Subject: Approval of Propulsion Fuels and Lubricating Oils Date: 7/29/11 Initiated by: ANE-111 AC No: 20-24C
1. Purpose. This advisory circular (AC) provides guidance applicable to adding fuels and oils as engine, aircraft, or auxiliary power unit (APU) operating limitations. It also provides acceptable methods, but not the only methods, that may be used to approve aircraft, engines, or APUs to operate with specified propulsion fuels and lubricating oils.
2. Applicability.
a. The guidance provided in this docum ent is directed to engine and APU manufacturers, airplane manufacturers, rotorcraft manufacturers, modifiers, and foreign regulatory authorities. This guidance also applies to manufacturers of aviation fuels and lubricating oils.
b. This material is neither mandatory nor regulatory in nature and does not constitute a regulation. It describes acceptable means, but not the only means, for demonstrating compliance with the applicable regulations. We (“the FAA”) will consider other methods an applicant may present to demonstrate compliance. Terms such as “should,” “shall,” “may,” and “must” are used only in the sense of ensuring applicability of this particular method of compliance when the method in this document is used.
While these guidelines are not mandatory, they are derived from extensive FAA and industry experience in determining compliance with the relevant regulations. If we find that following this AC would not result in compliance with the applicable regulations, we will not be bound by this AC, and we may require additional substantiation as the basis for finding compliance.
c. Projects proposing fuel s or lubricating oils identified by means other than an ASTM International aviation fuel specification, SAE International oil standard, or a brand name that meets an SAE International standard, governmental or military specification or other industry-based consensus organization specification, will be reviewed on a case-by-case basis.
d. This material does not change, create any additional, authorize changes in, or permit deviations from existing regulatory requirements.
U.S. Department of Transportation Federal Aviation Administration
Advisory Circular
3. Cancellation. AC 20-24B, Qualification of Fuels, Lubricants and Additives for Aircraft Engines, December 20, 1985, is cancelled.
4. Related Regulations. The following regulations from Title 14 of the Code of Federal Regulations (14 CFR) are some of the regulations that apply:
a. Section 33.7(b)(2) and (3), Engine ra tings and operating limitations (Fuel, Oil).
b. Section 23.1521(d), Powerplant limitations (Fuel grade).
c. Section 23.1522, Auxiliary power unit limitations.
d. Section 23.1583(b)(1), Operat ing limitations (Fuel grade).
e. Section 25.1521, Powerplant limitations.
f. Section 25.1583(b)(1), Operating limitations.
g. Section 27.1521(d), Powerplant limitations.
h. Section 27.1583(b)(1), Operating limitations.
i. Section 29.1521(d), Powerplant limitations.
j. Section 29.1583(b)(1), Operating limitations.
k. Section 91.9, Civil aircraft flight ma nual, marking, and placard requirements.
5. References and Related Reading.
a. FAA Guidance .
(1) Policy Memorandum ANE-2006-33.7-4- 1, “Policy for Diesel (Compression Ignition) Engine Certification,” September 6, 2007.
(2) Advisory Circular 23.1521-1B, “Type Certification of Automobile Gasoline in Part 23 Airplanes with Reciprocating Engines,” March 2, 1995.
(3) Advisory Circular 23.1521-2, Change 1, “Type Certification of Oxygenates and Oxygenated Gasoline Fuels in Part 23 Airplanes with Reciprocating Engines,” April 24, 1996.
(4) Advisory Circular 33.47-1, “Detona tion Testing in Reciprocating Aircraft Engines,” June 27, 1988.
(5) Advisory Circular 91-33A, “Use of Alternate Grades of Aviation Gasoline for Grade 80/87, and Use of Automotive Gasoline,” July 18, 1984.
(6) Policy Memorandum ANE-2010-33.7-5A, “Policy for Aviation Fuel and Oil Operating Limitations, § 33.7,” July 26, 2011.
b. Industry Guidance .
(1) ASTM International Standard D1655, “Standard Specification for Aviation Turbine Fuels.”
(2) ASTM International Standard D6615, “Standard Specification for Jet B Wide-Cut Aviation Turbine Fuels.”
(3) ASTM International Standard D7223, “Standard Specification for Aviation Certification Turbine Fuel.”
(4) ASTM International Standard D7566, “Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons.”
(5) ASTM International Standard D910, “Standard Specification for Aviation Gasolines.”
