guidance for obtaining installation approval for installed rechargeable lithium battery and battery systems on rotorcraft.
(B) Installation requirements for installed non-rechargeable lithium batteries have some common attributes with rechargeable lithium batteries. These batteries usually exhibit less capacity and a hazard risk proportional to the capacity, but may also supply a critical and required function.
1. Each non-rechargeable lithium battery installation should address the following ten objectives, which are critical for safe installation:
Objective 1: Maintain safe cell temperatures and pressures under all foreseeable operating conditions to prevent fire and explosion.
Objective 2: Prevent the occurrence of self-sustaining, uncontrollable increases in temperature or pressure.
Objective 3: Prevent any emission of explosive or toxic gases that may accumulate in hazardous quantities, either during normal operation or as a result of a failure.
Objective 4: Meet the flammable fluid fire protection requirements of § 29.863.
Objective 5: Prevent corrosive fluids or gases that may escape from damaging surrounding structure or adjacent systems, equipment, or electrical wiring.
Objective 6: Prevent any hazardous effect on rotorcraft structure or systems caused by the maximum amount of heat generated from any battery or individual cell failure.
Objective 7: Automatically control the discharge rate of each cell to prevent cell imbalance, back charging, overheating, and uncontrollable temperature and pressure.
Objective 8: Automatically disconnect the battery in the event of an overtemperature condition, cell failure, or battery failure.
Objective 9: Alert the flight crew if an equipment state or failure affects safe operation of the rotorcraft.
Objective 10: Have a means for the flight crew to determine the battery charge state (for required battery systems).
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Note: 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.
2. The following means of compliance (MOC) have been accepted to ensure that the battery meets the objectives discussed above. Some failures may still occur due to various factors beyond the control of the designer; these MOCs are also intended to protect the rotorcraft if such failures occur.
Note: Some of the methods below reference RTCA DO-347, Certification Test Guidance for Small and Medium Size Rechargeable Lithium Batteries and Battery Systems, dated December 18, 2013. Although DO-347 provides standards for small and medium size rechargeable lithium batteries, the FAA considers these tests appropriate as guidance for similar sized non-rechargeable lithium batteries. Procedures that are only applicable to rechargeable batteries (such as connecting input power) need not be performed.
When a test method specifies charging the battery before the test, a new fully charged battery should be used.
i. MOC for Objectives 1, 2 and 7:
(a) Meets the requirements in paragraph 3 of TSO-C142a, Nonrechargeable Lithium Cells and Batteries;
(b) Meets the criteria to pass in Appendix 1, Table 2 of TSO-C142a;
and
(c) Passes the following tests in RTCA Document DO- 347:
1. Section 2.3.7 Short-circuit Test of a Cell
2. Section 2.3.8 Short-circuit Test with Protection Enabled
3. Section 2.3.9 Short-circuit Test with Protection Disabled
4. Section 2.3.10 Insulation Resistance Test
5. Section 2.3.15 Thermal Runaway Containment Test: Perform step
e. of test method 2.3.15.1 in lieu of steps c. and d.
(d) Objective 1 requires that each individual cell within a battery be designed to maintain safe temperatures and pressures. These same issues are also critical at the battery level. Objective 2 requires the battery to be designed to prevent Page F - 78.9
propagation of a thermal event (i.e., self-sustained, uncontrollable increases in temperature or pressure) from one cell to adjacent cells.
ii. MOC for Objective 3: RTCA Document DO-347, section 3.1.3 discusses potential gas emissions from batteries and their effects. Acceptable means of complying with Objective 3 include using the tests required by the MOC for Objectives 1, 2 and 7 to demonstrate that all emitted gasses are contained or vented overboard through designed ports. Objective 3 does allow explosive and toxic gases to be uncontained and not vented overboard if they do not accumulate in hazardous quantities within the rotorcraft. If you choose to use the test data to demonstrate compliance by this means, explain how you will demonstrate that hazardous quantities of gases will not accumulate within the rotorcraft. If your design will have ports to vent gases overboard, ensure there is a means to protect ground personnel from exposure to these gases.
iii. MOC for Objective 4: Section AC 29.863 of this guidance, subparagraph (c), provides an acceptable method of compliance for flammable fluids.
iv. MOC for Objective 5:
(a) 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) that protects the surrounding structure and adjacent systems, equipment and electrical wiring.
(b) Any failure of the battery includes, but is not limited to, internal and external short circuit. See the tests listed in the MOC for Objectives 1, 2, and 7 for Failure Conditions that are evaluated.
v. MOC for Objective 6:
(a) Force a cell in the battery into thermal runaway by conducting the RTCA Document DO-347, section 2.3.15, Thermal Runaway Containment Test.
