AC 38-1

U.S. Department of Transportation Federal Aviation Administration

Subject: AIRPLANE FUEL EFFICIENCY

CERTIFICATION

Date: 12/13/2023 Initiated By: AEE-300 AC No: 38-1 1 This advisory circular (AC) contains information and provides guidance on the implementation of the fuel 2 efficiency certification requirements for airplanes that are required by Title 14 of the Code of Federal 3 Regulations (14 CFR) part 38. 4 5 6 7 Ralph Iovinelli 8 9 10 11 12 FAA Office of Environment and Energy 13 AEE-300 Emissions Division 14 15

12/05/2023 AC 38-1: 14 CFR Part 38 Airplane Fuel Certification 16 17 Table of Contents 18

1. Purpose ................................................................................................................................................... 1 19

1.1 Contents ................................................................................................................................................ 1 20

1.2 Advisory Nature ..................................................................................................................................... 1 21

1.3 Audience ............................................................................................................................................... 1 22

1.4 Intent...................................................................................................................................................... 1 23

1.5 Approval of Equivalent Procedures ....................................................................................................... 2 24

1.6 FAA Certification Process ..................................................................................................................... 2 25

1.7 Related Documents ............................................................................................................................... 2 26

1.8 Definitions and Abbreviations/Acronyms/Symbols ................................................................................ 2 27

2. References ............................................................................................................................................... 2 28

3. [Reserved] ............................................................................................................................................... 3 29

4. Development of Airplane Fuel Efficiency Regulations ...................................................................... 3 30

4.1 Establishment of Airplane Fuel Efficiency Regulations ......................................................................... 3 31

4.2 Relationship Between the EPA and the FAA ........................................................................................ 3 32

4.3 Relationship Between 14 CFR Part 38 and 40 CFR Part 1030 ............................................................ 3 33

4.4 Differences Between ICAO Annex 16 Volume III and 14 CFR Part 38 ................................................ 4 34

5. Part 38 Subpart A – General .................................................................................................................. 4 35

5.1 Section 38.1 Applicability ...................................................................................................................... 4 36

5.1.1 Modified Airplanes ........................................................................................... 6 37

5.1.2 Non-Applicability of the Fuel Efficiency Metric ................................................. 6 38

5.2 Certification of Lower Takeoff Mass Variant ......................................................................................... 7 39

5.3 Exemptions ............................................................................................................................................ 7 40

5.4 Incorporation by Reference ................................................................................................................... 7 41

5.5 Fuel Efficiency Compliance Demonstration Plans ................................................................................ 8 42

5.6 Fuel Efficiency Compliance Demonstration for Airplanes with Intermixed Engines ............................. 8 43

6. Expanded Discussion of 14 CFR part 38 Subpart B Requirements .................................................. 9 44

6.1 Fuel Efficiency Metric ............................................................................................................................ 9 45

6.2 Specific Air Range ............................................................................................................................... 10 46

6.3 SAR Data Analysis .............................................................................................................................. 11 47

6.3.1 SAR Measurement System ........................................................................... 11 48

6.3.2 Selection of Flight Test Data ......................................................................... 11 49

6.3.3 Distribution of Resulting SAR Points ............................................................. 14 50

6.3.4 Correction of SAR Data to Reference Specifications ..................................... 15 51

6.4 Equivalent Procedures ........................................................................................................................ 15 52

6.4.1 Example 1: FAA Approval based on existing data ......................................... 15 53

6.4.2 Example 2: FAA Approval of a change based on back-to-back testing ......... 15 54

6.4.3 Example 3: FAA Approval of a change based on analysis ............................ 16 55

6.4.4 Example 4: FAA Approval based on first principle models ............................ 16 56

6.5 Validity of Results – Confidence Interval ............................................................................................. 24 57

6.6 Reference Geometric Factor ............................................................................................................... 24 58

6.6.1 RGF General Guidelines ............................................................................... 24 59

6.6.2 Orthogonal Projection and Width Boundary .................................................. 24 60

6.6.3 Forward and Aft Boundaries ....................................................................... 25 61

6.6.4 Floor Plane ................................................................................................. 25 62

