12634 Federal Register / Vol. 89, No. 33 / Friday, February 16, 2024 / Rules and Regulations 

1 ‘‘The Secretary of Transportation, after 

consultation with the Administrator, shall prescribe 

regulations to insure compliance with all standards 

prescribed under section 7571 of this title by the 

Administrator. The regulations of the Secretary of 

Transportation shall include provisions making 

such standards applicable in the issuance, 

amendment, modification, suspension, or 

revocation of any certificate authorized by part A 

of subtitle VII of title 49 or the Department of 

Transportation Act.’’ 42 U.S.C. 7572 

2Federal Register Vol. 86, No. 6, Final Rule, 40 

CFR parts 87 and 1030 ‘‘Control of Air Pollution 

from Airplanes and Airplane Engines: GHG 

Emission Standards and Test Procedures,’’ 

Environmental Protection Agency, pp. 2136–2174. 

3 42 U.S.C. 7571 

4Federal Register Vol. 87, No. 115, Notice of 

Proposed Rulemaking, 14 CFR parts 21, 38, 121, 

and 125 ‘‘Airplane Fuel Efficiency Certification,’’ 

Federal Aviation Administration, pp. 36076–36091. 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Parts 21, 38, 121, and 125 

[Docket No.: FAA–2022–0241 Amdt. No. 

121–391, 125–75, 38–1, 21–107] 

RIN 2120–AL54 

Airplane Fuel Efficiency Certification 

AGENCY: Federal Aviation 

Administration (FAA), Department of 

Transportation (DOT). 

ACTION: Final rule. 

SUMMARY: This action adopts fuel 

efficiency requirements for certification 

of certain airplanes. These certification 

requirements implement the emissions 

standards adopted by the Environmental 

Protection Agency (EPA) to allow 

manufacturers to certificate their 

airplanes for fuel efficiency in the 

United States. This action also fulfills 

the FAA’s Clean Air Act obligations to 

enforce implementation of EPA’s 

aircraft emissions standards for 

greenhouse gas emissions. 

DATES: Effective April 16, 2024. 

The incorporation by reference of a 

certain publication listed in this rule is 

approved by the Director of the Federal 

Register as of April 16, 2024. 

ADDRESSES: For information on where to 

obtain copies of rulemaking documents 

and other information related to this 

final rule, see ‘‘How to Obtain 

Additional Information’’ in the 

SUPPLEMENTARY INFORMATION section of 

this document. 

FOR FURTHER INFORMATION CONTACT: For 

technical questions concerning this 

action, contact Ralph Iovinelli, Office of 

Policy, International Affairs, & 

Environment, Emissions Division (AEE– 

300), Federal Aviation Administration, 

800 Independence Avenue SW, 

Washington, DC 20591; telephone 202– 

267–3566; email ralph.iovinelli@faa.gov. 

SUPPLEMENTARY INFORMATION: 

I. Executive Summary 

A. Purpose of the Regulatory Action 

As a signatory State to the Chicago 

Convention, the United States must 

establish minimum standards consistent 

with those prescribed by the 

International Civil Aviation 

Organization (ICAO) on a wide range of 

aviation-related matters, including 

aircraft emissions, or file a difference. 

The United States’ adoption of the 2017 

ICAO carbon dioxide (CO2) emission 

standards for certain airplanes aligns 

United States law with the ICAO 

standards. 

Moreover, the Clean Air Act 

Amendments of 1970 (Clean Air Act) 

direct the U.S. Environmental 

Protection Agency (EPA) to adopt 

standards applicable to the emission of 

any air pollutant from any class of 

aircraft engines. The Clean Air Act also 

directs the Secretary of Transportation 

(and by delegation, the Administrator of 

the FAA) to implement the standards 

adopted by the EPA.1 On January 11, 

2021, the EPA published a final rule 

adopting new domestic airplane 

greenhouse gas (GHG) emissions 

standards in 40 Code of Federal 

Regulations (CFR) part 1030.2 As 

required by the Clean Air Act 3, the FAA 

is implementing those EPA standards 

through this final rule by adopting new 

certification regulations in 14 CFR part 

38 for fuel efficiency for certain covered 

airplanes. The applicability of these 

regulations and the regulatory emissions 

limits are the same as those adopted by 

ICAO in its airplane CO2 emission 

standards. 

This rulemaking establishes fuel 

efficiency certification requirements for 

certain subsonic jet airplanes with a 

maximum takeoff mass greater than 

5,700 kilograms and for certain 

propeller-driven airplanes with a 

maximum takeoff mass greater than 

8,618 kilograms. Under this final rule, 

an airplane is subject to these 

certification requirements: (1) at new 

(original) type certification; (2) upon 

manufacture of any covered airplane 

after January 1, 2028; or (3) when a 

modification to a covered airplane 

meets change criteria specified in the 

regulations. This rulemaking excepts 

from applicability airplanes used for 

firefighting, amphibious airplanes, 

airplanes lower than specific masses, 

reciprocating engine airplanes, nonpressurized airplanes, and certain 

specialized operations airplanes. 

For covered airplanes, a certification 

applicant must demonstrate that the 

airplane meets these new part 38 

requirements. The new part 38 

requirements established by this 

rulemaking prescribe fuel efficiency 

limits, which are the emission standards 

adopted by the EPA. This rulemaking 

expresses fuel efficiency limits as 

maximum permitted fuel efficiency 

metric (FEM) values that are determined 

by the maximum takeoff mass of the 

airplane. Thus, the applicant must 

determine an FEM value to demonstrate 

compliance against the applicable fuel 

efficiency limit. The two certifiable 

components of the FEM are the specific 

air range (SAR) and the reference 

geometric factor (RGF). The SAR 

represents the distance an airplane can 

travel per unit of fuel consumed and is 

determined by direct flight test 

measurement or use of a validated 

performance model. The RGF is a 

representation of airplane fuselage size 

based on the floor area of pressurized 

space in an airplane. The technical 

detail needed to determine the FEM 

value of an airplane is included in 

Appendix A to part 38. An applicant 

must receive FAA approval for all 

information the applicant uses to 

calculate the FEM value of an airplane. 

To comply with part 38, the FEM value 

must not exceed the airplane’s 

applicable fuel efficiency limit. 

In addition, to fully implement the 

EPA standards through the FAA’s 

certification process, this rulemaking 

makes corresponding changes to the 

FAA certification procedures in part 21 

to include compliance with part 38 as 

a certification requirement. Moreover, 

this rulemaking requires that the FEM 

value of the airplane, along with other 

part 38 compliance information, be 

placed in an FAA-approved section of 

the flight manual of the airplane. 

The FAA’s adoption of these 

certification requirements implements 

the emissions standards adopted by the 

EPA, allows manufacturers to certificate 

their airplane for fuel efficiency in the 

United States, and fulfills the statutory 

obligations of the FAA under the Clean 

Air Act. The FAA’s promulgation of this 

Airplane Fuel Efficiency regulation is 

the final step for the United States in 

implementing the 2017 ICAO carbon 

dioxide (CO2) emission standards for 

certain airplanes promulgated in Annex 

16 Volume III under the Chicago 

Convention. 

B. Changes Made in This Final Rule 

The FAA has adopted part 38 and 

sections of parts 21, 121, and 125 largely 

as they were proposed in a notice of 

proposed rulemaking (NPRM) that was 

published on June 15, 2022.4


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5Annex 16 to the Convention on International 

Civil Aviation, Environmental Protection, Volume 

III, ‘‘Aeroplane CO2 Emissions,’’ First Edition, July 

2017. https://store.icao.int/collections/annex-16- 

environmental-protection/products/annex-16- 

environmental-protection-volume-iii-aeroplane-co2- 

emissions. 

6Federal Register Vol. 86, No. 6, Final Rule, 40 

CFR parts 87 and 1030 ‘‘Control of Air Pollution 

from Airplanes and Airplane Engines: GHG 

Emission Standards and Test Procedures,’’ 

Environmental Protection Agency, pp. 2136–2174. 

The FAA considered the public 

comments it received on its proposal 

and the adopted rule reflects 

consideration of those comments. The 

FAA received over 60 comments on the 

NPRM, ranging from suggested 

typographical and grammatical edits to 

substantive comments on proposed 

regulatory text and language in the 

NPRM preamble. As a result of these 

comments, the FAA made changes 

throughout the regulatory text. For 

instance, the FAA revised the language 

in the applicability and change criteria 

sections (§§ 38.1 and 38.19) to clarify 

the applicability of part 38 to newly 

built airplanes and modifications to 

airplanes. These revisions clarify this 

final rule is not applicable to 

modifications of in-service airplanes 

that have not previously shown 

compliance to part 38 prior to the 

modification, except for manufacturers 

who are required to comply with part 38 

for in-production airplanes that have 

not received their first certificate of 

airworthiness as provided in the 

applicability section of this rule. The 

FAA also made edits to several 

technical requirements in Appendix A 

(e.g., center of gravity, airplane weight, 

fuel samples, flight test procedures, and 

calculations and corrections of test 

data). Revisions to sections within parts 

21 and 121 include: the inadvertent 

omission of the reference to these new 

fuel efficiency certification 

requirements in the certification 

provisions (§ 21.21), consistency edits 

(§ 21.93), and correction of an error 

(§ 121.141). 

II. Authority for This Rulemaking 

The FAA’s authority to issue rules on 

aviation safety is found in Title 49 of the 

United States Code (49 U.S.C.). Subtitle 

I, Section 106 describes the authority of 

the FAA Administrator. 

The Clean Air Act, 42 U.S.C. 7572, 

authorizes the Secretary of 

Transportation to implement aviation 

emission standards adopted by the EPA 

to insure compliance with the same. 

Furthermore, 49 CFR 1.83(c) delegates 

to the FAA Administrator the authority 

to carry out the functions of this section 

of the Clean Air Act. 

This rulemaking adopts regulations to 

insure compliance with the standards 

adopted by the EPA under the Clean Air 

Act in 40 CFR part 1030 to control the 

emissions of certain GHG emissions 

from airplanes. This rulemaking is 

issued under the authority described in 

42 U.S.C. 7572 and 49 CFR 1.83(c). 

III. Background 

A. General Background 

As a signatory State to the Chicago 

Convention, the United States must 

establish minimum standards consistent 

with those prescribed by ICAO or file a 

difference with ICAO if the United 

States’ standards differ from them in 

any particular respect. The Committee 

on Aviation Environmental Protection 

(CAEP) is a technical committee of the 

ICAO Council that assists in formulating 

ICAO policy and adopting Standards 

and Recommended Practices related to 

aircraft noise and emissions. The FAA 

represents the United States on CAEP, 

attending annual Steering Group 

meetings and CAEP triennial meetings, 

and contributing technical expertise to 

CAEP’s many working groups. The EPA 

serves as an advisor to the United States 

member of CAEP at the annual and 

triennial meetings and contributes 

technical expertise to the FAA and 

CAEP’s working groups on aviation 

emissions, pollution control technology, 

and environmental policy. Within 

CAEP, the FAA assists and advises the 

EPA on aviation-specific environmental 

issues, airplane and engine 

technologies, and airworthiness 

certification matters. 

In 2009, the ICAO Council and its 

Group on International Aviation and 

Climate Change (GIACC) developed a 

‘‘Programme of Action’’ to limit or 

reduce the impact of aviation on the 

climate. The program’s ‘‘basket of 

measures’’ included the reduction of the 

carbon footprint of international civil 

aviation, beginning with the 

development of a technology-based 

certification standard for CO2 emissions 

from subsonic airplanes. 

The CO2 standard-setting process 

included input from governments, 

airplane and engine manufacturers, nongovernmental environmental 

organizations, research institutions, and 

academics worldwide. The standardsetting process occurred in two 3-year 

phases. The first phase focused on the 

development of the CO2 certification 

requirement (i.e., a CO2 metric, test 

procedures, and measurement 

methodology). The second phase 

focused on the development of the CO2

standard itself (i.e., establishing 

regulatory limits, applicability, and 

assessments of cost effectiveness). The 

principles and key criteria that guided 

the process included the concepts that: 

—No certification requirements should 

be imposed that compromise airplane 

safety; 

—Airplane CO2 emissions should be 

reduced through the integration of 

fuel efficient technologies in airplane 

type designs; 

—Airplanes that incorporate differing 

generations of CO2 reduction 

technologies should be treated fairly 

and equitably; 

—Any adopted standard should be 

independent of airplane size, purpose 

or utilization; 

—The metric used should be robust and 

minimize unintended airplane and 

system design consequences; 

—Any adopted standard should use 

industry standard practices of 

measurement and correction; and 

—The implementation of any adopted 

standard should reflect a manageable 

and appropriate level of resources to 

be expended by national 

airworthiness authorities and 

manufacturers. 

In February 2016, CAEP agreed on a 

new CO2 emission standard for certain 

airplanes. ICAO adopted this new 

standard, set out in Annex 16, Volume 

III, in March 2017.5

In the United States, the Clean Air Act 

directs the EPA to adopt standards 

applicable to the emission of any air 

pollutant from any class of aircraft 

engines, which in the EPA 

Administrator’s judgment causes, or 

contributes to, air pollution which may 

reasonably be anticipated to endanger 

public health or welfare. The Clean Air 

Act also directs the Secretary of 

Transportation (and by delegation, the 

Administrator of the FAA) to implement 

the standards adopted by the EPA. The 

FAA implements these EPA standards 

by prescribing regulations in title 14 

CFR that require the certification of 

aircraft and aircraft engines to the EPA 

standards. 

On January 11, 2021, the EPA 

published a final rule 6 adopting new 

domestic airplane GHG emission 

standards in 40 CFR part 1030. In 

accordance with the Clean Air Act, the 

FAA is adopting new certification 

regulations for certain airplanes to 

insure compliance with the EPA 

standards. The FAA also supports the 

adoption of these standards because 

they are aligned with the principles and 

key criteria that guided the ICAO 

process. The applicability of these 


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7Federal Register Vol. 81, No. 7, Final Rule, 40 

CFR parts 87 and 1068 ‘‘Finding that Greenhouse 

Gas Emissions From Aircraft Cause or Contribute to 

Air Pollution That May be Reasonably Be 

Anticipated To Endanger Public Health and 

Welfare.’’ Environmental Protection Agency pp. 

54422–54475. 

8Both CO2 and N2O are constituents of EPA’s 

defined term ‘‘greenhouse gases,’’ which means an 

air pollutant that is the aggregate group of six 

greenhouse gases: CO2, N2O, methane, 

hydrofluorocarbons, perfluorocarbons, and sulfur 

hexafluoride. See 40 CFR 1030.105. 

regulations and the regulatory emissions 

limits in the United States are the same 

as those adopted by ICAO as its airplane 

CO2 emission standard in Annex 16, 

Volume III. 

The FAA, EPA, and ICAO each use 

different terminology to reference the 

same standards. In Annex 16 Volume 

III, ICAO references its standard as CO2

emissions because the amount of CO2

emitted is directly proportional to the 

amount of fuel burned by an airplane at 

cruise speed and altitude. ‘‘Airplane 

CO2 emissions’’ is a commonly used 

term that fits well within ICAO’s 

international goals to reduce the carbon 

footprint of aviation. More specifically, 

Part II of Annex 16 Volume III is titled 

‘‘Certification Standard for Aeroplane 

CO2 Emissions Based on the 

Consumption of Fuel.’’ 

Domestically, the EPA issued an 

endangerment finding for GHG 

emissions from airplane engines,7

which, in turn, required the EPA to 

issue GHG standards for airplane 

engines. The EPA rule establishes 

standards for GHGs in recognition of 

airplane engine emissions of CO2 and 

another GHG, nitrous oxide (N2O).8 The 

EPA did not set limits on N2O 

emissions, noting that they are small 

and are proportionally reduced as fuel 

consumption is reduced. Accordingly, 

the EPA adopted the fuel efficiency 

metric established by ICAO, which 

effectively limits both CO2 and N2O 

GHGs emitted by airplane engines. 

The FAA describes these same limits 

and procedures as measures of fuel 

efficiency, since this final rule 

prescribes a measurement of airplane 

performance determined by the SAR 

parameter to determine fuel efficiency. 

This measurement is akin to the fuelburn-based ICAO standard. The FAA 

intends that the fuel efficiency 

standards be the same as the standards 

that the EPA adopted in 40 CFR part 

1030. 

In summary, it is the FAA’s intent 

that the three standards—FAA’s fuel 

efficiency regulations in 14 CFR part 38, 

the EPA’s GHG emission standards in 40 

CFR part 1030, and ICAO’s CO2

emissions standards—be considered 

equivalent for purposes of 

implementation. 

The FAA is making final guidance 

material for part 38 available at the same 

time as this final rule and has placed the 

final Advisory Circular 38 (AC38) in the 

docket. 

B. Summary of the NPRM 

On June 15, 2022, the FAA published 

the NPRM titled ‘‘Airplane Fuel 

Efficiency Certification.’’ At the same 

time, the FAA also posted for comment 

in the NPRM docket draft guidance 

material for the proposal in the form of 

a draft AC38. 

In its NPRM, the FAA proposed the 

adoption of the EPA’s GHG standards as 

fuel efficiency standards for airplanes in 

a new 14 CFR part 38. The FAAproposed standards would impose 

requirements when an applicant seeks 

type certification. In general, the 

proposal applied to certain subsonic jet 

airplanes and certain propeller-driven 

airplanes above a specified mass. The 

FAA’s proposal also provided for use of 

the existing part 11 exemption process. 

Importantly, the NPRM provided the 

requirements for determining the fuel 

efficiency value for subsonic airplanes 

at certification. The proposal then 

established fuel efficiency limits as 

adopted by the EPA. For an airplane, the 

fuel efficiency limit would be based on 

a fuel efficiency value calculated using 

two primary parameters: the SAR and 

the RGF. The FAA proposal included an 

Appendix A, which contained the 

technical detail needed to determine the 

FEM value. For an airplane to comply 

with part 38, under the NPRM, the FEM 

value could not exceed the applicable 

fuel efficiency limit. 

In addition, to fully implement the 

EPA standards through the FAA’s 

certification process, for applicable 

airplanes the proposal included 

amendments to part 21 to include 

compliance with part 38, and to the 

operating regulations to ensure that 

flight manuals contained fuel efficiency 

certification information. The FAA 

solicited public comments on the NPRM 

and draft AC38 for a period of 61 days. 

The comment period on the NPRM 

closed on August 15, 2022. 

C. General Overview of Comments 

The FAA received 62 comments on 

the NPRM and the draft AC38. One of 

these comments was received and 

considered after the comment period 

closed. 

Most comments were from 

individuals. In addition, the agency 

received comments from several 

airplane and engine manufacturers and 

industry groups: Aerospace Industries 

Association (AIA), Airbus, Airlines for 

America (A4A), Airlines Pilots 

Association (ALPA), Avions de 

Transport Regional (ATR), Boeing, 

Embraer S.A. (Embraer), FedEx 

Corporation (FedEx), General Electric 

Aviation (GE), General Aviation 

Manufacturers Association (GAMA), 

Gulfstream Aerospace Corporation 

(Gulfstream), Modification and 

Replacement Parts Association 

(MARPA), National Business Aviation 

Association (NBAA), and the Port of 

Seattle. 

The FAA received nine comments 

generally supporting the rule as 

proposed. These commenters included 

ALPA, ATR, Port of Seattle, and some 

individuals. Fourteen commenters, 

including Boeing, AIA, A4A, Airbus, 

FedEx, GE, MARPA, Gulfstream, NBAA, 

GAMA, Embraer, and some individuals 

supported the rule generally but offered 

requests for clarifications, changes, or 

additional provisions. The FAA 

received comments from 39 individuals 

who opposed the proposed rule. 

The commenters raised overarching 

issues on the NPRM related to the 

FAA’s authority to issue the rule, the 

applicability of the rule, and potential 

costs of the rule. Commenters also 

requested clarifications and raised 

several technical issues. A discussion of 

comments requesting specific 

clarifications, changes, or revisions to 

the NPRM and the FAA’s responses to 

these requests is in Section IV, 

‘‘Discussion of Comments and the Final 

Rule.’’ 

IV. Discussion of Comments and the 

Final Rule 

The following summarizes the 

comments received to the NPRM and 

the FAA’s responses to these comments. 

A. FAA’s Part 38 Authority 

Comments: Several individuals 

commented that the proposed rule 

exceeded the FAA’s authority or was 

otherwise unnecessary for a wide 

variety of reasons. Conversely, other 

commenters indicated the proposed rule 

is needed to allow manufacturers to 

certificate their airplanes for fuel 

efficiency in the United States and 

would fulfill the FAA’s Clean Air Act 

statutory obligations. 

Response: The FAA disagrees with 

those commenters who indicated that 

the FAA exceeded its authority or that 

the rule was unnecessary. The proposed 

rule falls well within the FAA’s 

statutory mandate and is required by 

Section 7572 of the Clean Air Act. The 

Clean Air Act vests authority to regulate 

airplane emissions with both the EPA 

and the FAA. Section 7571 of the Clean 


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9Boeing commented that the proposed rule 

should update the DOT regulations in 49 CFR 

1.83(c) that delegate this authority to the FAA 

Administrator to reflect the new 40 CFR part 1030. 

Paragraph 1.83(c) delegates to FAA the authority to 

implement the standards adopted by the EPA under 

42 U.S.C. 7572. The FAA does not have the 

authority to amend 49 CFR 1.83(c) but will raise the 

issue to DOT. 

10Federal Register Vol. 86, No. 6, Final Rule, 40 

CFR parts 87 and 1030 ‘‘Control of Air Pollution 

from Airplanes and Airplane Engines: GHG 

Emission Standards and Test Procedures,’’ 

Environmental Protection Agency, pp. 2136–2174. 

11 In California v. EPA, a number of states and 

environmental organizations challenged EPA’s 

adoption of the standards in 40 CFR part 1030. The 

District of Columbia Circuit Court of Appeals held 

that the rule was within EPA’s authority under 42 

U.S.C. 7571 and that the agency reasonably 

explained its decision to harmonize its regulation 

with the ICAO standards. The Court also held that 

as the EPA had made the policy choice to align with 

ICAO standards, the EPA did not have a need to 

examine alternatives departing from the ICAO 

standards. 72 F.4th 308 (D.C. Cir. 2023). 

Air Act directs the EPA to adopt 

standards applicable to the emission of 

any air pollutant from any class of 

aircraft engines, which in the EPA 

Administrator’s judgment causes, or 

contributes to, air pollution that may 

reasonably be anticipated to endanger 

public health or welfare. Further, the 

EPA must consult with the FAA on 

these aircraft engine emissions 

standards. The EPA adopts these 

standards in title 40 of the CFR. 

After the EPA adopts the standards, 

section 7572 of the Clean Air Act directs 

the Secretary of Transportation (and by 

delegation, the Administrator of the 

FAA) 9 to implement the standards 

adopted by the EPA. The FAA 

implements these standards by adopting 

regulations in title 14 of the CFR that 

allow the certification of aircraft and 

aircraft engines to the EPA standards. In 

addition, the proposed rule is consistent 

with the FAA’s own statutes (49 U.S.C. 