Perform step e. of test method 2.3.15.1 in lieu of steps c. and d. when conducting this test.
(b) Show that the effects of the heat and any related effects do not constitute a hazard to the structure or systems of the rotorcraft. 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 Objective 6.
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vi. MOC for Objective 8: A well designed disconnection system will function during the tests required by the MOC for Objectives 1, 2 and 7 except for the test in RTCA Document DO-347, section 2.3.9, where the protection is already disabled. This is one of the means of preventing the Failure Conditions discussed in the Evaluation Criteria sections of RTCA Document DO-347 for these tests. Confirm the battery automatically disconnects from its discharging circuit during these tests.
vii. MOC for Objective 9: Objective 9 specifies flight crew alerting if the failure of a battery installation, in itself or in relation to a system that performs an aircraft-level function, could result in “unsafe system operating conditions.” The alert should comply with the applicable color requirement in § 29.1322. The applicant should refer to Section AC 29.1322 for an acceptable method of compliance.
viii. MOC for Objective 10: The following are examples of “means” for flight crew or maintenance personnel to determine the battery charge state:
(a) A manually activated system (e.g., push button) that displays the available charge of each battery unit.
(b) 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.
(c) Physical access that allows a maintenance person to measure the battery charge state.
3. The MOCs for Objectives 1 through 10 are only acceptable for required functions if ICAs include a check of the battery charge state within an interval that will ensure sufficient charge for each flight considering the worst-case scenario and replacement of the battery when the charge is not sufficient.
4. MOC for Very Small Non-Rechargeable Lithium Batteries: An acceptable MOC for Objectives 1 through 8 for non-rechargeable lithium battery installations that have less than 2 watt-hours of energy is showing these batteries meet Underwriters Laboratories (UL) 1642 or UL 2054.
(ix) Part 29 Compliance. Non -rechargeable lithium battery installations should satisfy each of the MOCs identified in this guidance to comply with all applicable part 29 requirements. The following provides means of compliance and other information on some part 29 requirements:
Page F - 78.11
(A) System Safety Assessment. Although these hazard conditions require specific functionalities and capabilities and address certain critical failure modes of nonrechargeable lithium batteries and their installations, the applicant must also meet the requirements of §§ 29.1301 and 29.1309. 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 § 29.1309. Application of § 29.1309(b) and (c) may result in required periodic maintenance actions or flight crew alerting features. For example, an over-temperature warning system may be necessary to allow the flight crew 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 § 29.1309(c). Such alerts, if provided, must comply with § 29.1322.
(B) The ICA should include the following provisions to comply with § 29.1529:
1. Maintenance requirements to replace each non-rechargeable lithium battery within an interval that will ensure there is sufficient charge to power equipment.
2. 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 FAA approval for installing a different battery. Refer to the battery Original Equipment Manufacturer’s maintenance manual.
3. Procedures to ensure that each non-rechargeable lithium battery has not:
i. Experienced degraded charge retention ability or other damage during storage.
ii. 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.
iii. Precautions to prevent mishandling of replacement nonrechargeable lithium batteries prior to their installation that could result in short-circuit or other unintentional damage.
Note: Acceptable procedures for paragraphs b.(2)(ix)(B)3.i. and
b.(2)(ix)(B)3.ii. may include a quality control process for packaging, storing, maintaining, and transporting non- Page F - 78.12
rechargeable lithium batteries, including reporting of dropped or damaged batteries.
Page F - 78.13
AC 29.1355. § 29.1355 (Amendment 29-14) DISTRIBUTION SYSTEM.
a. Explanation. None.
b. Procedures.
(1) When determining compliance with the portion of the rule that concerns supplying essential circuits in the event of reasonably probable faults or open circuits, the effects of tripped circuit breakers or blown fuses should be considered.
(2) Various means may be used to ensure an energy supply. Examples include duplicate electrical equipment, throwover switching, and multichannel or loop circuits separately routed.
(3) Essential load circuits are those circuits whose functioning is required to show regulatory compliance with the certification basis. In addition to those circuits specifically required by the regulations, this definition also includes those circuits required by general rules such as § 29.1309.
(4) An independent power source includes not only the electrical power source
(e.g., generator) but other items such as a regulator or a reverse current cutout that are necessary to make the electrical power source deliver power to a distribution bus.
When a regulatory requirement exists for two independent power sources, the required items should not be shared.