6.6.6 Floor Plane ................................................................................................. 26 63

6.6.7 RGF Sensitivity ........................................................................................... 26 64

6.7 Fuel Efficiency Limits ........................................................................................................................... 26 65

6.8 Change Criteria ................................................................................................................................... 27 66

7. Additional Guidance ............................................................................................................................. 28 67 Appendix 1: Definitions ............................................................................................................................ 29 68 Appendix 2: Abbreviations/Acronyms/Symbols .................................................................................... 30 69 Appendix 3: Correcting SAR Data to Reference Specifications .......................................................... 32 70 Appendix 4: Confidence Interval Evaluation .......................................................................................... 52 71 Appendix 5: References ........................................................................................................................... 71 72 73

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1. Purpose 74 75 This AC provides guidance on the implementation of fuel efficiency certification requirements for 76 airplanes. These guidelines provide an acceptable means of demonstrating compliance with the 77 regulations of Title 14 of the Code of Federal Regulations (14 CFR) part 38. The methods and procedures 78 described herein have been proposed as recommended certification practice for showing compliance with 79 the fuel efficiency requirements. 80 81 See Appendix 1 for definitions and Appendix 2 for acronyms, abbreviations, and symbols used throughout 82 this AC. 83 84

1.1 Contents 85 86 This Advisory Circular (AC) contains information describing the standards and requirements for new 87 aircraft fuel efficiency regulations in 14 CFR part 38. The information contained in this document sets 88 forth acceptable means, but not the sole means, by which compliance may be shown with the 89 requirements of 14 CFR part 38 (part 38). 90 91 In this AC, the word “paragraph” is used to refer to a part of the AC. The word “section” (or the symbol 92 “§”) is used to refer to a part of a regulation or statute. 93 94 Pursuant to §§ 231 and 232 of the Clean Air Act Amendments of 1970 (42 USC §§ 7571-7572), FAA’s 95 part 38 fuel efficiency regulations implement the standards adopted by U.S. Environmental Protection 96 Agency (EPA) in 40 CFR part 1030 (see paragraphs 4.1 - 4.3 of this AC) by enforcing the EPA 97 regulations at the time of certification. Any deviations from the procedures required under 14 CFR part 98 38 or 40 CFR part 1030 must be coordinated and approved by the Administrators of both the EPA and 99 FAA (see paragraphs 4.2 and 4.3 of this AC). Users of this AC, and those subject to the regulations of 100 part 38, are responsible for cognizance of any later amendments to 40 CFR part 1030 that may not be 101 reflected immediately in 14 CFR Part 38 or this AC. In such instances, applicants may contact the AEE-102 300 Emissions Division Manager with the FAA Office of Environment and Energy at 103 ralph.iovinelli@faa.gov for further guidance. 104 105

1.2 Advisory Nature 106 107 The contents of this AC do not have the force and effect of law and are not meant to bind the public in 108 any way. This AC is intended only to provide information to the public regarding compliance with existing 109 requirements under the law or agency policies. The use of mandatory language, such as “must” and 110 “require” in this AC describe a mandatory requirement established by statute or regulation that exists 111 independent of the material in this AC. The term “should” is used in this AC to indicate a 112 recommendation described in this document and not a requirement. This AC describes one or more 113 acceptable means, but not the only means, of complying with part 38 fuel efficiency certification 114 standards. If an applicant chooses to use the guidance presented here as an acceptable means of 115 compliance, it must be followed in all respects to be considered a valid means of compliance. 116 117

1.3 Audience 118 119 The intended audience for this AC includes airplane performance engineers, engine specialists, and 120 propulsion engineers from the FAA’s Aircraft Certification Service (AIR) and Aircraft Certification 121 Branches; aircraft and aircraft engine industry specialists; aircraft certification applicants; other 122 certification authorities, airlines, airport operators, engineering and scientific communities; and other 123 persons that are interested in the certification of airplanes to the fuel efficiency standards of part 38. 124 125

