# AC 20-184A: Guidance on Testing and Installation of Rechargeable Lithium Battery and Battery Systems on Aircraft - Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it) - Status: Current - Approved: September 18, 2026 - Last reviewed: September 18, 2026 - Family: AC 20-184 - Cancels: [AC 20-184](https://openairdocs.org/ac/20-184) - 14 CFR parts: 23, 25, 27, 29 - 14 CFR sections: [23.2525](https://www.ecfr.gov/current/title-14/section-23.2525), [25.1353](https://www.ecfr.gov/current/title-14/section-25.1353), [27.1353](https://www.ecfr.gov/current/title-14/section-27.1353), [29.1353](https://www.ecfr.gov/current/title-14/section-29.1353) - Pages: 54 - PDF: https://openairdocs.org/files/sha256/f2/40/f2402c97abdd38bf5569f097e8f24be48e024dbf4210e6fa551ada910dcc66a7 - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/DRSDOCID165781275620260921131205.0001 - DRS record last changed: September 29, 2026 - Page: https://openairdocs.org/ac/20-184 ## Versions - [AC 20-184A](https://openairdocs.org/ac/20-184) (Current), approved Sep 18, 2026, 54 pages - [AC 20-184](https://openairdocs.org/ac/20-184?v=879EC332FC7B149886257EFB0074F001) (Historical), approved Oct 15, 2015, 41 pages ## Text Each page's text from the PDF; open the PDF at a page with #page=N. ### Page 1 U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Guidance on Testing and Installation of Rechargeable Lithium Battery and Battery Systems on Aircraft Date: AC No: 20-184A Initiated By: AIR-626A This advisory circular (A C) pr ovides manufacturers, installers, and operators with an acceptable m eans, but not the only means, of compliance with title 14, Code of Federal Regulations (14 CFR), §§ 23.2525, 25.1353, 27.1353, 29.1353, and additional requirements related to the design, installation, operation, and maintenance of rechargeable lithium batteries and battery systems on aircraft. Additionally, the insta llation of the battery or battery system will require regulatory com pliance with the regulations referenced in table 2-1 of this AC. If you have any suggestions for improvements or changes, you may use the Advisory Circular Feedback form provided at the end of this AC. James D. Foltz Acting Aviation Director, Policy and Standards Division, Aircraft Certification Service ### Page 2 AC 20-184A TABLE OF CONTENTS Paragraph Page CHAPTER 1. INTRODUCTION … 1-1 1.1 Purpose … 1-1 1.2 Applicability … 1-1 1.3 Cancellation. … 1-1 1.4 Scope … 1-2 1.5 Rechargeable Lithium Batteries Covered in this AC … 1-2 1.6 Background … 1-3 **CHAPTER 2. INSTALLATION OF RECHARGEABLE LITHIUM BATTERIES ON** AIRCRAFT … 2-1 2.1 Certification Process. … 2-1 2.2 Acceptable Means of Compliance for Installation Approval. … 2-1 2.3 Test Requirements. … 2-5 2.4 Means of Compliance Testing and Validation … 2-5 2.5 System Safety Assessment … 2-6 2.6 Software. … 2-7 2.7 Complex Electronic Hardware … 2-7 2.8 State of Charge … 2-7 2.9 Flammability … 2-7 2.10 Instructions for Continued Airworthiness … 2-8 2.11 ICA Recommended Manufacturer’s Maintenance and Inspection Requirements … 2-9 **CHAPTER 3. MAINTENANCE AND OPERATIONAL CONSIDERATIONS FOR** LITHIUM BATTERY SYSTEMS … 3-1 3.1 Introduction … 3-1 3.2 Aircraft Battery Maintenance. … 3-1 3.3 Aircraft Battery Replacement. … 3-3 3.4 Aircraft Battery Storage and Handling. … 3-3 APPENDIX A. RELATED REGULATORY AND ADVISORY MATERIAL … A-1 A.1 Regulations. … A-1 A.2 Advisory Circulars … A-1 ii ### Page 3 AC 20-184A TABLE OF CONTENTS Paragraph Page A.3 Form … A-2 A.4 Handbooks. … A-3 A.5 Orders … A-3 A.6 Industry Documents … A-3 APPENDIX B. TERMS AND DEFINITIONS … B-1 B.1 For purposes of this AC, the following definitions apply: … B-1 **APPENDIX C. TYPICAL RECHARGEABLE LITHIUM BATTERY SPECIAL** CONDITIONS FOR TRANSPORT CATEGORY AIRPLANES … C-1 C.1 Typical Rechargeable Lithium Battery SCs Issued After August 2016. … C-1 **APPENDIX D. ACCEPTABLE METHOD OF COMPLIANCE WITH SPECIAL** **CONDITIONS FOR RECHARGEABLE LITHIUM BATTERIES ON TRANSPORT** CATEGORY AIRPLANES … D-1 D.1 Acceptable Methods of Compliance with Rechargeable Lithium Battery SCs … D-1 D.2 Issued SCs with Slightly Different Numerical Order and Wording. … D-1 D.3 Methods of Compliance with SCs. … D-1 D.4 Part 25 Compliance … D-4 **APPENDIX E. CORRELATION OF TRANSPORT CATEGORY AIRPLANE METHOD** **OF COMPLIANCE WITH SPECIAL CONDITIONS ISSUED PRIOR TO AUGUST** 2016 … E-1 E.1 Rechargeable Lithium Battery SCs Issued Before August 2016: … E-1 E.2 The Following Provides Correlation Between the Method of Compliance in Appendix D to the SCs Issued Before August 2016: … E-2 **APPENDIX F. REGULATIONS AND METHOD OF COMPLIANCE FOR** RECHARGEABLE LITHIUM BATTERIES FOR ROTORCRAFT … F-1 F.1 Regulatory Basis From Part 27 at Amendment 27-51 and Part 29 at Amendment 29-59. . … F-1 F.2 Advisory Circulars … F-1 F.3 Industry Document … F-1 F.4 Part 27 and 29 Regulations. … F-2 F.5 Method of Compliance. … F-2 iii ### Page 4 AC 20-184A TABLE OF CONTENTS Paragraph Page APPENDIX G. INSTALLATION OF RECHARGEABLE LITHIUM BATTERIES FOR SMALL AIRPLANES … G-1 G.1 Applicability. … G-1 G.2 Means of Compliance with Safety Objectives … G-1 G.3 Method of Compliance with Safety Objectives … G-2 G.4 Method of Compliance for Very Small Rechargeable Lithium Batteries Less Than 2 Watt-Hours … G-5 G.5 ICA Required by § 23.1529, Appendix A to Part 23 … G-6 G.6 Uncontained Engine or APU Rotor Failures: §§ 23.2410 and 23.2510 at Amendment 23-64. … G-6 G.7 Lithium Battery Installed in a Designated Fire Zone (DFZ) (§§ 23.2440 and 23.2510). . … G-7 G.8 Hazard Mitigations for Large Battery System Thermal Runaway Conditions … G-7 TABLES Number Page Table 2-1. Typical Airworthiness Regulations Concerning Lithium Battery Installations ... 2-2 iv ### Page 5 **AC 20-184A CHAPTER 1. INTRO DUCTION** 1.1 Purpose. This AC provides manufacturers and installers with an acceptable means, but not the only means, of compliance with §§ 2 3.2525, 25.1353, 27.1353, 29.1353, a nd additional commonly issued requirements related to the design, installation, operation, and maintenance of rechargeable lithium batteries and battery systems on aircraft. Note: For the purpose of this AC, installed rechargeable lithium batteries and battery systems will be referred to as lithium batteries. 1.2 Applicability. 1.2.1 The guidance provided in this AC is for manufacturers, modifiers, foreign regulatory authorities, Federal Aviation Administration (FAA) type certification engineers, and the Administrator’s designees. 1.2.2 This is a guidance document that contains a means and method of compliance that has been reviewed and accepted by the FAA. I ts content is not legally binding in its own right and will not be relied upon by the Department as a separate basis for affirmative enforcement action or other administrative penalty. Conformity with the guidance document is voluntary only. Nonconformity will not affect rights and obligations under existing statutes and regulations. 1.2.3 The FAA will consider other methods of demonstrating compliance that an applicant may elect to present. Terms such as “should,” “may,” and “must” are used only in the sense of ensuring applicability of this particular method of compliance when the acceptable method of compliance in this document is used. If the FAA becomes aware of circumstances in which following this AC would not result in compliance with the applicable regulations, the FAA may require additional substantiation as the basis for finding compliance. 1.2.4 If the means and methods of compliance referenced in this AC are accomplished with no deviations and coordinated with the FAA, the development of an issue paper is not necessary. Additional requirements may be necessary after assessing the installation, application, location, and operating environment. 1.3 Cancellation. This revision cancels AC 20-184, Guidance on Testing and Installation of Rechargeable Lithium Battery and Battery Systems on Aircraft, dated October 15, 2015. 1-1 ### Page 6 AC 20-184A 1.4 Scope. 1.4.1 Chapter 2 of this AC applies to the certification of installed lithium batteries on aircraft approved pursuant to Parts 23, 25, 27, and 29 for— • Type certificates (TCs), • Amended type certificates (ATCs), • Supplemental type certificates (STCs), • Amended supplemental type certificates (ASTCs), and • Parts manufacturer approvals (PMAs). Note: The guidance in chapter 2 also applies to the installation approval of installed lithium batteries on aircraft in accordance with the field approval process using FAA Form 337, Major Repair and Altercation (Airframe, Powerplant, Propeller, or Appliance), for major repairs and major alterations. 1.4.2 Chapter 3 of this AC provides guidance on maintenance and operational considerations for lithium batteries on aircraft. 1.5 Rechargeable Lithium Batteries Covered in this AC. 1.5.1 Lithium batteries are installed in various aircraft types and serve various purposes. Lithium batteries are different sizes, chemistries, and produced under different manufacturing processes. They also have different levels of complexity. Some benefits of lithium batteries include weight savings, high-energy density per unit volume, relatively constant voltage during discharge, and a long shelf life. Because of their highenergy content and potential thermal instability, lithium batteries can present hazards if improperly designed, manufactured, tested, used, and/or stored. Some of the uses for lithium batteries on today’s aircraft include, but are not limited to: • Emergency lighting; • Cockpit voice recorders, flight data recorders, and underwater locator beacons; • Main batteries for standby or emergency power; • Auxiliary power units (APUs) or main starting batteries; and • Special functions batteries (such as flashlights, electronic equipment, life vests, safety equipment, avionics equipment, communications equipment, and emergency medical equipment). 1.5.2 Lithium batteries have certain failure and operational characteristics, as well as maintenance requirements, t hat differ significantly from nickel-cadmium and lead-acid rechargeable batteries. The introduction of lithium batteries into aircraft raises some concern about associated battery m onitoring systems (such as temperature or state of charge), and such systems will be evaluated and tested regarding the expected extremes in the aircraft-operating environment. Lithium batteries typically have different 1-2 ### Page 7 AC 20-184A electrical impedance characteristics than lead-acid or nickel-cadmium batteries. Other components of the aircraft electrical system should be evaluated regarding these characteristics as a sy stem. 1.6 Background. 1.6.1 The proposed use of lithium batteries for equipment and systems on aircraft has prompted the FAA to review the adequacy of its guidance. 1.6.2 The users of lithium battery technology, from aircraft operators to personal computer users, consumer electronics manufacturers, and the electric vehicle industry, have noted safety problems with lithium batteries. These conditions may result from overcharging, over-discharging, flammability of cell components, and internal cell defects. In general, lithium batteries are significantly more susceptible to internal failures that can result in self-sustaining increases in temperature and pressure (that is, thermal runaway) than nickel-cadmium or lead-acid batteries. 1.6.2.1 Overcharging. Overcharging causes heating and destabilization of cell components, leading to a potentially unsafe condition. The liquid or paste-like electrolyte in lithium batteries can ignite, resulting in a self-sustaining fire or explosion. The severity of thermal runaway due to overcharging increases with increasing battery capacity because of the higher amount of electrolyte. 1.6.2.2 Over-discharging. Discharge of some types of lithium batteries beyond a certain voltage (typically 2.4 volts per cell) can cause corrosion of the cell electrodes, resulting in loss of battery capacity that cannot be reversed by recharging. This loss of capacity may not be detected by simple voltage measurements commonly available to the flightcrew when checking battery status. Additionally, over-discharging has the potential to lead to an unsafe condition such as a loss of battery capacity that may not be detected by the battery management system. 1.6.2.3 Flammability of Cell Components. Rechargeable lithium batteries use electrolytes, insulators, a nd other materials that are flammable. These materials can serve as a source of fire. 1.6.2.4 Internal Cell Defects. Undetected internal defects within a battery have the potential to cause an internal short circuit, which may lead to an unsafe condition such as an uncontrolled thermal runaway of the battery. These internal defects may not become apparent until long after the battery is in service. 1-3 ### Page 8 **AC 20-184A CHAPTER 2. INSTALLATION OF RECHARGEABLE LITHIUM BATTERIES ON AIRCRAFT** 2.1 Certification Process. This chapter provides certification guidance for the installation of rechargeable lithium batteries on aircraft. This AC can be used as a means of compliance with the requirements est ablished as applicable in the certification program. A pplicants should coordinate their certification program with the responsible certification branch as described in FAA Order 8110.4, Type Certification, through the certification project notification (CPN) process, FAA Order 8110.48, How to Establish the Certification Basis for Changed Aeronautical Products, or in FAA Order 8110.42, Parts Manufacturer Approval Procedures. 2.2 Acceptable Means of Compliance for Installation Approval. 2.2.1 Certification Plan. As part of the certification program as described in Order 8110.4, pr epare a certification plan describing all aspects of showing compliance for the installation of lithium batteries on the aircraft. The FAA recommends submitting the certification plan early in the certification process by providing the following items at a minimum: • Project description and schedule, • System description, including a description of the aircraft system interfaces and any aircraft system modifications made to accommodate the aircraft battery system installation, • System safety assessment, • Certification basis and means of compliance, i ncluding itemized methods of compliance with all applicable requirements, special conditions, and safety objectives (SOs), • Communication and coordination of the test plan(s), • Conformity plan, • Instructions for Continued Airworthiness (ICA), and • Compliance and substantiation documentation. Note: FAA Order 8110.4 provides directions on how to address the above provisions of a certification plan. 2.2.2 Compliance Checklist. 