(6) ASTM International Standard D6227, “Standard Specification for Grade UL82 and UL87 Unleaded Aviation Gasoline.”
(7) ASTM International Standard D 7547, “Standard Specification for Unleaded Aviation Gasoline.”
(8) ASTM International Standa rd Practice D4054, “Guideline for the Qualification and Approval of New Aviation Turbine Fuels and Fuel Additives.”
(9) ASTM International Subcommitt ee D.02.J Operating Procedures, Annex A6, “Guidelines for the Development and Acceptance of a New Aviation Fuel Specification For Spark-Ignition Reciprocating Engines.”
(10) Defence Standard 91-90: “Gasol ine, Aviation: Grades 80/87, 100/130 and 100/130 Low Lead. Joint service Designation: AVGAS 80, AVGAS 100 and AVGAS 100LL.”
(11) Defence Standard 91-91: “Turbi ne Fuel, Aviation Kerosine Type, Jet A-1 NATO Code: F-35, Joint Service Designation: AVTUR.”
(12) SAE International Surface Vehi cle Standard J1899, “Lubricating Oil, Aircraft Piston Engine (Ashless Dispersant).”
(13) SAE International Surface Vehi cle Standard J1966, “Lubricating Oils, Aircraft Piston Engine (Non-Dispersant Mineral Oil).”
(14) SAE International Aerospace St andard AS5780, “Specification for Aero and Aero Derived Gas Turbine Engine Lubricants.”
(15) ASTM International Standard Practice D6424, “Standard Practice for Octane Rating Naturally Aspirated Spark Ignition Aircraft Engines.”
(16) ASTM International Standard Practice D6812, “Standard Practice for Ground-Based Octane Rating Procedures for Turbocharged/Supercharged Spark Ignition Aircraft Engines.”
6. Definitions. The following definitions apply for the purposes of this AC:
a. Consensus . A general agreement, but not necessarily unanimity, that includes a process for attempting to resolve objections by interested parties. This process is a comment resolution process, which requires that all comments have been considered fairly and each objector is advised of the disposition of his or her objection(s) and the reasons why. Also, consensus body members may change their votes after reviewing the comments.
b. Voluntary Consensus Standards . Standards developed or adopted by voluntary consensus standards bodies, both domestic and international. ‘‘Technical standards that are developed or adopted by voluntary consensus standard bodies’’ is an equivalent term.
c. Voluntary Consensus Standards Bodies . Domestic or international organizations which plan, develop, establish, or coordinate voluntary consensus standards using agreed-upon procedures. ‘‘Voluntary, private sector, consensus standards bodies,’’ is equivalent to voluntary consensus standards bodies. Federal law encourages the participation of federal representatives in these bodies to increase the likelihood that the standards they develop will meet public and private sector needs. A voluntary consensus standards body has the following attributes:
(1) Openness;
(2) Balanced interests;
(3) An appeals process; and
(4) Consensus.
7. Background.
a. 14 CFR requires that type certificate applicants identify the fuel and oil grade or specifications that are used in their products during certification. Once compliance with
the airworthiness certification regulations has been demonstrated, the grade designation or specification becomes part of the airplane, rotorcraft, and engine operating limitations.
These operating limitations are specified in the type certificate data sheet (TCDS) and in the airplane flight manual (AFM) or rotorcraft flight manual (RFM). Aircraft operators are required by § 91.9 to only use fuels and oils listed in the AFM or RFM. These fuels and oils must, therefore, be identified with sufficient specificity to ensure that the engine and aircraft continue to meet their airworthiness certification basis during service.
b. Historically, the FAA has used the voluntary consensus standards from ASTM International (ASTM) or SAE International (SAE) to identify fuel and oil grades, designations, or specifications that were to be identified on a TCDS. Functionally, applicants showed (and continue to do so) that the product; for example, the engine, or airplane, operated as designed over its complete operating range using the proposed fuel or oil. Applicants made this showing during TC, amended TC, or supplemental TC (STC) programs. Once shown, the FAA issued the TC, amended TC, or STC with the fuel or oil identified as an operating limitation.
