CHAPTER 10. AIRCRAFT BATTERY INSTALLATIONS SECTION 1. GENERAL 1000. PURPOSE. This chapter contains structural and design considerations for the fabrication of aircraft battery installations.
1001. HAZARDS AND WARNINGS:
HANDLING PRECAUTIONS. Serious injury can result from carelessness while handling and working with batteries. Failure to heed these warnings could result in serious injury or death.
a. All tools must be insulated.
b. Care must be taken with all metal items to include clothing items such as belt buckles, zippers, metal fasteners and wallet chains, as well as jewelry items such as rings, watches, bracelets, and necklaces. All metal or conductive articles should be removed from your person when handling batteries.
c. Wear protective clothing and eye protection. The electrolyte can cause burns if in contact with skin or eyes. Do not touch eyes, nose, or mouth after handling batteries or acid.
d. Do not smoke or hold naked flames near batteries on charge. If allowed to accumulate in a confined space, the gases emitted during charge could cause an explosion. To prevent the accumulation of hydrogen gas in the manifold, do not charge a flooded electrolyte or vented battery on the bench with the cover on.
e. Do not service flooded or vented lead-acid and nickel-cadmium batteries in the same shop area, as cross contamination of acid and alkaline electrolytes may happen.
f. Always pour acid into water, NEVER pour water into acid.
g. Do not use petroleum spirits, trichloroethylene, or other solvents.
h. Know the location and use of emergency eyewash and shower nearest the battery charging area.
1002. ADDITIONAL REFERENCES (current editions).
a. AC 20-106, Aircraft Inspection for the General Aviation Aircraft Owner.
b. AC 43-4, Corrosion Control for Aircraft.
c. AC 120-27, Aircraft Weight and Balance Control.
d. Civil Aviation Regulation 6, Rotorcraft Airworthiness; Normal Category.
e. Federal Aviation Administration (FAA)-H-8083-1, Aircraft Weight and Balance Handbook.
f. FAA-H-8083-19, Plane Sense General Aviation Information.
1003. LOCATION REQUIREMENTS. The battery installation and/or its installation should provide:
a. Accessibility for Battery Maintenance and Removal. The installation should ensure that the battery could be easily installed or removed and serviced without removing seats, fairings, etc.
b. Protection from Engine Heat. If installed in the engine compartment the battery should be protected from extreme heat both during engine operation and after the engine has been shut down.
This kind of protection can be provided by a source of cooling air to the battery box or additional thermal Par 1000 Page 107
protection around the battery. Care should be taken not to interfere with the flow of engine-cooling air.
c. Protection from Mechanical Damage .
Vibration and other shock loads are a major cause of short battery life. Install the battery in a location that will minimize damage from airframe vibration and prevent accidental damage by passengers or cargo.
d. Passenger Protection. Insure that the battery is enclosed within a container/box so that passengers/crew are protected from any fumes or electrolytes that may be spilled as a result of battery overheating, minor crash, or un-intentional inverted flight.
e. Airframe Protection . To minimize damage to adjacent metal structures, fabric covering or electrical equipment can be accomplished by properly locating battery drains and vent discharge lines, and adequately venting the battery compartment. To protect the airframe structure and fluid lines apply asphaltic or rubber-based paint to the areas adjacent to and below the battery or battery box.
1004. AIRCRAFT STORAGE BATTERY DESIGN AND INSTALLATION.
a. Lead Acid.
(1) Each aircraft storage battery, whether approved to a Technical Standards Order (TSO) or not, must be designed as required by regulation and installed as prescribed by the manufacturer.
(2) No explosive or toxic gases emitted by any battery in normal operation, or as the result of any probable malfunction in the charging system or battery installation, may accumulate in hazardous quantities within the airplane.
(3) Corrosive fluids or gases that may escape from the battery may damage surrounding structures or adjacent essential equipment.
b. Nickel Cadmium.
(1) Each aircraft storage battery, whether approved to a TSO or not, must be designed as required by regulation and installed as prescribed by the manufacturer.
(2) Safe cell temperatures and pressures must be maintained during any probable charging and discharging condition. No uncontrolled increase in cell temperature may result when the battery is recharged (after previous complete discharge).
(a) At maximum regulated voltage or power;
(b) During a flight of maximum duration; and
(c) Under the most adverse cooling condition likely to occur in service.