106) that authorize the Administrator to 

issue regulations. 

On January 11, 2021,10 the EPA 

published a final rule adopting GHG 

emissions standards applicable to 

certain aircraft engines and airplanes in 

40 CFR part 1030. In accordance with 

the mandate under Section 7572, the 

FAA adopts this rule through new 

certification regulations in part 38 for 

certain airplanes to insure compliance 

with the EPA standards in 40 CFR part 

1030. 

B. FAA’s Role in Establishing Fuel 

Efficiency Standards 

Comments: Several commenters 

opined that the proposal was unrealistic 

or that the FAA was ‘‘simply bowing to’’ 

the EPA. Others said that the FAA 

should focus on other matters, such as 

safety. 

Response: As described in the 

‘‘General Background,’’ the FAA and the 

EPA both participated heavily in the 

ICAO working group and CAEP that 

established ICAO’s Aeroplane CO2

standard. Other entities also provided 

significant input into the process, 

including the affected global aviation 

industry and many other 

representatives. The standard that ICAO 

ultimately established was based on a 

process that considered views from all 

participants. This process resulted in 

the adoption of technology-following 

certification requirements that also 

prevent backsliding to less fuel-efficient 

airplanes. For the same reasons 

articulated in the principles and key 

criteria that guided the ICAO standard 

development process, the FAA 

supported and continues to support the 

adoption of the ICAO and EPA 

standards. 

Finally, as described in ‘‘FAA’s Part 

38 Authority,’’ the FAA is statutorily 

obligated to adopt the EPA standard. 

Comments: Other commenters 

suggested that the goals of the proposed 

regulation may already be met by the 

existing body of regulations or that 

industry was already incentivized to 

achieve fuel efficiency through market 

forces or otherwise. Some suggested that 

the industry had already achieved low 

emissions. 

Response: The CO2 standard-setting 

process at ICAO included input from 

many stakeholders, including airplane 

and engine manufacturers. In addition, 

the FAA received comments from 

several airplane and engine 

manufacturers, including Boeing, 

Gulfstream, Airbus, GE, Embraer, and 

ATR, as well as industry groups that 

represent the broader aviation 

manufacturers and airlines such as 

GAMA, AIA, A4A, and NBAA. In their 

comments on the proposed rule, these 

entities recognized the domestic and 

international need of expeditiously 

adopting these standards in order to 

establish a global fuel efficiency 

certification scheme for airplanes. The 

aviation industry has shown strong 

support for the standard, which is the 

first aviation standard aimed at 

improving airplane fuel efficiency and 

reducing CO2 emissions. 

C. Consideration of Other Alternatives 

Comment: A number of comments 

went beyond the scope of the proposed 

rule to suggest that the FAA should 

instead consider alternative means of 

achieving decreased CO2 emissions, 

such as adding a tax on fuel sales; 

increasing airplane registration fees; 

changing flight procedures; creating 

incentives to encourage operators to 

purchase newer, more fuel-efficient 

airplanes; restricting business jets; 

developing alternative fuels; or 

increasing the availability of alternative 

fuels. Other commenters indicated that 

the rule was not going far enough to 

improve fuel efficiency. 

Response: The FAA reiterates that 

part 38 is consistent with the FAA’s 

authority under its own statutes and the 

Clean Air Act. In particular, the purpose 

of this rule is to implement EPA’s GHG 

standards through the FAA certification 

process. Comments received requesting 

that FAA take an alternative approach to 

address fuel efficiency are not within 

the scope of the proposed rule.11

Comment: Other commenters were 

concerned that the proposed rule would 

result in manufacturers’ transitioning to 

alternative fuels, such as biofuels, or 

wanted clarity on the applicability of 

the proposed rule to hybrid airplanes or 

airplanes using alternative fuels. 

Response: This rule is a technologybased standard, aiming at measuring the 

performance of the airplane in terms of 

fuel efficiency, predicated on the ability 

of manufacturers to improve engine 

propulsion efficiency, aerodynamics, 

and airplane weight—all elements of the 

SAR parameter in the FEM. Neither the 

SAR nor the RGF parameters are 

affected by the type of fuel used in the 

airplane. Therefore, the FEM value does 

not change based on the fuel used in the 

airplane. 

As a general matter, the rule could 

apply to any airplanes meeting the 

applicability criteria of § 38.1, including 

hybrids or those using alternative fuels 

as long as those fuel(s) meet the 

applicable specifications in Appendix 

A. The FAA wants to clarify that the use 

of alternative fuels does not exempt 

covered airplanes from compliance with 

this rule. 

D. General Applicability (§ 38.1(a) and 

(b)) 

In the NPRM, the FAA proposed that 

part 38 would apply to certain subsonic 

jet airplanes and propeller-driven 

airplanes at three applicability points. 

These three points are airplanes (1) 

receiving original type certification on 

or after January 11, 2021; (2) 

manufactured after January 1, 2028, 

regardless of the date of type 

certification; and (3) type-certificated 

before the applicable compliance date 

but where a modification is made that 

would affect the fuel efficiency of the 

airplane after January 1, 2023. 

1. Discussion of Final Rule 

The FAA adopts the applicability 

requirements for part 38 in § 38.1(a) and 


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12For the purpose of FAA’s final rule, ‘‘covered 

airplanes’’ are defined the same as EPA’s definition 

in their final rule: ‘‘Civil subsonic jet airplanes 

(those powered by turbojet or turbofan engines and 

with a MTOM greater than 5,700 kilograms), as well 

as larger civil subsonic propeller driven airplanes 

(those powered by turboprop engines and with a 

MTOM greater than 8,618 kilograms).’’ 86 FR 2136 

(Jan. 11, 2021). 

(b). These paragraphs remain largely as 

proposed and have the same 

applicability as the EPA regulations. 

These paragraphs continue to provide 

for the applicability of these standards 

to certain subsonic jet airplanes and 

propeller-driven airplanes at three 

applicability points. After consideration 

of public comments, the FAA is revising 

the regulation to clarify the applicability 

of part 38 to the currently flying inservice airplanes as well as to proposed 

modifications to covered 12 airplanes 

that have received their type certificate. 

The regulation was also revised to make 

some other non-substantive changes to 

the text. These changes are discussed in 

this section. 

As developed by ICAO, the standards 

adopted by the EPA include three 

occasions on which an airplane 

becomes subject to the 40 CFR 1030 

standards. These same applicability 

points are included in § 38.1(a) and (b): 

(1) at new (original) type certification; 

(2) the manufacture of any covered 

airplane after January 1, 2028; or (3) a 

modification to a covered airplane that 

meets the change criteria of § 38.19. 

These change criteria pertaining to 

airplane modifications are described in 

further detail in § 38.19. The 

applicability points include: 

• New (Original) Type Certification 

Applicability: Paragraphs 38.1(a)(1)–(3) 

describe airplanes whose applications 

for original type certification were 

submitted after January 11, 2021. 

Although the ICAO standard on which 

these regulations are based was effective 

on January 1, 2020, for certifications of 

new type designs, the effective date of 

the EPA regulation was January 11, 

2021, for certifications of new type 

designs. Except for the effective date, 

the EPA and the FAA regulations have 

the same applicability as the ICAO 

standard. The difference in effective 

dates between the ICAO and EPA 

standards has no practical effect in the 

United States. In the twelve months 

between the effective date of the ICAO 

standard and the effective date of the 

EPA standards, the FAA received no 

applications for new type certification 

that would meet the applicability 

criteria of this rule. Although EPA’s 

GHG emissions standards are now 

applicable in the United States through 

40 CFR part 1030, the FAA did not 

receive an application for new type 

certification before the adoption of 

either EPA’s rule or the FAA’s rule. 

Once an airplane is type-certificated for 

fuel efficiency in accordance with this 

rule, all airplanes produced under that 

type certificate must comply with the 

fuel efficiency standards. 

• Manufacture of covered airplanes 

after January 1, 2028: Paragraphs 

38.1(a)(6)–(7) describe the second 

instance of applicability for covered 

airplanes manufactured after January 1, 

2028. These paragraphs address covered 

airplanes that are newly built after 

January 1, 2028, regardless of the date 

of type certification. Airplanes 

manufactured after this date would not 

be eligible for a first certificate of 

airworthiness unless compliance with 

part 38 has been shown. 

• A modification to a covered 

airplane that meets the change criteria 

of § 38.19: Paragraphs 38.1(a)(4)–(5) 

address modifications to covered 

airplanes whose type designs were not 

certified under this rule, where an 

application by the type certificate 

holder for a type design change is 

submitted on or after January 1, 2023, 

and the first certificate of airworthiness 

is issued with the modified type design 

that exceeds the change criteria in 

§ 38.19(c). In determining applicability 

under these paragraphs, a certification 

applicant must consider § 38.1(b), 

which addresses modifications made to 

covered airplanes and directs the reader 

to the change criteria in § 38.19. See 

section IV.N for a discussion on the 

change criteria in § 38.19. 

As noted, the FAA made a few nonsubstantive changes to the applicability 

provisions. The FAA added levels of 

designation to paragraph (a)(1) at the 

suggestion of the Federal Register to 

help clarify the two independent 

applicability provisions in § 38.1(a)(1). 

The FAA also fixed a minor 

typographical error in § 38.1(a)(6)(ii) 

and changed the order of the agencies 

identified in § 38.1(a)(4) to reflect that 

the FAA is issuing this rule. 

2. Public Comments and FAA Response 

Comments: Multiple commenters, 

such as A4A, AIA, Boeing, Airbus, 

FedEx, NBAA, and some individuals, 

requested clarification that the rule 

would not apply to in-service airplanes, 

consistent with the related EPA 

regulation and the applicable ICAO 

standard. These comments, summarized 

in the following sentences, included 

specific statements and questions 

related to the applicability of the rule to 

current in-service airplanes and 

modifications to such airplanes. Boeing 

requested clarity that individual inservice airplanes, whose type designs 

have not been previously certificated to 

part 38, and to which modifications are 

made by the owners/operators or other 

third parties, do not need to 

demonstrate compliance with part 38. 

Similarly, some of the commenters, 

including A4A, Airbus, and Boeing, 

requested that the FAA clarify the part 

38 applicability provisions regarding 

modified type designs and modified 

versions of airplanes to more clearly 

state that part 38 applies only when a 

type-certificate holder changes the type 

design of an airplane mid-production by 

applying for FAA approval of a 

modified type design. To clarify these 

concepts, the AIA, A4A, Airbus, and 

Boeing specifically requested that the 

FAA modify § 38.1(a)(4)(iii) and 

(a)(5)(iii) to add ‘‘by the holder of the 

type certificate’’ to explain that a third 

party would not be required to show 

compliance to part 38 when requesting 

a supplemental type certificate that aims 

to modify one or more individual inservice airplanes. 

In addition, Airbus requested that the 

FAA clarify the regulatory text in 

§ 38.1(b) by changing ‘‘prior version’’ to 

‘‘prior non-modified version’’ to 

emphasize that the prior version of the 

airplane is the one that does not include 

the modification. 

Response: The FAA intends this rule 

to have the same applicability as the 

related EPA regulation and the ICAO 

standard. As such, this final rule is not 

applicable to current in-service 

airplanes. Where a type certificate 

holder submits an application for a 

change in type design after January 1, 

2023, and the change meets the 

requirements of § 38.19(c), part 38 will 

apply to a newly built airplane 

incorporating this change in order to 

receive its first certificate of 

airworthiness. After January 1, 2028, 

part 38 will apply to all newly built 

airplanes receiving their first certificate 

of airworthiness. 

The FAA recognizes that determining 

the applicability of this rule to a specific 

airplane requires consideration of 

multiple sections in part 38. Although 

§ 38.1 addresses applicability in general, 

when an applicant requests a change in 

type design, it must also consider 

§ 38.19’s change criteria to determine 

the applicability of part 38. Sections 

38.1(a)(1) through (3) address newly 

built airplanes whose applications for 

original type certification were 

submitted after the specified dates. 

Sections 38.1(a)(4) and (5) provide 

applicability requirements for a 

modified version of an airplane whose 

type design was not certificated under 

part 38. Further, § 38.1(a)(4) and (5) 


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relate to a newly built airplane, 

receiving its first certificate of 

airworthiness, based on a type design 

change submitted by the type certificate 

holder on or after January 1, 2023, that 

exceeds the change criteria in § 38.19(c). 

On or after January 1, 2028, all newly 

built covered airplanes that meet the 

requirements of § 38.1(a)(6) and (7) must 

comply with part 38 to receive their first 

certificate of airworthiness. 

Section 38.1(b) makes the important 

connection to the § 38.19 change 

criteria. In § 38.1(b), part 38 applies to 

an airplane where an applicant requests 

a change in type design that meets the 

change criteria of § 38.19. Airplanes that 

have demonstrated compliance to this 

rule (i.e., those that do not fall in 

§ 38.1(a)(4) and (5)) and subsequently 

undergo modifications will need to redemonstrate compliance according to 

the change criteria shown in § 38.19(a) 

and (b). 

With the applicability context 

described in the previous paragraphs, 

the FAA agrees to revise the proposed 

§§ 38.1 and 38.19 to clarify part 38 

applicability to individual in-service 

airplanes and modifications to 

airplanes. The FAA recognizes that 

§ 38.1(a)(4)(iii) and (5)(iii) in the NPRM 

may have been interpreted, as 

commenters suggested, to require 

compliance with part 38 for any 

modifications to an airplane, even a 

currently in-service airplane. The FAA 

does not intend this applicability. This 

final rule slightly updates these 

paragraphs to clarify that this specific 

set of applicability requirements are for 

applications for a change in type design 

made by the type certificate holder. 

Specifically, in response to comments 

requesting clarity on modifications to 

airplanes under these specific 

applicability requirements, this rule 

revises § 38.1(a)(4)(iii) and (5)(iii) to 

state that compliance is required when 

‘‘an application by the type certificate 

holder for a type design change is 

submitted on or after January 1, 2023.’’ 

In combination with the rest of the 

requirements under § 38.1(a)(4) and (5), 

the part 38 now reads clearly that it 

does not apply to a type design change 

application for a currently in-service 

airplane that has not previously shown 

compliance to part 38. Only a newly 

built airplane with a change in type 

design by the type certificate holder, 

applied for on or after January 1, 2023, 

and exceeding change criteria in 

§ 38.19(c), would be required to comply 

with part 38. Therefore, the final rule 

clarifies that part 38 does not apply to 

currently in-service airplanes, including 

modifications, and instead focuses on 

newly built airplanes that incorporate 

modifications. 

Further, in proposed § 38.1(a)(4)(iv) 

and (a)(5)(iv), the words ‘‘for an airplane 

built’’ were redundant with the 

introductory text of § 38.1(a)(4) and (5), 

which already stated, ‘‘A subsonic jet 

airplane—’’ and ‘‘A propeller-driven 

airplane—’’, respectively. To correct this 

redundancy, this final rule removes ‘‘for 

an airplane built’’ from § 38.1(a)(4)(iv) 

and (a)(5)(iv). Also, this change is 

consistent with other changes FAA 

made to § 38.1(a)(4) and (5) to clarify to 

the applicability. This change does not 

alter the meaning of the paragraph. 

For consistency with and to fully 

respond to the comments on § 38.1(a), 

the FAA updates the proposed § 38.1(b) 

to reflect that part 38 applies to 

modifications that are based on an 

application for a change in type design 

and meet the change criteria of § 38.19. 

As part of these updates, the FAA 

moves the § 38.19 reference earlier in 

the paragraph to incorporate the change 

criteria more clearly in § 38.1(b). Also, 

the FAA revises § 38.1(b) to explicitly 

state that the applicability is tied to an 

application for a change in the type 

design. This better aligns with the text 

of § 38.1(a)(4) and (5). 

In response to Airbus’ request that to 

change ‘‘prior version’’ to ‘‘prior nonmodified version,’’ the FAA recognizes 

that ‘‘prior version’’ of an airplane may 

not have been described with sufficient 

detail. Based on these considerations, 

this rule also revises § 38.1(b) for 

consistency with § 38.1(a) to more 

accurately describe the state of an 

airplane before or after modifications, 

rather than using ‘‘prior version,’’ and to 

highlight the connection to the change 

criteria in § 38.19. 

Finally, because § 38.19(b) and (c) 

also use ‘‘prior version,’’ this rule makes 

similar consistency changes to these 

paragraphs. 

In summary, these edits to §§ 38.1(a) 

and (b) and 38.19(b) and (c) clarify that 

part 38 does not apply to current inservice airplanes. 

Comments: Airbus, A4A, and Boeing 

also recommended that table 1 in the 

NPRM be clarified to avoid the 

implication that part 38 be applied to 

in-service airplanes. 

Response: In lieu of providing an 

updated table 1 from the NPRM to 

provide a quick reference for 

applicability with examples, the FAA 

has provided a much more detailed 

discussion here to clarify applicability 

of part 38 to in-service airplanes in this 

section. 

Comments: Similar to comments 

requesting clarity on prior version of an 

airplane, Boeing, AIA, and A4A 

requested a definition of ‘‘subsequent 

version,’’ a term that appears in § 38.19, 

to clarify that modifications to 

individual in-service airplanes do not 

require application of the fuel efficiency 

standards. 

Response: This rule’s changes to 

§ 38.1 address the fact that current inservice airplanes, or modification to 

such airplanes, do not require 

compliance with this rule. Therefore, 

the FAA does not see a need to add a 

definition for the term ‘‘subsequent 

version.’’ 

Comments: Boeing requested that the 

FAA add a definition of ‘‘modified type 

design,’’ which is used in § 38.1(a)(4)(iv) 

and (5)(iv), because it was concerned 

that the lack of a definition could create 

potential ambiguity when the text is 

read together with the well-established 

aircraft certification regulations in part 

21 that address ‘changes in type design.’ 

Response: The FAA notes that the 

term ‘‘modified type design’’ in the 

context of § 38.1(a)(4)(iv) and (5)(iv), 

where it appears, refers to the final 

modified configuration of an airplane 

receiving its first certificate of 

airworthiness. 

The FAA is using the word modified 

for consistency with EPA’s regulations. 

For the purposes of part 38, the FAA 

uses the words ‘‘changed’’ and 

‘‘modified’’ interchangeably. 

Comment: Airbus recommended that 

the four (4) applicability requirements 

listed under § 38.1(a)(4) and (a)(5) 

should be joined by adding the 

conjunction ‘‘and’’ after each individual 

requirement to clarify that applicability 

to this rule consists of all four 

requirements in total. 

Response: The FAA reviewed the 

grammatical structure of § 38.1(a)(4) and 

(a)(5). As proposed, the four 

applicability requirements listed under 

each of these sections are separated by 

a semicolon in a list from (i) to (iv) with 

the conjunction ‘‘and’’ between the final 

two provisions (iii) and (iv), signifying 

that the ‘‘and’’ applies to all 

requirements in this list. This format 

follows the Office of the Federal 

Register (OFR) formatting practices, and, 

therefore, the repetition of ‘‘and’’ 

between each requirement is not 

required. The FAA believes this is the 

correct structure and will not 

incorporate Airbus’s recommendation to 

add an ‘‘and’’ after each requirement. 

Comment: Airbus further commented 

on several items such as changing the 

following text from the proposed rule: 

‘‘. . . an application . . .’’ to ‘‘. . . the 

application . . .’’ in paragraph 

(a)(4)(iii); ‘‘. . . type design is submitted 

. . .’’ to ‘‘. . . type design was 

submitted . . .’’ in paragraph (a)(4)(iii); 


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13 GE specifically incorporated by reference 

Boeing’s substantive, non-technical comments on 

the NPRM, including comments on the applicability 

to military aircraft and other requested changes for 

alignment with EPA and ICAO standards. GE also 

specifically incorporated by reference AIA’s 

substantive comments on the proposed rule, 

including comments on the inapplicability of the 

rule to state aircraft and modifications to an inservice aircraft. 

and ‘‘. . . for an airplane built . . .’’ to 

‘‘. . . for that airplane built . . .’’ in 

paragraph (a)(4)(iv). 

Response: The FAA does not agree 

with these suggestions. The FAA wrote 

this rule to apply to a wide range of civil 

airplanes and changing words to ‘‘that 

airplane’’ or ‘‘the application’’ adds a 

level of specificity that is not needed for 

this rule. The suggested change to ‘‘for 

that airplane built with’’ is not 

necessary because the FAA removed 

this phrase from §§ 38.1(a)(4)(iv) and 

(a)(5)(iv) in response to previously 

addressed comments. Regarding the 

change from ‘‘is’’ to ‘‘was,’’ the FAA 

notes that the verb tense of this rule is 

written in present tense. 

Comment: Airbus commented on 

§ 38.1(a)(6) and (a)(7) that the words 

‘‘An individual . . .’’ should be added 

to the beginning of these applicability 

paragraphs to reinforce that these 

requirements apply to individual 

airplanes. Airbus states this would be 

similar to the applicability language in 

ICAO Annex 16 Vol III, Part II, Chapter 

2, § 2.1.1(f)&(g). 

Response: The applicability language 

in § 38.1(a)(6) and (a)(7) has the same 

meaning as the ICAO Annex 16 Vol III 

language even if the terminology is 

slightly different. The applicability 

language in § 38.1(a)(6) and (a)(7) is 

written in singular form starting with: 

‘‘A subsonic jet airplane . . .’’ and ‘‘A 

propeller-driven airplane . . .’’ that has 

‘‘Its first certificate of airworthiness 

issued on or after January 1, 2028.’’ The 

word ‘‘a’’ already places the subject in 

singular form that clearly represents an 

individual airplane, which is consistent 

with the ICAO Annex 16 Vol III. For 

these reasons, it is not necessary to 

reinforce that these paragraphs apply to 

‘‘individual’’ airplanes. 

Comment: The GAMA commented 

that the applicability requirements for 

propellor-driven airplanes with 

maximum takeoff mass (MTOM) greater 

than 8,618 kilograms (kg), as used in the 

proposed rule, could include airplanes 

with maximum takeoff weight (MTOW) 

greater than 18,999.45 lbs when 8,618 

kilograms are converted to pounds. The 

GAMA noted that the mathematical 

conversion of an MTOM of 8,618 kg 

equates to 18,999.45 lbs, which is less 

then what is used for the MTOW limits 

of parts 21 and 23 for normal category 

airplanes. Therefore, the GAMA argues 

the proposed part 38 fuel efficiency 

standards would apply to FAA type 

certificated part 23 airplanes at the 

maximum allowable MTOW of 19,000 

lbs. The GAMA suggested two 

alternative approaches to address this 

potential unit conversion issue in § 38.1 

MTOM references: (1) use 8,619 kg in all 

instances for MTOM threshold for 

propeller-driven airplanes instead of 

8,618 kg; or (2) list both the applicable 

MTOM (mass) of 8,618 kg and MTOW 

(weight) 19,000 lbs. 