1.4 Intent 126 127 The intent of this AC is to provide guidance for complying with the fuel efficiency requirements of part 38. 128 129

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1.5 Approval of Equivalent Procedures 130 131 As provided in § 38.21, applicants may submit equivalent testing, measurement, and data reduction 132 procedures to comply with part 38 airplane fuel efficiency regulations that apply to their airplane. Any 133 such alternatives must be approved, in advance of part 38 compliance document submittals, by the 134 FAA’s Office of Environment and Energy (AEE), at FAA Headquarters in Washington DC. Further 135 information on equivalent procedures is provided in paragraph 6.4 of this AC. If you have further 136 questions, please contact the AEE-300 Emissions Division Manager with the Office of Environment and 137 Energy at ralph.iovinelli@faa.gov. 138 139

1.6 FAA Certification Process 140 141 As of publication of AC38-1, the fuel efficiency certification requirements of part 38 are newly adopted in 142 2023, and it is expected that the FAA and U.S. manufactures will gain experience with their application 143 through ongoing findings of compliance with part 38. The FAA-AIR line of business will work directly 144 with the applicant in this process, and FAA’s environmental office, AEE-300, is to remain fully involved 145 with the FAA-AIR line of business in all fuel efficiency compliance efforts to provide guidance as 146 experience is gained. Questions about part 38 from applicants should be submitted to the FAA-AIR line 147 of business, that will then confer with the FAA-AEE environmental office for their resolution. 148 149

1.7 Related Documents 150 151 Part 38 contains the fuel efficiency certification requirements for certain airplanes. These regulations 152 reference or are related to the following: 153 154

• Clean Air Act (CAA) §§ 231-232 (Aircraft Emissions Standards) Title 42 USC §§ 7571-7572. 155

• 40 CFR part 1030, Control of Greenhouse Gas Emissions from Engines Installed on Airplanes 156 157 Part 38 requirements are also referenced in the following regulations in 14 CFR: 158 159

• Part 21, Certification Procedures for Products and Articles including §§ 21.5, 21.17, 21.21, 21.29, 160

21.31, 21.93, 21.101, 21.115, 21.183, and 21.187, 161

• Part 121, Operating Requirements: Domestic, Flag, and Supplemental Operations including § 162

21.141, and 163

• Part 125, Certification and Operations: Airplanes Having a Seating Capacity of 20 or More 164 Passengers or a Maximum Payload Capacity of 6,000 Pounds or More; and Rules Governing 165 Persons on Board such Aircraft including § 125.75. 166 167 168

1.8 Definitions and Abbreviations/Acronyms/Symbols 169 170 Definitions are provided in Appendix 1 and abbreviations, acronyms, and symbols in this AC are 171 provided in Appendix 2. 172 173 174

2. References 175 176 This AC references the following: 177 178

• Clean Air Act Amendments of 1970 (CAA), 42 U.S.C. § 7571 et seq. 179

• Control of Greenhouse Gas Emissions from Engines Installed on Airplanes; Emission Standards 180 and Test Procedures, 40 CFR part 1030. 181

• International Civil Aviation Organization (ICAO) International Standards and Recommended 182 Practices, Annex 16 — Volume III — Aeroplane CO2 Emissions, May 2019 183

• International Civil Aviation Organization (ICAO) Environmental Technical Manual (Doc 9501), 184

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Volume III — Procedures for the CO2 Emissions Certification of Aeroplanes, May 2019 185 186 Additional references are provided in Appendix 5. 187 188

3. [Reserved] 189 190

4. Development of Airplane Fuel Efficiency Regulations 191 192 The United States is one of 193 signatory states to International Civil Aviation Organization's (ICAO) 193 Convention on International Civil Aviation (the Chicago Convention). Article 12 of the Chicago Convention 194 requires signatory states to keep their own regulations uniform, to the greatest extent possible, with those 195 established under the Chicago Convention. In March of 2017, the ICAO Council adopted a new CO2 196 Emissions Certification Standard with an effective date of July 2017. The ICAO considered three 197 categories of technology associated with the fuel efficiency of an airplane design (propulsion, 198 aerodynamics, and structures) in its adoption of a CO2 emissions certification standard for airplanes. 199 200

