aircraft engine manufacturers have relatively low 

production volumes and few frequently updated models for generating credits. Also, some 

manufacturers have more models than others and this could possibly lead to competitive 

distortions in the market. Further, opportunities for generating offsets would be limited by the 

proposal’s high thresholds for generating those credits. First, the thresholds would make 

incremental technology improvements ineligible for offsets even though they produce real 

environmental benefits. Second, limiting credits to the improvements that exceed the proposed 

margins would make it even more unlikely that any manufacturer could realistically generate 

offsets. 

Airlines may be caught in the middle of the proposed program because exemption applications 

are already costly and time consuming. In the context of using emission credits for exemptions, 

each situation would be unique and it would not be possible to match exemptions to credits, or to 

assess the further complexities of the “equivalency factors” described in the proposal. Finally, an 

airline’s delivery schedule would be held hostage to the manufacturer’s ability to justify credits 

based on some other engine that the airline is not buying. For these reasons, no offset program 

should be considered. 

Organization: Pratt and Whitney (PW) 

13 
 

 

 

 

 

 

 

 

 

Comment: The EPA lacks the legal authority to create such a program. Other emission offset 

programs are based on express grants of statutory authority. For example, credit programs are 

directly authorized by The Energy Independence and Security Act for use in the Corporate

Average Fuel Economy (CAFÉ) program. Also, the "averaging, banking, trading" ("ABT") 

offsets program for heavy-duty vehicles, though purportedly stemming from the general grant of 

authority in Clean Air Act section 202, is based on that section’s "integral relationship" with the 

non-conformance penalty ("NCP") provision in section 206(g) of the Clean Air Act. Nat’l 

Petrochemical & Refiners Ass’n v. EPA, 287 F.3d 1130, 1148 (D.C. Cir. 2002) (internal 

quotation marks omitted). Finally, no statutory authority exists in the CAA or any other statute 

for EPA to establish an offset program for aircraft emissions. 

The EPA proposal assumes that an offset program would create an incentive for manufacturers to 

build lower-emissions engines. On the contrary, manufacturers already have that incentive 

because using the lowest-emitting technology that is available maximizes the life of the engine. 

Such a program would simply create a windfall to manufacturers whose product lines are already 

capable of generating credits. 

The proposed program is not feasible based on the timeline EPA has identified for generating 

and using credits. Under the proposal, credits could be used for exemptions. Credits could not be 

generated beginning January 1, 2012. At the same time, the proposed exemptions are only 

available through 2016. Most engines that will be delivered in those four years have already been 

ordered and the production process already started. There is little, if any, opportunity for 

manufacturers to sell credit-generating engines in this narrow time window. 

Even if feasible, the proposed program would create an unlevel playing field for different 

manufacturers based on their product lines and business plans. Manufacturers that happen to 

have product lines capable of generating sufficient credits would instantly be at a regulatory and 

competitive advantage over manufacturers without this capability. The less fortunate 

manufacturers might be forced to pay a competitor for the right to build a competing product. 

Given that three manufacturers dominate the global market and are fiercely competitive, 

manufacturers are unlikely to help their competitors. Even if they did, it could raise antitrust 

concerns. 

In the event that EPA moves forward with the proposed program, PW believes the method for 

calculating offset credits must include an equivalency factor that allows credits generated from 

smaller airplanes to be used to justify exemptions for larger aircraft and vice-versa. This is 

essential to mitigate the substantial anti-competitive effects among manufacturers as previous 

described. Ideally the equivalency factor would be based on the useful life of the engines 

involved. However, EPA lacks specific knowledge in this area, so equivalency determinations 

need to be made on a case-by-case basis based on a simple, standardized table in the beginning 

of any assessment and then modified with input by the engine manufacturer. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers 

Association (GAMA) 

14 
 

 

 

 

 

 

 

 

 

Comment: The proposed emission offset program goes beyond the borders of CAEP, which has 

not endorsed such a plan to date. The limited number of aircraft engine types and models makes 

the effects of this type of program more pronounced on the aviation industry than in the 

automotive industry. Some manufacturers make only one or a few gas turbine engines subject to 

NOx standards, making this program impractical. It is critical that such a proposed program 

remain neutral and not cause disruptions to the industry. If EPA moves forward with an 

emissions offset program, it should work with manufacturers to ensure manufacturer neutrality. 

Finally, EPA should develop any program within ICAO. 

Organization: General Electric Aviation (GE) 

Comment: Any emissions offset program should be approved and adopted by the international 

community through ICAO/CAEP. With that in mind, GE is interested in further discussions of 

the voluntary option. This is particularly true if the program would be applicable to new engine 

designs and derivatives that are subject to the proposed Tier 8 standards, but are temporarily 

unable to meet those requirements. It would also be true if it created the incentive to adopt new 

technologies earlier than would otherwise be the case in the absence of such incentives. 

Response: We appreciate the concerns raised by the commenters regarding the proposed 

voluntary offset emission program. We are also encouraged by GE’s interest in further 

discussions about how this program may be useful in the context of the Tier 8 standards and a 

possible future Tier 8 production cutoff. EPA staff agrees that the proposal needs to be further 

developed to address certain aspects of the offset program. We have determined that the time it 

would take to sufficiently develop the program is incompatible with the need to promptly 

promulgate the Tier 6 production cutoff standard with a near-term effective date of January 1, 

2013. Therefore EPA is not including the voluntary emission offset program in the final rule at 

this time. Nonetheless, we continue to see value in such a program for the aviation industry and 

recommend continuing to consider such a regulatory flexibility in the future. 