Response: The FAA acknowledges 

that conversion from 8,618 kg to lbs 

equates to a weight that is 

approximately 0.5 lbs less than the 

19,000 lbs threshold of other FAA 

regulations. However, when applying 

the conversion in reverse, going from 

19,000 lbs to kg, the result is 0.25 kg 

greater than 8,618 kg. This difference of 

less than 1 lb or 1 kg is extremely small; 

it is unlikely that an airplane would fall 

within this conversion difference. 

Importantly, differences less than 1 lb or 

1 kg would not be reflected in either a 

TCDS or an airplane flight manual. 

Additionally, the use of kilograms as the 

applicability threshold is consistent 

with the EPA standards. For these 

reasons, the FAA finalizes the threshold 

as proposed in § 38.1(a)(3)(i). 

Comments: The MARPA requested 

that the FAA clarify that part 38 does 

not apply to parts manufactured by 

holders of a Parts Manufacturer 

Approval (PMA). In particular, the 

MARPA asked that the FAA include text 

in the preamble to the final rule stating 

that the rule applies only to the design 

and approval of type certificated 

products. In addition, the MARPA 

wanted this text to also state that the 

proposed rule does not apply to Parts 

Manufacturer Approval (PMA) 

manufacturers of modification and 

replacement parts under part 21 subpart 

K. 

Response: The FAA disagrees with 

adding the suggested text to the 

preamble. The applicability section does 

not apply to parts manufactured by 

holders of a PMA. Because these parts 

have the same fit, form, and function of 

the parts they replace they are not 

considered a change in type design. 

Comment: One individual thought 

that this rule would benefit those who 

use private airplanes for travel, 

implicitly indicating that those types of 

planes would not need to comply with 

part 38. 

Response: The FAA disagrees as the 

applicability of this rule includes all 

airplanes that meet the applicability 

requirements regardless of who is using 

the airplane or whether they are 

privately owned. The type of airplanes 

described by the commenter are not 

necessarily exempted from the rule. 

E. Exceptions to Applicability (§ 38.1) 

In the NPRM, the FAA proposed 

several exclusions to the applicability of 

part 38. Part 38 would not apply to 

airplanes with lesser MTOMs than those 

specified in § 38.1(a). Part 38 also would 

exclude airplanes that are designed for 

specialized operations (including the 

presence of unique design features to 

carry out those operations). The NPRM 

also would exclude amphibious 

airplanes, airplanes that have no 

pressurized areas, airplanes designed for 

firefighting, and airplanes powered by 

reciprocating aircraft engines. 

1. Discussion of the Final Rule 

In § 38.1(c), the FAA is adopting the 

same exclusions to part 38 that were 

adopted by the EPA and ICAO. The 

section is remaining as proposed, except 

for one minor non-substantive change in 

§ 38.1(c)(4) where the FAA switched the 

EPA and FAA references so that the 

FAA is identified first as the agency is 

issuing this rule. 

As finalized, part 38 does not apply 

to airplanes with lower MTOMs than 

those specified in § 38.1(a) and 

§ 38.1(c)(1) and (2)). The rule also 

excludes airplanes that are initially 

designed, or modified and used, for 

specialized operations (including the 

presence of unique design features to 

carry out those operations) from part 38, 

subject to a determination that a design 

for specialized operation is detrimental 

to fuel efficiency. The FAA and the EPA 

would make this determination at the 

time an airplane is presented for 

certification. Examples of such airplanes 

could include specialized cargo 

features, specialized missions, or crop 

dusting (§ 38.1(c)(4)). The rule excludes 

from part 38 the following: amphibious 

airplanes (as defined in § 38.3); 

airplanes that have no pressurized areas 

(described as having zero reference 

geometric factor (RGF)); airplanes 

designed for, or modified and used for, 

firefighting; and airplanes powered by 

reciprocating aircraft engines 

(§ 38.1(c)(3), (5), (6), and (7)). 

2. Public Comments and FAA Response 

Comments: Commenters, including 

Boeing and AIA (echoed by GE 13), 

requested that the FAA clarify and 

revise the regulatory text to explicitly 

state that the rule only applies to civil 

airplanes and not military airplanes. 

The AIA specifically requested 

clarification that part 38 did not apply 

to state airplanes, such as those used by 

military, customs, and police services, 


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14 87 FR at 36082. 

15 Volume III—Procedures for the CO2 Emissions 

Certification of Airplanes, § 2.1.3. 

16The FAA inadvertently included guidance from 

ICAO’s Environmental Technical Manual in the 

draft AC38 that was included in the docket for 

review with the NPRM. The exception has never 

been included in the part 38 rule text, and for the 

reasons discussed it has been removed from the 

final AC38. 

or other types of airplanes, such as 

rotorcraft or piston-engine airplanes. 

Boeing requested that the FAA clarify 

the language in § 38.1(a) so that the 

regulation explicitly stated that part 38 

only applied to civil airplanes as 

defined in 14 CFR 1.1. 

Boeing further requested a change in 

§ 38.1(a) from original type certification 

to original civil certification. Boeing 

believed this change and other 

consistency changes would remove any 

ambiguity and clarify that only 

airplanes seeking civil certification are 

subject to the rule. GE supported Boeing 

and AIA comments on this issue. 

Response: The FAA disagrees with 

the request to explicitly revise the 

regulatory text to state that the rule only 

applies to civil airplanes and not 

military airplanes. This rule addresses 

the certification of fuel efficiency for 

subsonic, civil airplanes.14 As defined 

in 14 CFR 1.1, civil aircraft are aircraft 

other than public aircraft. Public aircraft 

is an operational status under the 

statute, not a certification status, since 

any airplane operated by a valid 

government entity could be a public 

aircraft depending on its use. 49 U.S.C. 

40102(a)(41), 40125. Because the FAA 

cannot predict whether a type 

certificated airplane may be used for a 

public aircraft operation, and the status 

of that airplane may change from civil 

to public and back on a flight-by-flight 

basis, the FAA finds that this distinction 

is not appropriate for purposes of this 

rule. 

Further, the FAA disagrees with 

Boeing’s suggested change to original 

civil certification. The FAA does not 

reference its airworthiness certificates as 

‘‘civil certificates.’’ The FAA uses 

terminology such as ‘‘original type 

certificates,’’ consistent with part 21. 

Thus, the FAA declines to modify 

§ 38.1 as suggested by commenters. 

Comments: Commenters also 

suggested the FAA clarify that part 38 

does not apply to airplanes that are 

initially certificated as civil airplanes 

during the production process but 

immediately used for military 

operations. Both AIA and Boeing 

explicitly requested that the FAA add 

these types of airplanes to the list of 

airplanes not covered by the rule in 

§ 38.1(c). Boeing also requested 

corresponding changes to the draft 

Advisory Circular. These commenters 

indicated that these changes are 

consistent with the ICAO standards. In 

particular, they referenced the ICAO 

Environmental Technical Manual 

(ETM) 15 and its inclusion of these types 

of airplanes in a list of examples of 

specialized operational requirements. 

Because the FAA had included language 

in the NPRM to propose the same 

exclusions adopted by ICAO, Boeing 

stated the FAA should include language 

excluding these types of airplanes from 

coverage under part 38. Boeing stated 

the exception would be consistent with 

the examples for these airplanes in the 

ICAO guidelines (the ETM). Boeing also 

indicated that this exception would be 

consistent with past EPA and 

Department of Defense (DOD) practice, 

citing to the EPA’s 2012 Final Rule 

adopting new aircraft engine emissions 

standards for nitrogen oxides. 

Response: Commenters indicated that 

to be consistent with the ICAO 

standards, the FAA needs to exclude 

from part 38 a civil-certificated airplane 

immediately converted to military use. 

The FAA disagrees with the underlying 

premise that part 38 does not apply to 

civil certificated airplanes immediately 

converted to military use. The FAA 

regulations are consistent with ICAO 

Annex 16 Volume III standards, which 

contain no such exemption. The ICAO 

language suggesting the exception of 

military airplanes from CO2

applicability is in ICAO guidance (i.e., 

the ETM guidance document to Annex 

16 Volume III), not in the ICAO 

standards (i.e., Annex 16 Volume III).16

The FAA is not obligated to include in 

its standards any exception suggested in 

ICAO guidance that is not in the ICAO 

standard. 

The FAA has no authority over 

military airplanes involved in public 

aircraft operations, and its regulations 

do not apply to airplanes produced for 

the armed services. The FAA 

certification regulations apply only to 

airplanes that seek civil certification in 

the United States. When an airplane is 

produced, the FAA issues an 

airworthiness certificate for that 

airplane if it conforms to the type design 

and complies with all applicable civil 

regulations. FAA regulations do not 

consider intended use or conversion 

involved in airplane certification— 

either the airplane complies with all 

regulatory requirements and is eligible 

for a civil airworthiness certificate, or it 

does not. 

A manufacturer may produce 

airplanes and parts for the military 

without involving the FAA. If an 

applicant requests civil certification 

from the FAA, the applicant must 

satisfy all applicable regulations for that 

airplane regardless of the potential for 

that airplane’s use for military 

operations. 

In the United States, the FAA has no 

statutory authority over military 

airplanes involved in public aircraft 

operations. Part 38 does not apply to 

these airplanes; accordingly, these 

airplanes cannot be exempted or 

excluded from something that does not 

apply in the first place. For these 

reasons, the FAA does not see the need 

to modify § 38.1(c) in this respect. 

F. Definitions (§ 38.3) 

In the NPRM, the FAA proposed 

several definitions for part 38. These 

definitions would be specific to fuel 

efficiency certification. The proposed 

definitions included: amphibious 

airplane; ICAO Annex 16, Volume III; 

maximum takeoff mass (MTOM); 

performance model; reference geometric 

factor (RGF); specific air range (SAR); 

subsonic; and type certificated 

maximum passenger seating capacity. 

1. Discussion of the Final Rule 

The rule includes a definitions 

section as § 38.3. The section is adopted, 

as proposed, except this rule makes 

modifications to the definition of 

maximum takeoff mass (MTOM) based 

on comments received. 

2. Public Comments and FAA Response 

Comments: Some commenters suggest 

the FAA include additional definitions, 

such as ‘‘subsequent version’’ and 

‘‘modified type design.’’ 

Response: See responses to these 

comments that are discussed in section 

IV.D. 

Comments: The FAA received several 

comments on the definition of 

Maximum takeoff mass (MTOM) in 

§ 38.3. Specifically, Airbus commented 

that the definition of MTOM should be 

modified by replacing ‘‘maximum 

allowable’’ with ‘‘highest of all 

certified’’ takeoff masses. Airbus stated 

that the proposed definition could be 

misinterpreted and suggested clarifying 

that the MTOM represents the highest of 

all of the certified takeoff masses in the 

Type Certificate Data Sheet (TCDS). 

Airbus also suggested replacing 

‘‘approved certification basis’’ with 

‘‘Type Certificate Data Sheet’’ since the 

approved certification basis of a type 

design generally represents the set of 

applicable requirements to the type 


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design and it would be more exact to 

refer to the TCDS. 

Response: The FAA does not agree 

that ‘‘highest of all certified’’ should 

replace ‘‘maximum allowable’’ in the 

definition of MTOM. The MTOM is 

intended to mean the maximum takeoff 

mass an airplane type design is certified 

to and recorded in the TCDS. As 

mentioned by an individual commenter, 

the FAA agrees that the TCDS may 

contain several maximum takeoff 

masses for different variants of the same 

airplane type design, and the MTOM is 

the highest of these maximum takeoff 

masses. The comments reflected 

confusion around which maximum 

mass was meant—maximum structural, 

maximum takeoff for an airplane, or the 

maximum mass of several variants of 

similar design. The FAA does recognize 

that the definition as proposed was not 

clear on this point and is changing 

‘‘maximum allowable takeoff mass’’ to 

‘‘maximum certified takeoff mass,’’ 

which clarifies reference to certified 

MTOM values in the TCDS. The FAA 

also notes that the use of ‘‘maximum 

certified takeoff weight’’ (similar to 

maximum certified takeoff mass) is used 

in other parts of title 14 CFR, including 

parts 21, 25, and 36. 

Regarding the reference in the 

proposal to the ‘‘approved certification 

basis’’ and the requests to replace this 

phrase in the MTOM definition with 

‘‘TCDS,’’ the FAA agrees that the TCDS 

is the appropriate document to reference 

in determining the maximum takeoff 

weight for FAA-certified variants of the 

base model. However, the FAA decided 

to remove ‘‘approved certification basis’’ 

from the regulatory text, and not replace 

it with ‘‘TCDS,’’ because the change to 

‘‘maximum certified takeoff mass,’’ 

earlier in the definition addresses these 

concerns. Applicants may propose the 

use of the highest weight of an airplane 

type design to represent lower-weight 

variants. This allowance provides 

flexibility to applicants who may not be 

interested in certifying an individual 

FEM value for each lower weight 

variant. Such proposals will be 

considered on a case-by-case basis for 

FAA approval as provided in § 38.23. 

Comment: Boeing commented that the 

FAA should revise its description of the 

MTOM definition to clarify that MTOM 

is not an international standard term for 

airplane weight expressed in kilograms. 

Boeing indicated that its expression in 

kilograms is not integral to its meaning. 

Boeing requested that the FAA revise its 

description to state that the MTOM is 

the highest of all takeoff masses for the 

type design configuration. 

Similarly, an individual commented 

that although MTOM needs to be 

expressed in kilograms for use in 

showing compliance with the proposed 

requirements, MTOM is not an 

international standard term for airplane 

weight expressed in kilograms. In 

addition, the commenter noted that 

MTOM is the highest maximum takeoff 

mass specified for the airplane type 

design as stated in the airplane TCDS, 

and that the TCDS may contain several 

maximum takeoff masses (identified as 

maximum takeoff weights in the TCDS) 

for different weight variants for the 

same airplane type design. The 

commenter concluded by stating that 

the MTOM is the highest of these 

maximum takeoff masses. 

Response: The FAA acknowledges 

that in the NPRM preamble the FAA 

described MTOM as the international 

standard term of airplane weight 

expressed in kilograms. The FAA 

recognizes that this statement is 

incorrect as MTOM is not an 

international standard term for airplane 

weight. 

The FAA made minor revisions for 

clarification and moved the reference to 

kilograms to be more closely associated 

with the relevant terms. 

As a result, the FAA has modified the 

definition of MTOM in this final rule to 

be: 

The maximum certified takeoff mass, 

expressed in kilograms, for an 

airplane type design 

Comment: A commenter asked that 

the definition of MTOM include the 

phrase ‘‘for the purposes of complying 

with the requirements of this part.’’ 

Response: The FAA notes that § 38.3 

already begins with the phrase, ‘‘For the 

purpose of showing compliance with 

this part, the following terms have the 

specified meanings:.’’ Based on that, the 

FAA has not changed the definition as 

suggested by the commenter. 

Comment: Airbus provided a 

comment on the definition of 

‘‘Performance model’’ stating that in the 

phrase ‘‘using corrected flight test data 

that can be used to determine the 

specific air range values,’’ the word 

‘‘corrected’’ should be removed since 

test data in test conditions could also be 

used to validate a performance model. 

Response: The FAA disagrees with 

this change as it would cause a 

substantive difference between the FAA 

and the EPA and ICAO standards, both 

of which include the term ‘‘corrected 

flight test data’’ in the definition (See, 

e.g., 40 CFR 1030.105). A substantive 

difference would change the meaning, 

intent, or level of a particular 

requirement. 

G. Compatibility With Airworthiness 

Requirements (§ 38.4) 

As proposed, this section addressed 

compatibility between environmental 

and airworthiness standards. The NPRM 

intended to prohibit the sequencing of 

certification tests for an airplane that 

has not met the applicability 

airworthiness requirements. This 

requirement would ensure that no 

airworthiness requirements are 

compromised during the fuel efficiency 

certification. In addition, the FAA 

proposed to require that all the 

procedures used to conduct the flights 

to demonstrate fuel efficiency 

compliance be conducted in compliance 

with all airworthiness regulations that 

apply to the airplane. 

1. Discussion of the Final Rule 

The FAA received one comment on 

§ 38.4 regarding the sequencing of 

certification tests. The FAA did not 

make any changes to the section based 

on the comment and is adopting the 

section as proposed. 

2. Public Comments and FAA Response 

Comment: Gulfstream asked if an 

applicant, when developing an aeropropulsion model, could substantiate 

the score by conducting some of the 

testing (on a conforming test article) 

before 100% of airworthiness 

certification is complete. 

Response: The FAA recognizes that 

Gulfstream’s comment was in response 

to a sentence in the NPRM preamble 

noting that § 38.4 is intended to prohibit 

the sequencing of certification tests for 

an airplane that has not met the 

applicable airworthiness requirements. 

In response to Gulfstream’s question, 

the FAA clarifies that testing could be 

done on a type design conforming test 

article before 100% of the airworthiness 

certification is complete. The airplane 

configuration conformed for fuel 

efficiency testing purposes must 

represent the configuration sufficiently 

such that the FEM is representative of 

the final type design. The FAA must 

approve configuration(s) not completely 

conforming to the type design prior to 

testing. The FAA did not revise the 

regulatory text based on this comment. 

H. Exemptions (§ 38.5) 

In the NPRM, the FAA proposed a 

process for exemptions. The NPRM 

proposed that a petitioner submit 

petitions for exemption from any 

requirement in part 38 in accordance 

with 14 CFR part 11. The proposal also 

noted that the FAA would consult with 

the EPA on any request for exemption 

from the regulations of part 38. This 

proposed process is the same process 


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the FAA follows when it considers 

petitions for exemption from the engine 

emissions standards promulgated by the 

EPA under 40 CFR part 87 and by the 

FAA in 14 CFR part 34. 

1. Discussion of the Final Rule 

The FAA is adopting § 38.5 as 

proposed. In accordance with 42 U.S.C. 

7572, 49 CFR 1.83(a)(6) and (c), and 49 

U.S.C. 44701(f), the FAA may issue 

exemptions from its regulations when 

such exemption would be in the public 

interest. As adopted, § 38.5 continues to 

provide for submittal of petitions for 

exemption from any requirement in part 

38 in accordance with 14 CFR part 11. 

The FAA is adopting § 38.5 as proposed. 

2. Public Comments and FAA Response 

Comments: Some commenters, 

including AIA, A4A, Boeing, NBAA, 

and Airbus, expressed overall support 

for the FAA’s approach to addressing 

exemption requests from part 38. In 

particular, Boeing supported the use of 

the public interest standard under 49 

U.S.C. 44701 in considering 

exemptions. Several commenters 

requested clarity on the FAA process for 

exemptions in § 38.5. 

Response: The FAA will follow its 

standard process for petitions for 

exemption that are outlined in 14 CFR 

part 11. Section 11.15 of these 

regulations defines a petition for 

exemption and §§ 11.61 through 11.103 

contain the FAA’s regulatory process for 

exemptions. Part of what must be 

included in a petition for exemption is 

an explanation of why the proposed 

action will be in the public interest (14 

CFR 11.71). Section 38.5 adds a 

requirement to this process as it 

provides that the FAA consult with the 

EPA on each exemption petition before 

taking action. This process is the same 

as that followed when the FAA 

considers petitions for exemption from 

the engine emissions standards 

promulgated by the EPA under 40 CFR 

part 87 and by the FAA in 14 CFR part 

34. 

Comment: Airbus requested that the 

FAA provide information on the 

number of exemptions that could be 

granted and whether the FAA would 

follow the ICAO recommendations in 

granting exemptions. 

Response: How the FAA will process 

future exemptions under part 11 and the 

possible number of exemptions the FAA 

could issue is outside the scope of this 

rulemaking. Although ICAO provides 

some guidance on exemptions that 

member countries could consider, the 

FAA processes each request for 

exemption on a case-by-case basis. 

I. Incorporation by Reference (§ 38.7) 

In the NPRM, the FAA noted that it 

was reserving § 38.7 for materials to be 

incorporated by reference into part 38. 

As part of the final rule development, 

FAA assessed the references to external 

documents throughout the proposed 

rule and is incorporating by reference 

ICAO Doc 7488/3, Manual of the ICAO 

Standard Atmosphere (extended to 80 

kilometres (262 500 feet)), 1993 

(Manual) in § 38.7. The Manual was 

identified in the part 38 Appendix and 

the FAA did not receive any comments 

on the Manual. Specifically, this 

Manual is referenced in sections 

A38.2.1.3.1, A38.5.2.2.1.9, and 

A38.5.2.2.1.10 of Appendix A to part 38. 

In these sections, the applicant must use 

this Manual to establish certain 

reference specifications when 

determining SAR. 

The OFR has regulations concerning 

incorporation by reference (1 CFR part 

51). These regulations require that, for a 

final rule, agencies must discuss in the 

preamble the way in which the 

materials that the agency incorporated 

by reference are reasonably available to 

interested persons, and how interested 

parties can obtain the materials. In 

addition, in accordance with 1 CFR 

51.5(b), the agency must summarize the 

material in the preamble of the final 

rule. 

In accordance with the OFR’s 

requirements, the Manual provides the 

standard values of atmospheric 

parameters, the values of constants and 

coefficients, and the underlying 

equations used in the calculation of the 

atmospheric parameters. The Manual is 

intended for use in calculations in the 

design of airplanes, in presenting test 

results of airplanes and their 

components under identical conditions, 

and in facilitating standardization in the 

development and calibration of 

instruments. 

Interested persons can purchase this 

Manual from the ICAO Store at 999 

Robert-Bourassa Boulevard Montre ́al 

(Quebec) Canada H3C 5H7, 

(www.store.icao.int). 

J. Relationship to Other Regulations 

(§ 38.9) 

Section 38.9 in the proposed rule 

described the authority of the EPA and 

the FAA under the Clean Air Act to set 

and implement standards for aircraft 

engine emissions. In proposed § 38.9, if 

the EPA changed any requirement in 40 

CFR part 1030 that corresponded with a 

regulation in part 38, applicants could 

request a waiver for provisions as they 

appear in part 38 to comply with the 

changes; proposed § 38.9 also described 

the circumstances under which a waiver 

may be granted. 

This proposed section also provided 

that, unless otherwise specified in this 

part, all terminology and abbreviations 

in part 38, that are defined in 40 CFR 

part 1030, have the same meaning as 

specified in part 1030. 

The FAA did not receive comments 

on this section. However, the FAA did 

make some corrections to the text, 

including fixing a typographical error 

and an incorrect reference to the DOT 

delegations of authority to the FAA. 

Other than these corrections, the FAA is 

adopting this section as proposed. 