4.1 Establishment of Airplane Fuel Efficiency Regulations 201 202 49 USC § 40105(b)(1)(A) states that the Secretary of Transportation and FAA Administrator shall act 203 consistently with obligations of the United States Government under international agreements. For 204 development of aviation emissions standards, the FAA leads the U.S. delegation at ICAO meetings with 205 assistance from the EPA. 206 207

4.2 Relationship Between the EPA and the FAA 208 209 The Clean Air Act authorizes the EPA to set standards for aircraft engine emissions in the United States 210 (42 USC § 7571), while the FAA is authorized to enforce those standards. Section 7571 states the 211 following: 212 213

(2)(A) The Administrator shall, from time to time, issue proposed emission standards applicable to the 214 emission of any air pollutant from any class or classes of aircraft engines which in his 215 judgment causes, or contributes to, air pollution which may reasonably be anticipated to 216 endanger public health or welfare. 217 (B)(i) The Administrator shall consult with the Administrator of the Federal Aviation Administration 218 on aircraft engine emission standards. 219

(ii) The Administrator shall not change the aircraft engine emission standards if such change 220 would significantly increase noise and adversely affect safety. 221 222 The standards promulgated by the EPA in 40 CFR part 1030 apply to certain classes of engines used by 223 certain civil subsonic jet and propeller-driven airplanes (40 CFR part 1030.1). In developing airplane 224 emissions regulations, the CAA requires that the EPA consult with the FAA Administrator and ensure 225 that changes to emission standards do not significantly increase noise and adversely affect safety. 226 227

4.3 Relationship Between 14 CFR Part 38 and 40 CFR Part 1030 228 229 The fuel efficiency standards in 14 CFR part 38 implement those adopted by the EPA in 40 CFR part 230 1030. Accordingly, if the EPA takes any action to change any regulation or standard in 40 CFR part 1030 231 that is also promulgated in 14 CFR part 38, the Administrator of the FAA will grant a general 232 administrative waiver of those outdated requirements in 14 CFR part 38 until 14 CFR part 38 can be 233 amended to reflect the changes in 40 CFR Part 1030. (14 CFR § 38.9) The FAA will enforce the 40 CFR 234 part 1030 requirements, for which a waiver has been granted, as part of the 14 CFR part 38 fuel 235 efficiency certification. Under these circumstances, the certification documentation will reflect that it 236 complies with both 40 CFR part 1030 and 14 CFR part 38. 237 238 239

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4.4 Differences Between ICAO Annex 16 Volume III and 14 CFR Part 38 240 241 Under the Chicago Convention, the FAA is obligated to notify ICAO of any U.S. regulatory differences 242 between the ICAO standards and those adopted in the United States. The EPA refers to its regulations 243 as greenhouse gas emissions in part 1030; FAA refers to its regulations as airplane fuel efficiency; and 244 the ICAO standard is titled “Certification Standard for Aeroplane CO2 Emissions Based on the 245 Consumption of Fuel.” The FAA, EPA, and ICAO each use different terminology to reference the same 246 standards and there are no substantive differences with the meaning of these terms. The FAA has not 247 identified any substantive differences between U.S. regulations and Annex 16 Volume III. 248 249

5. Part 38 Subpart A – General 250 251

5.1 Section 38.1 Applicability 252 253 Section 38.1(a) requires fuel efficiency certification for certain subsonic jets, propeller-driven airplanes, 254 and modified airplanes. Fuel efficiency certification applicability is based on the date for which an 255 application for a type certificate is submitted. In general, the standards apply to airplanes with new type 256 designs (submitted on or after January 11, 2021); airplanes that were type certificated before January 257 11, 2021, but continue production with certain modifications on or after January 1, 2023; and all 258 airplanes that are in production on and after January 1, 2028. The exact terms of applicability should be 259 determined using the language of § 38.1, not from this brief description. 260 261 For subsonic jet and propeller-driven airplanes for which an application for a type certificate is submitted 262 on or after January 11, 2021, part 38 applies as specified in Table 5.1. See § 38.1(a)(1)-(3). 263 264 Table 5.1. 265 266 Fuel Efficiency Certification Applicability for New Airplane Designs 267 268 For an airplane that is a:

With a passenger seating capacity of:

With a maximum takeoff mass (MTOM) in kg of:

For which an application for original type certification is submitted:

Subsonic Jet 20 or more > 5,700 On or after January 11, 2021 Subsonic Jet 19 or fewer > 60,000 On or after January 11, 2021 Subsonic Jet 19 or fewer > 5,700 and < 60,000 On or after January 1, 2023 Propeller-driven --- > 8,618 On or after January 11, 2021 269 Table 5.2 shows part 38 applicability to newly produced modified versions of airplanes (i.e. airplanes 270 receiving their first certificate of airworthiness that are newly built with the modified type design) whose 271 type design was not required to have fuel efficiency certification under part 38, and for which an 272 application by the type certificate holder for a type design change is submitted on or after January 1, 273 2023. See § 38.1(a)(4)-(5) 274 275 Table 5.2. 276 277 Fuel Efficiency Certification Applicability for Modified Version of an Airplane Whose Type 278 Design was not certificated under part 38 279 280 For an airplane that is a:

With a maximum takeoff mass (MTOM) in kg of:

For which an application by a type certificate holder for a type design change is submitted:

Subsonic Jet > 5,700 On or after January 1, 2023

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Propeller-driven > 8,618 On or after January 1, 2023 281 Table 5.3 shows part 38 applicability to the production of individual airplanes for which the airplane type 282 design was not originally required to meet 14 CFR part 38. See §§ 38.1(a)(6)-(7). 283 284 Table 5.3. 285 286 Fuel Efficiency Certification Applicability for Airplanes issued Airworthiness Certificates 287 on or after January 1, 2028 288 289 For an airplane that is a:

With a maximum takeoff mass (MTOM) in kg of:

For which the first certificate of airworthiness is issued:

Subsonic Jet > 5,700 On or after January 1, 2028 Propeller-driven > 8,618 On or after January 1, 2028 290 Note: 14 CFR 38 and 40 CFR 1030 requirements apply based on aircraft thresholds such as MTOM 291 “greater than 8,618 kg,” while airworthiness applicability thresholds such as those of parts 21 and 23 292 might otherwise be expressed as 8,618 kg (19,000 lb). The FAA acknowledges that conversion from 293 8,618 kg to lbs is approximately 0.5 lbs less than the 19,000 lbs threshold of other FAA regulations. 294 However, when applying the conversion in reverse, going from 19,000 lbs to kg, the result is 295 approximately 0.25 kg greater than 8,618 kg. This less than 1 lb or 1 kg difference is extremely small 296 and it is unlikely that an airplane would fall within this conversion difference. Importantly, differences less 297 than 1 lb or 1 kg would not be reflected in either a type certificate data sheet (TCDS) or an airplane flight 298 manual. Additionally, the use of kilograms as the applicability threshold is consistent with the EPA 299 standard. 300 301 Table 5.4, below, provides examples of the applicability of part 38. 302 303 304 Table 5.4. 305 306 Examples of Part 38 Applicability 307 308 Individual Airplane Status Applicability Today Effective Dates for Applicability of part 38 Applicability when modified Fuel Efficiency Metric (FEM) Limit In service, and type is no longer being produced EX: 757 None None None None Airplanes still being produced EX: 787-9 None 1/1/2023 for newly built modified airplanes § 38.1(a)(4) -

(5);

or 1/1/2028 for all newly built airplanes § 38.1(a)(6) -

(7) Must comply with the in-production limit if:

(1) produced after 1/1/2023 (§

38.1(a)(4) – (5)); and

(2) includes a modification that changes the FEM value (§ 38.19(c)).

