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
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.
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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.
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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.
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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
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
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.
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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:
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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
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.
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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.
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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.
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