K. Fuel Efficiency Metric (§ 38.11) 

The NPRM proposed that the fuel 

efficiency of an airplane be determined 

by the amount of fuel it uses to travel 

a certain distance under prescribed 

conditions. This measure was proposed 

as the fuel efficiency metric (FEM). As 

proposed, for each airplane subject to 

part 38 (including an airplane subject to 

the change criteria of § 38.19), § 38.11 

would require the calculation of an FEM 

value using an equation identical to the 

one adopted by the EPA in 40 CFR 

1030.20. 

1. Discussion of the Final Rule 

The FAA is adopting § 38.11 as 

proposed. This section describes the 

FEM of an airplane. The FEM value is 

calculated using an equation identical to 

the one adopted by the EPA. The two 

primary components of the FEM are the 

SAR (provided in § 38.13) and the RGF 

(provided in § 38.15). As described in 

§ 38.11, the FEM is ultimately 

calculated by dividing the average SAR 

values by RGF in a universal equation 

to denote the fuel efficiency of any 

airplane in a manner that is transport 

capability neutral. 

2. Public Comments and FAA Response 

Comment: Gulfstream commented 

that the NPRM preamble description for 

§ 38.11 was confusing and highly 

simplified when it stated that dividing 

SAR by RGF results in a universal 

equation to denote the fuel efficiency of 

any airplane regardless of size. 

Response: The FAA notes that the 

preamble is not meant to reflect every 

detail of the rule, but rather summarizes 

its contents and elaborates as necessary. 

The statement was referring to the fuel 

efficiency metric equation, provided in 

§ 38.11, which is (1/SAR)average divided 

by RGF0.24. In describing it as a 

universal equation, the FAA was 

referring to the fact that these 

parameters also comprise the metric in 

ICAO’s international Aeroplane CO2

Emissions standard. 


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Comment: An individual commented 

that the FEM seems to be defined upside 

down because the higher the fuel 

efficiency value gets, the worse the 

airplane is, efficiency-wise. 

Response: The term ‘‘Fuel Efficiency 

Metric’’ (FEM), as used in this rule, is 

not a measure of airplane fuel 

efficiency, as commonly understood. 

This rule uses a newly defined term, 

FEM, that represents a correlation to the 

level of GHG emissions produced by the 

airplane. 

The ICAO designed the FEM system 

(the FEM metric plotted against MTOM) 

similarly to other ICAO environmental 

standards, where the FEM of an airplane 

must be below a limit line to pass the 

standard. In order to achieve this result, 

the parameter SAR was inversed (i.e., 1/ 

SAR). 

L. Specific Air Range (§ 38.13) 

Section 38.13 of the NPRM proposed 

the requirements for determining SAR, 

one of the two primary components of 

the FEM. 

1. Discussion of the Final Rule 

As adopted, Section 38.13 describes 

the SAR. The SAR is an aeronautical 

parameter used in the aviation industry 

to represent the distance an airplane can 

travel per unit of fuel consumed. In part 

38 it is used to represent the 

instantaneous fuel efficiency of an 

airplane at any point during stable 

cruise flight. The FAA made one minor 

revision to § 38.13(a)(2)(ii) by replacing 

‘‘made’’ with ‘‘submitted’’ to be 

consistent with the FAA’s intent. The 

FAA made a second minor revision to 

add the word ‘‘or’’ after § 38.13(a)(1) to 

indicate the requirements more clearly. 

Otherwise, the FAA is adopting this 

section as proposed. 

2. Public Comments and FAA Response 

Comment: Boeing suggested that 

§ 38.13(b), as proposed, could be 

overbroad and subject to 

misinterpretation as it could limit SAR 

calculations until the performance 

model is approved by the FAA. Boeing 

requested that the FAA change ‘‘are 

made’’ to ‘‘are submitted.’’ 

Response: The FAA agrees that this 

requirement could be read to mean 

applicants may not make SAR 

calculations, whether for compliance or 

not, until the performance model is 

approved by the FAA. That was not the 

intent of this requirement. In the final 

regulatory text, the word ‘‘made’’ is 

changed to ‘‘submitted.’’ 

Comment: Boeing commented that the 

SAR should be multiplied by the 

airplane’s instantaneous weight in order 

to be used as a measurement of fuel 

efficiency. Boeing suggested clarifying 

that in part 38, the term ‘‘efficiency’’ is 

used to represent the instantaneous fuel 

efficiency of an airplane at any point 

during stable cruise flight. Other 

individual commenters agreed with 

Boeing’s assertion that SAR alone does 

not measure the fuel efficiency of an 

airplane. 

Response: The FAA recognizes that 

the parameter SAR does not ‘‘measure’’ 

the instantaneous fuel efficiency. As 

stated above, SAR is the distance an 

airplane can travel per unit of fuel 

consumed to represent instantaneous 

fuel efficiency. Inherently, the 

determination of instantaneous SAR 

already includes the instantaneous 

weight of the airplane (i.e., structural 

efficiency in context of this rule), as 

well as the airplane aerodynamic and 

propulsive efficiencies of the airplane. 

The FAA agrees that, in this part, SAR 

is used to represent the instantaneous 

fuel efficiency of an airplane at any 

point during stable cruise flight. 

Comment: Gulfstream requested 

clarification of the FAA’s expectations 

for substantiation of the performance 

model and allowances for weight 

increases. 

Response: Although models may be 

built with first principles analysis or 

wind tunnel data, the model used to 

show compliance must be validated by 

flight test data and approved by the 

FAA. The FAA must also approve any 

allowances regarding models. See 

section 38.13. The AC38 contains 

additional related guidance. 

Comment: An individual commenter 

questioned the need for the statement to 

exclude auxiliary power units (APU) 

from the 1/SAR calculation in 

§ 38.13(c), stating that they would not 

normally need to be included. The 

commenter noted that if there was ever 

a design where they did need to be 

included for some reason, this 

requirement would preclude that. 

Another commenter said that APU 

usage for traditional airplanes should be 

included because the goal is to reduce 

the consumption of hydrocarbons rather 

than potentially shifting the location 

where hydrocarbons are burned from a 

place where they are included to one 

where they are not. 

Response: Section 38.13 specifically 

excludes APUs from the SAR 

calculation. The EPA’s standard in 40 

CFR 1030.23 also contains this 

exclusion and this is a key component 

of the standards. To comply with 42 

U.S.C. 7572 and maintain consistency 

with EPA’s standards in 40 CFR part 

1030, the FAA is adopting this 

paragraph as proposed. 

M. Reference Geometric Factor (§ 38.15) 

Section 38.15 of the NPRM proposed 

the requirements for determining RGF, 

one of the two primary components of 

the FEM. 

1. Discussion of the Final Rule 

As adopted, § 38.15 describes the 

RGF. The RGF is a representation of 

airplane fuselage size based on the floor 

area of pressurized space in an airplane 

and is flexible enough to account for 

single or multi-deck airplanes. This rule 

adopts changes from ‘‘cockpit’’ to ‘‘flight 

deck’’ to provide gender-neutral 

language without changing the meaning 

or intent. Other than this change, the 

FAA is adopting this section as 

proposed. 

2. Public Comments and FAA Response 

Comments: Some commenters, 

including A4A and Boeing, requested 

clarifications on FAA’s descriptions of 

the RGF. Specifically, they requested 

that the preamble state that the RGF is 

a representation of airplane fuselage size 

based on the floor area of pressurized 

space in an airplane and is flexible 

enough to account for single or multideck airplanes. They further stated that 

dividing SAR by RGF results in a 

universal equation to denote the fuel 

efficiency of any airplane in a manner 

that is transport capability neutral 

(which is the FEM). Boeing stated that 

this change was needed because RGF 

was not developed to account for 

productivity and load carrying 

capability, noting that RGF was 

included to achieve the aim of having a 

transport-capability-neutral metric. 

Response: The FAA agrees with A4A 

and Boeing’s characterization of RGF, 

specifically its purpose to create a 

transport capability neutral FEM, and 

the FAA believes the regulatory text is 

consistent with this description. As a 

result, FAA has determined that no 

changes to § 38.15 are necessary based 

on this comment. 

Comment: An individual commenter 

questioned the appropriateness of RGF. 

The commenter proposed an example to 

show that a poorly designed airplane 

could have a similar FEM value as a 

better-designed airplane. The 

commenter also questioned the value of 

the RGF concept when passengers or 

payload transported over a given 

distance, per unit of energy input could 

be considered instead. 

Response: The FAA disagrees. A 

specific goal of the standards are to 

avoid unintentionally incentivizing 

airplane manufacturers to design 

airplanes for specific operational 

objectives, such as payload-carrying 


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capability or mission range. The RGF is 

not intended to account for an airplane’s 

transport capabilities (e.g., its 

productivity or payload-carrying 

capability). Instead, the use of RGF in 

this regulation creates a transport 

capability neutral fuel efficiency metric. 

The FAA asserts that RGF is 

appropriate. 

The FEM system is designed to 

account for aerodynamic, structural (i.e., 

airplane weight), and propulsive 

efficiencies using its SAR parameter, 

and utilizes RGF to normalize those 

efficiencies across a broad range of 

MTOMs. If two airplanes have the same 

efficiencies in these three categories as 

well as in RGF, as described in the 

commenter’s example, then the FEM 

will be the same—regardless of whether 

the interior layout or sub-weight 

components of MTOM result in a poor 

design with respect to a particular 

operational purpose. 

N. Fuel Efficiency Regulatory Limits 

(§ 38.17) 

As proposed, § 38.17 incorporated, as 

fuel efficiency limits, the emission 

standards adopted by the EPA in 40 CFR 

1030.30. Airplanes subject to part 38 

would be required to demonstrate that 

the FEM value does not exceed the fuel 

efficiency limits in § 38.17. Using the 

applicable provision in § 38.1, the 

NPRM proposed calculating the fuel 

efficiency limit using the airplane’s 

MTOM and the equations listed in the 

last column of the table in § 38.17(b). 

The FAA did not receive comments 

on this section and is adopting it as 

proposed. 

O. Change Criteria (§ 38.19) 

As proposed, this section would 

apply the fuel efficiency requirement at 

the time certain modifications were 

made. The NPRM would adopt the EPA 

airplane change criteria of 40 CFR 

1030.35. The change criteria proposed 

in § 38.19 described the modifications 

affecting compliance. The requirements 

differ depending on whether or not the 

airplane had previously demonstrated 

compliance with part 38. 

1. Discussion of the Final Rule 

Section 38.19 provides the change 

criteria for modified airplanes. Section 

38.19 adopts the EPA airplane change 

criteria of 40 CFR 1030.35. 

As discussed in section IV.D. of this 

preamble, the third occasion when part 

38 applies is at the time certain 

modifications are made to the airplane. 

Airplanes routinely have modifications 

incorporated into their designs. A 

modification may require demonstration 

of compliance to part 38, regardless of 

whether the airplane was required to 

previously demonstrate compliance 

with part 38. 

The change criteria in § 38.19 describe 

the modifications which require 

compliance with part 38. The 

requirements differ depending on 

whether an airplane demonstrated 

compliance with part 38 before a 

modification is made, or whether an 

airplane was type certificated before 

January 1, 2023, and had not previously 

demonstrated compliance to this rule. 

The change criteria in § 38.19(a) 

indicates that a compliance 

demonstration to this new rule is 

required if a modification to an airplane, 

that has been shown to comply with 

§ 38.17, will increase the MTOM of the 

airplane as written in § 38.19(a)(1) or 

increases the FEM value above the 

thresholds provided in § 38.19(a)(2)(i) 

through (iii). Where an airplane has 

been shown to comply with § 38.17, for 

a modification that does not increase 

either the MTOM or the FEM value, 

then under section § 38.19(b) the 

airplane may retain the same FEM value 

as prior to modification. The last piece 

of the change criteria in § 38.19(c) 

provides that an airplane, which meets 

the applicability provisions of 

§ 38.1(a)(4) or (5) on or after January 1, 

2023, and before January 1, 2028, must 

demonstrate compliance if the 

incorporated modifications exceed 1.5% 

when comparing its FEM before and 

after the modifications. 

The FAA received several comments 

on this section. Some of these comments 

were directly related to § 38.1 because of 

the relationship between the regulatory 

text of §§ 38.1 and 38.19. As such, the 

FAA responded to some of the § 38.19 

comments in the related applicability 

responses (see IV.D. General 

Applicability). As a result of FAA 

responses to those comments in the 

general applicability discussion, FAA 

made changes to § 38.19(b) and (c). As 

a result of other comments, the FAA 

made minor clarification changes to 

§ 38.19(a)(2)(i) and (ii) and (b). Other 

than these changes, the FAA adopts the 

section as proposed. 

The FAA recognized that the change 

criteria as proposed in the NPRM may 

have been difficult to understand 

because it described the change criteria 

thresholds as ‘‘values’’ that could be 

confused with fuel efficiency metric 

‘‘values’’ described in § 38.11. The FAA 

made minor edits to the text in 

§ 38.19(a) to remove the potential for 

confusion by properly describing the 

change criteria as a threshold whereby 

changes in fuel efficiency metric values 

are compared to the thresholds in 

percentages. 

2. Public Comments and FAA Response 

Comment: Several commenters, 

including Embraer, Boeing, AIA, and 

Airbus, commented on § 38.19(b) that 

the text ‘‘this paragraph (b)’’ should say 

‘‘paragraph (a) of this section.’’ 

Response: The FAA agrees that this 

was a typographical error and has 

corrected the text. 

Comment: Airbus recommended that 

the non-cumulative (non-tracking) 

nature of changes that meet the change 

criteria, a core part of the change criteria 

developed by ICAO, should be 

mentioned in either part 38 or AC38. 

Response: The FAA disagrees. The 

FAA recognizes that the ICAO standard 

and the EPA rule do not require 

cumulative tracking of airplane 

modifications to a type design. In kind, 

the FAA also does not have such a 

requirement. Since there is no 

requirement to track cumulative 

modifications, the FAA does not see a 

need to include any explanation of 

modification tracking in either part 38 

or the AC38. 

Comment: Boeing asked to clarify 

§ 38.19(a)(2)(i) and (ii) by specifying the 

MTOM starting point associated with 

the percentage starting point in these 

two change criteria. 

Response: The FAA agrees these edits 

may help to clarify the requirement. The 

FAA has added the phrases ‘‘for an 

airplane with a MTOM of 5,700 kg’’ to 

clarify the 1.35 percent in 

§ 38.19(a)(2)(i) and ‘‘for an airplane with 

an MTOM of 60,000 kg’’ to clarify the 

0.75 percent in § 39.19(a)(2)(ii). 

Comment: Gulfstream requested that 

the FAA provide clarification for 

documentation expectations in 

§ 38.19(c). Gulfstream noted that it is 

not clear how it is determined and what 

the FAA expectation will be to 

document that a modification does not 

increase the FEM by more than 1.5%. 

Response: For context, § 38.19(c) 

requires an airplane that meets the 

criteria of § 38.1(a)(4) and (5) on or after 

January 1, 2023, and before January 1, 

2028, to demonstrate compliance with 

§ 38.17 if it incorporates any 

modification that increases the FEM 

value of the airplane by more than 1.5% 

prior to modification. 

Regarding the portion of Gulfstream’s 

comment on documentation 

expectations, the FAA will determine 

whether part 38 applies to a covered 

airplane according to the criteria in 

§ 38.19(c) and the supporting 

documentation provided by the 

applicant. This determination is part of 

the type design change certification 

process in § 21.93(d) and FAA will 

decide documentation expectations on a 


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17The FAA hosts but does not control the 

contents of the ICAO Airplane CO2 Certification 

Database located at: www.faa.gov/ 

headquartersoffices/apl/aee/icao-airplane-co2- 

certification-database. 

case-by-case basis depending on the 

complexity of the type design change. 

Comment: Gulfstream asked how a 

change in the FEM value is determined. 

Response: The requirements in part 

38 and its appendix provide the detailed 

information required to determine a fuel 

efficiency metric value for a type design, 

such as corrections, tolerances, and 

confidence intervals. The AC38 

provides additional detailed guidance 

and worked examples on how 

applicants can evaluate the FEM value 

for an airplane. 

Comment: An individual commented 

that the magnitude of change in the 

FEM value caused by the addition of a 

satellite antenna could be lower than in 

the example provided in that 

discussion. 

Response: The FAA acknowledges 

that FEM value changes due to 

modifications to airplanes could vary 

significantly. As provided in § 38.19, the 

FEM values can increase or decrease 

when there are modifications to an 

airplane that impact aerodynamics. 

The NPRM discussion for § 38.19 

intended to focus on how the change 

criteria thresholds work, rather than the 

specific examples themselves. This 

comment does not require changes to 

the regulatory text. 

P. FAA Approval Before Compliance 

Testing (§ 38.21) 

As proposed, § 38.21 would require 

FAA approval of all procedures, 

weights, configurations, and other 

information needed to calculate the 

FEM value of an airplane. As described 

in the NPRM, the FAA would not apply 

this section to data an applicant submits 

for validation following fuel efficiency 

certification by another authority. 

1. Discussion of the Final Rule 

As adopted, § 38.21 requires FAA 

approval of all information needed to 

calculate the FEM value of an airplane. 

The FAA approvals are necessary and 

establish the airplane configuration and 

fuel efficiency certification procedures. 

These procedures remain unchanged 

before fuel efficiency compliance tests 

are conducted. This section does not 

apply to data submitted for validation 

following fuel efficiency certification by 

another authority. The FAA received 

several comments on proposed § 38.21. 

The FAA adopts § 38.21 as proposed. 

2. Public Comments and FAA Response 

Comment: The GAMA requested that 

the FAA add the phrase ‘‘documented 

in compliance demonstration plans’’ 

before ‘‘approved by the FAA’’ to 

§ 38.21. 

Response: The FAA finds the 

proposed change to be too prescriptive. 

Section 38.21 requires FAA approval of 

certain items prior to compliance 

testing, including procedures, weights, 

configurations, and other information. 

These items are used to establish the 

fuel efficiency level. Compliance 

demonstration plans may be one way of 

providing this information to the FAA. 

However, the FAA intends to preserve 

the ability for applicants to use other 

mechanisms to provide the required 

information to the FAA. The GAMA’s 

proposed change would remove this 

flexibility. 

Q. Manual Information and Limitations 

(§ 38.23) 

As proposed, § 38.23 would require 

placement of the FEM value of the 

airplane, along with other part 38 

compliance information, in an FAAapproved section of the flight manual of 

the airplane. Inclusion of this 

information in the approved airplane 

flight manual would provide owners, 

operators, and flight crew with 

information regarding the airplane’s 

compliance with part 38. The FAA 

proposed that if a weight lower than the 

MTOM was used for fuel efficiency 

certification, then that lower weight 

becomes an operating limitation for that 

airplane and would be included in the 

operating limitations section of the 

flight manual. As provided in the 

NPRM, operators could not exceed the 

weight at which compliance with part 

38 was demonstrated, even if that 

weight was lower than the MTOM for 

the airplane under other airworthiness 

requirements. 

1. Discussion of the Final Rule 

The FAA made one change to this 

section in response to comments to 

specify that the manual include the fuel 

efficiency level as established in part 38. 

Other than the change to § 38.23(a)(1), 

the FAA adopts the regulation as 

proposed. 

2. Public Comments and FAA Response 

Comment: Boeing suggested clarifying 

the language in § 38.23(a)(1) to refer to 

compliance, as required by the part, 

rather than during certification. Boeing 

indicated that the proposed text could 

give rise to potential ambiguity with 

respect to an in-production airplane that 

complies with the fuel efficiency 

requirement in part 38, and compliance 

to part 38 need not be shown during 

type certification. Further, Boeing 

remarked that there is no reason that the 

compliance demonstration itself needs 

to be done during type certification and 

the FAA’s regulatory language should be 

sufficiently flexible to accommodate 

such an approach. 

Response: The FAA concurs with the 

change proposed by Boeing and has 

replaced ‘‘during type certification’’ 

with ‘‘as required by this part’’ in 

§ 38.23(a). The use of ‘‘as required by 

this part’’ more specifically refers to the 

part 38 requirements rather than the 

type certification process. 

Comment: Airbus suggested removing 

the requirement to publish certified fuel 

efficiency data in the flight manual by 

deleting §§ 38.23 and 21.5(b)(3). Airbus 

indicates that the adoption of these 

provisions would create deharmonization between certification 

authorities. Airbus instead suggests 

relying on the ICAO CO2 databank 

maintained by the FAA as well as 

through the EASA CO2 databank. Using 

the same justification, Airbus also 

requested that the FAA remove the 

proposed flight manual requirements 

from §§ 121.141(b) and 125.75. 

Airbus was also concerned that if the 

certification applicant chooses to certify 

several MTOMs against the new part 38, 

several flight manual supplements 

would have to be created and 

maintained for the same airplane model. 

Response: The FAA disagrees with 

removing the flight manual publication 

requirement. Although most 

information may be available through 

the ICAO CO2 database 17 or another 

certification authority-maintained 

database, these databases are either 

outside the FAA’s control or potentially 

incomplete, because manufacturers are 

not required to submit information to 

the database. For these reasons, the 

databanks may not provide a complete 

set of information and may not contain 

information for a particular airplane. 

The inclusion of fuel efficiency levels 

and MTOM in the flight manual 

associated with a serial number specific 

airplane allows anyone, including an 

authority, to determine the compliance 

state of an airplane. 

For these reasons, the FAA is 

retaining these requirements. 

Comment: Gulfstream asked if the 

industry could expect to see airports 

imposing fees or restrictions based on 

fuel efficiency, similar to noise, that 

would motivate an applicant to certify 

an airplane at a lower MTOM. 

Gulfstream recommended clarifying the 

potential for any benefit with artificially 

limiting the MTOM to a lower value 

than the design specification. 


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Response: The FAA cannot speculate 

as to whether third parties, such as 

airports, would impose fees or 

restrictions on airplanes based on these 

fuel efficiency values. 

R. Appendix A to Part 38 

As proposed, Appendix A provided 

the technical detail needed to determine 

the FEM value of an airplane required 

to demonstrate compliance with part 38. 

It also detailed the process and 

procedures an applicant needed to use 

when measuring an airplane for fuel 

efficiency. The proposal also described 

the data the applicant would submit to 

the FAA. 

1. Discussion of the Final Rule 

As adopted, Appendix A to part 38 

provides the technical, certificationspecific details an applicant needs to 

determine the FEM value of an airplane 

and demonstrate compliance with part 

38. The primary sources of the 

information contained in the appendix 

are Sections 2.5 and 2.6 of ICAO Annex 

16, Volume III, as well as appendices 1 

and 2 to that volume. These sources of 

information were not included in the 

EPA rule directly but were incorporated 

by reference. In coordination with the 

EPA, the FAA decided it was important 

to include such certification-related 

details in part 38 given the FAA’s 

responsibility to enforce the EPA rule 

within the FAA airplane certification 

framework. As a result, in this rule, the 

FAA does not incorporate this Annex 

information by reference but includes 

all the requirements from Annex 16 

Volume III using current United States 

certification terminology, format, and 

references. 

