For the purpose of this appendix, both a battery and battery system is referred to as a battery. A battery system consists of the battery and any protective, monitoring, and alerting circuitry or hardware inside or outside of the battery. It also includes vents (where necessary) and packaging. The Federal Aviation Administration (FAA) has issued several special conditions (SCs) for non-rechargeable lithium battery installations on transport category airplanes (and these SCs have been adopted by the DASA). These SCs are provided in Appendix C of this Annex.
This appendix provides an acceptable method of compliance with the non-rechargeable lithium battery SCs in Appendix C of this Annex and related 14 CFR part 25 requirements. It also provides guidance related to the applicability statements in previously issued non-rechargeable lithium battery SCs.
RTCA/DO-227A, Minimum Operational Performance Standards (MOPS) for Non-Rechargeable Lithium Batteries, sections 1 Purpose and Scope and 2 Equipment Performance Requirements and Test Procedures, provide design requirements and guidelines that are pertinent to designing safe batteries and to meeting part 25 installation requirements and these SCs. Consider each of these requirements and guidelines when designing cells and batteries.
Special Conditions 1 and 2 below 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 many of which are beyond the control of the designer. Therefore, these SCs as a whole are intended to protect the airplane and its occupants even when a failure occurs. These SCs are independent of each other. Demonstrating compliance with one of these SCs does not constitute compliance with the other SCs. The methods of compliance are as follows:
D.1.1 Method of Compliance (MOC) for SC 1. Show that the individual cells meet the requirements in RTCA/DO-227A, section 2.2.1 Cell Functional and Safety Requirements. Use the test procedures in RTCA/DO-227A, section 2.4.1 Cell Test Procedures and Criteria and show that the associated evaluation criteria are met.
D.1.2 Method of Compliance for SC 2. Whereas, SC 1 requires that each individual cell within a non-rechargeable lithium battery be designed to maintain safe temperatures and pressures, SC 2 addresses these same issues but for the entire battery. Special Condition 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. Show that the battery installation meets the requirements in RTCA/DO-227A, sections 2.2.2 Battery Functional and Safety Requirements and 2.2.3 End Item Functional and Safety Requirements. Use the test procedures in RTCA/DO-227A, sections 2.4.2 Battery Test Procedures and Criteria and 2.4.3 End Item Test Procedures and Criteria and show that the associated evaluation criteria are met. RTCA/DO-227A, section 2.2.2 states, “If a single-cell battery is identical to the cell being tested for qualification, then the battery tests in this section shall be conducted unless they are identical to the cell tests.” In these cases, where the battery tests are identical to the cell tests, show that the cell tests are met in lieu of the battery tests to support demonstrating compliance with SC 2.
D.1.3 Method of Compliance for SC 3 – 6. Use the worst case test data from the MOCs for SCs 1 and 2 to support demonstrating compliance with SCs 3 - 6. The DASA considers that the RTCA/DO-227A, section 2.4.3.2.2 End Item Thermal Runaway Containment Test usually provides these worst case data.
D.1.4 Method of Compliance for SC 3. RTCA/DO-227A, appendix A, section A.5 Battery Emission Hazard discusses potential gas emissions from batteries and their effects. An acceptable MOC with SC 3 includes using the tests required under SCs 1 and 2 to demonstrate that all emitted gases are contained or vented overboard (i.e., vented outside the airplane) through designed ports. Section D.2.1 System Safety Assessment of this policy statement provides guidance for conducting a system safety assessment for a design that vents these gases overboard. Special Condition 3 does allow explosive and toxic gases to be uncontained and not vented overboard, provided 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) when demonstrating compliance by this means.
D.1.5 Method of Compliance for SC 4. The amendment level of 25.863 is determined by 14 CFR 21.17 or 21.101, as appropriate. The amendment level is not determined by the issuance or effective date of the special conditions. The Aviation Rulemaking Advisory Committee (ARAC) draft Advisory Circular (AC) 25.863-1, Flammable Fluid Fire Protection (Aviation Rulemaking Advisory Committee (ARAC) draft Advisory Circular (AC) 25.863-1 http://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/TAEpihT5-9231998.pdf4) 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. When applying 25.863 to a battery installation, as explicitly 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. 25.1309(c) in accordance with FAA Policy Statement PS-ANM-100-00-113-1034, dated January 4, 2001.