In-production limit § 38.17(b)(5) -

(8) New (Original) Type: large jet § 38.1(a)(1) and (3) 1/11/2021 All airplanes;

New certification New type limit § 38.17(b)(1) -

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airplanes and propeller-driven airplanes required if triggered by change criteria (§

38.19(a))

(4) New (Original) Type: small airplanes § 38.1(a)(2) 1/1/2023 All airplanes;

New certification required if triggered by change criteria (§

38.19(a)) New type limit § 38.17(b)(1) 309 310 311 312

5.1.1 Modified Airplanes 313 314 Section 38.1(b) states that part 38 fuel efficiency requirements apply to an airplane for which an 315 application in type design is submitted that incorporates a modification that meets the change criteria in 316 § 38.19. A new airplane produced with modifications meeting the change criteria may not exceed the 317 applicable fuel efficiency limit of part 38. The applicability criteria for modified airplanes is described in 318 § 38.19 and guidance is provided in paragraph 6.8 of this AC. A modified airplane is subject to the 319 same fuel efficiency metric value limit in § 38.17 as the airplane was prior to modification. 320 321 Applicants may choose to apply for a new fuel efficiency metric certification value even when not 322 required by part 38. 323 324

5.1.2 Non-Applicability of the Fuel Efficiency Metric 325 326 Part 38 fuel efficiency certification requirements do not apply to: 327 328

(1) Subsonic jet airplanes having a MTOM at or below 5,700 kg. 329 330

(2) Propeller-driven airplanes having a MTOM at or below 8,618 kg. 331 332

(3) Amphibious airplanes. 333 334

(4) Airplanes initially designed, or modified and used, for specialized operations. These airplane 335 designs may include characteristics or configurations necessary to conduct specialized operations 336 that the FAA and the United States Environmental Protection Agency (EPA) have determined may 337 cause a significant increase in the fuel efficiency metric value. 338 339 The FAA shares some examples of specialized operations from the ICAO Environmental 340 Technical Manual, Volume 3, (ETM) that include: 341 342

• Airplanes with mission requirements for carrying cargo that is not possible by using less 343 specialized airplanes (e.g., ramped back cargo door);1 344

• Airplanes with mission requirements for conducting very short or vertical takeoffs and 345 landings; or 346

• Airplanes with mission requirements for conducting scientific, research or humanitarian 347 missions exclusive of commercial service. 348 349

(5) Airplanes designed with a reference geometric factor of zero. 350 351

(6) Airplanes designed for, or modified and used for, firefighting (i.e. dispensing firefighting materials). 352

1 Example includes hinged fuselage sections such as Airbus’ Beluga [A300-600].

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(7) Airplanes powered by reciprocating engines. 354 355 Generally, airplanes in categories (3), (4), (5) and (6) are designed or modified in such a way that their 356 designs are significantly different from the typical passenger or cargo-carrying airplanes. See 357 § 38.1(c). 358 359

5.2 Certification of Lower Takeoff Mass Variant 360 361 The calculation of specific air range (SAR) is based on reference masses that are a function of the 362 MTOM, which is defined in §38.3 as the maximum certified takeoff mass, expressed in kilograms, for an 363 airplane type design. The MTOM is intended to mean the maximum takeoff mass an airplane type 364 design is certificated to that is stated in the TCDS. The TCDS may contain several maximum takeoff 365 masses for different variants of the same airplane type design, and the MTOM is the highest of these 366 maximum takeoff masses. In other words, for a specific airplane type design, applicants may develop 367 multiple take-off mass (TOM) variants for operational purposes. The highest TOM variant of an 368 airframe/engine combination for which certification of that variant under part 38 will be sought must 369 demonstrate compliance with part 38.17. All lesser TOMs are considered to have the same fuel 370 efficiency certification value as at MTOM. 371 372 However, applicants may also apply for certification of fuel efficiency metric values for TOM variants 373 lower than MTOM. For such a case, the calculated reference airplane mass required by §38.13(b) and 374 the maximum permitted fuel efficiency certification limits shown in §38.17 would be based on the TOM 375 variant requested to be certified. The FEM value determined for such a lower TOM variant can be also 376 used for any TOM variants that are even lower than for that specific airplane type design. 377 378 If an applicant chooses to certify a lower TOM variant, the applicant should be aware that the FEM at the 379 highest weight variant (MTOM) of an airplane has the lowest margin to the regulatory limit level. 380 Certification at MTOM is required regardless of the certification of any lower TOM variants. The 1/SAR 381 value used in the FEM determination is calculated as an average of 1/SAR values that are established at 382 three reference masses (high, medium, and low). 383 384 In establishing the reference specifications for specific air range (SAR) determination, the highest SAR 385 value usually will be sought at the maximum range cruise condition at the reference specifications. A 386 greater non-linearity in the 1/SAR versus mass relationship could be introduced by a constraint unrelated 387 to the aerodynamic and propulsive efficiency of the airplane (e.g., an altitude pressurization limitation). In 388 this instance, particular care should be taken to ensure that the principle of the highest weight variant 389 having the lowest margin to the regulatory limit level continues to hold. 390 391