(5) Electrical system faults may occur that will result in a portion of the system (feeders, buses, etc.) being lost. Where por tions of the electrical system may be switched from one power source to another to compensate for a fault, it is important that the transfer action not result in the loss of the replacement source. Circuit design should be such as to assure this will not happen.
AC 29.1355A. § 29.1355 (Amendment 29-24) DISTRIBUTION SYSTEM.
a. Explanation. Amendment 29-24 provides clarification for availability of the remaining electrical power source after a failure of one of two independent power sources.
b. Procedures. All of the policy material pertaining to this section remains in effect with the addition that an automatic or manually selectable means is required to maintain operation of the equipment or system for which the two independent power sources were required.
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AC 29-2C, Chg 4 5/1/2014 AC 29.1357. § 29.1357 (Amendment 29-24) CIRCUIT PROTECTIVE DEVICES.
a. Explanation. Circuit protective dev ices are normally installed to limit the hazardous consequences of overloaded or faulted circuits. These devices are resettable (circuit breakers) or replaceable (fuses) to permit the crew to restore service when nuisance trips occur or when the abnormal circuit condition can be corrected in flight.
b. Procedures.
(1) Overvoltage protection is specifically required for category A rotorcraft. For category B rotorcraft, the possible types of operation should be considered in combination with the presence of an overvoltage condition in the generating system.
The regulatory requirement to support this assumption is § 29.1309(b). If the presence of an overvoltage condition in the electrical system will not cause a hazard to the rotorcraft, the electrical system could be approved for category B without overvoltage protection. If a hazardous condition will result from the overvoltage condition, then overvoltage protection must be provided.
(2) Automatic reset circuit breakers, which automatically reset themselves periodically, should not be applied as circuit protective devices. If an abnormal circuit condition cannot be corrected in flight, the decision to restore power to the circuit involves a careful analysis of the flight situation. The necessity of the circuit for continued safe flight should be weighed against the hazards of resetting on a possibly faulted circuit. Such an evaluation is proper ly an aircraft crew function that cannot be performed by automatic reset circuit breakers. To ensure crew supervision over the reset operation, circuit protective devices should be of such design that a manual operation is required to restore service after tripping. Circuit breakers must be designed such that the tripping mechanism cannot be overridden by the operating control, and these circuit breakers are known as the “trip free” type.
(3) Automatic reset circuit breakers may be used as integral protectors for electrical equipment (e.g., thermal cutouts) if circuit protection is also installed to protect the cable to the equipment.
(4) If the installation of a system is required as a prerequisite to showing compliance with the regulations, it is generally considered essential to some phase of flight or it would not be required. It follows that the circuit protective devices associated with those systems are generally considered essential to safety in flight and should therefore be accessible to the flight crew in the cockpit. These devices should be also readily accessible to the flight crew in the event it becomes necessary to manage smoke caused by an electrical failure. Their accessibility should also permit the flight crew to easily determine if they are in the “tripped” position prior to flight. This includes the basic electrical system, the distribution system, and utilization systems that are required. Some examples of required utilization systems are those specified by §§ 29.1303, 29.1305, 29.1307, 29.1381, 29.1383, 29.1385, 29.1401, and 29.1431.
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Where continued safe flight to the destination is considered to be sufficiently assured, certain required circuits have been excepted from being accessible to the crew in the cockpit. Voltmeter and ammeter circuit protec tive devices are examples of ones that have been excepted. Some utilization systems, although not specifically required by part 29, may be required because of the particular design presented for certification.
Circuit protective devices for systems in this category are considered required and must be accessible.
(5) The following are considered acceptable compliance with the “readily reset” provision of § 29.1357(d).
(i) For a crew of two pilots, it is satisfactory for one of the crewmembers to move his seat and loosen his shoulder harness in order to properly identify and reset or replace a circuit protective device. It is not satisfactory for one of the crewmembers to leave his crew station to reset the circuit protective device.
(ii) For a single pilot situation, with the seat belt and shoulder harness normally adjusted, the circuit protective device location should allow for identification of the opened circuit protector and reset capability while the pilot is flying the rotorcraft.
(6) A switch is a device intended for regular use to open or close a circuit. A circuit breaker is a device that protects a circuit by opening automatically at a predetermined current overload. Systems should be designed such that the primary means to remove or reset the power supply in normal operations is by means of a switch. The use of a circuit breaker for such normal operations is unacceptable, as it is not being used for its intended function.
Note: A switch-rated circuit breaker may be used for this function if it can be shown to be suitable for the number of switch cycles expected to be performed during the service life of the system.