Although we are deferring action on the proposed voluntary emission offset program for the time 

being, we believe that such programs are envisioned within the ETM language related to 

exemptions. Furthermore, we do not agree with the commenters who questioned the EPA's legal 

authority for adopting a voluntary emissions offset program as part of the aircraft engine 

emission standards. We are somewhat surprised by the industry commenters who questioned the 

authority for ABT programs outside of the narrow examples cited in their comments, and we are 

not yet persuaded by their claims. Note that the U.S. Court of Appeals for the D.C. Circuit has 

clearly stated that EPA has substantial discretion under the CAA section 231 to adopt final 

aircraft emission standards as the agency deems appropriate.(National Ass’n of Clean Air 

Agencies v. EPA 489 F.3d 1221 (D.C. Cir. 2007)) We also wonder to what extent their view 

represents the industry as a whole, including any aircraft engine manufacturers who also 

manufacture engines that are subject to other EPA regulations that provide for ABT without the 

“express” statutory authority the commenters claim is necessary. If in future actions we seek 

additional comments on the legality of ABT programs under our aircraft standards, we will be 

interested in receiving comments from other stakeholders in the mobile source arena who might 

have views regarding the arguments presented by the industry commenters above. 

15 
 

 

 

 

 

 

 

 

 

 

 

In the meantime, we note that several of our mobile source regulations, in addition to the rule 

cited by industry commenters, have long provided regulated industry with the flexibilities 

inherent in an ABT program, under the authority of, for example CAA section 213, and none of 

those subject industries have opposed the creation of such programs or questioned their legal 

basis. See, e.g., 40 C.F.R. part 89, subpart C (averaging, banking and trading provisions for 

nonroad compression-ignition engines); 40 C.F.R. part 90, subpart C (certification averaging, 

banking and trading provisions for nonroad spark-ignition engines at or below 19 kilowatts); 40 

C.F.R. part 91, subpart C (averaging, banking and trading provisions for marine spark-ignition 

engines); 40 C.F.R. part 92, subpart D (certification averaging, banking and trading provisions 

for locomotives and locomotive engines); 40 C.F.R. part 94, subpart D (certification averaging, 

banking and trading provisions for marine compression-ignition engines). EPA continues to 

believe that the legal basis of these ABT programs is sound. 

Issue: Non-LTO Emissions 

Organization: Aerospace Industries Association (AIA), General Aviation Manufacturers

Association (GAMA) and Pratt & Whitney (PW) 

Comment: EPA should clarify in the final rule that it is not regulating cruise (non-LTO) NOx 

emissions. EPA should not regulate cruise NOx for several reasons. First, according to the 

commenters, the Agency lacks legal authority as it has not made a finding that such specific

emissions endanger public health or welfare, as required under section 231(a)(2)A) of the 

Clean Air Act. Additionally, there is insufficient evidence to support such a specific finding,

noting that EPA cited only a single study on cruise NOx emissions in the NPRM. Further,

many cruise NOx emissions from flights departing from and landing at U.S. airports do not 

occur in domestic airspace. Finally, there is no generally-accepted technique for measuring 

cruise NOx emissions. 

Organization: Air Transport Association (ATA) 

Comment: It would be premature to rely on a single study for a wholly new and potentially

significant finding. The study EPA references acknowledges significant limitations, and

some ground-level pollutants are actually the product of precursor emissions from aircraft 

at altitude which may or may not be combined with local emissions from other sources.

EPA should continue to look at peer-reviewed work in this area before adopting a finding

on non-LTO NOx emissions. 

Response: As stated in the preamble to the proposed rule, our purpose in discussing nonLTO emissions was to present the limited analysis done to date that we are aware of and

request comment on it, as well as the existence of other relevant research. Clearly, nonLTO emissions are part of the overall inventory. Also, we believe that the research

conducted to date in this area suggests that continued examination of LTO and non-LTO 

emissions as they relate to ground-level health and welfare effects is warranted, regardless

of the scope of any prior endangerment finding regarding NOx emissions generally. We

also note that our pre-existing aircraft emissions standards, and our standards as revised, 

16 
 

 

 

 

do not expressly contain any limitation on operational applicability, although our test 

procedures are focused on measuring concentrations and determining mass emissions

through calculations during simulated aircraft landing-takeoff cycles (LTOs), consisting of 

at least the following four modes of engine operation: taxi/idle, takeoff, climbout, and

approach. 

Issue: Inventory Projections 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: EPA should not rely on the emissions estimates presented in Tables 2 and 3 of

the NPRM when issuing the final rule. The data in Tables 2 and 3, when compared side-byside, cannot be reconciled according to the commenters. The roughly three-fold increase in 

the relative contribution of aircraft NOx to total mobile source NOx shown in Table 2, in 

conjunction with the estimated nine percent increase in commercial air traffic shown in 

Table 3 suggests that NOx emissions from other mobile sources must decrease by a factor

of approximately three by 2020. EPA has not adequately justified how it generated the 

2020 estimates in Table 2. 