2.2.2.1 Rechargeable lithium battery installations must support all failure conditions identified in the system safety assessment for compliance with the rule. Therefore, all applicable airworthiness regulations r eferenced in table 2-1, at the applicable amendment level, need to be assessed if the 2-1 ### Page 9 AC 20-184A design contains or will contain a lithium battery installation. The installations should also meet the guidance in this chapter. Table 2-1. Typical Airworthiness Regulations Concerning Lithium Battery Installations 14 CFR Subject Matter Section 21.50(b) Instructions for continued airworthiness and manufacturer’s maintenance manuals having airworthiness limitations sections. Section 23.2210 Structural design loads. Section 23.2230 Limit and ultimate loads. Section 23.2235 Structural strength. Section 23.2250(a) Design and construction principles. Section 23.2265 Special factors of safety. Section 23.2270 Emergency conditions. Section 23.2315(a) Means of egress and emergency exits. Section 23.2320(c) Occupant physical environment. Section 23.2325 Fire protection. Section 23.2330 Fire protection in designated fire zones and adjacent areas. Section 23.2335 Lightning Protection Section 23.2440 Powerplant fire protection. Section 23.2500 Airplane level systems requirements. Section 23.2525 System power generation, storage, and distribution. Section 23.2600 Flightcrew interface. Section 23.2605 Installation and operation. Section 23.2610 Instrument markings,control markings, and placards. Section 23.2620 Airplane flight manual. Sections 25.301, 27.301, and 29.301 Loads. Sections 25.303, 27.303, and 29.303 Factor of safety. Sections 25.305, 27.305, and 29.305 Strength and deformation. Sections 25.307, 27.307, and 29.307 Proof of structure. Section 25.581 Lightning protection. 2-2 ### Page 10 AC 20-184A 14 CFR Subject Matter Sections 27.610 and 29.610 Lightning and static electricity protection. Sections 25.785, 27.785, and 29.785 Seats, berths, litters, safety belts, and harnesses. Sections 25.787(b), 27.787(b), and Cargo and baggage compartments. 29.787(b) Sections 25.831, 27.831, and 29.831 Ventilation. Sections 25.853, 27.853, and 29.853 Compartment interiors. Section 25.856(a) Thermal/Acoustic insulation materials. Sections 25.863, 27.863, and 29.863 Flammable fluid fire protection. Section 25.869 Fire protection: systems. Section 25.903(d) Turbine engine installations. Sections 25.1301, 27.1301, and Function and installation. 29.1301 Sections 25.1309, 27.1309, 29.1309, Equipment, systems, and installations. and 23.2510 Sections 25.1316, 27.1316, and Electrical and electronic system lightning 29.1316 protection. Sections 25.1317, 27.1317, 29.1317 High-intensity Radiated Fields (HIRF) Protection. and 23.2520 Section 25.1322 Warning, caution, and advisory lights. Section 25.1353 Electrical equipment and installations. Sections 27.1322 and 29.1322 Flightcrew alerting. Sections 25.1351, 27.1351, and Electrical systems and equipment, general. 29.1351 Sections 27.1353 and 29.1353 Energy storage systems. Sections 25.1355 and 29.1355 Distribution system. Sections 25.1357, 27.1357, and Circuit protective devices. 29.1357 Section 29.1359 Electrical system fire and smoke protection. Sections 25.1363 and 29.1363 Electrical system tests. Section 27.1365 Electric cables. Section 27.1367 Switches. Sections 25.1431 and 29.1431 Electronic equipment. Sections 23.1529, 25.1529, 27.1529, Instructions for Continued Airworthiness. and 29.1529 2-3 ### Page 11 AC 20-184A 14 CFR Subject Matter Sections 25.1541, 27.1541, and Markings and Placards, General. 29.1541 Sections 27.1559 and 29.1559 Limitations placard. Sections 25.1581, 27.1581, and Flight Manual, General. 29.1581 Sections 25.1583, 27.1583, and Operating limitations. 29.1583 Sections 25.1585, 27.1585, and Operating procedures. 29.1585 Part 25 subpart H Electrical Wiring Interconnection Systems (EWIS). 2.2.2.2 Additional compliance requirements (beyond those listed in table 2-1) pertaining to lithium batteries include: 2.2.2.2.1 Part 23. The FAA amended its airworthiness standards for Part 23. Amendment 23-64 became effective on August 30, 2017. See appendix G of this AC for specific guidance regarding rechargeable lithium battery installation in Part 23 airplanes. 2.2.2.2.2 Part 25. The FAA determined that rechargeable lithium batteries are novel and unusual with the state of technology, considering w hen Part 25 was codified, particularly § 2 5.1353. Therefore, typically, the FAA requires SCs for rechargeable lithium battery installations on transport category airplanes. Appendix C of this AC provides typical rechargeable lithium battery SCs for transport airplanes. Unless these SCs are issued on the specific airplane model being modified, the SCs do not apply to that specific airplane model. The FAA must issue SCs on rechargeable lithium batteries for a specific project if these SCs are not already published in the applicability section of the airplane model Type Certification Data Sheet (TCDS) as identified in FAA Order 8110.4C. Appendix D of this AC provides an acceptable means of compliance with these rechargeable lithium battery SCs. Note: Prior to August 2016, the FAA issued SCs with slightly different numerical ordering a nd wording than the SCs in appendix C of this AC. The method of compliance in appendix D of this AC is also applicable to those SCs. Appendix E of this AC correlates the method of compliance in appendix D of this AC to those SCs issued prior to August 2016. 2-4 ### Page 12 AC 20-184A 2.2.2.2.3 Parts 27 and 29. In the case of rotorcraft, see appendix F of this AC for means of compliance. 2.3 Test Requirements. 2.3.1 Environmental Test Requirements. 2.3.1.1 To ensure continuous safe function in the installed environments as required by §§ 23.2525, 25.1353, 27.1353, and 29.1353, applicants proposing designs that incorporate lithium battery systems must address environmental qualification standards outlined in: • RTCA DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment. • RTCA DO-311A, Minimum Operational Performance Standards for Rechargeable Lithium Battery (Systems). 2.3.1.2 These environmental tests are representative of the conditions the battery system may encounter during its life cycle. Applicants should consider the following areas when determining the scope and type of environmental tests— • Equipment configuration, • Installation-specific environment encountered on in-service platforms, • Duration of exposure periods, • Geographical locations, and • Frequency of environmental occurrences alone or in combination with other approved systems. Note: If the applicant wishes to use this AC to show compliance, it must be followed completely unless a deviation is proposed and accepted by the FAA. 2.4 Means of Compliance Testing and Validation. Follow the guidance in appendices D, E, F, a nd G of this AC to show compliance with the requirements and means of compliance for Part 23, 25, 27, and 29 aircraft. 2.4.1 Ground and Flight Test Requirements for Installed Lithium Batteries. 2.4.1.1 If the FAA requires ground and/or flight tests, per the compliance checklist in the certification plan, then the applicant should perform tests to demonstrate the lithium battery systems and the systems in which they are installed will perform as intended in the aircraft. 2-5 ### Page 13 AC 20-184A 2.4.1.2 If the FAA requires ground and/or flight tests, pe r the compliance checklist in the certification plan, then the applicant should perform the tests to demonstrate the lithium battery systems and the systems in which they are installed will not have any adverse effect on the aircraft. 2.4.1.3 If the FAA requires Electromagnetic Interference/Radio Frequency Interference (EMI/RFI) test, pe r the compliance checklist in the certification plan, then the applicant should perform the electromagnetic compatibility test described in AC 20-190, Aircraft Electromagnetic Compatibility Certification, to determine that the installation of the lithium battery does not have any adverse effect on aircraft systems and that the aircraft systems do not have any adverse effect on the lithium battery. This will demonstrate that the battery system functions as designed during normal aircraft operations. 2.5 System Safety Assessment. The safety assessment of the lithium battery installation should address the battery system, the aircraft interface, and the aircraft functional loads to which the battery system provides power. 2.5.1 Perform a system safety assessment to show compliance with §§ 25.1309, 27.1309, 29.1309 a nd 23.2510 a nd all applicable SCs with respect to lithium batteries. This assessment should address concerns associated with the installation of the lithium batteries and battery systems, the possibility of direct (or indirect) injury to a person, any adverse effect on crew function, or any adverse effect on other equipment and systems. These effects could be a result of normal operation or a failure in the lithium batteries. Y our safety system assessment should consider, but not be limited to, the following: • The levels of hazard associated with installation and use of lithium batteries. • Whether design assurance level of lithium batteries is appropriate for performance and safety requirements based on location and intended function. • No interference due to any failures of the lithium batteries. • System separation and zonal analysis. • Impact on flightcrew for normal and non-normal operation. • Impact of emergency procedure during egress. • Protection against fire, smoke, and electrical shock hazards. • Other safety analysis appropriate to the system being installed. • Statement of compliance for each requirement (SCs or SOs, as appropriate). 2-6 ### Page 14 AC 20-184A 2.5.2 Coordinate your assessment with the responsible certification branch to determine the depth of analysis required. Include a system description, a description of how the system is installed on the aircraft, and a list of functions and criticality. 2.6 Software. To ensure intended function and safe operation of the software when showing compliance with §§ 25.1301, 27.1301, 29.1301, 25.1309, 27.1309, 29.1309, 23.2505, 23.2510 a nd all other applicable regulations, all lithium batteries that use software should c omply with RTCA DO-178C, Software Considerations in Airborne Systems and Equipment Certification, or equivalent, for the appropriate design assurance level. You can find additional guidance in the following ACs referenced in appendix A: • AC 20-115D, Airborne Software Development Assurance Using EUROCAE ED- 12() and RTCA DO-178(); • AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes; • AC 25.1309-1B, System Design and Analysis; • AC 27-1B, Certification of Normal Category Rotorcraft; and • AC 29-2C, Certification of Transport Category Rotorcraft. 2.7 Complex Electronic Hardware. All lithium battery hardware that contains complex electronic hardware should c omply with the most recent revision of RTCA DO-254(), Design Assurance Guidance for Airborne Electronic Hardware, or AC 20-152A, Development Assurance for Airborne Electronic Hardware for compliance with §§ 2 3.1353, 23.2525, 25.1353, 27.1353, and 29.1353. 2.8 State of Charge. Lithium batteries not maintained at an adequate state of charge degrade at a significantly higher rate. Additionally, overcharging of individual cells could lead to thermal runaway. 2.9 Flammability. 2.9.1 Unlike nickel-cadmium and lead-acid cells, rechargeable lithium batteries use electrolytes and other materials that are flammable. This material can serve as a source of fuel for an external fire if a cell failure occurs. Lithium batteries have the potential to ignite spontaneously or experience thermal runaway, which involves an uncontrolled temperature and pressure increase, resulting in propagation to adjacent cells. 2.9.2 Pursuant to §§ 23.2325, 23.2330, 25.853, 27.853, 29.853, 25.863, 27.863, 29.863, a nd 25.869, aircraft battery equipment must meet the flammability requirements that ensure 2-7 ### Page 15 AC 20-184A the protection of structure and critical systems. Test the materials to ensure they meet applicable certification requirements. 2.9.3 The DOT/FAA/AR-00/12, Aircraft Materials Fire Test Handbook, Chapters 1 through 10 and Chapter 15 describe an acceptable method of compliance with Part 25, a ppendix F. If thermal and acoustic insulation material is used as part of the battery equipment and exposed, the requirements of § 2 5.856(a), a ppendix F , part VI, at amendment 25- 111 (or later amendment) must be met. Refer to the test methods described by AC 25.856-1, Thermal/Acoustic Insulation Flame Propagation Test Method Details. 2.10 Instructions for Continued Airworthiness. During the certification process of the lithium batteries (battery and/or installation), complete the ICA in accordance with the following: • Section 21.50(b); • Sections 23.1529, 25.1529, 27.1529, 29.1529; • Section 25.1729; • Part 23 appendix A ; • Part 27 appendix A; • Part 29 appendix A; • Part 25 appendix H ; and • FAA Order 8110.54A, Instructions for Continued Airworthiness, Responsibilities, Requirements, and Contents (or most recent revision). 2.10.1 Develop the ICA so it is compatible with other maintenance instructions for the aircraft. 2.10.2 Refer to Chapter 3 of this AC for additional details specific to the maintenance of lithium batteries on aircraft. 2.10.3 The ICA, in accordance with the applicable regulations referenced in paragraph 2.10, must contain an “Airworthiness Limitations” section. Pursuant to §§ 43.1 6 and 91.403, the “Airworthiness Limitations” section is FAA-approved and specifies maintenance requirements, unless the FAA has approved an alternative program. 2.10.4 When a lithium battery installation is proposed, the ICA should also include at least the following information: • Specifics of the lithium battery installation, including individual component part numbers and any other unique installation requirements, • Electrical wiring diagrams/schematics, electrical equipment drawings, • Maintenance instructions, basic control and operation, testing, servicing, maintenance schedule, inspection, troubleshooting, removing parts, replacing parts, 2-8 ### Page 16 AC 20-184A repairs, special tools, fixtures, e quipment, and component manual information when appropriate (reference p aragraph 3.10.6), a nd • Configuration control and storage instructions. 