D.1.6 Method of Compliance for SC 5. Show that when 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.1.7 Method of Compliance for SC 6. Show that the effects of the heat, and any related effects, from the tests performed under SCs 1 and 2 do not constitute a hazard to the structure or systems of the airplane. 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.1.8 Method of Compliance for SC 7. Pursuant to 25.1309(c), SC 7 requires flightcrew alerting when 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 AC 25.1309-1A System Design and Analysis for guidance. The ARAC recommended draft AC 25.1309-Arsenal, System Design and Analysis, dated June 10, 2002, also provides guidance that may be applied to a project if the applicant receives an equivalent level of safety finding to 25.1301 and 25.1309(c) in accordance with FAA Policy Statement PS-ANM-100-00-113-1034, dated January 4, 2001.
D.1.9 Method of Compliance for SC 8. The following are examples of “means” by which the flightcrew or maintenance personnel to determine the battery charge state:
A manually activated system (e.g., push button) that displays the available charge of each battery unit.
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.
Physical access that allows a maintenance person to measure the battery charge state.
The above “means” are acceptable only when the Instructions for Continued Airworthiness (ICA) include a requirement for a person to check the battery charge state within an interval that will ensure sufficient charge for the entire flight and to replace the battery when the charge is not sufficient.
D.1.10 Method of Compliance for Very Small, Button/Coin Non-Rechargeable Lithium Batteries. An acceptable MOC with SCs 1 through 6 for button/coin non-rechargeable lithium battery installations that have less than 2 watt-hours of energy is showing these batteries meet Underwriters Laboratories (UL) 1642.
Non-rechargeable lithium battery installations must comply with these SCs and all applicable part 25 and part 26 requirements. The following provides methods of compliance and other information for pertinent part 25 requirements:
D.2.1 System Safety Assessment. Pursuant to 25.1301, 25.1309 and 25.1709, and these SCs requirements for specific functionalities and capabilities, address certain critical failure modes of non-rechargeable lithium batteries and their installations, the applicant must also meet the requirements of 25.1301, 25.1309 and 25.1709, when applicable, in addition to these SCs. To date, in-service experience has shown that non-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. For button/coin batteries that have less than 2 watt-hours of energy and meet UL 1642, use the data from UL 1642 to support demonstrating compliance with 25.1309. For other non-rechargeable lithium batteries, use the worst case test data from section D.1.1 Method of Compliance for SC 1 and section D.1.2 Method of Compliance for SC 2 to support demonstrating compliance with 25.1309. As part of showing compliance with 25.1309, the applicant is to demonstrate that particular risks, as identified in SAE ARP 4761, Guidelines and Methods for Conducting Safety Assessment Process on Civil Airborne Systems and Equipment, such as 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 non-rechargeable lithium battery installations. For example, the applicant is to consider the effects of particular risks on any containment and venting provisions for a non-rechargeable lithium battery.
Application of 25.1309(b) and (c) 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 25.1309(c). Such alerts, when provided, must meet 25.1322. Refer to AC 25.1309-1A, AC 25.1322-1 Flight Crew 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.
Venting toxic and explosive gases from a non-rechargeable lithium battery failure through designed ports that lead outside of the airplane is a MOC with SC 3 as discussed in section D.1.4 Method of Compliance for SC 3. Pursuant to 25.1309, consider the hazards of exposure of these gases to ground personnel, air conditioning in-take and engine in-takes.
D.2.2 Section 25.1353 Electrical Equipment and Installations. Pursuant to 25.1353(b) and (c), each SC states that it applies to all non-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 to the other paragraphs of 25.1353.
D.2.3 Section 25.1529 Instruction for Continued Airworthiness (ICA). Pursuant to 25.1529, include in the ICA the following to show compliance with the regulation:
Maintenance requirements to replace each non-rechargeable lithium battery within an interval that will ensure there is sufficient charge to power equipment.
A requirement to only replace non-rechargeable lithium batteries with batteries from the same manufacturer with the same part number or to obtain a new approval for installing a different battery. Refer to the battery original equipment manufacturer maintenance manual.
Procedures to ensure that each non-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.
Precautions to prevent mishandling of replacement non-rechargeable lithium batteries prior to their installation which could result in short-circuit or other unintentional damage.
Acceptable procedures for item 3.b. above may include a quality control process for packaging, storing, maintaining and transporting non-rechargeable lithium batteries, including reporting of dropped or damaged batteries.