(7) If fuses are used, there should be spare fuses for use in flight equal to at least 50 percent of the number of fuses for each rating required for complete circuit protection. This only applies to fuses used to protect systems that are required to show compliance with the regulations. Spare provisions need not be made for non-required convenience type installations, although it is encouraged. The spare fuses should be stored in a location where they are readily accessible to the crew. If not directly visible to the crew, information regarding location of the spare fuses should be provided. One acceptable location is on the fuse panel in a holder with no wire terminations and identified “spare” with the “size.”
(8) Refer to MG 2 of this AC for specific tests of circuit protection for the total electrical system.
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AC 29-2C, Chg 4 5/1/2014 AC 29.1357A. § 29.1357 (Amendment 29-24) CIRCUIT PROTECTIVE DEVICES.
a. Explanation. Amendment 29-24 to the regulations provides the requirements for automatic reset circuit breakers and expands the requirements for disconnecting power sources and transmission equipment to include other malfunctions besides overvoltage. The overvoltage protection requirements are extended to both Category A and Category B rotorcraft. Clarification was added to the requirement for each essential load to have individual circuit protection.
b. Procedures.
(1) All of the policy material pertaining to this section remains in effect except that protection from hazardous overvoltage and other malfunctions that would damage equipment should be provided for both Category A and Category B rotorcraft. The protective sensing/switching devices should disconnect the overvoltage or other malfunctions with sufficient speed to prevent user equipment damage.
(2) In addition, each essential load should have individual circuit protection.
This generally means each electrical power consuming device should have individual protection. An exception may be simple syst ems with multiple lights in a single lighting system which would, in most cases, require only one circuit protective device. The decision of whether one or more protective devices are required, is based on how independent each of the loads should be to one another and what the penalty would be if one load faulted and deprived the remaining loads of electrical power.
Page F – 82
AC 29.1359. § 29.1359 ELECTRICAL SYSTEM FIRE AND SMOKE PROTECTION.
a. Explanation. This regulation requi res that all electrical system components meet the applicable fire and smoke protection provisions of §§ 29.831 and 29.863, and further requires that certain items in designated fire zones must be at least fire resistant.
This regulation becomes very significant when failure conditions are considered, and in accordance with the provisions of § 29.831 “reasonably probable failures” must be considered when assuring compliance.
b. Procedures.
(1) When selecting a type of wire, the burning characteristics of that wire are important. Both composition and quantity of resultant smoke and fumes should be considered. The impact of the smoke and fu mes on the aircraft cabin occupants should be accounted for.
(2) Wire qualified to MIL-W-25038 is normally used in circuits that “must be at least fire resistant.” Wire qualified to ot her specifications may also be satisfactory;
however, the provisions of the other specifications should be compared to the provisions of MIL-W-25038 to assure the critical areas are not compromised.
(3) Electrical connectors that are located in a designated fire zone and are used in emergency procedures should be at least fire resistant and capable of maintaining the integrity of the circuit. When evaluati ng these connectors, careful attention should be directed to the entire connector (the contact, the insert, and the shell).
(4) Wire insulated with KAPTON® polyimide film manufactured to MIL-W-81381A, has been used in aeronautical products with varying degrees of success. The U.S. Navy had such a bad service history with KAPTON ® insulated interconnect wire in aircraft that in the mid-1980’s the Navy no longer allowed the use of KAPTON® insulated wire. Although the FAA/AUTH ORITY has taken no such action, the use of KAPTON® insulated wire requires very special handling. The following areas should be observed when utilizing KAPTON® insulated wire:
(i) The instructions in the KAPTON® wire “Handling Manual” should be strictly followed. This manual may be obtained from E.I. Du Pont de Nemours and Company, Polymer Products Department, Industrial Film Division, Wilmington, Delaware 19898.
(ii) Use in special wind and moisture problem (SWAMP) areas, such as wheel wells, usually requires additional protection for the cable bundles.
(iii) The wire should not be exposed to a combination of either high stress (U.V. or physical) in the presence of water, high humidity, or high pH factor liquids.
Page F – 82.1
AC 29-2C, Chg 4 5/1/2014
(iv) The stiffness and permanent set (memory) of KAPTON® may cause chafing in unrestrained bundles or where KAPTON® insulated wire is bundled with wires of other insulation types.
(v) Care should be exercised in the stripping, stamping, and terminating of KAPTON® insulated wires.
NOTE: KAPTON® is a registered trademark of E.I. Du Pont de Nemours and Company.
Page F – 82.2