Appendix A to part 38 details the 

processes and procedures to be used 

when measuring an airplane for fuel 

efficiency. To comply with part 38, a 

certification applicant would need to 

determine the core parameters of the 

FEM, specifically the SAR and RGF. The 

specifications for the flight tests to 

gather airplane performance data are 

provided in Appendix A, including the 

formulas to be used to determine the 

SAR and RGF from data gathered during 

testing. The appendix also describes 

certification data that would be 

submitted to the FAA in the 

certification test report that is a part of 

fuel efficiency certification. 

The FAA received comments on 

several sections of Appendix A to part 

38. As a result of these comments, as 

well as consistency edits that result 

from the FAA’s responses to these 

comments, the FAA has made changes 

to proposed paragraphs A38.1.2.3.1, 

A38.1.2.3.4, A38.2.1.1.3, A38.2.1.1.6, 

A38.2.1.3.1, A38.2.1.3.2, A38.4.2.1.2, 

A38.4.2.1.3, A38.4.2.1.4.1, 

A38.4.2.1.4.2, A38.4.2.1.5.1, 

A38.4.2.1.5.2, A38.4.2.2, A38.4.2.2.1, 

A38.4.2.2.1.2, A38.4.2.2.1.4, 

A38.4.2.3.2.1, A38.4.2.3.2.2, 

A38.4.2.3.2.3, A.38.5.2.2.1.1, A38.6, 

A38.6.1.2, A38.6.3.7, A38.6.3.9, and 

A38.6.4. In general, the comments 

pertained to clarifications on airplane 

weighing and mass requirements, fuel 

sampling requirements, fuel kinematic 

viscosity requirements, airplane trim 

requirements, the use of standard 

United States aerospace terminology, 

engine deterioration, corrections to 

reference specifications, the reporting of 

data, the fixing titles of reference 

citations, and some minor typographical 

errors. 

Paragraph A38.2.1.3.1 identifies a 

reference specification for standard day 

atmosphere. As discussed in relation to 

§ 38.7, the FAA has determined that this 

specification needs to be incorporated 

by reference and has indicated that in 

A38.2.1.3.1 as well as the other 

paragraphs that include this same 

reference specification (i.e., paragraphs 

A38.5.2.2.1.9 and A38.5.2.2.1.10). Also, 

in paragraph A38.2.1.3.1, the FAA 

noticed that it inadvertently failed to 

include an ‘‘and’’ at the end of this 

paragraph, which is now included for 

consistency with the ICAO standard. 

The FAA corrected the section 

accordingly. In paragraphs 38.3.2, 

38.3.3, and 38.3.4, this rule adopts 

changes from ‘‘cockpit’’ to ‘‘flight deck’’ 

to provide gender-neutral language 

without changing the meaning or intent. 

Other than these changes, the FAA 

adopts the Appendix as proposed. 

2. Public Comments and FAA Response 

The comments and responses below 

are categorized based on the relevant 

appendix section. 

a. Appendix A to Part 38, A38.1

Introduction 

Comment: For proposed paragraphs 

A38.1.2.3.1 and A38.1.2.3.4, Airbus 

noted potential errors including a 

missing ‘‘and’’ between listed 

requirements of a performance model, 

and incorrect numbering of appendix 

sections where A38.1.2.3.4 should have 

been A38.1.2.3.3. 

Response: The FAA disagrees with 

the request to add an ‘‘and’’ at the end 

of A38.1.2.3.1. The FAA notes the 

proposal contained an ‘‘and’’ in the next 

to last item in the list and this is 

sufficient to make each of the items 

under A.38.1.2.3 a requirement. Thus, 

the FAA did not make this proposed 

change. However, with respect to the 

incorrect numbering in proposed 

A38.1.2.3.4, the FAA agrees that this is 

a typographical error and has corrected 

it. 

b. Appendix A to Part 38, A38.2

Reference Specifications for SAR Flight 

Tests 

Comment: For paragraph A38.2.1.1.3, 

Boeing suggested using standard 

industry terminology of ‘‘unaccelerated’’ 

instead of ‘‘unaccelerating.’’ 

Response: The FAA agrees that 

‘‘unaccelerated’’ is a more common 

aerospace industry terminology when 

describing steady-level flight, thus the 

FAA made the suggested changes. The 

FAA also made these same changes to 

paragraphs A38.4.2.2.1.2 and 

A38.5.2.2.1. 

Comment: For paragraph A38.2.1.1.5, 

Gulfstream requested confirmation that, 

when it uses a performance model, all 

the provided information in the section 

will be embedded in the model and 

additional corrections will not be 

required in the model results. 

Response: The FAA confirms that 

reference specifications are required for 

flight test data, which can be used to 

validate a performance model. 

Depending on how the performance 

model is built and on what data it is 

based, corrections may be necessary for 

SAR values calculated from the model. 

c. Appendix A to Part 38, A38.4

Certification Test Specifications 

Comment: For paragraph A38.4.2.1.2, 

Boeing requested to clarify the airplane 

weight and balance requirement by 

removing the words ‘‘prior to the test 

flight.’’ Boeing indicated it may be 

possible that the weight before flight 

may not be the best engineering value; 

because test data may, after post-flight 

weighing, suggest a more optimal means 

for establishing accurate weight. 

Response: The FAA agrees that this 

airplane weight requirement can be 

clarified, however disagrees with the 

proposed changes as they would cause 

a substantive difference (discussed in 

IV.F.) with the ICAO international 

standard that includes the words ‘‘prior 

to the test flight.’’ The FAA has revised 

the text to align with the ICAO 

international standard by changing the 

requirement to read: ‘‘The test airplane 

must be weighed. Any change in mass 

after the weighing and prior to the test 

flight must be accounted for.’’ During its 

review of this paragraph, the FAA 

recognized that the ‘‘and balance’’ text 

that was contained in the proposed 

A38.4.2.1.2 is not required given the 

various center of gravity requirements 

throughout Appendix A. After 

reviewing all center of gravity 

requirements in Appendix A, the FAA 


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made a clarifying change in A38.2.1.1.6 

by changing ‘‘a’’ to ‘‘the’’ in the 

proposed text (i.e., representative of a 

mid-CG point relevant to design cruise 

performance). The FAA’s clarifying 

change ensures there is no ambiguity as 

there is only one mid-CG point at each 

of the three reference airplane masses. 

Comment: For paragraphs A38.4.2.1.3, 

A38.4.2.1.4.1, A38.4.2.1.5.1, and 

A38.4.2.1.5.2, Boeing suggested 

correcting these reference citations by: 

(1) removing the word ‘‘specification’’ 

when referring to the external American 

Society for Testing and Materials 

(ASTM) documents, and (2) correcting 

the titles of the documents as needed. 

Response: The FAA agrees to these 

minor editorial changes and accepts 

them. The FAA also noticed, and 

corrected, that the word ‘‘titled’’ instead 

of ‘‘entitled’’ should have been used 

when quoting the titles of these 

documents. 

Comment: For paragraph 

A38.4.2.1.4.2, Airbus suggested that it 

did not understand the text ‘‘and may 

not have variations’’ at the end of the 

fuel sample requirement, because fuel 

samples are analyzed for each test flight 

and a single lower heating value is 

determined. 

Response: The FAA agrees with this 

reasoning and has revised the text to 

better align with the ICAO international 

standard regarding flexibility on 

variations and errors. The language now 

reads: 

The fuel sample may be 

representative of the fuel used for each 

flight test and should not have errors or 

variations due to fuel being uplifted 

from multiple sources, fuel tank 

selection, or fuel layering in a tank. 

Comment: For paragraph 

A38.4.2.1.5.2, Airbus requested an 

additional ASTM document be added 

for determining fuel kinematic viscosity. 

Response: The FAA disagrees because 

it would result in a substantive 

difference (discussed in IV.F.) with the 

ICAO international standard. In 

addition, the FAA notes that the words 

‘‘or as approved by the FAA’’ at the end 

of that paragraph allow applicants to 

seek approval of other methods for 

determining fuel kinematic viscosity, 

which is consistent with the ICAO 

standard. 

Comment: An individual commented 

on paragraph A38.4.2.2 regarding the 

use of the term ‘‘configuration.’’ They 

indicated that this section relates to 

criteria, procedures, or requirements 

and that it does not relate to 

configurations, which is a term used for 

defining an airplane configuration such 

as a flap position, gear position, or some 

aspect of the type design. 

Response: Upon review, the FAA 

acknowledges the word 

‘‘configuration(s)’’ does not accurately 

reflect the requirement. The 

requirement relates more to procedures 

on how the pilot should fly the airplane 

during flight testing. As such, the FAA 

has replaced the word 

‘‘configuration(s)’’ with the word 

‘‘procedure(s)’’ in A38.4.2.2 and 

A38.4.2.2.1. 

Comment: For paragraph 

A38.4.2.2.1.4, Boeing requested a 

change to the text ‘‘there are no changes 

in trim.’’ Boeing requested that the text 

be revised to allow some changes by 

stating that changes are to be avoided or 

minimized as practicable. Boeing 

explained that it may not be possible to 

eliminate all changes during flight 

because there may be unavoidable 

circumstances during flight; however, 

such changes may be accounted for 

through data analysis and 

interpretation. 

Response: The FAA agrees that inflight conditions may not make it 

possible to eliminate changes to some 

trim and engine settings, and that 

changes may be accounted for through 

post-flight data analysis. The FAA also 

notes that providing flexibility better 

aligns with the same recommendation 

in the ICAO international standard. 

Accordingly, the FAA revised the text to 

read as follows: 

Changes in trim or engine power/ 

thrust settings, engine stability and 

handling bleeds, or electrical and 

mechanical power extraction (including 

bleed flow) are avoided or minimized as 

practicable. 

Comment: For paragraph A38.4.2.3.2, 

Airbus explained that the requirement 

regarding airplane mass determination 

should provide for alternative methods, 

specifically by changing the word 

‘‘must’’ to ‘‘may.’’ 

Response: The FAA agrees that this 

requirement should allow additional 

methods to determine the mass of the 

airplane because the ICAO Annex 16 

Vol III also lists the two methods as 

recommended options for determining 

mass, not as required methods. 

Therefore, the FAA kept the word 

‘‘must,’’ but added a third option to 

A38.4.2.3.2.3: other methods as 

approved by the FAA. This third option 

will allow alternative methods in 

addition to the two options listed. 

d. Appendix A to Part 38, A38.5

Measurement of Specific Air Range 

Comment: For paragraph 

A38.5.2.2.1.7, Airbus suggested the 

sentence starting with the text ‘‘(s)ince 

engine deterioration is rapid when . . .’’ 

may not be grammatically correct. 

Response: The FAA notes that this is 

a partial sentence that is a lead-in to the 

two sub-paragraphs that follow it. In 

that context, the FAA does not see a 

need to make changes to this text. 

Comment: For paragraph 

A38.5.2.2.1.7.2, Boeing suggested 

replacing the proposed text, ‘‘. . . and 

no correction is permitted’’ with, ‘‘. . . 

and a correction to the reference 

deterioration level may be approved by 

the FAA.’’ Boeing asserted that 

technology and processes have 

advanced to the point where it is 

reasonable to employ engine 

deterioration corrections in certain 

circumstances. Boeing noted that it has 

successfully employed deterioration 

corrections on occasion and believes 

that the FAA provide flexibility for 

deterioration corrections if the FAA 

approves of the correction. 

Response: The FAA disagrees with 

providing the suggested flexibility for 

this requirement because this change 

would cause a substantive difference 

(discussed in IV.F.) with the ICAO 

international standard that precludes 

correction in these instances. 

Comment: For paragraph A38.5.3, 

Gulfstream commented that it is unclear 

how an applicant will manage 

confidence intervals when a 

performance model is used. 

Response: The AC38 provides 

guidance on determining and using 

confidence intervals. 

e. Appendix A to Part 38, A38.6

Submission of Certification Data to the 

FAA 

Comment: For paragraph A38.6, 

Airbus recommended edits to the 

proposed text to allow other analysis 

reports to convey the required 

information, not just the certification 

test report. 

Report: The FAA agrees that there are 

various types of reports during 

certification that could contain the 

required information. The FAA made 

the change from ‘‘certification test 

report’’ to ‘‘certification reports.’’ 

Comment: For paragraphs A38.6.1.2, 

A38.6.3.7, and A38.6.3.9, Airbus and 

Boeing noted typographical and 

reference errors, including a reference to 

§ 38.23(a)(3) that does not exist in 

A38.6.1.2, a correction to a semicolon in 

A38.6.3.7, and incorrect references 

within A38.6.3.9. 

Response: The FAA agrees and fixed 

the noted typographical and reference 

errors. 

Comment: For paragraph A38.6.4, 

Airbus requested that the FAA remove 

the text ‘‘defined in § 38.13(b).’’ Airbus 

indicated that this language suggested 

that the test measurements are 


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systematically done at the reference 

masses of the standard but that this was 

not the case when a performance model 

was used. 

Response: The FAA agrees that the 

reference to § 38.13(b) should be 

removed for the reasons Airbus stated 

and has removed the reference. In 

addition, the FAA’s review resulted in 

the need to clarify this requirement in 

paragraph A38.6.4 by clearly stating that 

SAR values, corrections from measured 

data to reference specifications, and 

finally the SAR values calculated from 

corrected data must be provided for the 

test measurement points. As such, the 

requirement has been updated to the 

following language: 

The measured SAR test data, all 

corrections of the measured data to the 

reference specifications, and the SAR 

values calculated from the corrected 

data must be provided. 

S. Other Revisions to 14 CFR 

The proposed rule set forth several 

amendments to part 21 to include 

compliance with part 38 as a 

requirement for type, supplemental 

type, or airworthiness certification using 

the applicability described in § 38.1. If 

adopted, the amendment proposed to 

part 21 would include adding references 

to part 38 in §§ 21.5, 21.17, 21.29, 21.31, 

21.93, 21.101, 21.115, 21.183, and 

21.187. The NPRM also proposed to 

adopt the move and redesignation of 

§ 21.187(c) to § 21.187(a)(3). The 

proposal also included amendments to 

the operating regulations (§§ 121.141 

and 125.75) for airplanes subject to part 

38. The revisions were included to add 

the certification information for fuel 

efficiency to the airplane flight manuals. 

1. Discussion of the Final Rule 

With some changes, this rule adopts 

the proposed changes to part 21 and 

§§ 121.141 and 125.75. 

In particular, in this final rule, the 

FAA also makes a change to § 21.93(d) 

by adding that a voluntary change that 

may increase the MTOM of that airplane 

is a ‘‘fuel efficiency change.’’ The 

proposal only identified an increase in 

the FEM value as a ‘‘fuel efficiency 

change.’’ This change was made to 

ensure consistency with the change 

criteria in § 38.19. 

Further, as a result of comments, the 

FAA made changes to §§ 21.21, 21.93, 

and 121.141. These changes ensure that 

the fuel efficiency requirements are 

appropriately included in part 21 and 

corrected an inadvertent change in 

§ 121.141. Other than these identified 

changes, the FAA adopts the 

amendments to part 21 and §§ 121.141 

and 125.75 as proposed. 

Finally, this rule adopts changes to 

§ 21.187 to provide gender-neutral 

language (from ‘‘He’’ to ‘‘The 

applicant’’) without changing the 

meaning or intent of the rule. 

The comments and responses are 

organized by the specific regulatory 

section. 

2. Public Comments and FAA Response 

a. Section 21.5: Airplane or Rotorcraft 

Flight Manual 

Comment: One individual commenter 

recommended adding ‘‘Rotorcraft Flight 

Manual’’ to the change proposed in 

§ 21.5(b)(3). 

Response: The FAA does not concur 

with adding ‘‘Rotorcraft Flight Manual’’ 

to the changes in § 21.5(b)(3) to 

accommodate the addition of part 38 

requirements as this rule only applies to 

fixed wing airplanes. 

Comment: One commenter stated 

§ 21.5 only pertains to airplanes and 

rotorcraft not type certificated with an 

Airplane or Rotorcraft Flight Manual 

and asked whether there were any such 

airplanes in existence that would be 

subject to part 38. 

Response: Section 21.5 applies to all 

airplanes that do not have flight time 

prior to March 1, 1979. Airplanes 

produced or certified on or after that 

date are required to have an approved 

flight manual. 

Comment: One individual proposed 

the airplane flight manual requirement 

should be placed in §§ 25.1581 and 

23.2620. They stated that it was also 

unclear how the requirement in § 21.5 

meshes with § 38.23. They thought the 

requirements of § 38.23 should either be 

placed in or reference the sections of 

parts 23 and 25 pertaining to Airplane 

Flight Manuals and airplane limitations. 

Response: The FAA disagrees with 

the requested amendments to parts 23 

and 25. Flight manual requirements are 

covered in the revised § 21.5. This final 

rule also amends the applicability 

requirements in other sections of part 21 

such that § 21.5 applies to part 23 and 

25 airplanes. Accordingly, the flight 

manuals for these airplanes must 

include the flight manual requirements 

of part 38. 

b. Section 21.21: Issue of Type 

Certificate: Normal, Utility, Acrobatic, 

Commuter, and Transport Category 

Aircraft; Manned Free Balloons; Special 

Classes of Aircraft; Aircraft Engines; 

Propellers 

Comment: Boeing recommended that 

the FAA revise § 21.21(b) and (b)(1) by 

adding ‘‘and fuel efficiency’’ to be 

consistent with proposed § 38.1(a)(1), 

(2) and (3) (for new-type airplanes 

seeking original type certification). 

Boeing noted that adding ‘‘fuel venting 

and exhaust emissions’’ to § 21.21 

would also be consistent with the FAA’s 

revision of § 21.29. 

Response: Section 21.21 identifies all 

the necessary requirements for receiving 

a type certificate. In order to fully 

effectuate part 38 into the type 

certification requirements, it is 

important to include this rule in 

paragraph (b) of this section. Further, 

the FAA agrees that consistency is 

necessary between §§ 21.21 and 21.29. 

Section 21.21 was revised to list fuel 

efficiency in addition to the other 

environmental requirements that an 

applicant must comply with in order to 

get a type certificate. The FAA has 

modified § 21.21 to include fuel 

efficiency. 

The FAA inadvertently revised 

§ 21.29 with a punctuation error in the 

proposed rule to state, ‘‘fuel venting and 

exhaust emissions, and fuel efficiency.’’ 

The FAA has corrected this in the final 

rule to state ‘‘fuel venting, exhaust 

emission, and fuel efficiency’’ to be 

consistent with § 21.21. 

c. Section 21.93: Classification of 

Changes in Type Design 

Comments: Gulfstream requested 

clarity on the use of the word 

‘‘voluntary’’ regarding type design 

changes in § 21.93(d). Gulfstream 

recollected that the ICAO language did 

not include the word ‘‘voluntary’’ and 

asked if it was the FAA’s intent to 

protect applicants from having to 

reverify part 38 compliance after a 

mandated design change. 

Response: The FAA’s intent was to 

prevent applicants from having to 

reverify part 38 compliance after a 

mandated design change. The FAA uses 

the word ‘‘voluntary’’ to describe the 

action initiated by an applicant to 

obtain an approval. On the other hand, 

non-voluntary or mandated changes, 

typically required by an authority, are 

needed to maintain the airworthiness of 

in-service airplanes as soon as possible 

for safety concerns. The ICAO Standards 

and Recommended Practices do not 

have a similar exception for authoritymandated changes to an airplane. It is 

the responsibility of the authority 

adopting the Annexes to provide their 

own procedures for handling mandated 

changes required for continued 

operational safety. 

Comments: Embraer noted that 14 

CFR 21.93(d) defines the term ‘fuel 

efficiency change’ that is not used 

within 14 CFR part 38. This leaves the 

applicability definition of 14 CFR part 

38 within § 38.19. On the other hand, 


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18This is an acronym in Portuguese for Brazilian 

Regulations for Civil Aviation. 

Embraer stated that ICAO/RBAC18 uses 

the definition of ‘‘derived version’’ to 

determine applicability. Although the 

definitions are similar, Embraer states 

this could generate interpretation 

problems when classifying a 

modification and, consequently, to 

define the involvement of the 

authorities. 

Response: The FAA is not defining a 

new term ‘‘fuel efficiency change’’ as 

Embraer indicates. This language refers 

to changes in the certified ‘‘fuel 

efficiency metric value’’ as provided in 

part 38. The applicability of § 38.1 

includes a direct reference to § 38.19 

(see in § 38.1(b)) and, therefore, includes 

modifications as part of applicability 

considerations. Similarly, ICAO 

includes modifications via a definition 

of ‘‘derived versions’’ that is contained 

outside the applicability provisions. 

d. Other Part 21 Sections 

Comments: Boeing suggested adding 

additional text to §§ 21.101(a), 

21.115(a)(3), 21.183(j), and 21.187(a)(4) 

that direct a reader to specific 

applicability sections of part 38. Boeing 

was concerned that, as drafted, these 

sections could mistakenly be read to 

mean that an obligation to demonstrate 

compliance with part 38 applies 

automatically upon any application for 

approval of a modification in type 

design for any airplane, including an inservice airplane, regardless of whether 

the requirements of §§ 38.1 and 38.19 

are met. 

Response: The FAA disagrees. Section 

21.93(d) refers to part 38 for purposes of 

maintaining compliance with part 38. 

Part 38 is the appropriate regulatory 

location to determine which sections of 

part 38 apply in a particular 

circumstance. 

Further, the FAA has revised the 

applicability requirements in part 38 to 

clarify its applicability to modifications 

in type design for any airplane, 

including an in-service airplane. See 

FAA’s responses to comments in section 

IV.D. For these reasons, the FAA is not 

adopting the suggested changes. 

e. Section 121.141 (Airplane Flight 

Manual) and 125.75 (Airplane Flight 

Manual) 

Comment: One individual commenter 

noted that changing the word ‘‘may’’ to 

‘‘must’’ is a significant change in 

§ 121.141(b), making it mandatory to 

revise the performance section of the 

Airplane Flight Manual when operators 

create their own manual. The 

commenter also noted that this change 

was not consistent with the proposal to 

change § 125.75(b), which does not 

change a similar ‘‘must’’ in the existing 

text to ‘‘may.’’ The commenter also 

recommended that if FAA meant to 

change the language to ‘‘must’’ in 

§ 121.141(b), the FAA should make a 

corresponding change in § 125.75(b) and 

explain the change in the preamble. 

Response: The FAA concurs that the 

text added to § 121.141(b) should have 

said ‘‘may revise’’ not ‘‘must revise.’’ 

This was an inadvertent change from 

existing text. Accordingly, the final rule 

text is corrected to ‘‘may revise’’ and the 

FAA does not need to make the 

suggested change to § 125.75(b). 

T. Costs 

A number of individuals commented 

generally regarding their concerns about 

the monetary costs of the rule. 

The FAA conducted an analysis of the 

costs and benefits of the proposed rule. 