Organization: Air Transport Association (ATA)Comment: “...concurs with the analysis

presented in the Preamble to the Proposed Rule on the contribution of NOx emissions from

aircraft in the landing and takeoff (LTO) cycle – defined to be emissions released at or

below 3000 feet – to emissions inventories and local air quality effects. Both EPA and 

ICAO/CAEP have a well-documented understanding of these emissions and their

relationship to local air quality. “ 

Response: Our purpose in including the emissions inventories in the NPRM was twofold.

First, we wanted to identify the size of the aircraft inventory. Second, we wanted to show

how that inventory compared to the emissions from other source categories. With this 

information the reader would have a better understanding of how aircraft cause and

contribute to air pollution. 

Our justification for this final rule is twofold. First, section 231(a)(2)(A) of the CAA

authorizes the EPA Administrator to “from time to time, issue proposed emission standards

applicable to emissions of any air pollution from any class or classes of aircraft engines

which in his judgment causes, or contributes to air pollution which may reasonably be 

anticipated to endanger public health or welfare.” In a 1997 action, we found “(1) that the 

public health and welfare is endangered in several air quality regions by violation of the 

National Ambient Air Quality Standards (NAAQS) for NOx (which contributes to ozone) and

CO; and (2) that airports and aircraft are now or are projected to be, significant sources of

emissions of NOx and CO in some of the air quality control regions in which the NAAQS are 

being violated.”5 Under the authority of the Act and our subsequent finding, we are thus

updating our aircraft NOx regulations. Second, this final rule moves to make U.S. emissions 

5 See 62 FR 25355, 25358 (May 8, 1997) 

17 
 

 

 

 

 

 

 

regulations consistent with those adopted by ICAO/CAEP. As an ICAO member, it is

incumbent upon us to do so as a party to the Chicago convention. 

Regarding the extreme reductions in non-aircraft mobile source NOx emissions in the 

future, these reductions are the result of aggressive federal emission regulations adopted

by EPA at various times and are not easily summarized in a single document. The specific

sources of the emissions inventories for the various mobile source categories can be found

in the air quality modeling technical support document (TSD) developed in support of the 

proposed Federal Transport Rule Phase 1.6 

Issue: Annual Production Report to EPA 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA), and Pratt & Whitney (PW) 

Comment: “The EPA must recognize that production data is proprietary confidential

business information (“CBI”) and must be protected as such. In 40 C.F.R. § 2.208, the EPA

lists five factors for identifying CBI, all of which are applicable in this case. Production data 

(a) has not expired as confidential, (b) is protected by engine manufacturers, (c) is not 

reasonably obtainable without the manufacturer’s consent, (d) is not specifically required

to be disclosed by statute, and (e) if disclosed would cause substantial harm to the 

manufacturer’s competitive position through data mining. The Final Rule, therefore, should

exempt, at the outset, all production data received through annual reporting requirements,

from Freedom of Information Act (“FOIA”) requests or other methods of public disclosure.

Cf. Confidentiality Determinations for Data Required Under the Mandatory Greenhouse Gas

Reporting Rule, 76 Fed. Reg. 30782 (May 26, 2011) (shielding categories of CBI obtained

through the Mandatory Greenhouse Gas Reporting Rule from public disclosure, after

assessing the information under 40 C.F.R. § 2.208).” 

Response: We appreciate the concern that the manufacturers and their associations have 

on this topic. However, we do not believe that it is appropriate in this final rule to adopt a 

blanket categorical CBI determination for engine production volumes. In other EPA

regulations for mobile sources, there is a long history of required annual reporting of

production and sales data without a broad categorical determination of this data 

considered as CBI. 

In response to the comments, however, EPA is adding a provision to the final rule that is 

consistent with how EPA has addressed CBI claims for submitted information under other 

mobile source rules. More specifically, this provision is patterned after our existing

regulations for nonroad compression-ignition engines, small nonroad spark-ignition

engines, marine spark-ignition engines, locomotives and marine compression ignition 

engines (as contained in 40 CFR parts 89.7, 90.4, 91.7 92.4 and 94.4, respectively). It sets 

forth how EPA would treat – on a case by case basis – submitted data which would, and 

6 “Federal Transport Rule Phase 1 (TR1) Emission Inventory for Air Quality Modeling Technical Support 

Document, June 30, 2010, available in public docket EPA-HQ-OAR-2010-0687. 

18 
 

 

 

would not, be covered by a CBI claim from the manufacturer as provided by 40 CFR part 2.

The addition of this provision will ensure that no information that is legitimately protected

CBI gets inadvertently released to the public. EPA believes this fully addresses the 

commenters’ concerns expressed above, and is a logical outgrowth of our proposed rule. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: “Within the NPRM, the EPA requests reporting from all gas turbine and

turboprop engine manufacturers. Small engines less than 6Klbf and turboprops are 

required only to meet the smoke standards, so it would be appropriate for manufacturers

of these engines to supply only this information. 

More specifically, 76 Fed. Reg. 45035-45036, wherein the expectations for the reporting

requirements are outlined, small engines and turboprops will not be able to provide NOx,

UHC or CO emissions (since these were not required or acquired in support of FAR Part 34

certification) nor will the fuel flow or pressure ratio be supplied (since these values based

upon a reference standard engine was not required or acquired in support of FAR Part 34)

at any mode of operation. In many older engine cases, the smoke number (by mode) may

not be available and thus only the characteristic peak smoke value will be reported.” 

