AC 20-184A

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

AC 20-184A

TABLE OF CONTENTS Paragraph Page

CHAPTER 1. INTRODUCTION1-1

1.1 Purpose1-1

1.2 Applicability1-1

1.3 Cancellation.1-1

1.4 Scope1-2

1.5 Rechargeable Lithium Batteries Covered in this AC1-2

1.6 Background1-3

CHAPTER 2. INSTALLATION OF RECHARGEABLE LITHIUM BATTERIES ON

AIRCRAFT2-1

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 Validation2-5

2.5 System Safety Assessment2-6

2.6 Software.2-7

2.7 Complex Electronic Hardware2-7

2.8 State of Charge2-7

2.9 Flammability2-7

2.10 Instructions for Continued Airworthiness2-8

2.11 ICA Recommended Manufacturer’s Maintenance and Inspection Requirements2-9

CHAPTER 3. MAINTENANCE AND OPERATIONAL CONSIDERATIONS FOR

LITHIUM BATTERY SYSTEMS3-1

3.1 Introduction3-1

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 MATERIALA-1

A.1 Regulations.A-1

A.2 Advisory CircularsA-1

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AC 20-184A

TABLE OF CONTENTS Paragraph Page

A.3 FormA-2

A.4 Handbooks.A-3

A.5 OrdersA-3

A.6 Industry DocumentsA-3

APPENDIX B. TERMS AND DEFINITIONSB-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 AIRPLANESC-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 AIRPLANESD-1

D.1 Acceptable Methods of Compliance with Rechargeable Lithium Battery SCsD-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 ComplianceD-4

APPENDIX E. CORRELATION OF TRANSPORT CATEGORY AIRPLANE METHOD

OF COMPLIANCE WITH SPECIAL CONDITIONS ISSUED PRIOR TO AUGUST

2016E-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 ROTORCRAFTF-1

F.1 Regulatory Basis From Part 27 at Amendment 27-51 and Part 29 at Amendment 29-59.

.F-1

F.2 Advisory CircularsF-1

F.3 Industry DocumentF-1

F.4 Part 27 and 29 Regulations.F-2

F.5 Method of Compliance.F-2

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AC 20-184A

TABLE OF CONTENTS Paragraph Page APPENDIX G. INSTALLATION OF RECHARGEABLE LITHIUM BATTERIES FOR

SMALL AIRPLANESG-1

G.1 Applicability.G-1

G.2 Means of Compliance with Safety ObjectivesG-1

G.3 Method of Compliance with Safety ObjectivesG-2

G.4 Method of Compliance for Very Small Rechargeable Lithium Batteries Less Than 2

Watt-HoursG-5

G.5 ICA Required by § 23.1529, Appendix A to Part 23G-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 ConditionsG-7

TABLES Number Page Table 2-1. Typical Airworthiness Regulations Concerning Lithium Battery Installations ... 2-2 iv

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.

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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

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.

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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

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.

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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

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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.

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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.

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