2.11 ICA Recommended Manufacturer’s Maintenance and Inspection Requirements. The ICA, in accordance with the applicable regulations referenced in paragraph 2.10, must contain the recommended manufacturer’s maintenance and inspection requirements to ensure batteries whose function is required for safe operation of the aircraft will perform their intended function when installed. The ICA must contain: 2.11.1 Operating instructions and equipment lim itations in an installation manual (Type Certification) or a supplemental installation maintenance manual (Supplemental Type Certification). 2.11.2 Installation procedures and limitations sufficient to ensure cells or batteries, when installed according to the installation procedures, still meet the airworthiness requirements of the aircraft. The limitations must identify any unique aspects of the installation. 2.11.3 Maintenance requirements for measurements of battery capacity at appropriate intervals to ensure the battery whose function is required for safe operation of the aircraft will perform its intended function when installed in the aircraft. 2.11.4 Scheduled servicing information to replace batteries at the manufacturer’s recommended replacement interval. 2.11.5 Maintenance and inspection requirements for a visual check of the battery and/or charger degradation. 2.11.6 The ICA should also contain maintenance procedures for lithium batteries in spares storage to prevent the replacement of batteries with batteries that have experienced degraded charge retention ability or other damage due to prolonged storage. 2.11.7 The ICA, in accordance with the applicable regulations referenced in paragraph 2.10, must contain instructions to replace batteries based on the original equipment manufacturer (OEM) maintenance manual. Replacement of individual cells within lithium batteries must be approved by the OEM and the FAA. Do not mix cells from different manufacturers within a lithium battery, unless an alternate means proposed by the OEM and approved by the FAA exists. 2-9 ### Page 17 **AC 20-184A CHAPTER 3. MAINTENANCE AND OPERATIONAL CONSIDERATIONS FOR LITHIUM** **BATTERY SYSTEMS** 3.1 Introduction. Lithium batteries can be hazardous if not maintained a nd handled properly. This chapter provides guidance for maintenance considerations for aircraft lithium b atteries. Maintenance requirements are part of the ICA that must comply with § 21.50 and to the applicable 23.1529, 25.1529, 27.1529, 29.1529 sections. This AC has appendices that include further relevant references to assist in compliance (i.e. recording pertinent maintenance data to document the service life of the lithium battery and battery system to ensure the airworthiness of the battery system and aircraft). 3.2 Aircraft Battery Maintenance. Manufacturer procedures for maintenance should be followed because maintenance and inspection requirements for aircraft lithium batteries vary based on the type of chemical technology and physical construction of the battery. Performance of lithium batteries at any time in a given installation will depend on several factors that include but are not limited to the following (refer to 14 CFR § 43.1 3 for additional requirements): 3.2.1 Lithium Battery Chemistry. The electrolyte used in lithium batteries can be a highly reactive substance and care must be observed in maintaining the lithium batteries in accordance with both the OEM maintenance manual and the applicable regulations referenced in table 2-1. 3.2.2 Age Management. To determine the life and age of the installed lithium battery, record the installation date of the battery. During normal battery maintenance, document battery age in either the aircraft maintenance log or the shop maintenance log. Do not keep batteries in service longer than recommended by the manufacturer. 3.2.3 State of Charge. State of charge of the lithium battery is determined by the cumulative effect of charging and discharging the battery. In a normal electrical charging system, the generator or alternator restores a battery to full charge during a flight regardless of use before flight. However, safeguards must be implemented to ensure the aircraft does not begin flight with a battery not sufficiently charged to accomplish its intended function of continued safe flight and landing of the aircraft in accordance with the applicable regulations referenced in table 2-1. (See appendix E , Note 1, for the definition of “sufficiently charged”.) 3.2.4 State of Health. Determine the state of health of the lithium battery by r ecording various parameters including t he following: 3-1 ### Page 18 AC 20-184A • Length of time the battery has been installed and in service. • The state of charge of the battery. The output of this function may be used for dispatch or maintenance purposes. 3.2.5 Mechanical Integrity. In accordance with the applicable regulations referenced in table 2-1, and to ensure proper mechanical integrity, the battery must be inspected to ensure it is free of any physical damage before use. Then the battery must be installed and connected properly. The buildup of explosive gases can be avoided by incorporating positive battery venting for the battery and battery compartment systems. Check periodically to ensure the venting system is securely connected and oriented in accordance with the maintenance manual’s installation procedures. Follow the procedures approved for the specific aircraft and battery system to ensure the battery system is capable of delivering the specified performance. The venting system should account for specific installation requirements of the aircraft. 3.2.6 Reliability of Charging/Monitoring Systems. Follow the manufacturer’s recommendation for maintenance inspections concerning the battery charging and monitoring systems. 3.2.7 Shop-Level Maintenance Procedures. In accordance with the applicable regulations referenced in table 2-1, shop procedures must follow the manufacturer’s recommendations (refer to § 43.13 for additional requirements). 3.2.8 Aircraft Battery Inspection. Evidence of impending battery failure can sometimes be detected by a general visual inspection. Manufacturer-recommended inspections should include the following actions: • Inspect battery terminals and all other connections for evidence of corrosion, pitting, arcing, and burns. Clean as required. • Inspect the battery for improper installation (loose terminal screws, battery terminal links, or connector). • Inspect the battery mounting. • Inspect for evidence of physical damage. 3.2.9 Prior to the installation on aircraft, batteries in a rotable stock (which are parts and components that are easily exchanged between product) must be functionally checked at the battery manufacturer’s recommended inspection intervals in accordance with the applicable regulations referenced in table 2-1. Some failure modes may include degraded charge retention capability or other damage due to prolonged storage. 3-2 ### Page 19 AC 20-184 A 3.3 A ircraft Battery Replacement. 3.3.1 Ensure replacement batteries are in airworthy condition. An airworthy battery is one that has been conformed, installed, and tested on the aircraft as required by the FAA accepted ICA. Refer to the battery manufacturer maintenance manuals for proper maintenance of lithium b atteries. Refer to the aircraft maintenance procedures for the replacement of lithium batteries. 3.3.2 The ICA should include the manufacturer’s requirements for the mandatory battery replacement schedule (airworthiness limitation section) and periodic maintenance. 3.3.3 The installation process for lithium batteries can vary significantly across different aircraft systems. Always consult the specific aircraft manuals for detailed instructions on how to properly remove and install batteries. This ensures adherence to safety and technical specifications unique to each aircraft model. 3.3.4 Always inspect for corrosion and moisture on battery interfaces when replacing batteries. Failure to do so can lead to serious issues. Corrosion disrupts electrical connectivity, diminishing power efficiency and risking system failures. Moisture increases the risk of short circuits, potentially causing power losses and fire hazards. Ensure these inspections are part of your regular maintenance routine to maintain battery reliability and safeguard against potential safety risks. 3.3.5 The maintenance record should reflect all battery replacements. Record the expiration date of the battery. 3.3.6 The lithium batteries should be replaced with an approved battery for the specific aircraft application. 3.3.7 Deep discharge may result in a potential unsafe condition. Replace the battery based on the manufacturer’s recommendation. 3.4 Aircraft Battery Storage and Handling. 3.4.1 Following the manufacturer’s recommended storage procedures will permit users to achieve the best results from their batteries. 3.4.2 Storage requirements vary with the battery type. Record the date of charging and, if the battery is not used within the manufacturer’s recommended interval, service the battery per the manufacturer’s recommendation. 3.4.3 To maintain battery integrity, follow the manufacturer’s recommendation for charged batteries that are being held in “ready for service” areas. 3.4.4 Handling procedures and precautions vary with battery size and configuration. Follow the manufacturer’s recommendation to prevent mishandling of the battery. 3-3 ### Page 20 AC 20-184A 3.4.5 Follow the manufacturer’s recommended procedure to prevent electrostatic discharge during storage and handling. 3.4.6 For packaging and shipping, f ollow the manufacturer’s recommended procedures. 3.4.7 Check batteries before use for any leakage or deformity. Do not use the batteries if there is any evidence of leakage or deformity. 3.4.8 Aircraft vibration and/or contact oxidation can result in poor electrical connections. Ensure proper connector maintenance procedures are followed. 3.4.9 Observe the following precautions when handling lithium batteries: • Do not store lithium batteries with other hazardous or combustible materials. • Do not heat or incinerate lithium batteries. • Do not dispose of lithium batteries with other waste unless allowed by applicable regulations. • Use special care in handling lithium batteries. Do not open, puncture, crush, disassemble, or subject batteries to physical abuse. 3.4.10 Lithium batteries can be a personal safety hazard due to the possibility of lethal shock and must be labeled to clearly indicate the hazard in accordance with the applicable regulations referenced in table 2-1. 3.4.11 Follow all manufacturer’s recommended safety precautions and procedures. 3.4.12 Material Safety Data Sheets must be enclosed with lithium batteries for shipping i n accordance with the applicable regulations referenced in table 2-1. A ppropriate information from the MSDS should also be incorporated into the Component Maintenance Manuals (CMMs) and Aircraft Maintenance Manuals (AMMs) as warnings and cautions, as appropriate. 3.4.13 Always wear protective clothing, including gloves and safety goggles, when handling and disposing of lithium batteries. Proper disposal procedures should be followed to avoid environmental hazards and comply with applicable environmental regulations. 3-4 ### Page 21 AC 20-184A Appendix A APPENDIX A. RELATED REGULATORY AND ADVISORY MATERIAL The following regulatory and advisory materials are related to this AC: A.1 Regulations. The following 14 CFR regulations are related to this AC. You can download the full text of these regulations from the Federal Register website at www.ecfr.gov. • Part 21, Certification Procedures for Products and Articles. • Part 23, Airworthiness Standards: Normal Category Airplanes. • Part 25, Airworthiness Standards: Transport Category Airplanes. • Part 27, Airworthiness Standards: Normal Category Rotorcraft. • Part 29, Airworthiness Standards: Transport Category Rotorcraft. • Part 43, Maintenance, Preventive Maintenance, Rebuilding, and Alteration. • Part 145, Repair Station. A.2 Advisory Circulars. The following ACs are related to the guidance in this AC. The latest version of each AC referenced in this document is available on the FAA website at FAA Advisory Circulars and on the Dynamic Regulatory System. • AC 20-115D, Airborne Software Development Assurance Using EUROCAE ED- 12() and RTCA DO-178(), dated July 21, 2017. • AC 20-128A, Design Considerations for Minimizing Hazards caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor Failure, dated March 25, 1997. • AC 20-135A, Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria, dated September 29, 2025. • AC 20-136B, Aircraft Electrical and Electronic System Lightning Protection, dated September 7, 2011. • AC 20-152A, Development Assurance for Airborne E lectronic Hardware, dated October 7, 2022. • AC 20-158B, The Certification of Aircraft Electrical and Electronic Systems for Operation in the High-intensity Radiated Fields (HIRF) Environment, dated May 20, 2024. • AC 20-190, Aircraft Electromagnetic Compatibility Certification, dated June 1, 2018. A-1 ### Page 22 AC 20-184A Appendix A • AC 2 1 -16G, RTCA Document DO-160 versions D, E, and F , “Environmental Conditions and Test Procedures for Airborne Equipment”, dated June 22, 2011. • AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes, dated November 17, 2011. • AC 23-17C, Systems and Equipment Guide for Certification of Part 23 Airplanes and Airships, dated November 17, 2011. • AC 25-16, Electrical Fault and Fire Prevention and Protection, dated April 5, 1991. • AC 25.856-1, Thermal/Acoustic Insulation Flame Propagation Test Method Details, dated June 24, 2005. • AC 25.863-1, (Aviation Rulemaking Advisory Committee (ARAC) draft) Flammable Fluid Fire Protection, U nder Development. • AC 25.1309-1B, System Design and Analysis, dated August 30, 2024. • AC 25.1322-1, Flightcrew Alerting, dated December 13, 2010. • AC 25.1581-1, Airplane Flight Manual, dated October 16, 2012. • AC 25.1701-1, Certification of Electrical Wiring Interconnection Systems on Transport Category Airplanes, dated December 4, 2007. • AC 27-1B, Certification of Normal Category Rotorcraft, dated June 23, 2023. • AC 29-2C, Certification of Transport Category Rotorcraft, dated June 23, 2023. • AC 43.13-1B, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, dated September 8, 1998. • AC 43.13-2B, Acceptable Methods, Techniques, and Practices—Aircraft Alterations, dated March 3, 2008. • AC 120-16G, Air Carrier Maintenance Programs, dated January 4, 2016. • AC 120-42B, Extended Operations (ETOPS and Polar Operations), dated June 13, 2008. A.3 Form. The following FAA forms are available on the FAA forms website at https://www.faa.gov/forms/. • FAA Form 337, Major Repair and Altercation (Airframe, Powerplant, Propeller, or Appliance), dated October 01, 2006. • FAA Form 8130-3, Major Repair and Alteration (Airframe, Powerplant, Propeller, or Appliance), dated October 1, 2006. A-2 ### Page 23 A.4 Handbooks. The following handbooks are available on the Federal Aviation Administration Fire Safety website at https://www.fire.tc.faa.gov/Reports/reports.asp. You should refer to the latest version for guidance. • DOT/FAA/AR-00/12, Aircraft Materials Fire Test Handbook, dated April 2000. • DOT/FAA/AR-04/26, Flammability Assessment of Bulk-Packed, Non-rechargeable Lithium Primary Batteries in Transport Category Aircraft, dated June 2004. A.5 Orders. The following orders are available on the Dynamic Regulatory System. You should refer to the latest version for guidance. • FAA Order 8110.4C, Type Certification, dated October 20, 2023. • FAA Order 8110.42D, Parts Manufacturer Approval Procedures, dated October 27, 2023. • FAA Order 8110.48A, How to Establish the Certification Basis for Changed Aeronautical Products, dated July 21, 2017. • FAA Order 8110.52B, Type Validation and Post-type Validation Procedures, dated September 29, 2017. • FAA Order 8110.54A, Instructions for Continued Airworthiness Responsibilities, Requirements, and Contents, dated October 23, 2010. • TSO C179b, Rechargeable Lithium Batteries and Systems, dated March 23, 2018. A.6 Industry Documents. A.6.1 International Electrotechnical Commission (IEC). IEC document IEC 62133, Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications - Part 2: Lithium systems, dated February 7, 2017, is related to the guidance in this AC. The document is available online at https://webstore.iec.ch/en/. **A.6.2 RTCA.