Organization: Pratt & Whitney (PW) 

Comment: “...emissions reporting for a particular engine model should only be required to

the extent that engine model is subject to EPA regulations. In its Notice, EPA proposes to

require manufacturers to report HC, CO, NOx, smoke, and CO2 emissions data for all models,

including smaller turbofan engines, which EPA acknowledges are only subject to smoke 

standards. 76 Fed. Reg. at 45,035-36. Those reporting requirements are not feasible for

small turbofan engines because there are no standardized procedures for measuring

emissions other than smoke. Without consistent measurement procedures applied within 

and across manufacturers, EPA will not be able to gather valid data. Moreover, even if there 

were standardized procedures, imposing additional reporting requirements for

unregulated emissions on smaller engines would create an unreasonable burden on 

manufacturers of those engines. Some of those engines may be in very limited production,

meaning test engines may not be available, and any previously-existing data may have been 

gathered years before using non-standard testing methods. Forcing manufacturers to

undertake expensive new testing now for emissions EPA does not even regulate is an 

unreasonable demand.” 

Organization: Williams International 

Comment: “...It is recognized that the referenced NPRM is generally applicable to engines

with rated thrust greater than 26.7 kN. However, Section III, subpart D, “Annual Reporting

Requirement” states that the annual reporting requirement, in particular, will also “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.” Smoke number total, smoke number 

19 
 

 

 

 

 

 

over each segment of the entire LTO cycle and smoke number characteristic level can be 

provided. 

Also included in this section of the NPRM are the proposed elements that are to be 

provided in the annual report. The requirement to report the following elements is of

concern to Williams International: 

• Reference pressure ratio 

• Mass total and over each segment of the landing-takeoff (LTO) cycle for UHC, CO, NOx, 

and CO2 

• Fuel flow total and over each segment of the LTO cycle 

U.S. manufactured gas turbine engines that are installed in U.S. manufactured Part 23 and

Part 25 aircraft must show compliance to the 14 CFR Part 34 fuel venting and exhaust 

emissions requirements. FAA issues regulations under 14 CFR Part 34 to ensure 

compliance with EPA regulations under 40 CFR Part 87 and to reflect the requirements of

ICAO Annex 16, Volume II. The only requirement in 14 CFR Part 34 relevant to turbofan 

engines with rated thrust less than 26.7 kN is the control of smoke emissions, measured by

smoke number (reference section 34.21(e)(1) of 14 CFR Part 34). The maximum smoke 

number regulation limit is a function of rated thrust only and therefore reference pressure 

ratio determination is not required. In addition, smoke number measurement procedures

do not require the measurement and correction of fuel flow at any of the LTO mode 

settings.” 

For turbofan engines with rated thrust less than 26.7 kN, manufacturers will be unable to 

provide HC, CO, NOx or CO2 emissions, as well as fuel flow and reference pressure ratio.

They would like to understand how having only smoke number emission information from

small engine manufacturers aligns with the objectives of the NPRM. 

Response: Our intent was to require this more specific data set that related only to

currently regulated emissions. We did not intend for manufacturers to have to conduct 

additional testing to obtain new data for this reporting. Therefore, we are requesting that 

all manufacturers of turbine engines report specific information regarding their engine 

fleet in order to verify that we have accurate emission records. Currently, as turbofan 

engines under 26.7kN thrust and turboprop engines are only regulated with respect to 

their smoke number, for these engines we will only be requesting data addressing engine 

ID, production volume and values related to smoke number. More specifically, we will be 

requesting the following information for these engines: 

• Company corporate name as listed on the engine type certificate 

• Engine type (turbofan, mixed turbofan, or turboprop) 

• Calendar year for which reporting 

20 
 

 

 

 

 

 

 

• 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) 

• 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) 

• Date of issue of type certificate and/or exemption, i.e. month and year 

• 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 for emissions certification purposes, identify the 

original certificated engine model. 

• Engine sub-model that received the original type certificate for the engine type 

certificate family 

• Production volume of the sub-model for the previous calendar year, or if engine is

no longer produced, state that the engine model is not in production and list the date of

manufacture (month and year) of the last engine produced 

• Regarding the above production volume report, specify (if known) the number of

engines that are intended for use on new aircraft and the number intended for use as

certified (nonexempt) spare engines on in-use aircraft 

• 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) 

• Smoke number total and over each segment of the entire Landing and Takeoff Cycle 

(LTO) (i.e. Take-off, Climbout, Approach, Taxi/Ground Idle) 

• Smoke number characteristic level 

• Number of tests run per sub-model 

• Number of engines tested per sub-model 

Regarding how the reporting of smoke information aligns with the objectives of the NPRM,

we note that the only currently accepted method for estimating aircraft PM emissions is

EPA/FAA’s First Order Approximation version 3a (FOA3a) methodology, which is

incorporated into FAA’s Emissions and Dispersion Modeling System (EDMS). EDMS is the 

official aviation environmental compliance tool in the U.S., and EPA works closely with FAA

as an active member of FAA’s EDMS design review group to maintain model robustness. In

the absence of actual PM data from aircraft engines, the FOA3a methodology relies upon 

21 
 

 

 

 

 

 

smoke number information in order to estimate non-volatile PM emissions. Without 

reliable smoke number data, then the FOA3a methodology is rendered useless and would

adversely affect EPA’s ability to calculate emission inventories that underpin policies and

guidance. Thus, we believe that the reasons stated in the NPRM in support of the reporting

requirement in general apply equally and specifically to the reporting of smoke 

information. 