5.3 Exemptions 392 393 Pursuant to 49 U.S.C. § 44701(f), the Administrator may grant an exemption from a regulatory 394 requirement if the Administrator finds the exemption is in the public interest. An application for an 395 exemption from any requirements of part 38 must be submitted to the Administrator in accordance with 396 part 11. For all § 38.5 exemption requests, denials, or grants, AEE will be the responsible FAA office and 397 will consult with EPA’s Designated Program Officer and other FAA offices as needed before taking any 398 action. Petitioners for part 38 exemptions are encouraged to contact AEE prior to filing exemption 399 requests. 400 401

5.4 Incorporation by Reference 402 403 Section 38.7 incorporates, by reference, ICAO Doc 7488/3, Manual of the ICAO Standard Atmosphere 404 (extended to 80 kilometres (262 500 feet)), 1993. ICAO Doc 7488/3 provides the standard values of 405 atmospheric parameters, the values of constants and coefficients, and the underlying equations used in 406 the calculation of the atmospheric parameters. The manual is intended for use in calculations in the 407 design of airplanes, in presenting test results of airplanes and their components under identical 408

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conditions, and in facilitating standardization in the development and calibration of instruments. ICAO 409 Doc 7488/3 is referenced in the Appendix to part 38, paragraphs A38.2.1.3.1, A38.5.2.2.1.9, and 410 A38.5.2.2.1.10. In these paragraphs, the applicant must use ICAO Doc 7488/3 to establish certain 411 reference specifications when determining SAR. Interested persons can purchase ICAO Doc 7488/3 412 from the ICAO Store at 999 Robert-Bourassa Boulevard Montréal (Quebec) Canada H3C 5H7, 413 (www.store.icao.int). 414 415

5.5 Fuel Efficiency Compliance Demonstration Plans 416 417 Prior to undertaking a demonstration of fuel efficiency, the applicant must submit procedures, weights, 418 configurations, and other information or data that are used to establish a fuel efficiency level to the FAA. 419 This submission must contain a complete description of the methodology and procedures by which an 420 applicant proposes to demonstrate compliance with part 38. This submission must be approved by an 421 FAA certification office in accordance with §38.21. 422 423 Use of any equivalent procedures or technical procedures not otherwise specified in part 38 must be 424 approved by AEE and documented in the submission as stated in §38.21. The submission should 425 include the following information: 426 427

a. A description of the applicable sections of part 38 for the airplane 428

b. Airplane description, including type, model number, and if applicable, the specific design 429 being certificated. The applicant should demonstrate and document the conformity of the test 430 airplane, particularly with regard to those parts which might affect the test airplane’s fuel 431 efficiency metric (FEM). 432

c. FEM certification methodology which should include the means of compliance and proposed 433 equivalent procedures. 434

d. Test plan that would include: 435 436

i. Test description. Test methods to comply with the test stability conditions in Appendix 437 A § A38.4.2.2.2 of part 38; 438 ii. Test points. The planned number of test points and the planned test conditions in 439 terms of weight or mass, center of gravity position, altitude, and speed; 440 iii. Airplane mass. The procedures for determining the mass of the airplane is in 441 Appendix A § A38.4.2.3 of part 38; and 442 iv. Test fuel properties. The procedures for determining the test fuel properties is in 443 Appendix A § A38.4.2.1.3 through A38.4.2.1.5 of part 38. 444 445

e. Deliverables: List the documents that should show compliance with Appendix A § 38.6 of part 446