As described in the preliminary 

regulatory impact analysis (RIA) that 

accompanied the proposal, in the 

absence of the FAA’s rule aircraft 

manufacturers would have to certify to 

the fuel efficiency standards through 

foreign authorities. As a result, the rule 

reduces the cost of this certification by 

enabling certification through the FAA. 

Therefore, the FAA does not expect this 

rule will impose an undue burden on 

industry, an increase in the cost of air 

travel, or other negative economic 

impacts commenters attribute to the 

rule. Regarding the need for government 

intervention, airplane fuel efficiency has 

increased as the standard is technologyfollowing, but the rule prevents 

backsliding to less fuel-efficient 

airplanes. The FAA also noted that the 

rule may generate minimal benefits 

since the ICAO designed the standard in 

such a way that most airplanes would 

already meet the standard. 

Boeing asserted that footnote 8 in the 

preliminary RIA contradicted the EPA’s 

unambiguous intent with respect to the 

inapplicability of its GHG standards to 

modifications of individual in-service 

airplanes. The footnote stated that 

owners or operators that modify an 

airplane that was not certificated to the 

proposed fuel efficiency standard may 

also need to comply with the rule when 

the modifications are made. The 

National Business Aviation Association 

(NBAA) also asserted that in the 

preliminary RIA, the FAA failed to 

analyze the financial impact this rule 

may have on the current fleet. 

Specifically, it stated that operators 

seeking to modify their airplanes 

through a Supplemental Type 

Certificate (STC) may have to complete 

additional modifications or data 

analysis to meet the FEM, resulting in 

additional costs. The NBAA encouraged 

the FAA to consider this submission 

prior to applying this rule to modified 

airplanes. 

The FAA asserts that there will be no 

economic impact on the current fleet 

stemming from this rule. The FAA 

agrees that owners or operators that 

modify an airplane that was not 

certificated to the fuel efficiency 

standards will not need to comply with 

the rule when those modifications are 

made. The rule does not apply to the inservice fleet that was not certified to the 

fuel efficiency standard, including any 

future modifications. As such, there will 

be no impact on the current fleet for 

operators seeking to modify their 

airplane through an STC. The FAA 

deleted the referenced footnote 8 in the 

final RIA. 

V. Regulatory Notices and Analyses 

Federal agencies consider impacts of 

regulatory actions under a variety of 

executive orders and other 

requirements. First, Executive Order 

12866 and Executive Order 13563 direct 

that each Federal agency shall propose 

or adopt a regulation only upon a 

reasoned determination that the benefits 

of the intended regulation justify the 

costs. Second, the Regulatory Flexibility 

Act of 1980 (Pub. L. 96–354) requires 

agencies to analyze the economic 

impact of regulatory changes on small 

entities. Third, the Trade Agreements 

Act (Pub. L. 96–39) prohibits agencies 

from setting standards that create 

unnecessary obstacles to the foreign 

commerce of the United States. Fourth, 

the Unfunded Mandates Reform Act of 

1995 (Pub. L. 104–4) requires agencies 

to prepare a written assessment of the 

costs, benefits, and other effects of 

proposed or final rules that include a 

Federal mandate that may result in the 

expenditure by State, local, and Tribal 

governments, in the aggregate, or by the 

private sector, of $100 million or more 

(adjusted annually for inflation) in any 

one year. The current threshold after 

adjustment for inflation is $177 million 

using the most current (2022) Implicit 

Price Deflator for the Gross Domestic 

Product. The FAA has provided a 

detailed Regulatory Impact Analysis 

(RIA) in the docket for this rulemaking. 

This portion of the preamble 

summarizes the FAA’s analysis of the 

economic impacts of this rule. 

In conducting these analyses, the FAA 

has determined that this rule: will result 

in benefits that justify costs; is not a 

‘‘significant regulatory action’’ as 

defined in section 3(f) of Executive 

Order 12866, as amended by Executive 

Order 14094; will not have a significant 


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19Small Business Administration (SBA). 2022. 

Table of Size Standards. Effective July 14, 2022. 

www.sba.gov/document/support--table-sizestandards. 

economic impact on a substantial 

number of small entities; will not create 

unnecessary obstacles to the foreign 

commerce of the United States; and will 

not impose an unfunded mandate on 

State, local, or Tribal governments, or 

on the private sector. 

A. Summary of the Regulatory Impact 

Analysis 

The FAA identified three United 

States manufacturers that would be 

affected by the rule. Manufacturers will 

incur certification costs even in the 

absence of the rule since they would 

pursue certification with foreign 

authorities. Certification tasks will vary 

greatly depending on the stage of the 

airplane development process (e.g., new 

type certificate, supplemental type 

certificate, etc.). Additionally, the first 

fuel efficiency certification project 

undertaken by any one manufacturer 

may require more resources because of 

the new processes and the need for new 

data generation. The FAA used 

information provided by the affected 

airplane manufacturers to construct a 

timeline of when these costs would be 

incurred over a 10-year period, and the 

cost savings from domestic certification 

enabled by the rule. 

Because the EPA standards apply to 

airplanes certificated in the United 

States even in the absence of the rule, 

there are no incremental benefits 

associated with the FAA’s action; 

however, the rule will result in cost 

savings by enabling United States 

manufacturers to certificate to the 

standards domestically. Annualized 

costs savings may be approximately $0.4 

million using discount rates of 3 percent 

and 7 percent (a present value over 10 

years of $3.5 million to $2.9 million, 

using discount rates of 3 percent and 7 

percent, respectively). 

Please see the RIA available in the 

docket for more details. 

B. Regulatory Flexibility Act 

The Regulatory Flexibility Act (RFA) 

of 1980, (5 U.S.C. 601–612), as amended 

by the Small Business Regulatory 

Enforcement Fairness Act of 1996 (Pub. 

L. 104–121) and the Small Business Jobs 

Act of 2010 (Pub. L. 111–240), requires 

Federal agencies to consider the effects 

of the regulatory action on small 

business and other small entities and to 

minimize any significant economic 

impact. The term ‘‘small entities’’ 

comprises small businesses and not-forprofit organizations that are 

independently owned and operated and 

are not dominant in their fields, and 

governmental jurisdictions with 

populations of less than 50,000. 

As described in the RIA, the FAA 

identified three United States 

manufacturers that would be affected by 

the proposed rule. Based on the Small 

Business Administration (SBA) size 

standard for aircraft manufacturing 

(Table 1), all three manufacturers are 

large businesses. If an agency 

determines that a rulemaking will not 

result in a significant economic impact 

on a substantial number of small 

entities, the head of the agency may so 

certify under section 605(b) of the RFA. 

Therefore, as provided in section 605(b) 

and based on the foregoing, the head of 

FAA certifies that this rulemaking will 

not result in a significant economic 

impact on a substantial number of small 

entities. 

TABLE 1—SMALL BUSINESS SIZE

STANDARDS: AIR TRANSPORTATION

NAICS 

code Description Size standard 

336411 Aircraft manufacturing.1,500 employees. 

Source: SBA (2022).19

NAICS = North American Industrial Classification System. 

C. International Trade Impact 

Assessment 

The Trade Agreements Act of 1979 

(Pub. L. 96–39), as amended by the 

Uruguay Round Agreements Act (Pub. 

L. 103–465), prohibits Federal agencies 

from establishing standards or engaging 

in related activities that create 

unnecessary obstacles to the foreign 

commerce of the United States. 

Pursuant to these Acts, the 

establishment of standards is not 

considered an unnecessary obstacle to 

the foreign commerce of the United 

States, so long as the standard has a 

legitimate domestic objective, such as 

the protection of safety and does not 

operate in a manner that excludes 

imports that meet this objective. The 

statute also requires consideration of 

international standards and, where 

appropriate, that they be the basis for 

United States standards. 

The FAA has assessed the potential 

effects of this rule and finds that it does 

not create an unnecessary obstacle to 

foreign commerce. The United States 

has adopted the same airplane emission 

standards as ICAO and many of its 

member States. This rule is the next step 

in insuring compliance with the 

internationally recognized standard. 

D. Unfunded Mandates Assessment 

The Unfunded Mandates Reform Act 

of 1995 (2 U.S.C. 1531–1538) governs 

the issuance of Federal regulations that 

require unfunded mandates. An 

unfunded mandate is a regulation that 

requires a State, local, or Tribal 

government or the private sector to 

incur direct costs without the Federal 

government having first provided the 

funds to pay those costs. The FAA 

determined that this final rule will not 

result in the expenditure of $177 

million or more by State, local, or Tribal 

governments, in the aggregate, or the 

private sector, in any one year. 

This rule does not contain such a 

mandate; therefore, the requirements of 

title II of the Act do not apply. 

E. Paperwork Reduction Act 

The Paperwork Reduction Act of 1995 

(44 U.S.C. 3507(d)) requires that the 

FAA consider the impact of paperwork 

and other information collection 

burdens imposed on the public. 

According to the 1995 amendments to 

the Paperwork Reduction Act (5 CFR 

1320.8(b)(2)(vi)), an agency may not 

collect or sponsor the collection of 

information, nor may it impose an 

information collection requirement 

unless it displays a currently valid 

Office of Management and Budget 

(OMB) control number. 

This action contains the following 

new information collection requirement. 

As required by the Paperwork 

Reduction Act of 1995 (44 U.S.C. 

3507(d)), the FAA has submitted these 

information collection amendments to 

OMB for its review. The OMB control 

number for this action is 2120–0815. 

Summary 

The regulations, adding a new part 38 

to 14 CFR that requires certification for 

fuel efficiency, includes a collection of 

data from certification applicants. 

Certain data collected by the respondent 

during its certification flight tests are to 

be included in a certification test report 

that is submitted to the FAA. Those data 

are described in Appendix A to part 38. 

The information in the test report is 

used by the agency to determine 

whether the subject airplane complies 

with the fuel efficiency requirements 

promulgated by the EPA and the FAA. 

Without such information, the FAA 

would not have the complete record of 

an airplane’s fuel efficiency 

performance and would be unable to 

issue a type or airworthiness certificate. 

Use 

Respondent’s data will be used to 

determine compliance with the fuel 

efficiency standards established by the 


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20 65 FR 67249 (Nov. 6, 2000). 

21FAA Order No. 1210.20 (Jan. 28, 2004), 

available at www.faa.gov/documentLibrary/media/ 

1210.pdf. 

EPA under the requirements of the 

Clean Air Act. The FAA is required by 

the Clean Air Act to implement those 

standards, which is done at the time of 

airplane certification. 

Respondent’s test data will not be 

maintained by the FAA following a 

certification determination. The 

certification test report is not available 

to the public. The regulation also 

requires that certain values be listed in 

the flight manual of the airplane, which 

is given to the purchaser of an airplane. 

Respondents (including number of): 

The FAA anticipates three respondents 

to the collection of information. 

Frequency: The FAA anticipates that 

respondents will provide responses 

annually (averaged). 

Annual Burden Estimate: Table 1 

provides the FAA’s estimates of annual 

reporting (submittal of certification 

data) and recordkeeping (manual 

information) burden. 

TABLE 1—SUMMARY OF ANNUAL

BURDEN

Category Reporting Recordkeeping 

# of respondents ........... 3 3 

# of responses per 

respondent 2 2 

Time per response 

(hours) ....... 2 8 

Total # of 

responses 6 6 

Total burden 

(hours) 12 48 

F. International Compatibility 

In keeping with United States’ 

obligations under the Convention on 

International Civil Aviation, it is FAA 

policy to conform to International Civil 

Aviation Organization (ICAO) Standards 

and Recommended Practices to the 

maximum extent practicable. The FAA 

has reviewed the corresponding ICAO 

Standards and Recommended Practices 

and has identified no substantive 

differences with these regulations. 

G. Environmental Analysis 

FAA Order 1050.1F identifies FAA 

actions that are categorically excluded 

from preparation of an environmental 

assessment or environmental impact 

statement under the National 

Environmental Policy Act (NEPA) in the 

absence of extraordinary circumstances. 

The FAA has determined this 

rulemaking action qualifies for the 

categorical exclusion identified in 

paragraph 5–6.6f for regulations and 

involves no extraordinary 

circumstances. 

VI. Executive Order Determinations 

A. Executive Order 13132, Federalism 

The FAA has analyzed this final rule 

under the principles and criteria of 

Executive Order (E.O.) 13132, 

Federalism. The FAA has determined 

that this action will not have a 

substantial direct effect on the States, or 

the relationship between the Federal 

Government and the States, or on the 

distribution of power and 

responsibilities among the various 

levels of government, and, therefore, 

will not have federalism implications. 

B. Executive Order 13175, Consultation 

and Coordination With Indian Tribal 

Governments 

Consistent with Executive Order 

13175, Consultation and Coordination 

with Indian Tribal Governments,20 and 

FAA Order 1210.20, American Indian 

and Alaska Native Tribal Consultation 

Policy and Procedures,21 the FAA 

ensures that Federally Recognized 

Tribes (Tribes) are given the opportunity 

to provide meaningful and timely input 

regarding proposed Federal actions that 

have the potential to have substantial 

direct effects on one or more Indian 

Tribes, on the relationship between the 

Federal government and Indian Tribes, 

or on the distribution of power and 

responsibilities between the Federal 

government and Indian Tribes; or to 

affect uniquely or significantly their 

respective Tribes. At this point, the FAA 

has not identified any unique or 

significant effects, environmental or 

otherwise, on Tribes resulting from this 

final rule. 

C. Executive Order 13211, Regulations 

That Significantly Affect Energy Supply, 

Distribution, or Use 

The FAA analyzed this final rule 

under E.O. 13211, Actions Concerning 

Regulations that Significantly Affect 

Energy Supply, Distribution, or Use 

(May 18, 2001). The FAA has 

determined that it is not a ‘‘significant 

energy action’’ under the executive 

order and not likely to have a significant 

adverse effect on the supply, 

distribution, or use of energy. 

D. Executive Order 13609, Promoting 

International Regulatory Cooperation 

Executive Order 13609, Promoting 

International Regulatory Cooperation, 

promotes international regulatory 

cooperation to meet shared challenges 

involving health, safety, labor, security, 

environmental, and other issues and 

reduce, eliminate, or prevent 

unnecessary differences in regulatory 

requirements. The FAA has analyzed 

this action under the policy and agency 

responsibilities of Executive Order 

13609. The FAA has determined that 

this action will eliminate differences 

between United States aviation 

standards and those of other civil 

aviation authorities by adopting the 

airplane certification regulations needed 

to comply with the standards adopted 

by ICAO and the EPA. 

VII. Additional Information 

A. Electronic Access and Filing 

A copy of the NPRM, all comments 

received, this final rule, and all 

background material may be viewed 

online at www.regulations.gov using the 

docket number listed above. A copy of 

this final rule will be placed in the 

docket. Electronic retrieval help and 

guidelines are available on the website. 

It is available 24 hours each day, 365 

days each year. An electronic copy of 

this document may also be downloaded 

from the Office of the Federal Register’s 

website at www.federalregister.gov and 

the Government Publishing Office’s 

website at www.govinfo.gov. A copy 

may also be found at the FAA’s 

Regulations and Policies website at 

www.faa.gov/regulations_policies. 

Copies may also be obtained by 

sending a request to the Federal 

Aviation Administration, Office of 

Rulemaking, ARM–1, 800 Independence 

Avenue SW, Washington, DC 20591, or 

by calling (202) 267–9677. Commenters 

must identify the docket or notice 

number of this rulemaking. 

All documents the FAA considered in 

developing this final rule, including 

economic analyses and technical 

reports, may be accessed in the 

electronic docket for this rulemaking. 

B. Small Business Regulatory 

Enforcement Fairness Act 

The Small Business Regulatory 

Enforcement Fairness Act (SBREFA) of 

1996 requires the FAA to comply with 

small entity requests for information or 

advice about compliance with statutes 

and regulations within its jurisdiction. 

A small entity with questions regarding 

this document may contact its local 

FAA official, or the person listed under 

the FOR FURTHER INFORMATION CONTACT


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heading at the beginning of the 

preamble. To find out more about 

SBREFA on the internet, visit 

www.faa.gov/regulations_policies/ 

rulemaking/sbre_act/. 

List of Subjects 

14 CFR Part 21 

Aircraft, Aviation safety, Exports, 

Imports, Reporting and recordkeeping 

requirements. 

14 CFR Part 38 

Air Pollution Control, Aircraft, 

Incorporation by reference. 

14 CFR Part 121 

Air carriers, Aircraft, Airmen, Alcohol 

abuse, Aviation safety, Charter flights, 

Drug abuse, Drug testing, Reporting and 

recordkeeping requirements, Safety, 

Transportation. 

14 CFR Part 125 

Aircraft, Airmen, Aviation safety, 

Reporting and recordkeeping 

requirements. 

The Amendment 

In consideration of the foregoing, the 

Federal Aviation Administration 

amends chapter I of title 14, Code of 

Federal Regulations as follows: 

PART 21—CERTIFICATION 

PROCEDURES FOR PRODUCTS AND 

ARTICLES 

■ 1. The authority citation for part 21 

continues to read as follows: 

Authority: 42 U.S.C. 7572; 49 U.S.C. 

106(f), 106(g), 40105, 40113, 44701–44702, 

44704, 44707, 44709, 44711, 44713, 44715, 

45303. 

■ 2. Amend § 21.5 by adding paragraph 

(b)(3) to read as follows: 

§ 21.5 Airplane or Rotorcraft Flight 

Manual. 

* * * * * 

(b) * * * 

(3) Documentation of compliance 

with part 38 of this chapter, in an FAAapproved section of any approved 

airplane flight manual. Such material 

must include the fuel efficiency metric 

value as calculated under § 38.11 of this 

chapter, and the specific paragraph of 

§ 38.17 of this chapter with which 

compliance has been shown for that 

airplane. 

■ 3. Amend § 21.17 by revising 

paragraph (a) introductory text to read 

as follows: 

§ 21.17 Designation of applicable 

regulations. 

(a) Except as provided in §§ 25.2, 

27.2, and 29.2 of this subchapter, and in 

parts 26, 34, 36, and 38 of this 

subchapter, an applicant for a type 

certificate must show that the aircraft, 

aircraft engine, or propeller concerned 

meets— 

* * * * * 

■ 4. Amend § 21.21 by revising 

paragraphs (b) introductory text and 

(b)(1) to read as follows: 

§ 21.21 Issue of type certificate: normal, 

utility, acrobatic, commuter, and transport 

category aircraft; manned free balloons; 

special classes of aircraft; aircraft engines; 

propellers. 

* * * * * 

(b) The applicant submits the type 

design, test reports, and computations 

necessary to show that the product to be 

certificated meets the applicable 

airworthiness, aircraft noise, fuel 

venting, exhaust emission, and fuel 

efficiency requirements of this 

subchapter and any special conditions 

prescribed by the FAA, and the FAA 

finds— 

(1) Upon examination of the type 

design, and after completing all tests 

and inspections, that the type design 

and the product meet the applicable 

noise, fuel venting, emissions, and fuel 

efficiency requirements of this 

subchapter, and further finds that they 

meet the applicable airworthiness 

requirements of this subchapter or that 

any airworthiness provisions not 

complied with are compensated for by 

factors that provide an equivalent level 

of safety; and 

* * * * * 

■ 5. Amend § 21.29 by revising 

paragraphs (a)(1)(i) and (b) to read as 

follows: 

§ 21.29 Issue of type certificate: import 

products. 

(a) * * * 

(1) * * * 

(i) The applicable aircraft noise, fuel 

venting, exhaust emissions, and fuel 

efficiency requirements of this 

subchapter as designated in § 21.17, or 

the applicable aircraft noise, fuel 

venting, exhaust emissions, and fuel 

efficiency requirements of the State of 

Design, and any other requirements the 

FAA may prescribe to provide noise, 

fuel venting, exhaust emission, and fuel 

efficiency levels no greater than those 

provided by the applicable aircraft 

noise, fuel venting, exhaust emissions, 

and fuel efficiency requirements of this 

subchapter as designated in § 21.17; and 

* * * * * 

(b) A product type certificated under 

this section is determined to be 

compliant with the fuel venting and 

exhaust emission standards of part 34 of 

this subchapter, the noise standards of 

part 36 of this subchapter, and the fuel 

efficiency requirements of part 38 of this 

subchapter. Compliance with parts 34, 

36, and 38 of this subchapter is certified 

under paragraph (a)(1)(i) of this section, 

and the applicable airworthiness 

standards of this subchapter, or an 

equivalent level of safety, with which 

compliance is certified under paragraph 

(a)(1)(ii) of this section. 

■ 6. Amend § 21.31 by revising 

paragraph (e) to read as follows: 

§ 21.31 Type design. 

* * * * * 

(e) Any other data necessary to allow, 

by comparison, the determination of the 

airworthiness, noise characteristics, fuel 

efficiency, fuel venting, and exhaust 

emissions (where applicable) of later 

products of the same type. 

■ 7. Amend § 21.93 by adding paragraph 

(d) to read as follows: 

§ 21.93 Classification of changes in type 

design. 

* * * * * 

(d) For the purpose of maintaining 

compliance with part 38 of this chapter, 

any voluntary change in the type design 

of an airplane that may increase the fuel 

efficiency metric value or the MTOM of 

that airplane is a ‘‘fuel efficiency 

change’’, in addition to being a minor or 

major change as classified in paragraph 

(a) of this section. 

■ 8. Amend § 21.101 by revising 

paragraph (a) to read as follows: 

§ 21.101 Designation of applicable 

regulations. 

(a) An applicant for a change to a type 

certificate must show that the change 

and areas affected by the change comply 

with the airworthiness requirements 

applicable to the category of the product 

in effect on the date of the application 

for the change and with parts 34, 36, 

and 38 of this chapter. Exceptions are 

detailed in paragraphs (b) and (c) of this 

section. 

* * * * * 

■ 9. Amend § 21.115 by revising 

paragraph (a) to read as follows: 

§ 21.115 Applicable requirements. 

(a) Each applicant for a supplemental 

type certificate must show that the 

altered product meets applicable 

requirements specified in § 21.101 

and— 

(1) In the case of an acoustical change 

described in § 21.93(b), show 

compliance with the applicable noise 

requirements of part 36 of this chapter; 

(2) In the case of an emissions change 

described in § 21.93(c), show 

compliance with the applicable fuel 

venting and exhaust emissions 


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requirements of part 34 of this chapter; 

and 

(3) In the case of a fuel efficiency 

change described in § 21.93(d), show 

compliance with the applicable fuel 

efficiency requirements of part 38 of this 

chapter. 

* * * * * 

■ 10. Amend § 21.183 by adding 

reserved paragraph (i) and adding 

paragraph (j) to read as follows: 

§ 21.183 Issue of standard airworthiness 

certificates for normal, utility, acrobatic, 

commuter, and transport category aircraft; 

manned free balloons; and special classes 

of aircraft. 