In cases of older engines where smoke number by mode is not known, we do not believe it 

is appropriate to require additional engine testing to provide smoke number by mode.

Thus, EPA is amending the regulatory text to allow for the reporting of only the total smoke 

number in cases where smoke data by mode does not exist for current production engines. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: “An additional technical correction, in 76 Fed. Reg. 45035, we point out that 

even if an engine has no production during a 12 month period it would not necessarily be 

categorized as “out of production” as suggested. Different terminology should be used.” 

Organization: General Electric (GE) 

Comment: “With respect to production status (in- or out of production), in the case of a 

specific engine sub-model that has not been manufactured in the previous year, should that 

sub-model be reported as out of production if it still is offered for sale, but there are no

current firm orders for future deliveries?” 

Response: If no engines of a specific model were produced in the previous 12 months and

the engine model is not “out of production”, the manufacturer should list “zero” (0) as

number of engines produced for year in question. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: “...NOx is not currently a regulated greenhouse gas in the U.S., and we are 

uncertain why reporting of this information would be of assistance to the EPA. Further, we 

do not believe this information would be beneficial or accurate information for the general

public as it is based only on an airport landing and takeoff (LTO) cycle. Similarly, small

engine reporting of smoke also would not be logical to factor into GHG reporting.” 

Response: It appears that the commenter has confused this proposed rule to update our

aircraft emission standards with a separate rulemaking on Greenhouse Gas (GHG) emission 

reporting. Our proposed reporting requirements are completely separate from EPA’s 

“Mandatory Reporting of Greenhouse Gases” that was finalized in October. 

The data that is being requested in our proposal is directly related to conducting accurate 

emission inventories from aircraft turbine engines. These data will also aid us with 

22 
 

 

 

 

 

 

developing appropriate public policies regarding aircraft exhaust emissions through our

standard setting role under the Clean Air Act (CAA) for engine standards. 

In order to ease the burden to the manufacturers, EPA is requiring turbine engine 

manufacturers to report data from both rules to us in one report. This all encompassing

report will reduce duplicate reporting of items such as engine ID and manufacturer, while 

allowing EPA access to pertinent emission data. In the proposal, we had identified the 

items that would reduce reporting burden by placing a (GHG) image next to the reporting

data request, and maybe this is the source of the commenter’s confusion. 

As a point of clarification, the commenter is not entirely correct in stating that NOx is not 

currently regulated as a greenhouse gas in the U.S. We have, in fact, identified NOx from

aircraft as a greenhouse gas and LTO NOx is already required to be reported to EPA as 

described above. However, as aircraft NOx emissions are currently regulated, we have not 

promulgated aircraft NOx standards aimed specifically at controlling greenhouse gases. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: “The NPRM proposes some changes in reporting requirements from that of the 

ICAO emissions databank. We thank the EPA for understanding the difficulties of reporting,

and agree that the entries in the databank should be at least 2 dp, the smoke and HC values

reported to 1 dp, and all other values such as OPR and thrust should be reported to at least 

3 significant figures. Manufacturers have taken the initiative within ICAO to improve the 

emissions databank to reflect this viewpoint.” 

Response: We note this comment is somewhat confusing as it seems to generally express

support for our proposed emissions certification regulations while primarily addressing an 

issue outside of the scope of this rulemaking, namely that of reporting data to ICAO’s 

emissions databank. We do note a difference in the suggested reporting standard for

smoke number (one decimal place) compared to what we proposed for emissions

certification (three significant figures). We also note that our provisions for significant 

figure reporting were proposed in the context of emissions certification rather than annual

production reporting. However, as this comment seems to address the annual reporting

provision, and our provisions for significant figure reporting in the emissions certification 

process would carry over to the annual production reports, we are addressing this

comment here in the context of the production reporting requirement. 

We recognize the value to industry of having consistent reporting requirements across

organizations and platforms where possible. Further, we recognize our role in achieving

such consistent reporting requirements, both through working with relevant industries

and organizations to develop appropriate requirements, and in implementing these 

requirements in our own regulations. Thus, we took part in discussions among ICAO’s 

Certification Task Group (CTG) to work toward streamlining emissions data reporting

among EASA, ICAO, and EPA. At these discussions, it was agreed to by subject matter 

23 
 

 

 

 

 

 

experts from industry, EASA, EPA, and FAA that at least three significant figures are 

appropriate for all of the different data types which will be required under our reporting

program, as we proposed, with the exception of Smoke Number (SN). Since a smoke 

number measurement typically is only accurate within +/- 2 or 3 SN; the CTG advised that 

reporting SN to more than a single decimal point would imply a level of accuracy that is not

statistically supported for the measurement. We agree with the CTG and are making the 

appropriate revisions in the final regulatory text to require smoke numbers be reported to

one decimal place. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: “Within the Proposed Rule, the EPA requests that manufacturers provide to

them a production report. This request extends beyond manufacturers located in the 

United States, which can prove difficult. It also may be difficult to separate spare and new

engines with certain sales; to do so correctly would require additional monitoring.” 