(1) Thereafter, when applicants proposed adding new fuels or oils to an existing TC or STC, those new fuels or oils were also identified by ASTM or SAE industry-based consensus grade designations or specifications. As with the original showing, applicants then showed that the product’s airworthiness certification basis remained intact. After the showing, the FAA identified the fuel or oil grade, designation, or specification, as an operating limitation.
c. The FAA has also historically recogn ized the MIL-STD process and the controls in place in governmental bodies. Accordingly, the FAA has accepted their grades, designations, and specifications as sufficient to meet its regulatory needs related to identifying fuels and oils as operating limitations on a TCDS.
d. FAA continues to accept this histori cal approach to identifying new fuels and oils through a consensus-based industry organization, or governmental, or military standard. And after the proper regulatory showing, the identified fuel or oil can be identified as an operating limitation on a type certificate.
(1) Accordingly, fuels identified by an ASTM International aviation fuel specification, governmental or military specification, or other industry-based consensus organization specification, are identified in sufficient detail to meet the FAA’s needs related to identifying a fuel by grade, designation, or specification on a TC, amended TC, or STC.
(2) Oils identified by an SAE Internatio nal oil standard or a brand name that meets an SAE International standard, governmental or military specification, or other industry based consensus organization specification, are identified in sufficient detail to meet the FAA’s needs related to identifying an oil by grade or specification on a TC, amended TC, or STC.
e. Applicants proposing a fuel or oil fo r a product should first contact the Engine and Propeller Directorate (E&PD) and provide proof that an industry voluntary consensus, governmental, or military organization has issued the standard or specification they propose for addition to a TC, or as an STC. The applicant should then coordinate with the cognizant aircraft certification office(s) (ACOs) and Directorate(s) to develop compliance plans and conduct the engine, airplane or APU certification programs. The applicant may proceed with the certification program with a preliminary version of the industry consensus-based, military, or governmental specification, but must substantiate that the tested fuel or oil meets the final, issued version of the specification before final issuance of the FAA design approval.
f. Once the applicant successfully comp letes the compliance plan, the proposed fuel or oil, as identified by specification, grade, or designation, may be included as an operating limitation on the product TCDS. It will of course also be identified in the operating and installation instructions, flight manuals, and other service documents.
Further, a successful completion of the compliance plan means an applicant successfully demonstrates that the product when operated on the proposed fuel or oil continues to meet the certification requirements of the specific engine, APU, and aircraft (e.g., 14 CFR parts 21, 23, 25, 27, 29, 33 and 35, TSO C77, etc.).
8. Aviation Fuel.
a. Historically Accepted Aviation Fuel Specifications.
(1) The primary specification for Jet A and Jet A-1 turbine engine aviation fuel is ASTM International Standard D1655, “Standard Specification for Aviation Turbine Fuels.” This specification describes acceptable materials for producing turbine engine fuel, required properties that the fuel must meet, and test methods to measure those properties. The oversight of this specification is performed by ASTM International Subcommittee D.02.J on Aviation Fuels.
(2) U.S. Military fuel specifications. The following are examples of military aviation fuel specifications. These specifications are operating limitations on some U.S.
products:
(a) MIL-DTL-83133, Detail Specification, Turbine Fuel, Aviation Kerosene Type, JP-8, and JP-8+100 issued by the U.S. Department of Defense (DOD).
(b) MIL-DTL-5624, Detail Specificatio n, Turbine Fuel, Aviation, Grades JP-4 and JP-5, issued by the U.S. DOD.
(3) Turbine engine international fuel specifications. The following are examples of international aviation fuel specifications. These specifications are operating limitations on some U.S. products:
(a) Defence Standards 91-91, “Turbi ne Fuel, Aviation Kerosene Type, Jet A-1” and 91-87, “Turbine Fuel, Aviation Kerosine Type, Containing Fuel System Icing Inhibitor” issued by the United Kingdom (U.K.) Ministry of Defence. These standards are produced for the Defence Fuels and Lubricants Committee in collaboration with the U.K. Aviation Fuels Committee (AFC).
(b) CAN/CGSB-3.23, “Aviation Tu rbine Fuel, Kerosene Type” which includes grades Jet A and Jet A-1, and CGSB 3.24: “Aviation Turbine Fuel (Military Grades JP-5 and JP-8)” issued by the Canadian General Standards Board.
(c) GOST 10227, “Jet Fuels Specificat ion,” including grades TS-1 and RT, issued by the Russia State Standard Committee. These are the predominant fuels used in Russia, the Commonwealth of Independent States, and some East European countries.
(d) “No. 3 Jet Fuel,” according to GB6537, issued by China’s National Technology Supervisory Bureau. This describes the fuel predominately offered at major international airports in China.