38. 447 448

5.6 Fuel Efficiency Compliance Demonstration for Airplanes with Intermixed Engines 449 450 Typically, an applicant demonstrates compliance with part 38 for an airplane type design in which all 451 engines are of the same design. If there are engines of different design on an airplane, the design is 452 commonly referred to as having an “engine intermix” configuration, An applicant may choose to 453 demonstrate compliance of an airplane type design that includes an engine intermix. 454 In such a case, the applicant may, subject to the approval of the FAA, demonstrate compliance in one of 455 three ways: 456 457

a. In accordance with the test procedures defined in part 38, the test airplane must be 458 representative of the intermix arrangement for which certification is requested; or 459

b. In cases where the FEM value has been established for airplanes on which each of the 460 intermix engine models has been exclusively installed, compliance can be demonstrated on 461 the basis of either: 462

i. The average of the fuel efficiency evaluation metrics for identical airplanes on which each 463 of the intermix engine models has been exclusively installed; or 464

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ii. The highest fuel efficiency evaluation metric for identical airplanes on which each of the 465 intermix engine models has been exclusively installed. 466 467 468

6. Expanded Discussion of 14 CFR part 38 Subpart B Requirements 469 470

6.1 Fuel Efficiency Metric 471 472 The fuel efficiency metric (FEM) in § 38.11 is a transport capability neutral measure of airplane fuel 473 efficiency. The FEM system is intended to promote advances in technologies that contribute to 474 improvements in fuel efficiency (structural, propulsive, and aerodynamic efficiencies) as well as 475 differentiate among generations of such technologies. In addition, the fuel efficiency metric system was 476 designed to accommodate a wide range of technologies and designs that manufacturers may employ to 477 improve the fuel efficiency of an airplane in a manner that is transport capability neutral. The FEM 478 system is based on three elements associated with airplane technology and design: 479 480

1. Cruise point fuel burn performance; 481

2. Airplane size; and 482

3. Airplane mass. 483 484 Section 38.11 requires that, for each airplane subject to part 38, a fuel efficiency metric value is 485 calculated using the following equation (rounded to three decimal places): 486 487 𝐹𝐹𝐹𝐹𝐹𝐹𝐹𝐹 𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐸𝐹𝐹𝐸𝐸𝐸𝐸𝐸𝐸 m𝐹𝐹𝑒𝑒𝑒𝑒𝐸𝐸𝐸𝐸 𝑣𝑣𝑣𝑣𝐹𝐹𝐹𝐹𝐹𝐹 = � 1𝑆𝑆𝑆𝑆𝑆𝑆�𝑎𝑎𝑎𝑎𝑎𝑎 𝑆𝑆𝑅𝑅𝐹𝐹0.24 488 489 The specific air range (SAR) is determined in accordance with § 38.13. The reference geometric factor 490 (RGF) is determined in accordance with § 38.15. SAR is expressed in units of km traveled per kg of fuel 491 burned, while RGF is dimensionless. The FEM value uses the inverse of SAR, (1/SAR)avg , so FEM is 492 expressed in units of kg of fuel burned per km of flight. The fuel efficiency metric is determined using an 493 average of three SAR test points that are normalized by RGF, which is a geometric factor representing 494 the physical size of an airplane. A lower FEM value represents greater fuel efficiency. An overview of the 495 fuel efficiency metric system elements is shown in Figure 6-1, below. 496 497 Fig. 6-1. 498 499 Overview of the fuel efficiency metric system elements 500 501 502 Unlike the specific fuel consumption (SFC) of an engine, which provides the engine’s fuel consumption 503 per unit of thrust (i.e., fuel efficiency of thrust production by an individual engine), SAR is a measure of 504 fuel efficiency at the airplane level. Specifically, SAR provides the distance an airplane can travel per 505