Response: It is not clear what the actual concern regarding production reporting is, as the 

comment did not provide any examples or specifics as to the nature of the issue. We note,

however, that AIA represents both domestic and foreign aircraft engine manufacturers,

which makes it even more difficult to understand why the reporting would be an issue only

for manufacturers with production facilities outside of the U.S. We further note that no 

such concerns regarding the difficulty of reporting for domestic manufacturers were 

expressed, either by AIA/GAMA or any individual manufacturers directly. It would seem a 

simple thing for manufacturers to track any production of engines covered by our 

standards, regardless of where they are produced. Further, engine manufacturers tend to

have an extremely limited number of manufacturing facilities for their engine production,

and barring specific examples of the potential difficulties, we do not see how a company

that manufactures such a limited quantity of such a specialized and expensive product 

might have difficulty monitoring its production quantities throughout its company. We 

note that foreign manufacturers of a wide variety of other nonroad engines and equipment 

routinely track and provide production data to us as part of their participation in our 

emissions standards’ averaging, banking and trading programs. Thus, we do not believe 

that engines being manufactured in a foreign country and that are subject to our standards

provide any unique circumstances that would make it more difficult to track their

production. Similarly, it is hard to imagine what the difficulty would be regarding

separating spare engines from new for purposes of reporting given that the two types of

engines will be easily differentiated by the labels they will be required to carry. Further,

the permanent record for each excepted spare engine must indicate that it was produced as

an excepted spare, much like current FAA regulations require that the permanent record of

an exempted engine must indicate that status.7 Therefore, EPA is promulgating the 

production report without change. 

7 14 CFR 45.13(a)(7)(ii) 

24 
 

 

 

Organization: Pratt and Whitney (PW) 

Comment: The final rule should expressly state that engines that are both manufactured

and sold outside of the United States are not subject to production data reporting

requirements. Under the extraterritoriality principle, the commenter argued, EPA lacks the 

legal authority to subject foreign-made and foreign sold engines to reporting requirements.

Two U.S. Supreme Court rulings support the general proposition that unless a contrary 

intent appears, United States law is meant to apply only within the territorial jurisdiction of

the United States, Equal Employment Opportunity Comm’n v. Arabian American Oil Co., 499 

U.S. 244, 248 (1991) and Morrison v. Nat’l Austl. Bank Ltd., 130 S. Ct. 2869, 2878 (2010).

Also two lower court rulings holding that CERCLA and RCRA do not have extra-territorial

application, Arc Ecology v. United States Dep't of the Air Force, 294 F. Supp. 2d 1152 (N.D. 

Cal. 2003) and Amlon Metals, Inc. v. FMC Corp., 775 F. Supp. 668 (S.D.N.Y. 1991). Finally,

expressly excluding foreign-made and foreign-sold engines is consistent with EPA’s stated 

goal in requiring production data: to acquire accurate inventories of the domestic aircraft 

fleet. 76 Fed. Reg. at 45,035 (EPA needs to “understand how current gaseous emissions

standards are affecting the current fleet”). 

Response: We do not believe it is necessary to promulgate the regulatory language the 

commenter requests. Both our proposed regulatory text at section 87.42, and our preamble

discussion of the proposed reporting requirements (76 FR at 45035-36) explained that the 

proposed reporting requirements would apply to 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. Thus, the scope of the proposed reporting

requirement extends just as far as the scope of EPA emission standards, which extend just 

as far as the United States' certificating authority. Unless an engine which is both

manufactured and sold outside of the United States is intended to operate in U.S. airspace,

it is not subject to our emissions standards. The relevant regulatory text for this is §87.3 of

the proposed regulations, which addresses the general applicability of the entire part 87. It 

specifically limits the applicability to only those aircraft required by FAA to meet our 

standards. Since FAA does not require aircraft that will never operate in the United States

to meet our standards, such aircraft are not subject to our reporting requirements. 

Consequently, EPA does not agree that the cases cited by the commenter have any

relevance to the scope of our proposed reporting requirement -- we are not attempting to

apply the requirement in an extra-territorial manner beyond the reach of the standards

and U.S.-issued type certificates that reflect the standards. This could indeed include 

engines that are "foreign-made" and "foreign-sold" that may be used in a manner that

makes them subject to our standards and necessitate U.S. certification. It is reasonable and

appropriate for us to require reporting of such information under section 114 of the Clean 

Air Act, as it will help us to understand how gaseous emission standards are affecting the 

current aircraft fleet, to conduct accurate emissions inventories, and to develop sound

public policy approaches and possible future emission standards. 

Organization: General Electric Aviation (GE) 

25 
 

 

 

 

 

 

Comment: We request that EPA clarify the following aspects of the proposed reporting

provisions: 

•	 “87.42(c)(2)(v) requires identifying if an engine sub-model is a derivative engine for

certification purposes. We are unsure whether this information already appears on 

the Type Certificate Data Sheet, and if not, how we can document the engine’s status. 

•	 87.42(c)(2)(vi) requires reporting of the engine sub-model that received the 

original type certificate. Typically, several sub-models appear on a new type 

certificate. Should all of these original sub-models be listed in such a case?
 