* * * * * 

(i) [Reserved] 

(j) Fuel efficiency requirements. No 

original standard airworthiness 

certificate may be issued under this 

section unless the applicant has 

demonstrated that the type design 

complies with the applicable fuel 

efficiency requirements of part 38 of this 

chapter. 

■ 11. Amend § 21.187 by revising 

paragraph (a) to read as follows: 

§ 21.187 Issue of multiple airworthiness 

certification. 

(a) An applicant for an airworthiness 

certificate in the restricted category, and 

in one or more other categories except 

primary category, is entitled to the 

certificate, if— 

(1) The applicant shows compliance 

with the requirements for each category, 

when the aircraft is in the configuration 

for that category; 

(2) The applicant shows that the 

aircraft can be converted from one 

category to another by removing or 

adding equipment by simple 

mechanical means; 

(3) The aircraft complies with the 

applicable requirements of part 34 of 

this subchapter; and 

(4) The airplane complies with the 

applicable requirements of part 38 of 

this subchapter. 

* * * * * 

■ 12. Add part 38 to read as follows: 

PART 38—AIRPLANE FUEL 

EFFICIENCY CERTIFICATION 

Subpart A—General 

Sec. 

38.1 Applicability. 

38.3 Definitions. 

38.4 Compatibility with airworthiness 

requirements. 

38.5 Exemptions. 

38.7 Incorporation by reference. 

38.9 Relationship to other regulations. 

Subpart B—Determining Fuel Efficiency for 

Subsonic Airplanes 

38.11 Fuel efficiency metric. 

38.13 Specific air range. 

38.15 Reference geometric factor. 

38.17 Fuel efficiency limits. 

38.19 Change criteria. 

38.21 Approval before compliance testing. 

38.23 Manual information and limitations. 

Appendix A to Part 38—Determination of 

Airplane Fuel Efficiency Metric Value 

Authority: 42 U.S.C. 4321 et seq., 7572; 49 

U.S.C. 106(g), 40113, 44701–44702, 44704; 49 

CFR 1.83(c) 

Subpart A—General 

§ 38.1 Applicability. 

(a) Except as provided in paragraph 

(c) of this section, an airplane that is 

subject to the requirements of 40 CFR 

part 1030 may not exceed the fuel 

efficiency limits of this part when 

original type certification under this 

title is sought. This part applies to the 

following airplanes: 

(1) A subsonic jet airplane that has— 

(i) Either— 

(A) A type-certificated maximum 

passenger seating capacity of 20 seats or 

more; 

(B) A maximum takeoff mass (MTOM) 

greater than 5,700 kg; and 

(C) An application for original type 

certification that is submitted on or after 

January 11, 2021; 

(ii) Or— 

(A) A type-certificated maximum 

passenger seating capacity of 19 seats or 

fewer; 

(B) A MTOM greater than 60,000 kg; 

and 

(C) An application for original type 

certification that is submitted on or after 

January 11, 2021. 

(2) A subsonic jet airplane that has— 

(i) A type-certificated maximum 

passenger seating capacity of 19 seats or 

fewer; 

(ii) A MTOM greater than 5,700 kg, 

but not greater than 60,000 kg; and 

(iii) An application for original type 

certification that is submitted on or after 

January 1, 2023. 

(3) A propeller-driven airplane that 

has— 

(i) A MTOM greater than 8,618 kg; 

and 

(ii) An application for original type 

certification that is submitted on or after 

January 11, 2021. 

(4) A subsonic jet airplane— 

(i) That is a modified version of an 

airplane whose type design was not 

certificated under this part; 

(ii) That has a MTOM greater than 

5,700 kg; 

(iii) For which an application by the 

type certificate holder for a type design 

change is submitted on or after January 

1, 2023; and 

(iv) For which the first certificate of 

airworthiness is issued with the 

modified type design. 

(5) A propeller-driven airplane— 

(i) That is a modified version of an 

airplane whose type design was not 

certificated under this part; 

(ii) That has a MTOM greater than 

8,618 kg; 

(iii) For which an application by the 

type certificate holder for a type design 

change is submitted on or after January 

1, 2023; and 

(iv) For which the first certificate of 

airworthiness is issued with the 

modified type design. 

(6) A subsonic jet airplane that has— 

(i) A MTOM greater than 5,700 kg; 

and 

(ii) Its first certificate of airworthiness 

issued on or after January 1, 2028. 

(7) A propeller-driven airplane that 

has— 

(i) A MTOM greater than 8,618 kg; 

and 

(ii) Its first certificate of airworthiness 

issued on or after January 1, 2028. 

(b) The requirements of this part 

apply to an airplane for which an 

application for a change in type design 

is submitted that includes a 

modification that meets the change 

criteria of § 38.19. A modified airplane 

may not exceed the applicable fuel 

efficiency limit of this part when 

certification under this chapter is 

sought. A modified airplane is subject to 

the same fuel efficiency limit of § 38.17 

as the airplane was certificated to prior 

to modification. 

(c) The requirements of this part do 

not apply to: 

(1) Subsonic jet airplanes having a 

MTOM at or below 5,700 kg. 

(2) Propeller-driven airplanes having 

a MTOM at or below 8,618 kg. 

(3) Amphibious airplanes. 

(4) Airplanes initially designed, or 

modified and used, for specialized 

operations. These airplane designs may 

include characteristics or configurations 

necessary to conduct specialized 

operations that the FAA and the United 

States Environmental Protection Agency 

(EPA) have determined may cause a 

significant increase in the fuel efficiency 

metric value. 

(5) Airplanes designed with a 

reference geometric factor of zero. 

(6) Airplanes designed for, or 

modified and used for, firefighting. 

(7) Airplanes powered by 

reciprocating engines. 

§ 38.3 Definitions. 

For the purpose of showing 

compliance with this part, the following 

terms have the specified meanings: 

Amphibious airplane means an 

airplane that is capable of takeoff and 


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landing on both land and water. Such 

an airplane uses its hull or floats 

attached to the landing gear for takeoff 

and landing on water, and either 

extendable or fixed landing gear for 

takeoff and landing on land. 

ICAO Annex 16, Volume III means 

Volume III of Annex 16 to the 

Convention on International Civil 

Aviation. 

Maximum takeoff mass (MTOM) is 

the maximum certified takeoff mass, 

expressed in kilograms, for an airplane 

type design. 

Performance model is an analytical 

tool (or a method) validated using 

corrected flight test data that can be 

used to determine the specific air range 

values for calculating the fuel efficiency 

metric value. 

Reference geometric factor (RGF) is a 

non-dimensional number derived from a 

two-dimensional projection of the 

fuselage. 

Specific air range (SAR) is the 

distance an airplane travels per unit of 

fuel consumed. Specific air range is 

expressed in kilometers per kilogram of 

fuel. 

Subsonic means an airplane that has 

not been certificated under this title to 

exceed Mach 1 in normal operation. 

Type certificated maximum passenger 

seating capacity means the maximum 

number of passenger seats that may be 

installed on an airplane as listed on its 

type certificate data sheet, regardless of 

the actual number of seats installed on 

an individual airplane. 

§ 38.4 Compatibility with airworthiness 

requirements. 

Unless otherwise approved by the 

FAA, an airplane used to demonstrate 

compliance with this part must meet all 

of the airworthiness requirements of this 

chapter required to establish the type 

certification basis of the airplane, for 

any condition under which compliance 

with this part is being demonstrated. 

Any procedure used to demonstrate 

compliance, and any flight crew 

information developed for 

demonstrating compliance with this 

part, must be consistent with the 

airworthiness requirements of this 

chapter that constitute the type 

certification basis of the airplane. 

§ 38.5 Exemptions. 

A petition for exemption from any 

requirement of this part must be 

submitted to the Administrator in 

accordance with and meet the 

requirements of part 11 of this chapter. 

The FAA will consult with the EPA on 

each exemption petition before taking 

action. 

§ 38.7 Incorporation by reference. 

The ICAO Doc 7488/3, Manual of the 

ICAO Standard Atmosphere (extended 

to 80 kilometres (262 500 feet)) (1993), 

referenced in sections A38.2.1.3.1, 

A38.5.2.2.1.9, and A38.5.2.2.1.10 of 

appendix A to this part, is incorporated 

by reference into this part with the 

approval of the Director of the Federal 

Register under 5 U.S.C. 552(a) and 1 

CFR part 51. All approved material is 

available for inspection at the FAA and 

at the National Archives and Records 

Administration (NARA). Contact FAA 

at: Office of Rulemaking (ARM–1), 800 

Independence Avenue SW, Washington, 

DC 20590 (telephone 202–267–9677). 

For information on the availability of 

this material at NARA, visit 

www.archives.gov/federal-register/cfr/ 

ibr-locations.html or email 

fr.inspection@nara.gov. The ICAO Doc 

7488/3 is available for purchase from 

the ICAO Store at 999 Robert-Bourassa 

Boulevard Montre ́al (Quebec) Canada 

H3C 5H7, (https://store.icao.int/). 

§ 38.9 Relationship to other regulations. 

In accordance with certain provisions 

of the Clean Air Act Amendments of 

1970 (CAA) (42 U.S.C. 7571 et seq.), the 

United States Environmental Protection 

Agency (EPA) is authorized to set 

standards for aircraft engine emissions 

in the United States, while the FAA is 

authorized to ensure compliance with 

those standards under a delegation from 

the Secretary of Transportation (49 CFR 

1.83). The fuel efficiency limits in 

§ 38.17 are intended to be the same as 

that promulgated by the EPA in 40 CFR 

part 1030. Accordingly, if the EPA 

changes any regulation in 40 CFR part 

1030 that corresponds with a regulation 

in this part, a certification applicant 

may request a waiver of those 

provisions as they appear in this part in 

order to comply with part 1030. In 

addition, unless otherwise specified in 

this part, all terminology and 

abbreviations in this part that are 

defined in 40 CFR part 1030 have the 

meaning specified in part 1030. 

Subpart B—Determining Fuel 

Efficiency for Subsonic Airplanes 

§ 38.11 Fuel efficiency metric. 

For each airplane subject to this part, 

or to determine whether a modification 

makes an airplane subject to this part 

under the change criteria of § 38.19, a 

fuel efficiency metric value must be 

calculated, using the following 

equation, rounded to three decimal 

places: 

Where: 

The SAR is determined in accordance with 

§ 38.13, and the RGF is determined in 

accordance with § 38.15. The fuel 

efficiency metric value is expressed in 

units of kilograms of fuel consumed per 

kilometer. 

§ 38.13 Specific air range. 

(a) For each airplane subject to this 

part, the SAR of an airplane must be 

determined by either: 

(1) Direct flight test measurements; or 

(2) Using a performance model that is: 

(i) Validated by actual SAR flight test 

data; and 

(ii) Approved by the FAA before any 

SAR calculations are submitted. 

(b) For the airplane model, establish 

a 1/SAR value at each of the following 

reference airplane masses: 

(1) High gross mass: 92 percent 

MTOM. 

(2) Low gross mass: (0.45 * MTOM) + 

(0.63 * (MTOM∧0.924)). 

(3) Mid gross mass: simple arithmetic 

average of high gross mass and low 

gross mass. 

(c) To obtain (1/SAR)avg as required to 

determine the fuel efficiency metric 

value described in § 38.11, calculate the 

average of the three 1/SAR values 

described in paragraph (b) of this 

section. Do not include auxiliary power 

units in any 1/SAR calculation. 

(d) All determinations made under 

this section must be made in accordance 

with the procedures applicable to SAR 

as described in appendix A to this part. 

§ 38.15 Reference geometric factor. 

For each airplane subject to this part, 

determine the airplane’s nondimensional RGF for the fuselage size of 

each airplane model, calculated as 

follows: 

(a) For an airplane with a single deck, 

determine the area of a surface 


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Fuel Efficiency metric value 
12656 Federal Register / Vol. 89, No. 33 / Friday, February 16, 2024 / Rules and Regulations 

(expressed in m∧2) bounded by the 

maximum width of the fuselage outer 

mold line projected to a flat plane 

parallel with the main deck floor and 

the forward and aft pressure bulkheads 

except for the crew flight deck zone. 

(b) For an airplane with more than 

one deck, determine the sum of the 

areas (expressed in m∧2) as follows: 

(1) The maximum width of the 

fuselage outer mold line, projected to a 

flat plane parallel with the main deck 

floor by the forward and aft pressure 

bulkheads except for any crew flight 

deck zone. 

(2) The maximum width of the 

fuselage outer mold line at or above 

each other deck floor, projected to a flat 

plane parallel with the additional deck 

floor by the forward and aft pressure 

bulkheads except for any crew flight 

deck zone. 

(c) Determine the non-dimensional 

RGF by dividing the area defined in 

paragraph (a) or (b) of this section by 1 

m∧2. 

(d) All measurements and 

calculations used to determine the RGF 

of an airplane must be made in 

accordance with the procedures for 

determining RGF in section A38.3 of 

appendix A to this part. 

§ 38.17 Fuel efficiency limits. 

(a) The fuel efficiency limits in this 

section are expressed as maximum 

permitted fuel efficiency metric values, 

as calculated under § 38.11. 

(b) The fuel efficiency metric value of 

an airplane subject to this part may not 

exceed the following, rounded to three 

decimal places: 


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For airplanes 

described With a MTOM ... The maximum permitted fuel efficiency metric value is ... 

in ... 

(1) Section 

38.l(a)(l) 5,700 < MTOM _:s 60,000 kg 10 (-2.73780 + (0.681310 * log (MTOM)) + (-0.0277861 • (log (MTOM))"2)) 10 10 

and (2) 

(2) Section 

8,618 < MTOM _:s 60,000 kg 10 (-2.73780 + (0.681310 * log (MTOM)) + (-0.0277861 • (log (MTOM))"2)) 10 10 

38.l(a)(3) 

(3) Section 

38.l(a)(l) 60,000 < MTOM :S 70,395 kg 0.764 

and (3) 

(4) Section 

38.l(a)(l) MTOM > 70,395 kg 10 (-1.412742 + (-0.020517 * log (MTOM)) + (0.0593831 • (log (MTOM))"2)) 10 10 

and (3) 

(5) Section 

38.l(a)(4) 5,700 < MTOM _:s 60,000 kg 10 (-2.57535 + (0.609766 * log (MTOM)) + (-0.0191302 • (log (MTOM))"2)) 10 10 

and (6) 

(6) Section 

38.l(a)(S) 8,618 < MTOM _:s 60,000 kg 10 (-2.57535 + (0.609766 • log (MTOM)) + (-0.0191302 • (log (MTOM))"2)) 10 10 

and (7) 

(7) Section 

38.l(a)(4) 60,000 < MTOM _:s 70,107 kg 0.797 

through (7) 

(8) Section 

38.l(a)(4) MTOM > 70,107 kg 10 (-1.39353+ (-0.020517 • log (MTOM)) + (0.0593831 • (log (MTOM))"2)) 10 10 

through (7) 
12658 Federal Register / Vol. 89, No. 33 / Friday, February 16, 2024 / Rules and Regulations 

§ 38.19 Change criteria. 

(a) For an airplane that has been 

shown to comply with § 38.17, any 

subsequent version of that airplane must 

demonstrate compliance with § 38.17 if 

the subsequent version incorporates a 

modification that either increases: 

(1) The maximum takeoff mass; or 

(2) The fuel efficiency metric value by 

a percentage that is more than the 

following calculated thresholds. 

(i) For airplanes with a MTOM greater 

than or equal to 5,700 kg, the threshold 

decreases linearly from 1.35 percent for 

an airplane with a MTOM of 5,700 kg 

to 0.75 percent for an airplane with a 

MTOM of 60,000 kg. 

(ii) For airplanes with a MTOM 

greater than or equal to 60,000 kg, the 

threshold decreases linearly from 0.75 

percent for an airplane with a MTOM of 

60,000 kg to 0.70 percent for airplanes 

with a MTOM of 600,000 kg. 

(iii) For airplanes with a MTOM 

greater than or equal to 600,000 kg, the 

threshold is 0.70 percent. 

(b) For an airplane that has been 

shown to comply with § 38.17, and for 

any subsequent version of that airplane 

that incorporates modifications that do 

not increase the MTOM or the fuel 

efficiency metric value in excess of the 

levels shown in paragraph (a) of this 

section, the fuel efficiency metric value 

of the modified airplane may be 

reported to be the same as the value 

prior to modification. 

(c) For an airplane that meets the 

criteria of § 38.1(a)(4) or (5), on or after 

January 1, 2023, and before January 1, 

2028, the airplane must demonstrate 

compliance with § 38.17 if it 

incorporates any modification that 

increases the fuel efficiency metric 

value of the airplane prior to 

modification by more than 1.5 percent. 

§ 38.21 Approval before compliance 

testing. 

All procedures, weights, 

configurations, and other information or 

data that are used to establish a fuel 

efficiency level required by this part or 

in any appendix to this part (including 

any equivalent procedures) must be 

approved by the FAA prior to use in 

certification tests intended to 

demonstrate compliance with this part. 

§ 38.23 Manual information and 

limitations. 

(a) Information in manuals. The 

following information must be included 

in any FAA-approved section of a FAAapproved Airplane Flight Manual or 

combination of approved manual 

material: 

(1) Fuel efficiency level established as 

required by this part; and 

(2) Maximum takeoff mass at which 

fuel efficiency level was established. 

(b) Limitation. If the fuel efficiency of 

an airplane is established at a weight 

(mass) that is less than the maximum 

certificated takeoff weight (mass) used 

to establish the airworthiness of the 

airplane under this chapter, the lower 

weight (mass) becomes an operating 

limitation of the airplane and that 

limitation must be included in the 

limitations section of any FAAapproved manual. 

Appendix A to Part 38—Determination 

of Airplane Fuel Efficiency Metric 

Value 

A38.1 Introduction 

A38.2 Reference specifications for SAR 

flight tests 

A38.3 Determination of reference geometric 

factor (RGF) 

A38.4 Certification test specifications 

A38.5 Measurement of specific air range 

A38.6 Submission of certification data to 

the FAA 

A38.1 Introduction 

A38.1.1 This appendix describes the 

processes and procedures for determining the 

fuel efficiency metric value for an airplane 

subject to this part. 

A38.1.2 Methods for Determining Specific 

Air Range (SAR) 

A38.1.2.1 SAR may be determined by 

either— 

A38.1.2.1.1 Direct flight test measurement 

at the SAR test points, including any 

corrections of test data to reference 

specifications; or 

A38.1.2.1.2 Use of a performance model. 

A38.1.2.2 For any determination made 

under section A38.1.2.1.1 of this appendix, 

the SAR flight test data must have been 

acquired in accordance with the procedures 

defined in this appendix and approved by 

the FAA. 

A38.1.2.3 For any determination made 

under section A38.1.2.1.2 of this appendix, 

the performance model must: 

A38.1.2.3.1 Be verified that the model 

produces the values that are the same as 

FAA-approved SAR flight test data; 

A38.1.2.3.2 Include a detailed description 

of any test and analysis method and any 

algorithm used so as to allow evaluation by 

the FAA; and 

A38.1.2.3.3 Be approved by the FAA before 

use. 

A38.2 Reference Specifications for SAR 

Flight Tests 

A38.2.1 The following reference 

specifications must be established when 

determining SAR values for an airplane. No 

reference specification may exceed any 

airworthiness limit approved for the airplane 

under this chapter. See section A38.5 of this 

appendix for further information. 

A38.2.1.1 Reference specifications at the 

airplane level: 

A38.2.1.1.1 Airplane at the reference 

masses listed in § 38.13(b); 

A38.2.1.1.2 A combination of altitude and 

airspeed selected by the applicant; 

A38.2.1.1.3 Airplane in steady, 

unaccelerated, straight and level flight; 

A38.2.1.1.4 Airplane in longitudinal and 

lateral trim; 

A38.2.1.1.5 Airplane gravitational 

acceleration when travelling in the direction 

of true North in still air at the reference 

altitude and a geodetic latitude of 45.5 

degrees, based on g0 (g0 is 9.80665 m/s2, 

which is the standard acceleration due to 

gravity at sea level and a geodetic latitude of 

45.5 degrees); 

A38.2.1.1.6 A reference airplane center of 

gravity (CG) position selected by the 

applicant to be representative of the mid-CG 

point relevant to design cruise performance 

at each of the three reference airplane 

masses; and 

A38.2.1.1.7 A wing structural loading 

condition defined by the applicant that is 

representative of operations conducted in 

accordance with the airplane’s maximum 

payload capability. 

A38.2.1.2 Reference specifications at the 

engine level: 

A38.2.1.2.1 Electrical and mechanical 

power extraction and bleed flow relevant to 

design cruise performance, as selected by the 

applicant; 

Note 1 to A38.2.1.2.1—Power extraction 

and bleed flow attributable to the use of 

optional equipment such as passenger 

entertainment systems need not be included. 

A38.2.1.2.2 Engine stability bleeds 

operating according to the manufacturer’s 

normal schedule for the engine; and 

A38.2.1.2.3 Engines with at least 15 cycles 

or 50 engine flight hours. 

A38.2.1.3 Other reference specifications: 

A38.2.1.3.1 ICAO standard day atmosphere 

(Doc 7488/3, 3rd edition 1993, titled 

‘‘Manual of the ICAO Standard Atmosphere 

(extended to 80 kilometres (262 500 feet))’’) 

(incorporated by reference, see § 38.7); and 

A38.2.1.3.2 Fuel lower heating value equal 

to 43.217 MJ/kg (18,¥580 BTU/lb). 

A38.2.2 If any test conditions are not the 

same as the reference specifications of this 

appendix, the test conditions must be 

corrected to the reference specifications as 

described in section A38.5 of this appendix. 

A38.3 Determination of Reference 

Geometric Factor (RGF) 

A38.3.1 This section provides additional 

information for determining the RGF, as 

required by § 38.15. 

A38.3.2 The area that defines RGF includes 

all pressurized space on a single or multiple 

decks including aisles, assist spaces, 

passageways, stairwells and areas that can 

accommodate cargo or auxiliary fuel 

containers. It does not include permanent 

integrated fuel tanks within the cabin, or any 

unpressurized fairings, crew rest or work 

areas, or cargo areas that are not on the main 

or upper deck (e.g., ‘loft’ or under floor 

areas). RGF does not include the flight deck 

crew zone. 

A38.3.3 The aft boundary to be used for 

calculating RGF is the aft pressure bulkhead. 

The forward boundary is the forward 

pressure bulkhead, not including the flight 

deck crew zone. 


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A38.3.4 Areas that are accessible to both 

crew and passengers are not considered part 

of the flight deck crew zone. For an airplane 

that has a flight deck door, the aft boundary 

of the flight deck crew zone is the plane of 

the flight deck door. For an airplane that has 

no flight deck door or has optional interior 

configurations that include different 

locations of the flight deck door, the aft 

boundary is determined by the configuration 

that provides the smallest available flight 

deck crew zone. For airplanes certificated for 

single-pilot operation, the flight deck crew 

zone is measured as half the width of the 

flight deck. 