** The following RTCA (formerly Radio Technical Commission for Aeronautics) documents are related to the guidance in this AC. Unless otherwise specified, use the latest FAA-accepted revision for guidance. If the document is revised after publication of this AC, you should verify that the FAA accepts the subsequent revision or update as an acceptable form of guidance. The documents can be ordered online at https://www.rtca.org. • RTCA DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment, dated December 8, 2010. AC 20-184A Appendix A A-3 ### Page 24 AC 20-184A Appendix A • RTCA DO-178 (), Software Considerations in Airborne Systems and Equipment Certification, dated December 13, 2011. • RTCA DO-254 (), Design Assurance Guidance for Airborne Electronic Hardware, dated April 19, 2000. • RTCA DO-311A, Minimum Operational Performance Standards for Rechargeable Lithium Battery (Systems), dated December 19, 2017. A.6.3 Society of Automotive Engineers (SAE) International. The following SAE Aerospace Recommended Practice (ARP) documents are related to the guidance in this AC. Unless otherwise specified, use the latest FAA-accepted revision for guidance. If the document is revised after publication of this AC, you should verify that the FAA accepts the subsequent revision or update as an acceptable form of guidance. The documents are available online at: https://www.sae.org. • ARP4754A, Guidelines for Development of Civil Aircraft and Systems, dated December 20, 2010. • ARP4761, Guidelines for Conducting the Safety Assessment Process on Civil Aircraft, Systems, and Equipment, dated December 1, 1996. A.6.4 UL. The following UL (formerly Underwriters Laboratories) documents are related to the guidance in this AC. The documents are available online at https://www.shopulstandards.com/. Refer to the latest version of the referenced document for guidance. • UL 1642, Lithium Batteries, dated October 12, 2022. • UL 2054, Household and Commercial Batteries, dated March 10, 2022. A-4 ### Page 25 AC 20-184A Appendix B APPENDIX B. TERMS AND DEFINITIONS B.1 For purposes of this AC, the following definitions apply: B.1.1 Battery. One or more electrically connected cells, having positive and negative terminals. A battery may include inter-cell connectors, protective devices, circuitry, and other components. B.1.2 Battery System. The equipment being qualified and installed that includes a standalone or an embedded battery and may also include additional hardware that is required to comply with standard RTCA DO-311A. B.1.3 Cell. A single electrochemical unit that exhibits a voltage across its two terminals and is used as a component of a battery. B.1.4 Charged Battery. A battery that has been fully charged in accordance with the manufacturer’s instructions or as defined in the design documentation. B.1.5 Continued Safe Flight and Landing.1 The aircraft is capable of continued controlled flight and landing, possibly using emergency procedures, without requiring exceptional pilot skill or strength. Upon landing, some aircraft damage may occur as a result of a failure condition. B.1.6 Failure. An occurrence that affects the operation of a component, part, or element such that it can no longer function as intended (this includes both loss of function and malfunction). Note that errors may cause failures if the failures are directly traced to the errors. B.1.7 Redundancy. The presence of more than one independent means for accomplishing a given function or flight operation. B.1.8 Serviced Battery. A battery fully prepared and maintained in accordance with the battery manufacturer’s instructions or as defined in the design documentation. 1 14 CFR section 23.2000(b) B-1 ### Page 26 AC 20-184A Appendix B B.1.9 S ervice Life . The maximum combined storage and installed life of an undischarged cell or battery. Service life cannot be greater than shelf life and will be stated by the equipment manufacturer. The end of service life is indicated by a “replace-by” or expiration date. Service life is equivalent to useful life. B.1.10 Shelf Life. The maximum period at which an undischarged cell or battery stored under standard conditions retains 80 percent of rated ampere-hour capacity (RTCA DO-311A). The cell/battery manufacturer specifies shelf life. B-2 ### Page 27 AC 20-184 A Appendix C APPENDIX C. TYPICAL RECHARGEABLE LITHIUM BATTERY SPECIAL CONDITIONS FOR TRANSPORT CATEGORY AIRPLANES C.1 Typical Rechargeable Lithium Battery SCs Issued After August 2016. In lieu of § 25.1353(b)(1) through (4) at amendment 25-123 or § 25.1353( c)(1) through (4) at earlier amendments, each rechargeable lithium battery installation must: C.1.1 Be designed to maintain safe cell temperatures and pressures under all foreseeable operating conditions to prevent fire and explosion. C.1.2 Be designed to prevent the occurrence of self-sustaining, uncontrollable increases in temperature or pressure, and automatically control the charge rate of each cell to protect against adverse operating conditions, such as cell imbalance, back charging, overcharging, and overheating. C.1.3 Not emit explosive or toxic gases, either in normal operation or as a result of its failure, that may accumulate in hazardous quantities within the airplane. C.1.4 Meet the requirements of § 25.863. C.1.5 Not damage surrounding structure or adjacent systems, equipment, or electrical wiring from corrosive fluids or gases that may escape in such a way as to cause a major or more severe failure condition. C.1.6 Have provisions to prevent any hazardous effect on airplane structure or systems caused by the maximum amount of heat it can generate due to any failure of it or its individual cells. C.1.7 Have a failure sensing and warning system to alert the flightcrew if its failure affects safe operation of the airplane. C.1.8 Have a monitoring and warning feature that alerts the flightcrew when its charge state falls below acceptable levels if its function is required for safe operation of the airplane. C.1.9 Have a means to automatically disconnect from its charging source in the event of an over-temperature condition, cell failure or battery failure. Note: A battery system consists of the battery; battery charger; and any protective, monitoring, and alerting circuitry or hardware inside or outside of the battery. It also includes vents (where necessary) and packaging. For the purpose of this special condition, a battery and the battery system are referred to as a battery. C-1 ### Page 28 AC 20-184A Appendix D APPENDIX D. ACCEPTABLE METHOD OF COMPLIANCE WITH SPECIAL CONDITIONS FOR RECHARGEABLE LITHIUM BATTERIES ON TRANSPORT CATEGORY AIRPLANES D.1 Acceptable Methods of Compliance with Rechargeable Lithium Battery SCs. An acceptable method of compliance with the rechargeable lithium battery SCs in appendix C and related Part 25 requirements is provided in paragraphs D.3 a nd D.4. Applicants who propose the SCs in appendix C of this document for their project should submit a letter indicating this to the certification branch responsible for their project. D.2 Issued SCs with Slightly Different Numerical Order and Wording. Prior to August 2016, the FAA issued SCs with slightly different numerical order and wording than the SCs in appendix C. The method of compliance in paragraph D.3 is also applicable to those SCs. Appendix E correlates the method of compliance in paragraph D.3 t o those SCs issued prior to August 2016. D.3 Methods of Compliance with SCs. RTCA DO-311A, Minimum Operational Performance Standards for Rechargeable Lithium Batteries and Battery Systems, section 2.1 General Requirements provides design requirements and guidelines that are pertinent to designing safe batteries and to meeting Part 25 requirements and the SCs. Consider each of these requirements and guidelines when designing cells and batteries. The FAA does not consider appendix C of DO-311A an acceptable alternate method for battery thermal runaway containment tests (paragraph 2.4.5.5). D.3.1 SCs 1 and 2 are intended to ensure that the cells and batteries are designed to eliminate the potential for uncontrollable failures. However, a certain number of failures may still occur due to various factors, many of which are beyond the control of the designer. Therefore, these SCs are intended to protect the airplane and its occupants even if a failure occurs. D.3.2 These SCs are independent of each other. Demonstrating compliance with one of these SCs does not necessarily constitute compliance with the other SCs. The following is an acceptable method of compliance for each of the SCs: D.3.3 Method of Compliance for SCs 1 and 2. D.3.3.1 Whereas SC 1 requires that each individual cell within a rechargeable lithium battery be designed to maintain safe temperatures and pressures, SC 2 addresses these same issues but for the entire battery. SC 2 requires that the battery be designed to prevent propagation of a thermal event, such as self-sustained, uncontrollable increases in temperature, or pressure from one cell to adjacent cells. D-1 ### Page 29 AC 20-184A Appendix D D.3.3.2 S how that very small button/coin batteries that have less than 2 watt-hours of energy meet UL 1642, UL 2054 or International Electrotechnical Commission (IEC) 62133. Show that other batteries meet the requirements in RTCA DO-311A, sections 2.2 Equipment Requirements – Standard Conditions (which are applicable according to RTCA DO-311A, section 2.4.2) and 2.3 Equipment Requirements – E nvironmental Conditions. Consider that batteries with less than 2 watt-hours of energy that are not button/coin batteries, or do not meet UL 1642, UL 2054, or IEC 62133, to be energy category 2 batteries. D.3.3.3 Use the test procedures in RTCA DO-311A, section 2.4 Equipment Test Procedures to show that the requirements of RTCA DO-311A, section 2.2 are met. Note that RTCA DO-311A, table 2-2, provides a test matrix that defines which tests are required for each category of battery, along with the order of the testing. Note: Provide the FAA with the video of the testing conducted for RTCA DO-311A section 2.4.5.5. D.3.4 Method of Compliance for SCs 3-6. Paragraphs D.3.5 through D.3.8 provide a method of compliance with SCs 3-6. Show compliance with SCs 3-6 using data related to a worst-case event where all battery cells go into thermal runaway. To accomplish this, use the worst-case test data from paragraph D.3.3, Method of Compliance for SCs 1 and 2. If none of those tests produce an event where all battery cells go into thermal runaway, coordinate with the Policy and Standards Division’s (AIR-600) Technical Policy Branch to determine either an acceptable revision to the test method of one of those tests, or an acceptable analysis based on your test data, to obtain data representative of this condition. F or button/coin rechargeable lithium batteries that have less than 2 watt-hours of energy and meet UL 1642, UL 2054, or IEC 62133, paragraph D.3.12 pr ovides a method of compliance with SCs 3-6. D.3.5 Method of Compliance for SC 3. D.3.5.1 RTCA DO-311A, section 3.2.1 Hazardous Battery Emissions discusses potential gas emissions from batteries and their effects. An acceptable method of compliance with SC 3 includes using the tests required under paragraph D.3.4, Method of Compliance for SCs 3-6, to demonstrate that all emitted gases are contained or vented overboard (i.e., vented outside the airplane) through designed ports. Paragraph D.4.1, System Safety Assessment, of this appendix provides guidance for conducting a system safety assessment for a design that vents these gases overboard. D.3.5.2 SC 3 does allow explosive and toxic gases to be uncontained and not vented overboard if they do not accumulate in hazardous quantities within the airplane. Consider the gases emitted from not only the cells but also D-2 ### Page 30 AC 20-184A Appendix D the battery materials (e.g., insulation separators) when demonstrating compliance by this means. D.3.6 Method of Compliance for SC 4. D.3.6.1 The amendment level of § 25.863 is determined by § 21.17 or § 21.101, a s appropriate. The amendment level is not determined by the issuance or effective date of the SCs. D.3.6.2 The ARAC draft AC 25.863-1, Flammable Fluid Fire Protection, (under development), gives acceptable guidance on § 25.863. Section 25.863 is a “fail-safe” regulation that requires means to minimize the likelihood of a fire and the resultant hazards if fire does occur. D.3.6.3 When applying § 25.863 to a battery