•	 87.42(c)(3) requires reporting of calendar year production of each sub-model. We

interpret this to mean, and seek your confirmation, that “production” in this case is

the actual number of engine assemblies delivered to customers in a given calendar 

year... 

•	 87.42(c)(3) requires reporting of the engine sub-model for each engine produced.

In some cases, engines are delivered to the airframe manufacturer without submodel specific control software. What should be reported?” 

Response: With respect to §87.42(c)(2)(v), engines certified as derivative engines, must be 

approved as derivatives by FAA. We expect the manufacturer to keep track of this status 

for reporting. With respect to §87.42(c)(2)(vi), where an original type certificate covers

multiple sub-models, the manufacturer should treat the sub-model that was tested as the 

original sub-model. 

With respect to §87.42(c)(3), the manufacturer should base its reports on the date of

delivery to the airframe manufacturer. For engines delivered without a final sub-model 

status, it is important to note that the production report for a given production year does

not need to be reported until two months after that production year ends. So in most cases,

the manufacturer will have time to ascertain the engine’s sub-model when installed before 

submitting its production report. Nevertheless, we recognize that sometimes a 

manufacturer will not know the engine’s ultimate sub-model until after it submits its 

report. In such cases the manufacturer may do any of the following: 

1) List the sub-model that was shipped or the most probable sub-model.

2) List all potential sub-models.

3) State “Unknown Sub-Model”. 

Once the manufacturer had complete information, it would then amend its report. 

Issue: Supersonic Aircraft Engines 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

26 
 

 

 

Comment: “We do not believe section E. Proposed Standards for Supersonic Aircraft 

Turbine Engines should be included in this NPRM. Within CAEP it was agreed that 

standards are “not appropriate for future products” and therefore should not be done so

independently by the U.S. EPA.” 

Response: Our objective is to adopt standards that are equivalent to ICAO/CAEP standards

to meet U.S. treaty obligations under the Convention on International Civil Aviation. The

proposal to adopt the NOx and CO emission standards for turbine engines that are used to

propel aircraft at sustained supersonic speeds-- to complement our existing HC standard

for these engines – would meet this objective. It is irrelevant if CAEP has declared or stated

that standards are not appropriate for future engines of supersonic aircraft because NOx

and CO standards for this category of engines remain in ICAO’s Annex 16, Volume IV,

International Standards and Recommended Practices. As stated above, we intend to have 

our aircraft engine emission standards remain equivalent to ICAO/CAEP standards to meet 

our treaty obligations. As part of EPA’s continued participation in CAEP proceedings, we 

will keep abreast of any ICAO/CAEP action regarding emission standards for future engines

of supersonic aircraft. Therefore, EPA is promulgating the standards applicable to engines

used on supersonic aircraft as proposed. 

Issue: Annual Reporting Burden and Cost 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: The cost estimate for reporting burden is underestimated, especially for the first 

report. There is no guidance yet on what should be contained in the reports. 

Response: The information collection request (ICR) we submitted to the Office of

Management and Budget estimated the annual burden and cost per respondent (i.e.,

basically each engine manufacturer) to be 6 hours and $365. We believe AIA/GAMA

understood our cost estimate to be for the whole effort to compile the specified

information. However, our cost estimate relates only to the incremental burden of sending

EPA the information that has already been prepared for submission to ICAO and/or FAA.

We believe our estimate accurately reflects the additional burden associated with the 

requirement to send EPA the specified information. We also note that the annual estimate 

is based on the fact that information which is initially reported, but remains unchanged,

does not need to be reported again in subsequent years. This could mean that subsequent 

annual reports for an engine sub-model may only contain the annual production volume for

that sub-model. Further, as noted in the previous discussion of reporting requirements, we 

are streamlining these reporting requirements by combining them with the greenhouse gas

reporting requirements, allowing manufacturers to comply with both requirements with a 

single data submission. Therefore, we are making no changes to the burden estimates in 

the ICR. 

27 
 

 

 

 

 

 

Regarding the second point made by the commenter, once the requirement is in 

place, we will consider publishing a guidance regarding any further clarification that is

needed. We expect to provide an electronic reporting format that will include information 

regarding data fields, formatting the information, and submitting the files to EPA. 

Issue: Humidity Correction Factor 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: The value for humidity when speaking of Standard day conditions (76 FR 45046) 

differs from Annex 16; EPA specifies “0.00” while CAEP specifies 0.00634. EPA should 

follow the same figure as used by CAEP. 

Response: The standard humidity value of 0.00 percent applies under our existing

regulations and we did not propose to revise it. This value is slightly lower than the value of

0.00634 included in Annex 16. Although this difference has little practical impact, in 

response to the comment, EPA is changing our regulations to be consistent with the Annex. 

Issue: Regulatory Text Terminology 

Organization: Air Transport Association (ATA) 

Comment: Regulatory definitions of “tiers” should reference their source CAEP standards

for the sake of transparency 

Response: We are not including regulatory cross-references between tiers of EPA

standards and levels of CAEP standards. We do consider the CAEP standards in setting our

standards, and generally attempt to ensure that manufacturers can produce a single 

product that complies with both EPA and CAEP standards as adopted by foreign 

authorities. However, in the context of implementing U.S. regulations, the CAEP standards

are not directly applicable or enforceable. We believe the naming convention using tiers

appropriately emphasizes that it is the EPA emission standards that apply. 