A38.3.5 Figures A38–1 and A38–2 of this 

appendix provide a notional view of the RGF 

boundary conditions. 


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Figure A38-1 to Appendix A to Part 38-Cross-sectional view 

Airplane with single deck Airplane with upper deck 

Fuselage outer mold line (OML) 

••••••••••••••••••••••••••• ■■■■■■■■■■ ■■■■■■■■■■■■■■■■■■■ 

■ ■ ■ ■ Maximum width of fuselage OML for single and upper deck 

- Actual floor area 
12660 Federal Register / Vol. 89, No. 33 / Friday, February 16, 2024 / Rules and Regulations 

A38.4 Certification Test Specifications 

A38.4.1 Certification Test 

Specifications. This section prescribes 

the specifications under which an 

applicant must conduct SAR 

certification tests. 

A38.4.2 Flight Test Procedures 

A38.4.2.1 Before a Test Flight. The 

test flight procedures must include the 

following elements and must be 

approved by the FAA before any test 

flight is conducted: 

A38.4.2.1.1 Airplane conformity. The 

test airplane must conform to the 

critical configuration of the type design 

for which certification is sought. 

A38.4.2.1.2 Airplane weight. The test 

airplane must be weighed. Any change 

in mass after the weighing and prior to 

the test flight must be accounted for. 

A38.4.2.1.3 Fuel. The fuel used for 

each flight test must meet the 

specification defined in either ASTM 

D1655–15 (titled ‘‘Standard 

Specification for Aviation Turbine 

Fuels’’), UK MoD Defense Standard 91– 

91, Issue 7, Amendment 3 (titled 

‘‘Turbine Fuel, Kerosene Type, Jet A–1, 

NATO Code F–35; Join Services 

Designation; AVTUR’’), or as approved 

by FAA. 

A38.4.2.1.4 Fuel lower heating value. 

The lower heating value of the fuel used 

on a test flight must be determined from 

a sample of fuel used for the test flight. 

The lower heating value of the fuel 

sample must be used to correct 

measured data to reference 

specifications. The determination of 

lower heating value and the correction 

to reference specifications are subject to 

approval by the FAA. 

A38.4.2.1.4.1 The fuel lower heating 

value may be determined in accordance 

with ASTM D4809–13 ‘‘Standard Test 

Method for Heat of Combustion of 

Liquid Hydrocarbon Fuels by Bomb 

Calorimeter (Precision Method)’’, or as 

approved by the FAA. 

A38.4.2.1.4.2 The fuel sample may be 

representative of the fuel used for each 

flight test and should not have errors or 

variations due to fuel being uplifted 

from multiple sources, fuel tank 

selection, or fuel layering in a tank. 

A38.4.2.1.5 Fuel specific gravity and 

viscosity. When volumetric fuel flow 

meters are used, the specific gravity and 

viscosity of the fuel used on a test flight 

must be determined from a sample of 

fuel used for the test flight. 

A38.4.2.1.5.1 The fuel specific gravity 

may be determined in accordance with 

ASTM D4052–11 ‘‘Standard Test 

Method for Density, Relative Density, 

and API Gravity of Liquids’’, or as 

approved by FAA. 

A38.4.2.1.5.2 The fuel kinematic 

viscosity may be determined in 

accordance with ASTM D445–15 (titled 

‘‘Standard Test Method for Kinematic 

Viscosity of Transparent and Opaque 

Liquids (and Calculation of Dynamic 

Viscosity)’’), or as approved by FAA. 

A38.4.2.2 Flight Test Procedures and 

Test Condition Stability. An applicant 

must conduct each flight test in 

accordance with the flight test 

procedures and the stability conditions 

as follows: 

A38.4.2.2.1 Flight Test Procedure. 

The following procedures must be 

maintained during each flight used to 

gather data for determining SAR values: 

A38.4.2.2.1.1 To the extent that is 

practicable, the airplane is flown at 

constant pressure altitude and constant 

heading along isobars; 

A38.4.2.2.1.2 The engine thrust/ 

power setting is stable for unaccelerated 

level flight; 

A38.4.2.2.1.3 The airplane is flown as 

close as practicable to the reference 

specifications to minimize the 

magnitude of any correction; 

A38.4.2.2.1.4 Changes in trim or 

engine power/thrust settings, engine 

stability and handling bleeds, or 

electrical and mechanical power 

extraction (including bleed flow) are 

avoided or minimized as practicable; 

and 

A38.4.2.2.1.5 There is no unnecessary 

movement of on-board personnel. 

A38.4.2.2.2 Test Condition Stability. 

To obtain a valid SAR measurement, the 

following conditions must be 

maintained during each test flight, 

including the indicated tolerances for at 

least 1 minute while SAR data is 

acquired: 

A38.4.2.2.2.1 Mach number within 

±0.005; 


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Forward 

boundary 

Tapered outer skin width, 

measured at the frame station 

Forward 

boundary 

Permanent integrated fuel 

tanks within cabin 

Figure A38-2 to Appendix A to Part 38. Longitudinal view 

Aft boundary 

Forward 

boundary with 

non-crew seat 

zone area 
Federal Register / Vol. 89, No. 33 / Friday, February 16, 2024 / Rules and Regulations 12661 

A38.4.2.2.2.2 Ambient temperature 

within ±1 °C; 

A38.4.2.2.2.3 Heading within ±3 

degrees; 

A38.4.2.2.2.4 Track within ±3 degrees; 

A38.4.2.2.2.5 Drift angle less than 3 

degrees; 

A38.4.2.2.2.6 Ground speed within 

±3.7 km/h (±2 kt); 

A38.4.2.2.2.7 Difference in ground 

speed at the beginning of the SAR 

measurement from the ground speed at 

the end of the SAR measurement within 

±2.8 km/h/min (±1.5 kt/min); and 

A38.4.2.2.2.8 Pressure altitude within 

±23 m (±75 ft). 

A38.4.2.2.3 Alternatives to the stable 

test condition criteria of section 

A38.4.2.2.2 of this appendix may be 

used provided that stability is 

sufficiently demonstrated to the FAA. 

A38.4.2.2.4 Data obtained at test 

points that do not meet the stability 

criteria of section A38.4.2.2.2 may be 

acceptable as an equivalent procedure, 

subject to FAA approval. 

A38.4.2.2.5 SAR measurements at the 

test points must be separated by either: 

A38.4.2.2.5.1 Two minutes; or 

A38.4.2.2.5.2 An exceedance of one or 

more of the stability criteria limits 

described in A38.4.2.2.2. 

A38.4.2.3 Verification of Airplane 

Mass at Test Conditions 

A38.4.2.3.1 The procedure for 

determining the mass of the airplane at 

each test condition must be approved by 

the FAA. 

A38.4.2.3.2 The mass of the airplane 

during a flight test is determined by 

subtracting the fuel used from the mass 

of the airplane at the start of the test 

flight. The accuracy of the 

determination of the fuel used must be 

verified by: 

A38.4.2.3.2.1 Weighing the test 

airplane on calibrated scales before and 

after the SAR test flight; 

A38.4.2.3.2.2 Weighing the test 

airplane before and after another test 

flight that included a cruise segment, 

provided that flight occurs within one 

week or 50 flight hours (at the option of 

the applicant) of the SAR test flight and 

using the same, unaltered fuel flow 

meters; or 

A38.4.2.3.2.3 Other methods as 

approved by the FAA. 

A38.5 Measurement of Specific Air 

Range 

A38.5.1 Measurement System 

A38.5.1.1 The following parameters 

must be recorded at a minimum 

sampling rate of 1 Hertz (cycle per 

second): 

A38.5.1.1.1 Airspeed; 

A38.5.1.1.2 Ground speed; 

A38.5.1.1.3 True airspeed; 

A38.5.1.1.4 Fuel flow; 

A38.5.1.1.5 Engine power setting; 

A38.5.1.1.6 Pressure altitude; 

A38.5.1.1.7 Temperature; 

A38.5.1.1.8 Heading; 

A38.5.1.1.9 Track; and 

A38.5.1.1.10 Fuel used (for the 

determination of gross mass and CG 

position). 

A38.5.1.2 The following parameters 

must be recorded: 

A38.5.1.2.1 Latitude; 

A38.5.1.2.2 Engine bleed positions 

and power off-takes; and 

A38.5.1.2.3 Power extraction 

(electrical and mechanical load). 

A38.5.1.3 The value of each parameter 

used for the determination of SAR 

(except for ground speed) is the simple 

arithmetic average of the measured 

values for that parameter obtained 

throughout the stable test condition 

described in section A38.4.2.2.2 of this 

appendix. 

A38.5.1.4 For ground speed, the value 

is the rate of change of ground speed 

during the SAR test measurement. The 

rate of change of ground speed during 

the SAR measurement must be used to 

evaluate and correct any acceleration or 

deceleration that might occur during the 

SAR measurement. 

A38.5.1.5 Each measurement device 

must have sufficient resolution to 

determine that the stability of a 

parameter defined in section A38.4.2.2.2 

of this appendix is maintained during 

SAR measurement. 

A38.5.1.6 The SAR measurement 

system consists of the combined 

instruments and devices, and any 

associated procedures, used to acquire 

the following parameters necessary to 

determine SAR: 

A38.5.1.6.1 Fuel flow; 

A38.5.1.6.2 Mach number; 

A38.5.1.6.3 Altitude; 

A38.5.1.6.4 Airplane mass; 

A38.5.1.6.5 Ground speed; 

A38.5.1.6.6 Outside air temperature; 

A38.5.1.6.7 Fuel lower heating value; 

and 

A38.5.1.6.8 CG. 

A38.5.1.7 The SAR value is affected 

by the accuracy of each element that 

comprises the SAR measurement 

system. The cumulative error associated 

with the SAR measurement system is 

defined as the root sum of squares (RSS) 

of the individual accuracies. 

A38.5.1.8 If the absolute value of the 

cumulative error of the overall SAR 

measurement system is greater than 1.5 

percent, a penalty equal to the amount 

that the RSS value exceeds 1.5 percent 

must be applied to the SAR value that 

has been corrected to reference 

specifications (see section A38.5.2 of 

this appendix). If the absolute value of 

the cumulative error of the overall SAR 

measurement system is less than or 

equal to 1.5 percent, no penalty will be 

applied. 

A38.5.2 Calculation of Specific Air 

Range from Measured Data 

A38.5.2.1 Calculating SAR. SAR must 

be calculated using the following 

equation: 

SAR = TAS/Wf

Where: 

TAS is the true airspeed and Wf is total 

airplane fuel flow. 

A38.5.2.2 Correcting Measured SAR 

Values to Reference Specifications 

A38.5.2.2.1 The measured SAR values 

must be corrected to the reference 

specifications listed in A38.2 of this 

appendix. Unless otherwise approved 

by the FAA, corrections to reference 

specifications must be applied for each 

of the following measured parameters: 

A38.5.2.2.1.1 Acceleration/ 

deceleration (energy). Drag 

determination is based on an 

assumption of steady, unaccelerated 

flight. Acceleration or deceleration 

occurring during a test condition affects 

the assessed drag level. The reference 

specification is in section A38.2.1.1.3 of 

this appendix. 

A38.5.2.2.1.2 Aeroelastics. Wing 

aeroelasticity may cause a variation in 

drag as a function of airplane wing mass 

distribution. Airplane wing mass 

distribution will be affected by the fuel 

load distribution in the wings and the 

presence of any external stores. The 

reference specification is in section 

A38.2.1.1.7 of this appendix. 

A38.5.2.2.1.3 Altitude. The altitude at 

which the airplane is flown affects the 

fuel flow. The reference specification is 

in section A38.2.1.1.2 of this appendix. 

A38.5.2.2.1.4 Apparent gravity. 

Acceleration, caused by the local effect 

of gravity, and inertia, affect the test 

weight of the airplane. The apparent 

gravity at the test conditions varies with 

latitude, altitude, ground speed, and 

direction of motion relative to the 

Earth’s axis. The reference gravitational 

acceleration is the gravitational 

acceleration for the airplane travelling 

in the direction of true North in still air 

at the reference altitude, a geodetic 

latitude of 45.5 degrees, and based on g0

(see section A38.2.1.1.5 of this 

appendix). 

A38.5.2.2.1.5 CG position. The 

position of the airplane CG affects the 

drag due to longitudinal trim. The 

reference specification is in section 

A38.2.1.1.6 of this appendix. 

A38.5.2.2.1.6 Electrical and 

mechanical power extraction and bleed 

flow. Electrical and mechanical power 

extraction, and bleed flow affect the fuel 


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12662 Federal Register / Vol. 89, No. 33 / Friday, February 16, 2024 / Rules and Regulations 

flow. The reference specifications are in 

sections A38.2.1.2.1 and A38.2.1.2.2 of 

this appendix. 

A38.5.2.2.1.7 Engine deterioration 

level. The requirement in section 

A38.2.1.2.3 of this appendix addresses 

the minimum deterioration of an engine 

that is used to determine SAR. Since 

engine deterioration is rapid when an 

engine is new, when used for SAR 

determination: 

A38.5.2.2.1.7.1 Subject to FAA 

approval, an engine having less 

deterioration than the reference 

deterioration level in section 

A38.2.1.2.3 of this appendix must 

correct the fuel flow to the reference 

deterioration using an approved 

method. 

A38.5.2.2.1.7.2 An engine with greater 

deterioration than the reference 

deterioration level in section 

A38.2.1.2.3 of this appendix may be 

used, and no correction is permitted. 

A38.5.2.2.1.8 Fuel lower heating 

value. The fuel lower heating value 

defines the energy content of the fuel. 

The lower heating value directly affects 

the fuel flow at a given test condition. 

The reference specification is in section 

A38.2.1.3.2 of this appendix. 

A38.5.2.2.1.9 Reynolds number. The 

Reynolds number affects airplane drag. 

For a given test condition the Reynolds 

number is a function of the density and 

viscosity of air at the test altitude and 

temperature. The reference Reynolds 

number is derived from the density and 

viscosity of air from the ICAO standard 

atmosphere at the reference altitude (see 

sections A38.2.1.1.2 and A38.2.1.3.1 of 

this appendix, incorporated by reference 

see § 38.7). 

A38.5.2.2.1.10 Temperature. The 

ambient temperature affects the fuel 

flow. The reference temperature is the 

standard day temperature from the 

ICAO standard atmosphere at the 

reference altitude (see section 

A38.2.1.3.1 of this appendix, 

incorporated by reference see § 38.7). 

Note 2 to A38.5.2.2.1.10—Post-flight 

data analysis includes the correction of 

measured data for data acquisition 

hardware response characteristics (e.g., 

system latency, lag, offset, buffering, 

etc.). 

A38.5.2.2.2 Correction methods are 

subject to the approval of the FAA. 

A38.5.2.3 Using Specific Air Range to 

Determine the Fuel Efficiency Metric 

Value 

A38.5.2.3.1 Calculate the SAR values 

for each of the three reference masses as 

described in § 38.13, including any 

corrections to reference specifications, 

as required under this part. The final 

SAR value for each reference mass is the 

simple arithmetic average of all valid 

test points at the appropriate gross mass, 

or derived from a validated performance 

model. No data acquired from a valid 

test point may be omitted unless 

approved by the FAA. 

A38.5.2.3.2 When an FAA-approved 

performance model is used, 

extrapolations to aircraft masses other 

than those tested may be approved 

when such extrapolations are consistent 

with accepted airworthiness practices. 

Since a performance model must be 

based on data covering an adequate 

range of lift coefficient, Mach number, 

and thrust specific fuel consumption, no 

extrapolation of those parameters is 

permitted. 

A38.5.3 Validity of Results 

A38.5.3.1 A 90 percent confidence 

interval must be calculated for each of 

the SAR values at the three reference 

masses. 

A38.5.3.2 If the 90 percent confidence 

interval of the SAR value at any of the 

three reference airplane masses— 

A38.5.3.2.1 Is less than or equal to 

±1.5 percent, the SAR value may be 

used. 

A38.5.3.2.2 Exceeds ±1.5 percent, a 

penalty equal to the amount that the 90 

percent confidence interval exceeds 

±1.5 percent must be applied to the SAR 

value, as approved by the FAA. 

A38.5.3.3 If clustered data is acquired 

separately for each of the three gross 

mass reference points, the minimum 

sample size acceptable for each of the 

three gross mass SAR values is six. 

A38.5.3.4 If SAR data is collected over 

a range of masses, the minimum sample 

size is 12 and the 90 percent confidence 

interval is calculated for the mean 

regression line through the data. 

A38.6 Submission of Certification 

Data to the FAA 

The following information must be 

provided to the FAA in the certification 

reports for each airplane type and model 

for which fuel efficiency certification 

under this part is sought. 

A38.6.1 General Information 

A38.6.1.1 Designation of the airplane 

type and model: 

A38.6.1.2 Configuration of the 

airplane, including CG range, number 

and type designation of engines and, if 

fitted, propellers, and any modifications 

or non-standard equipment expected to 

affect the fuel efficiency characteristics; 

A38.6.1.3 MTOM used for 

certification under this part; 

A38.6.1.4 All dimensions needed for 

calculation of RGF; and 

A38.6.1.5 Serial number of each 

airplane used to establish fuel efficiency 

certification in accordance with this 

part. 

A38.6.2 Reference Specifications. The 

reference specifications used to 

determine any SAR value as described 

in section A38.2 of this appendix. 

A38.6.3 Test Data. The following 

measured test data, including any 

corrections for instrumentation 

characteristics, must be provided for 

each of the test measurement points 

used to calculate the SAR values for 

each of the reference masses defined in 

§ 38.13(b): 

A38.6.3.1 Airspeed, ground speed and 

true airspeed; 

A38.6.3.2 Fuel flow; 

A38.6.3.3 Pressure altitude; 

A38.6.3.4 Static air temperature; 

A38.6.3.5 Airplane gross mass and CG 

for each test point; 

A38.6.3.6 Levels of electrical and 

mechanical power extraction and bleed 

flow; 

A38.6.3.7 Engine performance; 

A38.6.3.7.1 For jet airplanes, engine 

power setting; or 

A38.6.3.7.2 For propeller-driven 

airplanes, shaft horsepower or engine 

torque, and propeller rotational speed; 

A38.6.3.8 Fuel lower heating value; 

A38.6.3.9 When volumetric fuel flow 

meters are used, fuel specific gravity 

and kinematic viscosity (see section 

A38.4.2.1.5. of this appendix); 

A38.6.3.10 The cumulative error 

(RSS) of the overall measurement 

system (see section A38.5.1.7 of this 

appendix); 

A38.6.3.11 Heading, track and 

latitude; 

A38.6.3.12 Stability criteria (see 

section A38.4.2.2.2 of this appendix); 

and 

A38.6.3.13 Description of the 

instruments and devices used to acquire 

the data needed for the determination of 

SAR, and the individual accuracies of 

the equipment relevant to their effect on 

SAR (see sections A38.5.1.6 and 

A38.5.1.7 of this appendix). 

A38.6.4 Calculations and Corrections 

of SAR Test Data to Reference 

Specifications. The measured SAR test 

data, all corrections of the measured 

data to the reference specifications, and 

the SAR values calculated from the 

corrected data must be provided for 

each of the test measurement points. 

A38.6.5 Calculated Values. The 

following values must be provided for 

each airplane used to establish fuel 

efficiency certification in accordance 

with this part: 

A38.6.5.1 SAR (km/kg) for each 

reference airplane mass and the 

associated 90 percent confidence 

interval; 

A38.6.5.2 Average of the 1/SAR 

values; 

A38.6.5.3 RGF; and 

A38.6.5.4 Fuel efficiency metric 

value. 


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Federal Register / Vol. 89, No. 33 / Friday, February 16, 2024 / Rules and Regulations 12663 

PART 121—OPERATING 

REQUIREMENTS: DOMESTIC, FLAG, 

AND SUPPLEMENTAL OPERATIONS 

■ 13. The authority citation for part 121 

continues to read as follows: 

Authority: 49 U.S.C. 106(f), 106(g), 40103, 

40113, 40119, 41706, 42301 preceding note 

added by Pub. L. 112–95, sec. 412, 126 Stat. 

89, 44101, 44701–44702, 44705, 44709– 

44711, 44713, 44716–44717, 44722, 44729, 

44732; 46105; Pub. L. 111–216, 124 Stat. 

2348 (49 U.S.C. 44701 note); Pub. L. 112–95 

126 Stat 62 (49 U.S.C. 44732 note). 

■ 14. Amend § 121.141 by revising 

paragraph (b) introductory text to read 

as follows: 

§ 121.141 Airplane flight manual. 

* * * * * 

(b) In each airplane required to have 

an airplane flight manual in paragraph 

(a) of this section, the certificate holder 

shall carry either the manual required 

by § 121.133, if it contains the 

information required for the applicable 

flight manual and this information is 

clearly identified as flight manual 

requirements, or an approved Airplane 

Manual. If the certificate holder elects to 

carry the manual required by § 121.133, 

the certificate holder may revise the 

operating procedures sections and 

modify the presentation of performance 

data, except for the information required 

by § 38.23 of this chapter identifying 

compliance with the fuel efficiency 

requirements of part 38 of this chapter, 

from the applicable flight manual if the 

revised operating procedures and 

modified performance data presentation 

are— 

* * * * * 

PART 125—CERTIFICATION AND 

OPERATIONS: AIRPLANES HAVING A 

SEATING CAPACITY OF 20 OR MORE 

PASSENGERS OR A MAXIMUM 

PAYLOAD CAPACITY OF 6,000 

POUNDS OR MORE; AND RULES 

GOVERNING PERSONS ON BOARD 

SUCH AIRCRAFT 

■ 15. The authority citation for part 125 

continues to read as follows: 

Authority: 49 U.S.C. 106(f), 106(g), 40113, 

44701–44702, 44705, 44710–44711, 44713, 

44716–44717, 44722. 

■ 16. Amend § 125.75 by revising 

paragraph (b) to read as follows: 

§ 125.75 Airplane flight manual. 

* * * * * 

(b) Each certificate holder shall carry 

the approved Airplane Flight Manual or 

the approved equivalent aboard each 

airplane it operates. A certificate holder 

may elect to carry a combination of the 

manuals required by this section and 

§ 125.71. If it so elects, the certificate 

holder may revise the operating 

procedures sections and modify the 

presentation of performance from the 

applicable Airplane Flight Manual if the 

revised operating procedures and 

modified performance data presentation 

are approved by the Administrator. Any 

approved equivalent must include the 

information required by § 38.23 of this 

chapter identifying compliance with the 

fuel efficiency requirements of part 38 

of this chapter. 

Issued under authority provided in 42 

U.S.C. 4321 et seq., 7572, 49 U.S.C. 106(f), 

40133, 44701–44701, 44703, and 44704 in 

Washington, DC. 

Michael Gordon Whitaker, 

Administrator. 

[FR Doc. 2024–02330 Filed 2–15–24; 8:45 am] 

BILLING CODE 4910–13–P 


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