installation, if required by SC 4, conduct a hazard assessment assuming that a battery failure ignites any resultant flammable fluids or gases, and provide provisions to address the associated hazards. This may result in the need to provide a battery enclosure that vents overboard. D.3.7 Method of Compliance for SC 5. Show that if fluid escapes the battery, it is not corrosive or it is managed in a way (e.g., contained, isolated, or vented overboard) to protect the surrounding structure and adjacent systems, equipment, and electrical wiring. D.3.8 Method of Compliance for SC 6. D.3.8.1 Show that the effects of heat, and any related effects, from the tests performed under paragraph D.3.4, Method of Compliance for SCs 3-6, do not constitute a hazard to the structure or systems of the airplane. D.3.8.2 If the effects of the heat or any related effects constitute a hazard to the structure or systems of the airplane, design mitigation at the airplane level may be applied to bring the design into compliance with this SC. D.3.9 Method of Compliance for SC 7. SC 7 has the same purpose as that of § 25.1309(c), but is specific to the lithium battery, which is to require flightcrew alerting if the failure of a battery installation, in itself or in relation to a system that performs an airplane-level function, could result in “unsafe system operating conditions” as stated in § 25.1309(c). The alert must meet the applicable paragraphs of § 25.1322. The applicant should refer to the current version of AC 25.1309-1B, System Design and Analysis, for guidance. D.3.10 Method of Compliance for SC 8. D.3.10.1 Conduct a safety assessment in accordance with § 25.1309 to determine if the flightcrew alert is a warning, caution, or advisory, taking into account D-3 ### Page 31 AC 20-184A Appendix D all phases of flight. The alert level is determined by § 25.1309 a nd must meet the applicable paragraphs of § 25.1322. D.3.10.2 Have a means for the flightcrew and maintenance personnel to determine the battery charge state if the battery’s function is required for safe operation of the airplane. D.3.11 Method of Compliance for SC 9. Confirm the battery automatically disconnects from its charging source during the tests required by paragraph D .3.4, Method of Compliance for SCs 3-6, except for the tests where the protection is already disabled. This is one of the means of preventing the failure conditions discussed in RTCA DO-311A. D.3.12 Method of Compliance for Very Small Button or Coin Rechargeable Lithium Batteries. For button/coin rechargeable lithium battery installations that have less than 2 watthours of energy, an acceptable method of compliance with SCs 1-6 and 9 is to show these batteries meet UL 1642, UL 2054, or IEC 62133. For very small button/coin rechargeable lithium batteries that do not meet UL 1642, UL 2054, or IEC 62133, show compliance with SCs 3-6 using data related to the worst-case test data from paragraph D.3.3 Method of compliance for SC 1 and 2. D.4 Part 25 Compliance. Rechargeable lithium battery installations, typically, must comply with applicable SCs and Parts 25 and 26 requirements. The following paragraphs provide methods of compliance and other information for pertinent Part 25 requirements: D.4.1 System Safety Assessment. D.4.1.1 Although these SCs require specific functionalities and capabilities and address certain critical failure modes of rechargeable lithium batteries and their installations, the applicant must also meet the requirements of §§ 25.1301, 25.1309, a nd 25.1709, when applicable, in addition to these SCs. To date, in-service experience has shown that rechargeable lithium battery thermal/pressure runaway conditions are not extremely improbable. Assume such failures could occur sometime during the life of the battery installation when demonstrating compliance with § 25.1309 except for button/coin batteries that have less than 2 watt-hours of energy and meet UL 1642, UL 2054, or IEC 62133. For button/coin batteries that have less than 2 watt-hours of energy and meet UL 1642, UL 2054, or IEC 62133, use the data from one of these UL or IEC standards to support demonstrating compliance with § 25.1309. For other rechargeable lithium batteries, use the worst-case data indicated in paragraph D.3.4, Method of Compliance for SCs 3 – 6, t o support demonstrating compliance with § 25.1309. D-4 ### Page 32 AC 20-184A Appendix D D.4.1.2 As part of showing compliance with § 25.1309, t he applicant is to demonstrate that particular risks, such as identified in SAE ARP4761A, Guidelines and Methods for Conducting Safety Assessment Process on Civil Airborne Systems and Equipment, an uncontained rotor burst, tire debris, fire, lightning, or bird strike will not compromise continued safe flight and landing. The applicant is to consider the effects of particular risks—both internal and external—to rechargeable lithium battery installations. For example, the applicant is to consider the effects of particular risks on any containment and venting provisions for a rechargeable lithium battery. D.4.1.3 Application of § 25.1309(b) and (c) may result in required periodic maintenance actions or flightcrew alerting features. For example, an overtemperature warning system may be necessary to allow the flightcrew to manage potentially unsafe system operating conditions. Provide rationale for alerting requirements (or for why an alert is not needed) in the system safety assessment of the battery installations to demonstrate compliance with § 25.1309(c). Such alerts, if provided, must meet § 25.1 322. Refer to AC 25.1309-1B, System Design and Analysis; AC 25.1322-1, Flightcrew Alerting; AC 25.1581-1 Airplane Flight Manual; and AC 25.1701-1, Certification of Electrical Wiring Interconnection Systems on Transport Category Airplanes, for further guidance. Note 1: For compliance with Section 25.1309, please use the guidance provided in AC 25.1309-1B. Note 2: Venting toxic and explosive gases from a rechargeable lithium battery failure through designed ports that lead outside of the airplane is a method of compliance with SC 3 as discussed in paragraph D.3.5 Method of Compliance for SC 3. In this case, consider the hazards of exposure of these gases to ground personnel, air conditioning intake and engine in-take in accordance with § 25.1309. D.4.2 Section 25.1353 Electrical Equipment and Installations. The SC states that it applies to all rechargeable lithium battery installations in lieu of § 25.1353(b)(1) through (4) at amendment 25-123 or § 25.1353( c)(1) through (4) at earlier amendments. This statement does not relieve an applicant from demonstrating compliance with the other paragraphs of § 25.1353. D.4.3 Section 25.1529 ICA. Include in the ICA the following to comply with § 25.1529: D.4.3.1 A requirement to only replace rechargeable lithium batteries with batteries from the same manufacturer with the same part number, or to obtain a new FAA approval for installing a different battery. Refer to the battery’s original equipment manufacturer maintenance manual. D.4.3.2 Procedures to ensure that each rechargeable lithium battery has not: D-5 ### Page 33 AC 20-184A Appendix D 1. Experienced degraded charge retention ability or other damage during storage. 2. Been damaged from environmental or physical impacts such as mechanical shock, vibration, heat, a nd possible abuses encountered during storage, transportation prior to their installation, or maintenance activities on or around them. D.4.3.3 Precautions to prevent mishandling of replacement rechargeable lithium batteries prior to their installation, which could result in short-circuit or other unintentional damage. Note: Acceptable procedures for paragraph D.4.3.2 item 2 m ay include a quality control process for packaging, storing, maintaining, and transporting rechargeable lithium batteries, including directions to report dropped or damaged batteries. D.4.4 Section 25.1729 ICA; Electrical Wiring Interconnection Systems (EWIS). EWIS maintenance and inspection tasks required by § 25.1729 a re to ensure that EWIS components associated with rechargeable lithium batteries are sufficient to prevent degradation of any EWIS component that is designed and installed to support compliance with these SCs. D.4.5 Sections 25.903(d) and 25.1309 Uncontained Engine or APU Rotor Failures. D.4.5.1 As part of showing compliance with § 25.1309, t he FAA expects the applicant to demonstrate that a foreseeable event originating from outside of a rechargeable lithium battery, such as an uncontained rotor burst, will not impact the airworthiness of the aircraft preventing continued safe flight and landing. An applicant may propose fail-safe design features that encase and safely vent the hazardous byproducts of a failure originated from within the battery to show compliance with the rechargeable lithium battery SC. However, a rotor failure could defeat such safety features depending on the location of the battery installation. If an applicant proposes to install a rechargeable lithium battery in a rotor burst zone, the applicant must ensure the means of compliance with the SC remain effective considering potential rotor failures that could damage the battery. D.4.5.2 Regarding compliance with § 25.903( d)(1) turbine engine rotor failures, AC 20-128A, Design Considerations for Minimizing Hazards caused by Uncontained Turbine Engine and Auxiliary Power Unit Rotor Failure, provides guidance on fragmentation characteristics and the boundaries of the locations in which applicants are expected to evaluate the effects of impact damage following an uncontained rotor burst. If an applicant proposes to install a rechargeable lithium battery in a rotor burst zone, the applicant must assess the rotor-burst-induced damage to the battery to show compliance with § 25.903(d)(1) in conjunction with showing compliance with the rechargeable lithium battery SC. In this case, provide D-6 ### Page 34 AC 20-184A Appendix D a proposed method of compliance w ith the FAA. Alternatively, locate the battery outside of the rotor burst zone. D.5 Hazard Mitigations for Large Battery System Thermal Runaway Conditions. Airplanes requiring high-capacity batteries may increase the severity level and adverse effects resulting from a battery thermal runaway condition, or any other hazards. As stated earlier, using RTCA DO-311A, including articles approved under TSO-C179b, is an accepted approach for addressing the thermal runaway aspects of rechargeable lithium battery installations. All applicable airworthiness regulations must be addressed and complied with. RTCA DO-311A and TSO-C179b provide a testing standard and article-level approval that requires additional integration and mitigation strategies in order to fully comply with the applicable airworthiness regulations on the aircraft. The FAA outlines the following guidance in Section D.5.1 to address verification aspects of lithium battery thermal runaway conditions for RTCA DO-311A, section 2.4.5.5. All other tests within RTCA DO-311A are applicable as stated in the industry consensus standard. Note: Due to the significance of technical and regulatory issues regarding Hazard Mitigations for Large Battery System Thermal Runaway Conditions (D.5), coordination with the FAA is required. D.5.1 Battery Thermal Runaway Containment Test (RTCA DO-311A, Section 2.4.5.5). Coordinate as soon as possible with the FAA on the proposed design methodology. D.5.1.1 RTCA DO-311A, section 2.4.5.5 describes the test methods for battery thermal runaway containment that are designed to force the entire battery into a thermal runaway state. This may not be feasible for very large highcapacity systems. To address the feasibility of very large high-capacity battery system testing, this section of the AC defines a module or sub-pack as a battery system divided into smaller configurations to help in testing and validating the safety implication of the battery system. The battery and battery system can be designed into several smaller modules or sub-packs. Each module has an assembly of cells electrically connected and enclosed in a single enclosure. Each sub-pack has an assembly of electrically connected modules that is enclosed by a single enclosure. The venting design of the sub-pack, module, and cells needs to be considered in the mitigation strategy. D.5.1.2 To successfully comply with the requirement of RTCA DO-311A, section 2.4.5.5 test, it is acceptable to use a modularized/sub-pack battery system design. D-7 ### Page 35 AC 20-184A Appendix E APPENDIX E. CORRELATION OF TRANSPORT CATEGORY AIRPLANE METHOD OF COMPLIANCE WITH SPECIAL CONDITIONS ISSUED PRIOR TO AUGUST 2016 Prior to August 2016, the FAA issued SCs with slightly different order and wording than the SCs in appendix C. The method of compliance in appendix D is also applicable to those SCs. The intent of this appendix is to correlate the method of compliance in appendix D to those earlier SC s. E.1 Rechargeable Lithium Battery SCs Issued Before August 2016: In lieu of the requirements of § 25.1353(c)(1) through (c)(4) at amendment 25-113, all rechargeable lithium batteries, and battery systems on [airplane model] must be designed and installed as follows: 1. Safe cell temperatures and pressures must be maintained during any foreseeable charging or discharging condition and during any failure of the charging or battery monitoring system not shown to be extremely remote. The rechargeable lithium battery installation must preclude explosion in the event of those failures. 2. Design of the rechargeable lithium batteries must preclude the occurrence of selfsustaining, uncontrolled increases in temperature or pressure. 3. No explosive or toxic gases emitted by any rechargeable lithium battery in normal operation, or as the result of any failure of the battery charging system, monitoring system, or battery installation not shown to be extremely remote, may accumulate in hazardous quantities within the airplane. 4. Installations of rechargeable lithium batteries must meet the requirements of § 2 5.863(a) through (d). 5. No corrosive fluids or gases that may escape from any rechargeable lithium battery may damage surrounding structure or any adjacent systems, equipment, or electrical wiring of the airplane in such a way as to cause a major or more severe failure condition, in accordance with § 25.1309(b) and applicable regulatory guidance. 