Issue: Derivative Engines 

Organization: Aerospace Industries Association (AIA), General Aviation Manufacturers

Association (GAMA), and General Electric Aviation (GE) 

Comment: The EPA proposed to adopt the ETM provisions that would be used to evaluate if

the emission characteristics of a modified engine design were significant enough from the 

parent engine’s emission certification basis so that a demonstration of compliance with

newer emission standards is necessary, or if it is a “derivative” version of the original

model with no emissions changes. As a general matter, the EPA should not codify the ETM 

language. The ETM will evolve over time and rigid EPA regulations will not, even allowing

for FAA flexibility to use good engineering judgment if necessary when deciding what is 

28 
 

 

 

 

 

and is not a derivative. It is better to just let FAA rely on the ETM guidance in its decision 

making. 

Response: Regarding the adoption of ETM language into EPA regulations, the Clean Air Act 

directs EPA to establish air pollution emission standards for aircraft engines. (See 42 U.S.C.

7551 (a)(2)(A).) Implementation of this statutory directive mandates that we specify fully

enforceable air pollution control requirements for aircraft engines. This in turn requires

that we establish such standards and any other associated requirements in regulatory

form. As noted by the commenters, the ICAO ETM itself is a guidance document for use by

aviation authorities. It does not represent a standard or any other enforceable regulatory

requirement. In the particular case cited by the commenters, they appear to ask that FAA

be given unlimited discretion to determine which engines are subject to each new tier of 

standards. Such unlimited discretion is inconsistent with our responsibilities under the 

Clean Air Act. 

We also disagree with the comment suggesting that the ETM will evolve over time, but the 

EPA regulations will not. As a working member of ICAO’s Committee on Aviation 

Environmental Protection, we will participate in developing any relevant revisions to the 

ETM and may make appropriate adjustments to our regulations as needed. 

We continue to believe that the ETM specifications for “no emissions change” are 

appropriate objective criteria for derivative engines. Thus, because we must codify 

regulatory provisions to objectively specify when engines are considered to be “derivative 

engines”, EPA is finalizing regulatory provisions consistent with the ICAO ETM guidance. 

Organization: Air Transport Association (ATA), Dassault-Aviation (DA), and Pratt and

Whitney (PW) 

Comment: The proposed regulatory text for determining if a new engine design is a 

derivative of an existing engine model contains a substantial deviation from the expressed

intent of the rule as described in EPA’s preamble and the ETM guidance. Specifically the 

ETM provides that “If a modified engine remains on the existing type certificate, it may

retain the existing certification basis of the parent engine if the modification(s) ...results in 

a decrease of the absolute emissions levels....” The proposed part 87.7 provides that the 

certificate holder must demonstrate that “...the proposed derivative engine model’s 

emissions meet the applicable standards and differ from the original model’s emission 

rates only within...” specified ranges for each pollutant. For example, the specified range is

+ or – 3 g/kN for NOx. This is more stringent than the ETM, and could discourage cleaner

engines that are not clean enough to meet next tier of standards. The final rule should be 

consistent with the ETM to prevent this untoward effect. 

Response: We agree that the regulations should allow for such engines to be considered

derivatives, even if the difference was outside the “no emission change” range. This 

29 
allowance is consistent with the ETM and was inadvertently left out of our proposed

language. EPA is adding this allowance to the final regulations. 

Organization: Aerospace Industries Association (AIA) and General Aviation Manufacturers

Association (GAMA) 

Comment: The preamble to the proposed rule states that “...engine models represented by

characteristic levels at least 5 percent below all applicable standards would be allowed to

demonstrate equivalency by engineering analysis. In all other cases, the manufacturer

would be required to test the new engine model to show that its emissions met the 

equivalency criteria.” 

In the above quoted text, the term “new model’ is used. This is the wrong term because it 

would be referring to changes made to an existing engine. This could cause an engine 

manufacturer to conduct an additional emissions test in cases where a very small change 

was made to the engine due to a performance or engine weight change. We recommend

this be altered to allow a manufacturer to consider “...such emissions changes by analysis

prior to this point, and only if such analysis revealed a deterioration that pushed the engine 

very close to the emission limits that the manufacturer be requested to complete an engine 

emissions test.” 

The proposed regulatory text states that if the characteristic level of the original

certificated engine model before modification is at or above 95 percent of the applicable 

standard for any pollutant, you must measure the proposed derivative engine model’s 

emissions for all pollutants to demonstrate the derivative engine’s resulting characteristic

levels will not exceed the applicable emission standards. The use of the terms “you must 

measure” also implies further engine testing when additional analysis may likely prove 

sufficient. 

Response: We want to clarify that this text explicitly requires engine testing when an 

original engine’s emission are within 5% of any emission standard. This text does not 

allow engineering analysis in such cases. We continue to believe this to be the appropriate 

policy. Given the greater uncertainty of engineering analysis relative to actual testing, we 

cannot rely on it for engines very close to the standard. This provision is also consistent 

with the ETM. Therefore, EPA is promulgating the language as proposed. 

In response to the comment on the term “new model” we are revising the regulations to say

“new engine configuration”. 

30