(4) Reciprocating Spark Ignition (SI) fu el specification(s). ASTM International Standard D910, “Standard Specification for Aviation Gasolines,” is the primary specification for reciprocating SI engine aviation fuel. This specification describes acceptable materials for producing leaded aviation gasoline, required properties that the fuel must meet, and test methods to measure those properties. The ASTM International Subcommittee D.02.J on Aviation Fuels oversees this industry specification. Other specifications for reciprocating SI engine aviation fuel include:
(a) ASTM International Standa rd D6227, “Standard Specification for Grade UL82 and UL87 Unleaded Aviation Gasoline.”
(b) ASTM International Standard D7547, “Standard Specification for Unleaded Aviation Gasoline.”
(c) ASTM D7592, “Standard Speci fication for Specification for Grade 94 Unleaded Aviation Gasoline Certification and Test Fuel.”
(d) Defence Standard 91-90, “Gas oline, Aviation: Grades 80/87, 100/130 and 100/130 Low Lead,” issued by the U.K. Ministry of Defence. This standard is produced for the Defence Fuels and Lubricants Committee in collaboration with the U.K.
AFC.
(e) Russian GOST 1012-72 “Aviation petrols - Specifications” issued by the Russia State Standard Committee.
(f) GB/T1787-79(88) issued by Ch ina’s National Technology Supervisory Bureau.
b. Operating Limitations for Aviation Fuel .
(1) Operating limitations are part of the type design for each certificated product. The following regulations are some of the regulations that apply to fuel operating limitations:
(a) Engine operating limitations for fuel are required by § 33.7(b)(2) (reciprocating engine) and § 33.7(c)(2) (turbine engine).
(b) Airplane operating limitati ons for fuel are required by § 23.1521(d) (Normal category) and § 25.1521(b)(2) and (c)(2) (Transport category).
(c) APU operating limitations for fuel are required by § 25.1522.
(d) Rotorcraft operating limitati ons for fuel are required by § 27.1521(d) (Normal category) and § 29.1521(d) (Transport category).
(2) The FAA has determined that ASTM International aviation fuel specifications are acceptable specifications and may be identified as operating limitations for fuel. When ASTM fuel specifications are specified, the root number of the ASTM fuel specification (e.g., D1655) and the fuel types or grades used in successfully completing the compliance demonstration, will be listed in the engine and aircraft TCDS.
Manufacturers will also list them in the documents referenced in the TCDS. For STC projects, the fuel specification root number and fuel types or grades will be listed in the limitations section of the STC. When applicants present a fuel specification from another industry based consensus organization or a governmental or military specification, they should present sufficient information regarding how the specification is identified to permit adequate reference as an operating limitation.
(3) Special Considerations.
(a) Minor Revisions. Fuel speci fications are often revised, changing criteria, materials, or processes. These changes are typically not extensive enough to require a new specification; rather, they are incorporated into the existing specification as new suffix numbers.
(b) Drop-In Jet Fuels. ASTM St andard D1655, “Standard Specification for Aviation Turbine Fuels,” defines specification criteria for conventional jet fuel. This specification requires that the jet fuel be produced from conventional raw materials, such as petroleum, tar sands, or shale oil. However, new processing techniques are emerging that will allow jet fuel to be produced from other raw materials, such as biomass, natural gas, or coal. ASTM International has issued two standards intended to facilitate the evaluation of jet fuel produced from non-conventional sources and the integration of these fuels into the existing supply system and onto existing aircraft.
1 ASTM International Standard Practice D4054, “Guideline for the Qualification and Approval of New Aviation Turbine Fuels and Fuel Additives,” provides a procedure for evaluating new jet fuels or significant modifications to existing fuels to determine if the new fuel is suitable for aviation use. Seemingly minor changes to specification properties or criteria may result in changes in a fuel’s performance, but the laboratory, rig, and engine tests specified in D4054 are sufficient to fully evaluate the fit for purpose or suitability of new fuels with engine and airframe fuel systems. D4054 evaluation is conducted for both new fuels and revisions to existing fuel properties to verify that the resulting fuel is fit for purpose for aviation use. If the new or revised fuel is found to possess performance characteristics and chemical compositions essentially identical to conventional jet fuel, then it is called a “drop-in fuel.” The U.S. DOD has developed a similar document, MIL-HDBK-510-1, for the evaluation of fuels to be used on military aircraft.