6. Each rechargeable lithium battery installation must have provisions to prevent any hazardous effect on structure or essential systems caused by the maximum amount of heat the battery can generate during a short circuit of the battery or of its individual cells. 7. Lithium battery installations must have a system to control the charging rate of the battery automatically, designed to prevent battery overheating or overcharging, and, i) A battery temperature sensing and over-temperature warning system with a means for automatically disconnecting the battery from its charging source in the event of an over-temperature condition, or, ii) A battery failure sensing and warning system with a means for automatically disconnecting the battery from its charging source in the event of battery failure. E-1 ### Page 36 AC 20-184A Appendix E 8. A ny rechargeable lithium battery installation, the function of which is required for safe operation of the airplane, must incorporate a monitoring and warning feature that will provide an indication to the appropriate flight crewmembers whenever the state-of-charge of the batteries has fallen below levels considered acceptable for dispatch of the airplane. 9. The instructions for continued airworthiness required by § 25.1529 must contain maintenance requirements to ensure that the battery is sufficiently charged at appropriate intervals specified by the battery manufacturer and the equipment manufacturer that contain the rechargeable lithium battery or rechargeable lithium battery system. This is required to ensure that rechargeable lithium batteries and rechargeable lithium battery systems will not degrade below specified ampere-hour levels sufficient to power the airplane systems for intended applications. The instructions for continued airworthiness must also contain procedures for the maintenance of batteries in spares storage to prevent the replacement of batteries with batteries that have experienced degraded charge retention ability or other damage due to prolonged storage at a low state of charge. Replacement batteries must be of the same manufacturer and part number as approved by the FAA. Precautions should be included in the instructions for continued airworthiness maintenance instructions to prevent mishandling of the rechargeable lithium battery and rechargeable lithium battery systems, which could result in short-circuit or other unintentional impact damage caused by dropping batteries or other destructive means that could result in personal injury or property damage. Note 1: The term “sufficiently charged” means that the battery will retain enough of a charge, expressed in ampere-hours, to ensure that the battery cells will not be damaged. A battery cell may be damaged by lowering the charge below a point where the battery experiences a reduction in the ability to charge and retain a full charge. This reduction would be greater than the reduction that may result from normal operational degradation. Note 2: These special conditions are not intended to replace § 25.1353(c) in the certification basis of the [airplane model]. These special conditions apply only to rechargeable lithium batteries and lithium battery systems and their installations on [airplane model]. The requirements of § 25.1353(c) remain in effect for batteries and battery installations on [airplane model] that do not use lithium batteries. E.2 The Following Provides Correlation Between the Method of Compliance in Appendix D to the SCs Issued Before August 2016: • Method of Compliance for Pre-August 2016 SCs 1 and 2. Appendix D, section D.3.3, Method of Compliance for SCs 1 and 2, provides a method of compliance. • Method of Compliance for Pre-August 2016 SC 3. Appendix D, sections D.3.4, Method of Compliance for SCs 3 – 6, and D.3.5, Method of Compliance for SC 3, provide a method of compliance. E-2 ### Page 37 AC 20-184A Appendix E • Method of Compliance for Pre-August 2016 SC 4. Appendix D, sections D.3.4, Method of Compliance for SCs 3 – 6 and D.3.6, Method of Compliance for SC 4, provide a method of compliance. • Method of Compliance for Pre-August 2016 SC 5. Appendix D, sections D.3.4, Method of Compliance for SCs 3 – 6 a nd D.3.7, Method of Compliance for SC 5, provide a method of compliance. • Method of Compliance for Pre-August 2016 SC 6. Appendix D, sections D.3.4, Method of Compliance for SCs 3 – 6 and D.3.8, Method of Compliance for SC 6, provide a method of compliance. • Method of Compliance for Pre-August 2016 SC 7. Section D.3.3, Method of Compliance for SCs 1 and 2 demonstrates that rechargeable lithium batteries are designed to prevent overheating and overcharging. Section D.3.11, Method of Compliance for SC 9, provide additional applicable guidance. • Method of Compliance for Pre-August 2016 SC 8. Appendix D, section D.3.10, Method of Compliance for SC 8, provides applicable guidance. • Method of Compliance for Pre-August 2016 SC 9. SC 9 contains specific requirements related to ICAs that must be met. Section 25.1529 is another independent, applicable regulation. Section D.4.3, Section 25.1529 Instructions for Continued Airworthiness (ICA), applies to § 25.15 29. E-3 ### Page 38 AC 20-184A Appendix F APPENDIX F. REGULATIONS AND METHOD OF COMPLIANCE FOR RECHARGEABLE LITHIUM BATTERIES FOR ROTORCRAFT The method of compliance provided in this appendix is to establish an approach to show compliance for rechargeable lithium batteries and their installation on rotorcraft. This AC is also intended to ensure, as required by §§ 27.601, 29.601, 27.1309, 29.1309, 27.1353, and 29.1353, that the installation does not present a hazard to the rotorcraft and its occupants. F.1 Regulatory Basis From Part 27 at Amendment 27-51 and Part 29 at Amendment 29-59. F.1.1 Regulations codified at 14 CFR §§ 27.601 and 29.601 require that the design must not have features or details that experience has shown to be hazardous or unreliable. F.1.2 Regulations codified at 14 CFR §§ 27.863 and 29.863 require a means of minimizing the probability of ignition of flammable fluids or vapors that might leak from flammable liquid sources and the resultant hazards in the event of ignition. F.1.3 Regulations 27.1301 and 29.1301 require that each system is appropriate for its intended function and is labeled and installed according to its limitations and function. F.1.4 Regulations 27.1309 and 29.1309 state that required systems must perform their intended function under any foreseeable operating conditions; systems must be designed to prevent hazards to the rotorcraft in the event of a probable malfunction or failure. F.1.5 Regulations 27.1353 and 29.1353 require in part that energy storage systems must be designed and installed to maintain safe cell temperatures and pressures so that no explosive or toxic gases can accumulate in hazardous quantities, and that corrosive fluids or gases cannot damage surrounding structures or essential systems. F.1.6 Regulations 27.1529 and 29.1529 require that the ICA be prepared. F.2 Advisory Circulars. • AC 27-1B, Certification of Normal Category Rotorcraft. • AC 29-2C, Certification of Transport Category Rotorcraft. F.3 Industry Document. RTCA DO-311A, Minimum Operational Performance Standards for Rechargeable Lithium Batteries and Battery Systems. F-1 ### Page 39 AC 20-184A Appendix F F.4 Part 27 and 29 Regulations. The following regulations are identified as critical for safe installation of rechargeable lithium batteries. Each rechargeable lithium battery installation must show that the following are met: F.4.1 Sections 27.1353(a) and 29.1353(a). Energy storage systems must provide automatic protective features for any conditions that could prevent continued safe flight and landing. F.4.2 Sections 27.1353(b) and 29.1353(b). Energy storage systems must not emit any flammable, explosive, or toxic gases, smoke, or fluids that could accumulate in hazardous quantities within the rotorcraft. F.4.3 Sections 27.1353(c) and 29.1353(c). Corrosive fluids or gases that escape from the system must not damage surrounding structures, adjacent equipment, or systems necessary for continued safe flight and landing. F.4.4 Sections 27.1353(d) and 29.1353(d). The maximum amount of heat and pressure that can be generated during any operation or under any failure condition of the energy storage system or its individual components must not result in any hazardous effect on rotorcraft structure, equipment, or systems necessary for continued safe flight and landing. F.4.5 Sections 27.1353(e) and 29.1353(e). Energy storage system installations required for continued safe flight and landing of the rotorcraft must have monitoring features and a means to indicate to the pilot the status of all critical system parameters. Note: An energy storage system consists of individual battery cell(s), a battery assembly, and any protective monitoring and alerting circuitry or hardware inside or outside of the battery. It may also include vents (when necessary) and packaging. For the purpose of this guidance, a battery and battery system are referred to as a battery. F.5 Method of Compliance. The following method of compliance is acceptable to ensure that the battery complies with §§ 27.1353(a) and 29.1353(a) through §§ 27.1353(e) and 29.1353(e) discussed in the paragraphs above. F.5.1 RTCA DO-311A, Minimum Operational Performance Standards for Rechargeable Lithium Batteries and Battery Systems, section 2.1 General Requirements provides design requirements and guidelines that are pertinent to designing safe batteries and to meeting Part 27 and 29 applicable requirements and the regulations shown in paragraph F.4 above. Section 2.2, Equipment Requirements – Standard Conditions, defines the minimum functional requirements for battery cells, batteries, and end items. Each F-2 ### Page 40 AC 20-184A Appendix F subsection in section 2.2 references a specific test procedure found in section 2.4. Test procedures and evaluation criteria specifically for cells, batteries, and end items are outlined in section 2.4 corresponding to each of the functional and safety requirements. Test conditions are defined in section 2.3. Consider each of these requirements and guidelines when designing cells and batteries. F.5.2 Sections 27.1353(a) and 29.1353(a) are intended to ensure that the cells and batteries are designed to eliminate the potential for uncontrollable failures. However, a certain number of failures will still occur due to various factors, many of which are beyond the control of the designer. Therefore, these regulations, as a whole, are intended to protect the rotorcraft and its occupants even if a failure occurs. F.5.3 These regulations are independent of each other. Demonstrating compliance with one of these regulations does not constitute compliance with the other regulations. An acceptable method of compliance for each regulation is as follows: F.5.4 Method of Compliance for §§ 27.1353(a) and 29.1353(a). F.5.4.1 Sections 27.1353(a) and 29.1353(a) require that the cell and battery be designed to prevent propagation of a thermal event, such as self-sustained, uncontrollable increases in temperature or pressure from one cell to adjacent cells. F.5.4.2 Show that the batteries meet the requirements in RTCA DO-311A, sections 2.2, Equipment Requirements – St andard Conditions (which are applicable according to RTCA DO-311A, section 2.4.2) and 2.3 Equipment Requirements – E nvironmental Conditions. Consider that batteries with less than 2 watt-hours of energy that are not button/coin batteries, or do not meet UL 1642, UL 2054, or IEC 62133, to be energy category 2 batteries. Use the test procedures in RTCA DO-311A, section 2.4, Equipment Test Procedures, to show that the requirements of RTCA DO-311A, section 2.2 are met. Note that RTCA DO-311A, table 2-2 provides a test matrix that defines which tests are required for each category of battery, along with the order of the testing. F.5.4.3 Provide the FAA with the video of the testing conducted for RTCA DO- 311A section 2.4.5.5. F.5.5 Method of Compliance for §§ 27.1353(b) and 29.1353(b). F.5.5.1 An acceptable means of complying with §§ 27.1353(b) and 29.1353(b) includes using any tests used to demonstrate compliance with unde r §§ 27.1352(a) and 29.1353(a) to demonstrate that all emitted gases are contained or vented overboard (i.e., vented outside the rotorcraft) through designed ports. If the design has ports to vent gases overboard, show that there are means to protect ground personnel from exposure to these gases and to prevent re-ingestion, for example through engine in-take or air F-3 ### Page 41 AC 20-184A Appendix F conditioning in-take, in accordance with §§ 27.13 01, 29.1301, 27.1309, and 29.1309. The applicant should refer to the current AC 27-1B and AC 29-2C for guidance on §§ 27.1309 and 29.1309. F.5.5.2 Sections 27.1353(b) and 29.1353(b) allow explosive and toxic gases to be uncontained and not vented overboard if they do not accumulate in hazardous quantities within the rotorcraft. Consider the gases emitted from not only the cells but also the battery materials (e.g., insulation separators) when demonstrating compliance by this means. F.5.5.3 While each paragraph of section(s) 27.1352 and 29.1353 needs to be evaluated specifically, it may be possible to use the results of testing conducted for §§ 27.1352(a) and 29.1353(a) for compliance with §§ 27.1353(b) and 29.1353(b). Therefore, if there were gases emitted from the end item (RTCA DO 311A, Category C) during the testing of RTCA DO-311A, section 2.4.5.5, i n compliance with §§ 27.1353(a) and 29.1353(a), the emitted gases must be collected and evaluated for the volume and constituents of the gas. This would provide the ability to evaluate the dissipation and hazard level of these emissions in the location in which the end item is installed. F.5.6 Method of Compliance for §§ 27.1353(c) and 29.1353(c). Show that if fluid escapes the battery during testing of regulations 27.1353(a) and 29.1353(a), it is not corrosive or it is managed in a way (e.g., contained, isolated, or vented overboard) to protect the surrounding structure and adjacent systems, equipment, and electrical wiring of the rotorcraft. F.5.7 Method of Compliance for §§ 27.1353(d) and 29.1353(d). F.5.7.1 Show that the effects of the heat, and any related effects, from the tests performed under §§ 27.1353(a) and 29.1353(a) do not constitute a hazard to the structure or systems of the rotorcraft necessary for operations, maintenance and continued safe flight and landing. F.5.7.2 If the effects of the heat or any related effects constitute a hazard to the structure or systems of the rotorcraft, design mitigation at the aircraft level may be applied to bring the design into compliance with regulations 27.1353(d) and 29.1353(d). F.5.8 Method of Compliance for §§ 27.1353(e) and 29.1353(e). F.5.8.1 Sections 27.1353(e) and 29.1353(e) require flightcrew alerting to monitor features and have a means to indicate to the pilot of critical system parameters, which may otherwise lead to an unsafe operating condition. Flightcrew alerting is required if a battery installation failure affects continued safe flight and landing. The effect of the battery failure on other systems that perform functions required for safe flight and landing must F-4 ### Page 42 AC 20-184A Appendix F also be considered. The alert must meet the applicable paragraphs of §§ 27.1301, 29.1301, 27.1309, a nd 29.1309. The applicant should refer to the current AC 27-1B and AC 29-2C for guidance on compliance with §§ 27.1322, 29.1322, 27.1301, 29.1301, 27.1309, a nd 29.1309. F.5.8.2 The following are examples of means for flightcrew or maintenance personnel to determine the battery charge state, which is a critical system parameter: 1. A manually activated system (e.g., push button) that displays the available charge of each battery unit. 2. An automatic system that records the available charge of each battery unit on an appropriate interval and makes it available to maintenance personnel before the next flight. 