D.2.4 Section 25.1729 Electrical Wiring Interconnection Systems (EWISs) ICA. Pursuant to 25.1729, Electrical Wiring Interconnection Systems (EWISs) maintenance and inspection tasks required are to ensure that EWIS components associated with non-rechargeable lithium batteries are sufficient to prevent degradation of any EWIS component that is designed and installed to support compliance with these SCs.
D.2.5 Sections 25.903(d) and 25.1309 Uncontained Engine or Auxiliary Power Unit (APU) Rotor Failures. Pursuant to 25.1309, the applicant is expected to demonstrate that a foreseeable event originating from outside of a non-rechargeable lithium battery, such as an uncontained rotor burst, will not compromise continued safe flight and landing. An applicant may propose fail-safe design features that encase and safely vent the hazardous by-products of a failure originated from within the battery to show compliance with the non-rechargeable lithium battery SCs. However, a rotor failure could defeat such safety features depending on the location of the battery installation. If an applicant proposes to install a non-rechargeable lithium battery in a rotor burst zone, the applicant must ensure the means of compliance to the SCs remain effective considering potential rotor failures that could damage the battery.
Regarding compliance to 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 non-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 non-rechargeable lithium battery SCs. In this case, provide a proposed method of compliance to the DASA. Alternatively, locate the battery outside of the rotor burst zone.
As explained in Appendix C, the FAA determined from non-rechargeable lithium battery incidences that part 25 does not contain adequate safety standards for installing these batteries on transport category airplanes. The FAA addressed this issue on new certification projects for transport category airplanes by requiring changes involving non-rechargeable lithium batteries to comply with special conditions. However, the FAA previously approved many non-rechargeable lithium battery installations that were not shown to comply with special conditions. Therefore, to improve the safety of follow-on airplanes that are delivered with these installations, the FAA included a paragraph in the applicability section of non-rechargeable lithium battery special conditions similar to the following:
These special conditions are not applicable to changes to previously certified non-rechargeable lithium battery installations where the only change is either cosmetic or to relocate the installation to improve the safety of the airplane and occupants. Previously certified non-rechargeable lithium battery installations, as used in this paragraph, are those installations approved for certification projects applied for on or before the effective date of these special conditions. A cosmetic change is a change in appearance only, and does not change any function or safety characteristic of the battery installation. These special conditions are also not applicable to unchanged, previously certified non-rechargeable lithium battery installations that are affected by a change in a manner that improves the safety of its installation. The FAA determined that these exclusions are in the public interest because the need to meet all of the special conditions might otherwise deter these design changes that improve safety.
This statement is intended to allow the Authority or type certificate holders to identify approved lithium battery installations that are a fire safety concern, which are not necessarily unsafe such that the Authority would issue an airworthiness directive, and implement a design change that improves the safety of it on follow-on airplane deliveries without having to show compliance with the special conditions. The FAA considered that requiring new substantiation data for meeting the special conditions may prevent type certificate holders from implementing these improvements.
The special condition applicability exclusion, which relates to improving the safety of previously approved installations, only applies to the below conditions and each condition must be met:
A change to a baseline airplane type certificated on or before the effective date of the special condition. That is, the follow-on airplane change must be compared to a single, baseline airplane (i.e., a distinct serial number airplane). Other changes between the follow-on airplane and baseline airplane may exist, but all of those changes must be approved as part of the follow-on airplane changes. Otherwise, the proposed baseline airplane is not actually the baseline airplane.
Previously approved non-rechargeable lithium battery installations on baseline airplanes where a fire safety concern, which may not be considered unsafe such that the Authority would issue an airworthiness directive, is identified. This exclusion does not cover a situation where a battery is moved to an arguably better location, but either location is considered fine in terms of fire safety.
A change that provides a substantial, fire safety improvement.
For minor software changes to avionics devices that contain non-rechargeable lithium batteries, where the software functional changes have no effect on and are not affected by an existing installed battery. Applicants should demonstrate that the change has no effect on the battery or the associated special conditions.
Applicants, who propose to use this special condition applicability exclusion statement, should provide the DASA information to show how their proposal meets each of the above conditions. This includes providing a detailed assessment of the battery installation on the baseline airplane and the improvement due to the proposed change considering a battery thermal runaway failure for both installations. The assessment should:
Consider the battery thermal runaway effects of heat, explosive energy, projecting debris and toxic gases.
Address the proximity of the battery to occupants, critical systems and equipment, structure, and any other installations that could be a hazard if exposed to a battery thermal runaway (e.g., oxygen bottles/lines, fuel lines).