2 ASTM issued ASTM Standard Specification D7566, “Aviation Turbine Fuel Containing Synthesized Hydrocarbons,” for drop-in fuels that have been qualified to ASTM D4054. Because D7566 fuels meet or exceed the requirements of D1655 fuels, both of these specifications are cross-referenced to allow D7566 fuels to be redesignated as D1655 fuels. A redesignated fuel can move seamlessly through the ground distribution infrastructure without separate tracking. The redesignated fuel can also be used in aircraft without amending the operating limitations of those aircraft.
3 If the fuel is a drop-in fuel and the currently specified operating limitations are adequate to accommodate the fuel, as in D7566 or D1655 fuels, then further FAA testing is not required.
4 TC/STC holders do not need to revise aviation fuel operating limitations to use D7566 fuels that have been redesignated to D1655 fuels, if the existing operating limitations include D1655 fuels.
(c) ASTM Non-Applicable Fuel Specifications. Non-applicable ASTM fuel specifications are those ASTM specifications for which the scope does not include aircraft engines, or does not explicitly include the intended type of aircraft or aircraft engine. For these special cases, the operating limitation needs to reference both the specification root number and the issue suffix number or revision level. TC/STC holders must apply for a TC/STC amendment each time the revision number changes. Nonapplicable ASTM fuel specifications that have been approved as operating limitations are listed below.
1 ASTM International Standard D4814, “Standard Specification for Automotive Spark Ignition Engine Fuel.” For example, the operating limitation is listed as D4814-10 for a certification project initiated in calendar year (CY) 2010.
2 ASTM International Standard D4806, Standard Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use as Automotive Spark-
Ignition Engine Fuel. For example, the operating limitation is listed as D4806-10 for a certification project initiated in CY 2010.
(d) Aircraft Diesel Engines Using Jet Fuel. Reciprocating compression ignition engines (diesel engines) are typically designed to operate on aviation turbine fuel due to the wide availability of this fuel at airports. The ASTM specification for aviation turbine fuel is D1655. This is a non-applicable specification for diesel engines because the specification scope does not include aviation diesel engines. Therefore, the operating limitation needs to reference both the specification root number and the issue suffix number or revision level. This will require the TC/STC holder to apply for a TC/STC amendment each time the revision number changes. For example, the operating limitation should be listed as D1655-10 for a project initiated in CY 2010.
(e) Other governmental military or industry voluntary consensus-based standards, designations, or specifications. If an applicant proposes to specify an aviation fuel identified by another governmental, military or industry voluntary consensus-based standard, designation, or specification, then the applicant should present sufficient information to show that the specification provides an equivalent level of property, performance, and quality control.
c. Operating Limitations for Aviation Fuel: Certification Compliance Plans .
(1) The E&PD is the FAA’s technical focal point for aviation fuel. The E&PD will coordinate with the cognizant directorate and the assigned ACO to identify the applicable airworthiness certification requirements. Applicable airworthiness requirements are those FAA aircraft, aircraft engine, or APU regulatory standards for which showing compliance is contingent on fuel properties and product performance using the fuel. Applicable regulations may include, but not be limited to, those regulations listed in appendices 2 and 3.
(2) Applicants should present an issued industry consensus-based, governmental or military fuel specification to the assigned ACO and work with that ACO to develop a compliance plan. The E&PD will oversee the compliance plan development conducted by the ACO, applicant, and other cognizant directorate (if applicable).
(3) The certification project may be in itiated with a preliminary version of the industry consensus-based, military or governmental fuel specification. However, FAA design approval and issuance of the STC or amended TC will not occur until the fuel used during the certification testing is shown to meet the criteria of the final, issued specification when that specification is issued.
(4) An applicant’s compliance plan should address all applicable airworthiness certification standards, some of which are discussed below. Sound testing techniques and thorough data analysis should be well documented in the compliance plan. Accordingly, close contact and frequent coordination are recommended to ensure the plan is developed with minimal delay.
(5) An applicant’s compliance plan s hould also address the effects of mixing the proposed new aviation fuel with other existing types of aviation fuel, such as mixing of conventional Jet A fuel with synthetic Jet A fuel. Data generated during development of the industry consensus-based, governmental or military fuel specification may be used to support this task.
(6) Applicants must demonstrate that the engine and the airplane or rotorcraft in which the engine is installed continue to meet all certification standards when operating with the new fuel.
(7) New Technical Standard Order (T SO) APU approvals, or major changes or STCs to existing APU TSO approvals, that include a new fuel operating limitation should include the applicable requirements and performance standards from the latest revision of TSO C77 in the compliance plan.