3. Physical access that allows a maintenance person to measure the battery charge state. Note: The above means are acceptable only if the ICA includes a requirement for a person to check the battery charge state within an interval that will ensure sufficient charge for the entire flight, considering the worst-case scenario, and to replace the battery when the charge is not sufficient. F.5.8.3 After completing all the required tests and validation, based on the method of compliance for each regulation, provide a summary of all the evaluation criteria and reportable items listed in each test. F.5.9 Method of Compliance for Very Small Rechargeable Lithium Batteries Less Than 2 Watt-Hours. Compliance with UL 1642, UL 2054, or IEC 62133 is an acceptable method of compliance to show §§ 27.1353(a) and 29.1353(a) through §§ 27.1352(e) and 29.1353(e) are met for very small button/coin rechargeable lithium batteries installations with less than 2 watt-hours of energy. F.5.10 Additional Part 27 and 29 Compliance. Rechargeable lithium battery installations must satisfy each means of compliance identified in this AC and all applicable Part 27 and 29 requirements. The following provides methods of compliance and other information related to compliance with Part 27 a nd 29 requirements. F.5.10.1 System Safety Assessment. Although these hazard conditions require specific functionalities and capabilities and address certain critical failure modes of rechargeable lithium batteries and their installations, the applicant must also meet the requirements of §§ 27.1301, 29.1301, 27.1309, 29.1309, 27.1353, and 29.1353. To date, in-service experience has shown that rechargeable F-5 ### Page 43 AC 2 0-184A Appendix F lithium battery thermal/pressure runaway conditions are not extremely improbable. Assume such failures could occur sometime during the life of the battery installation when demonstrating compliance with §§ 27.1309 and 29.1309. Application of §§ 27.1309 and 29.1309 may result in required periodic maintenance actions or flightcrew alerting features. For example, an over-temperature warning system may be necessary to allow the flightcrew to manage potentially unsafe system operating conditions. Provide rationale for alerting requirements (or for why an alert is not needed) in the system safety assessment of the battery installations to demonstrate compliance with §§ 27.1309 and 29.1309. Such alerts, if provided, must meet §§ 27.1322 and 29.1322. F.5.10.2 The ICA should include the following provisions to comply with §§ 27.1529 a nd 29.1529: 1. Maintenance requirements to replace each rechargeable lithium battery within an interval or monitoring based on state of health that will ensure there is sufficient charge to power equipment. 2. A requirement to only replace rechargeable lithium batteries with batteries from the same manufacturer with the same part number or to obtain a new FAA approval for installing a different battery. Refer to the battery Original Equipment Manufacturer’s maintenance manual. 3. Procedures to ensure that each rechargeable lithium battery has not: (a) Experienced degraded charge retention ability or other damage during storage. (b) Been damaged from environmental or physical impacts such as mechanical shock, vibration, heat, and possible abuses encountered during storage, transportation prior to their installation or maintenance activities on or around them. 4. Precautions to prevent mishandling of replacement rechargeable lithium batteries prior to their installation which could result in shortcircuit or other unintentional damage. Note: Acceptable procedures for paragraph F.5.10.2(3) above may include a quality control process for packaging, storing, maintaining, and transporting rechargeable lithium batteries, including reporting of dropped or damaged batteries. F.5.10.3 Uncontained Engine or APU Rotor Failures: § 29.1309. As part of showing compliance with § 29.1309, the FAA expects the applicant to demonstrate that a foreseeable event originating from outside of a rechargeable lithium battery, such as an uncontained rotor burst, will not compromise continued safe flight and landing. While you may use failsafe design features that encase and safely vent the hazardous by products of a failure originated from within the battery to show F-6 ### Page 44 AC 20-184 A Appendix F compliance with regulations applicable to rechargeable lithium battery systems, depending on the location of the battery installation, a rotor failure could defeat such safety features. If you propose to install a rechargeable lithium battery in a rotor burst zone, then you must ensure the means of compliance with the regulations remains effective, considering potential rotor failures that could damage the battery. F.5.10.4 Turbine Engine Rotor Failures: § 29.903(d)(1). AC 20-128A provides guidance on fragmentation characteristics, and the boundaries of the locations in which applicants are expected to evaluate the effects of impact damage, following an uncontained rotor burst. If you propose to install a rechargeable lithium battery in a rotor burst zone, then you must assess the rotor-burst-induced damage to the battery in your plan for showing compliance with § 29.903(d)(1), in conjunction with complying to regulations applicable to the rechargeable lithium battery. Clearly state your method of compliance in your response to this section of the AC. Alternatively, the battery must be located outside of the rotor burst zone. F.5.11 Hazard Mitigations for Large Battery System Thermal Runaway Conditions. Note: Due to the significance of technical and regulatory issues, coordinate as soon as possible with the FAA. F.5.11.1 Aircraft requiring high-capacity batteries may increase the severity level and adverse effects resulting from a battery thermal runaway condition, or any other hazards. As stated earlier, using RTCA DO-311A, including articles approved under TSO-C179b, is an accepted approach for addressing the thermal runaway aspects of rechargeable lithium battery installations. All applicable airworthiness regulations must be addressed and complied with. RTCA DO-311A and TSO-C179b, provide a testing standard, and article-level approval that requires additional integration and mitigation strategies to fully comply with the applicable airworthiness regulations on the rotorcraft. F.5.11.2 In addition, the FAA outlines guidance in F.5.11.3 to address verification aspects of lithium battery thermal runaway conditions for the RTCA DO- 311A section 2.4.5.5. All other tests within RTCA DO-311A are applicable as stated in the industry consensus standard. F.5.11.3 Battery Thermal Runaway Containment Test (RTCA DO-311A, section 2.4.5.5). Note: Coordinate as soon as possible with the FAA on the proposed method of compliance for this section. F.5.11.3.1 RTCA DO-311A, section 2.4.5.5 describes the test methods for battery thermal runaway containment that are designed to force the entire battery F-7 ### Page 45 AC 2 0-184A Appendix F into a thermal runaway state. This may not be feasible for very large highcapacity systems. To address the feasibility of very large high-capacity battery system testing, this section of the AC defines a module or sub-pack as a battery system divided into smaller configurations to help in testing and validating the safety implication of the battery system. The battery and battery system can be designed into several smaller modules or sub-packs. Each module has an assembly of cells electrically connected and enclosed in a single enclosure. Each sub-pack has an assembly of electrically connected modules that is enclosed by a single enclosure. The venting design of the sub-pack, module, and cells need to be considered in the mitigation strategy. F.5.11.3.2 To successfully comply with the requirement of the RTCA DO-311A section 2.4.5.5 test, it is acceptable to use a modularized/sub-pack battery system design. F-8 ### Page 46 AC 20-184A Appendix G APPENDIX G. INSTALLATION OF RECHARGEABLE LITHIUM BATTERIES FOR SMALL AIRPLANES G.1 Applicability. G.1.1 Regulations applicable to installing rechargeable lithium batteries that provide power to small airplanes are §§ 23.2005, 23.2010, 23.2325(g), 23.2410, 23.2500, 23.2505, 23.2510, 23.2525, 23.2605, a nd 23.1529, a ppendix A, at amendment 23-64. G.1.2 The applicant must meet the current requirements of P art 23 at amendment 23-64 in the areas of change for the rechargeable lithium battery installation, and may use means and methods in this AC on certification projects2 with an original certification basis prior to amendment 23-64, so long as they are not contrary to any special conditions already part of the certification basis. G.1.3 This appendix does not address compliance with applicable crashworthiness and survivable emergency landing requirements with respect to the rechargeable lithium battery. G.2 Means of Compliance with Safety Objectives. The applicant must comply with the following SOs, including all other applicable airworthiness regulations, w hen using the means of compliance in this AC for the installation of rechargeable lithium batteries. G.2.1 SO 1: Be designed to maintain safe cell temperatures and pressures under all foreseeable operating conditions to prevent fire and explosion. G.2.2 SO 2: Be designed to prevent the occurrence of self-sustaining, uncontrollable increases in temperature or pressure, and automatically control the charge rate of each cell to protect against adverse operating conditions, such as cell imbalance, back charging, overcharging, and ove rheating. G.2.3 SO 3: Not emit explosive or toxic gases, either in normal operation or as a result of its failure, that may accumulate in hazardous quantities within the airplane. G.2.4 SO 4: Meet the requirements of § 23. 2325(g) regarding areas where flammable fluids or vapors might escape by leakage. G.2.5 SO 5: Not damage surrounding structure or adjacent systems, equipment, components, or electrical wiring from corrosive or any other fluids or gases that may escape in such a way as to cause a major or more-severe failure condition. 2 Including TCs, STCs, ATCs, and ASTCs. G-1 ### Page 47 AC 20-184A Appendix G G.2.6 SO 6: Have provisions to prevent any hazardous effect on airplane structure or systems caused by the maximum amount of heat it can generate due to any failure of it or its individual cells. G.2.7 SO 7: Have a failure sensing and warning system to alert the flightcrew if its failure affects safe operation of the airplane. G.2.8 SO 8: Have a monitoring and warning feature that alerts the flightcrew when its charge state falls below acceptable levels if its function is required for safe operation of the airplane. G.2.9 SO 9: Have a means to disconnect from its charging source in the event of an overtemperature condition, cell failure, or battery failure. G.3 Method of Compliance with Safety Objectives. G.3.1 RTCA DO-311A provides data used to demonstrate that rechargeable lithium battery installations meet the means of compliance SOs when using this AC for compliance. G.3.2 RTCA DO-311A, s ection 2.1, General Requirements, provides design requirements and guidelines that are pertinent to designing safe batteries and meeting Part 23 requirements and the means of compliance SOs. Consider each of these requirements and guidelines when designing cells and batteries. G.3.3 RTCA DO-311A, sections 1.4, 1.5, 1.6, a nd 2.1 provide guidelines and general requirements that are pertinent to designing and installing safe lithium batteries on aircraft. G.3.4 SOs 1 and 2 are intended to ensure that the cells and battery are designed to eliminate the potential for uncontrollable failures. However, a certain number of failures will still occur due to various factors beyond the control of the designer. Therefore, the means of compliance SOs, as a whole, are intended to protect the airplane and its occupants if failure occurs. G.3.5 The following method of compliance must be used to comply with the means of compliance in G.2 a bove. Means of compliance SOs are independent of each other. Demonstrating compliance with one of these SOs does not constitute compliance with the other SOs. G.3.5.1 SO 1: Designed to maintain safe cell temperatures and pressures under all foreseeable operating conditions to prevent fire and explosion. Method of Compliance with SO 1: 1. Show that batteries meet the requirements in RTCA DO-311A, sections 2.2, Equipment Requirements – St andard Conditions (which are applicable according to section 2.4.2) and section 2.3, Equipment Requirements – E nvironmental Conditions. G-2 ### Page 48 AC 2 0-184A Appendix G 2. Use the test procedures in section 2.4, Equipment Test Procedures, to show that the requirements of section 2.2 are met. G.3.5.2 SO 2: Designed to prevent the occurrence of self-sustaining, uncontrollable increases in temperature or pressure, and automatically control the charge rate of each cell to protect against adverse operating conditions, such as cell imbalance, back charging, overcharging, and overheating. Method of Compliance with SO 2: 1. SO 2 addresses the same issues for the entire battery as SO 1 for the individual cell. The battery must be designed to prevent propagation of a thermal event due to any operational or fault conditions, such as selfsustained, uncontrollable increases in temperature or pressure. 2. RTCA DO-311A, section 2.4.2, table 2-2, provides a test matrix that defines which tests are required for each category of battery, along with the order of the testing. 3. Provide the FAA with the video of the testing conducted for RTCA DO-311A, s ection 2.4.5.5. G.3.5.3 SO 3: Not emit explosive or toxic gases, either in normal operation or as a result of its failure, that may accumulate in hazardous quantities within the airplane. Method of Compliance with SO 3: 1. RTCA DO-311A, section 3.2.1, Hazardous Battery Emissions, discusses potential gas emissions from batteries and their effects. All emitted gases must be contained or vented overboard (i.e., vented outside the airplane) through designed ports. 2. SO 3 does allow explosive and toxic gases to be uncontained and not vented overboard if they do not accumulate in hazardous quantities within the airplane. Consider the gases emitted from not only the cells but also the battery materials (e.g., insulation separators). Provide substantiation to this requirement in terms of analysis and test results. Use the test results of SO 1 and SO 2 for SO 3. 3. An acceptable means of complying with SO 3 includes using the tests required under SO 1 and SO 2 to demonstrate that all emitted gases are contained or vented overboard (i.e., vented outside the aircraft) through designed vent ports. If the design has ports to vent gases overboard, show that there are means to protect ground personnel from exposure to these gases and to prevent re-ingestion, for example through engine in-take or air conditioning in-take, in accordance with § 23.2510. 4. If there were gases emitted from the end item under RTCA DO 311A Category C during the testing of RTCA DO-311A, s ection 2.4.5.5, i n G-3 ### Page 49 AC 2 0-184A Appendix G compliance with SO 1 and SO 2, the emitted gases must be collected and evaluated for the volume and constituents of the gas. This would provide the ability to evaluate the dissipation and hazard level of these emissions in the location in which the End Item is to be installed. G.3.5.4 SO 4: Meet the requirements of § 23.2325(g). Method of Compliance with SO 4: 1. Section 23.2325(g) requires minimizing the likelihood of a fire and the resultant hazards if fire does occur. Both battery electrolyte and any coolant fluid, if present, are considered fluid systems when evaluating § 23.2325( g). 2. Perform a safety assessment to identify and evaluate associated hazards and their severity. Mitigate and minimize all hazards resulting from a battery failure. G.3.5.5 SO 5: Not damage surrounding structure or adjacent systems, equipment, components, or electrical wiring from corrosive or any other fluids or gases that may escape in such a way as to cause a major or more-severe failure condition. Method of Compliance with SO 5: 1. Show that if fluid escapes the battery, it is not corrosive or it is managed in a way (e.g., contained, isolated, or vented overboard) to protect the surrounding structure and adjacent systems, equipment, components, and electrical wiring. 2. Evaluate test results after conducting tests per RTCA DO-311A, including a system safety assessment for failure conditions. Use test results of SO 1 and SO 2 for SO 5 substantiations. Mitigation at the airplane level may be applied to bring the design into compliance. 3. The intent is to show that if fluid escapes the battery during the testing for compliance with SO 1 and SO 2, it is not corrosive or it is managed in a way (e.g., contained, isolated, or vented overboard) to protect the surrounding structure and adjacent systems, equipment, and electrical wiring. G.3.5.6 SO 6: Have provisions to prevent any hazardous effect on airplane structure or systems caused by the maximum amount of heat it can generate due to any failure of it or its individual cells. Method of Compliance with SO 6: 1. Show that the effects of heat and any related effects from conducting tests per RTCA DO-311A do not create a hazard to the structure or systems of the airplane. The maximum heat to be considered must be equal to or greater than the heat generated from the worst-case thermal G-4 ### Page 50 AC 2 0-184A Appendix G runaway containment test agreed to in this appendix ( e.g., tests performed for SO 1 and 2). 2. If the effects of the heat or any related effects constitute a hazard to the structure or systems of the airplane, mitigation at the airplane level may be applied to bring the design into compliance. 3. The temperature of the gases and the enclosure need to be provided. This temperature will help show that the effects of the heat, and any related effects, from the tests performed under SO 1 and SO 2 do not constitute a hazard to the structure or systems of the aircraft. G.3.5.7 SO 7: Have a failure sensing and warning system to alert the flightcrew if its failure affects safe operation of the ai rplane. Method of Compliance with SO 7: 1. Ensure adequate flightcrew alerting because failure effects of a battery installation to airplane level functions could result in unsafe system operating conditions. 2. RTCA DO-311A, section 2.1.4.2, Battery Warning Features, discusses warning circuits and signals. G.3.5.8 SO 8: Have a monitoring and warning feature that alerts the flightcrew when its charge state falls below acceptable levels if its function is required for safe operation of the airplane. Method of Compliance with SO 8: 1. Have a means for the flightcrew and maintenance personnel to determine the battery charge state if the battery’s function is required for safe operation of the airplane. 2. Use a system safety assessment to determine the alert level. G.3.5.9 SO 9: Have a means to disconnect from its charging source in the event of an over-temperature condition, cell failure, or battery failure. Method of Compliance with SO 9: 1. In accordance with the applicable rules listed in paragraph 2.2.2, table 2-1, the battery must be capable of disconnecting itself from the charging source to prevent failure conditions, including satisfying SO 1 and SO 2. 2. Not applicable to the cases where RTCA DO-311A has protection disabled as a prerequisite for the test. G.4 Method of Compliance for Very Small Rechargeable Lithium Batteries Less Than 2 Wat t-Hours. Compliance with UL 1642, UL 2054, or IEC 62133 is an acceptable method of compliance to show §23.2525 that SO 1 – S O 6, and SO 9 requirements are met for G-5 ### Page 51 AC 20-184A Appendix G very small button/coin rechargeable lithium battery installations with less than 2 watthours of energy. G.5 ICA Required by § 23.1529, Appendix A to Part 23. Include the following in the ICA, to comply with § 23.1529, a ppendix A to Part 23: G.5.1 Maintenance requirements to replace each rechargeable lithium battery within an interval o r monitoring based on state of health that will ensure there is sufficient charge to power equipment. G.5.2 A requirement to only replace rechargeable lithium batteries with batteries from the same manufacturer with the same part number or to obtain a new FAA approval for installing a different battery. Refer to the battery Original Equipment Manufacturer maintenance manual. G.5.3 Procedures to ensure that each rechargeable lithium battery has not: • Experienced degraded charge retention ability or other damage during storage. • Been damaged from environmental or physical impacts such as mechanical shock, vibration, heat, and possible abuses encountered during storage, transportation prior to their installation or maintenance activities on or around them. G.5.4 Precautions to prevent mishandling of replacement rechargeable lithium batteries prior to their installation that could result in short-circuit or other unintentional damage. G.6 Uncontained Engine or APU Rotor Failures: §§ 23.2410 and 23.2510 at Amendment 23-64. G.6.1 In general, as part of showing compliance with §§ 23.2410 a nd 23.2510, the FAA expects the applicant to demonstrate that a foreseeable event o riginating from outside of a rechargeable lithium battery, such as an uncontained rotor burst, will not compromise continued safe flight and l anding. You may use fail-safe design features that encase and safely vent the hazardous byproducts of a failure originated from within the battery to show compliance with the rechargeable lithium battery SOs. Depending on the location of the battery installation, a rotor failure could defeat such safety features. If a rechargeable lithium battery is installed in a rotor burst zone, ensure the means of compliance with the SOs remains effective considering potential rotor failures that could damage the battery. G.6.2 Regarding compliance with § 23.2410 for turbine engine rotor failures, AC 20-128A provides guidance on fragmentation characteristics and the boundaries of the locations in which applicants are expected to evaluate the effects of impact damage following an uncontained rotor burst. For a rechargeable lithium battery—except for very small button/coin cells with less than 2 watt-hours of energy that meet UL 1642, U L 2054, or IEC 62133—assess the r otor-burst-induced damage to the battery in a plan for showing G-6 ### Page 52 AC 20-184A Appendix G compliance with § 23.2410 in conjunction with complying with the rechargeable lithium battery SOs. Clearly state the method of compliance in your response to this section of the AC. G.7 Lithium Battery Installed in a Designated Fire Zone (DFZ) (§§ 23.244 0 and 23.2510). G.7.1 Installation in a DFZ should be avoided, but may be acceptable if the battery location does not create an additional hazard. The external fire threat to the battery when it is located in a DFZ is a 2000°F flame for 15 minutes per AC 20-135, Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards, and Criteria. The heat generated by this flame may cause multiple cells to enter thermal runaway along with damage to the battery containment system resulting in uncontrolled fire or explosion. G.7.2 In accordance with § 23.2440(c)(1) and any other applicable airworthiness regulation references in table 2-1 of AC 20-184A, the battery must contain or vent any thermal runaway and pr event introduction of additional hazards when exposed to a 2000°F flame for 15 minutes. Test by exposing the battery installation design (including any vents) to a 2000°F flame for 15 minutes per AC 20-135. Ensure no additional hazards are introduced. For all batteries installed in a DFZ, minimize the risk of fire in the DFZ. Some examples are: G.7.2.1 Directing and venting (if the design includes a vent) any potential flames or flammable material from the battery out of the fire zone. Any vent system included in the design must continue to function in the event of a thermal runaway of the battery, otherwise it must not create an additional hazard from its failure. G.7.2.2 Using fireproof materials in the construction of the battery installation design. G.7.2.3 Providing adequate shielding to protect the battery and vent, if any, from direct flames to ensure the battery remains below a temperature that could compromise the thermal runaway containment integrity when exposed to a powerplant fire condition. G.8 Hazard Mitigations for Large Battery System Thermal Runaway Conditions. Airplanes requiring high-capacity batteries may increase the severity level and adverse effects resulting from a battery thermal runaway condition or any other hazards. Using RTCA DO-311A, including articles approved under TSO-C179b, is an accepted approach for addressing the thermal runaway aspects of rechargeable lithium battery installations. All applicable airworthiness regulations must be addressed and complied with. RTCA DO-311A, as well as TSO-C179b, provide a testing standard and articlelevel approval that requires additional integration and mitigation strategies in order to G-7 ### Page 53 AC 20-184A Appendix G fully comply with the applicable airworthiness regulations on the aircraft. The level of acceptable risk will be commensurate with the Part 23 level 1, 2, 3, or 4 aircraft. In addition, the FAA outlines guidance in paragraph G.8.1 to address verification aspects of lithium battery thermal runaway conditions for the RTCA DO-311A, s ection 2.4.5.5. All other tests within RTCA DO-311A are applicable as stated in the industry consensus standard. Note: Due to the significance of technical and regulatory issues, coordinate as soon as possible with the FAA. G.8.1 Battery Thermal Runaway Containment Test (RTCA DO-311A, Section 2.4.5.5). G.8.1.1 RTCA DO-311A, section 2.4.5.5, describes the test methods for battery thermal runaway containment that are designed to force the entire battery into a thermal runaway state. This may not be feasible for very large highcapacity systems. To address the feasibility of very large high-capacity battery system testing, this section of the AC defines a module or sub-pack as a battery system divided into smaller configurations to help in testing and validating the safety implication of the battery system. The battery and battery system can be designed into several smaller modules or sub-packs. Each module has an assembly of cells electrically connected and enclosed in a single enclosure. Each sub-pack has an assembly of electrically connected modules that is enclosed by a single enclosure. The venting design of the sub-pack, module, and cells need to be considered in the mitigation strategy. G.8.1.2 To successfully comply with the requirement of the RTCA DO-311A, section 2.4.5.5, test, it is acceptable to use a modularized/sub-pack battery system design. Note: Coordinate as soon as possible with the FAA on the proposed design methodology (i.e., modularized/sub-pack battery system design). G-8 ### Page 54 OMB Control Number: 2120-0746 Expiration Date: 12/31/2027 Advisory Circular Feedback Form Paperwork Reduction Act Burden Statement: A federal agency may not conduct or sponsor, and a person is not required to respond to, nor shall a person be subject to a penalty for failure to comply with a collection of information subject to the requirements of the Paperwork Reduction Act unless that collection of information displays a currently valid OMB Control Number. The OMB Control Number for this information collection is 2120-0746. 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