(8) Applicable Regulations for Engine s and APUs. See appendix 2 of this AC, paragraphs 1, 2, and 3 for a list of some regulations that may apply to projects to add an aviation fuel specification as an operating limitation. Additional guidance on some airworthiness standards follows. The following is by no means exclusive, and is provided as a recommended starting point only. Applicants should, therefore, obtain from the E&PD, as the FAA’s fuel focal point, guidance on the regulations with which they will need to show compliance.
(a) Fuel composition can significan tly affect material properties and durability (see §§ 33.15, 33.53, and 33.91). Applicants should demonstrate materials compatibility of the fuel-wetted materials, including elastomers, seals, and metallic components. This can be accomplished by a combination of soak testing and component testing or by other methods that the applicant proposes and which become part of the applicant's compliance plan. In some cases, materials compatibility data generated during the ASTM fuel specification development may be used. This may require testing of both used and unused non-metallic parts, such as elastomers and seals, if the fuel is to be used on engines previously operated with other types of fuel.
(b) Applicants should consider seve ral factors when demonstrating that an engine operating with a new fuel does not result in an unsafe condition. For example, differences or changes in combustion characteristics such as temperature and pressure, deposit accumulation, octane demand, fuel lubricity, fuel vaporization, and materials responses or affects, and others, should be evaluated by test or analysis. Applicants who propose a longer, mature engine maintenance interval or Time Between Overhaul (TBO) for a new engine, or propose to maintain the intervals or TBO of an existing, mature engine, may need to perform a long duration engine test beyond that specified in §§ 33.49 or 33.87 to show compliance to §§ 33.15 and 33.19 (see §§ 33.15, 33.19, 33.49, and
33.87).
(c) Applicants should evaluate en gine cooling requirements as different fuels may change combustion characteristics and thereby impact cooling requirements.
This is particularly important for reciprocating engines where fuel characteristics can impact cylinder temperatures (see § 33.21).
(d) The engine fuel system should function properly with the proposed fuel throughout its complete operating range under all flight and atmospheric conditions. Fuel density, vaporization, and low temperature properties may affect fuel system performance under certain conditions (see § 33.51). For spark ignition reciprocating engine fuels, carburetor icing and vapor lock tendencies should be evaluated (see §§ 33.35 and 33.67).
(e) Avoiding engine detonation a nd demonstrating acceptable detonation margins are critical requirements for spark ignition reciprocating engines. A fuel must demonstrate adequate anti-knock margin under the worst-case operating conditions to prevent destructive detonation. Due to the variation in accuracy and responsiveness of detonation measurement systems, the detonation measurement test method the applicant intends to use should be approved by the FAA (see § 33.47 and AC 33.47-1).
(f) Fuel composition and properties can significantly affect the ability to support combustion at certain points in the engine operating envelope. Applicants should therefore evaluate engine operability with the new fuel for all operating and atmospheric conditions approved for the engine. Engine starting, acceleration, deceleration, and steady-state operation should be evaluated by test or analysis for all approved operating conditions (see §§ 33.51 and 33.89).
(9) Applicable Regulations for Airpla nes and Rotorcraft. See appendix 3 of this AC, paragraph 1 for a list of some regulations that may apply to projects for adding a new aviation fuel as an operating limitation. Additional guidance on some airworthiness standards follows. The following is by no means exclusive and is provided as a recommended starting point only. Applicants should, therefore, obtain from the E&PD as the FAA’s fuel focal point, and the appropriate airplane directorate, guidance on regulations with which they will need to show compliance.
(a) Applicants should evaluate the e ffect of differences in fuel properties such as density on aircraft weight and center of gravity and aircraft structure (see §§ 25.23, 25.25, 25.29, 23.23, 23.25, 23.29, 27.25, 27.27, 27.29, 29.25, 29.27, and
29.29).
(b) Applicants should evaluate the e ffect of differences in fuel properties, such as density, energy content and combustion characteristics, on aircraft performance (see §§ 25.105, 25.117, 25.119, 25.121, 23.53, 23.69, 23.77, 27.51, 27.65, 27.67, 29.51,
29.65, and 29.67).
(c) Applicants should demonstrate materials compatibility of the fuel wetted materials, including elastomers, seals, metallic components, fuel bladders, and fuel tanks. This can be done by a combination of soak testing and component testing (see