(3) Compliance with paragraph 1004b(2) must be shown by tests unless experience with similar batteries and installations has shown that maintaining safe cell temperatures and pressures presents no problem.
(4) No explosive or toxic gases emitted by any battery in normal operation, or as the result of any probable malfunction in the charging system or battery installation, may accumulate in hazardous quantities within the airplane.
(5) Corrosive fluids or gases that may escape from the battery may damage surrounding structures or adjacent essential equipment.
1005. DUPLICATION OF THE MAN- UFACTURER’S INSTALLATION. The availability of readymade parts and attachment fittings may make it desirable to consider the location and/or type of installation selected and designed by the airframe manufacturer. Appreciable savings in time and work may be realized if previously approved data and/or parts are used.
1006. OTHER INSTALLATIONS. If the battery installation has not been previously approved, or if the battery is to be installed or Par 1003 Page 108
Par 1005 Page 109 relocated in a manner or location other than provided in previously approved data, perform static tests on the completed installation as outlined in chapter 1.
Because of the concentrated mass of the battery, the support structure should also be rigid enough to prevent undue vibration or undue shock, which may lead to early structural failure.
1007. DELIVERY INSPECTION. When the battery is unpacked, a thorough inspection should be made to ensure that no damage occurred during shipment. Inspect the shipping container as well as the battery. Before putting the battery into service, perform a safety check by following these points carefully.
a. Damage. See if any liquid has spilled into the shipping container. This may indicate that a cell is damaged. Check for dented, cracked, or discolored areas on the sides and bottom of the battery case. Check for cracked cell cases or covers.
Do not place a damaged battery into service.
b. Shorting Straps. Some nickel-cadmium batteries are shipped with shorting devices across the main power receptacle output terminals. Before subjecting a battery to electrical service this device must be removed.
c. Electrical Connections. Test all terminal hardware to ensure tightness. Poor electrical contact between mating surfaces may reduce discharge voltage, cause local overheating and damage the battery.
NOTE: Before charging the battery read and become familiar with the manufacturer’s charge procedures.
1008. BATTERY INSTALLATION AND REMOVAL. The following instructions are generic. See the airframe manufacturer’s maintenance manuals or STC for instructions specific to a particular aircraft model.
a. Removal.
(1) Set master switch to the OFF position and tag the switch.
(2) Disconnect any external power supply.
(3) Open battery compartment access panels.
(4) Disconnect battery quick disconnect plug or remove terminal bolts and disconnect battery cables from battery terminals. Always disconnect the ground cable first and install the ground cable last.
(5) Disconnect battery ventilation tubes, if any.
(6) Unlock battery hold down clamps or remove battery hold down bars. Disengage battery.
(7) Carefully remove battery.
WARNING: Batteries are heavy.
Use appropriate lifting devices or equipment. Use battery handles where provided.
b. Installation.
(1) Inspect the battery for damage.
Cracks in metal or plastic containers are not permitted. Dents in metal containers that impinge on the interior plastic container are not acceptable.
(2) Set master switch to the OFF position and tag (explain what should be on the tag “Do not turn on master switch”).
(3) Disconnect any external power supply and tag (explain what should be on the tag “Do not connect external power”).
(4) Open battery compartment access panels.
(5) Ensure the battery container or tray is clean and dry. Treat and paint any corrosion areas.
(6) Install battery in battery container or tray.
WARNING: Batteries are heavy.
Use appropriate lifting devices or equipment. Use battery handles where provided.
(7) Engage battery hold down hardware, torque and safety wire per airframe manufacturer’s maintenance manual.
(8) Connect battery vent tubes.
(9) Connect battery quick disconnect plug, any auxiliary connector or for ring terminals, install with bolt and lock washer. Torque terminal bolts as recommended by the manufacturer.
(10) Replace electrical compartment access panel.
(11) Perform an operational test.
(12) Update aircraft weight and balance data, if necessary.
(13) Update equipment list, if applicable.
(14) Make a log book entry with battery serial number and date of installation.
1009. THRU 1012. RESERVED
FIGURE 10-1. TYPICAL BATTERY INSTALLATION IN THE AIRCRAFT
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SECTION 2. LEAD ACID BATTERY INSTALLATIONS 1013. GENERAL. In a lead acid battery the voltage will slowly drop as opposed to a nickelcadmium battery. These batteries are typically less expensive, do not require temperature sensor monitoring, require virtually no maintenance, and when unable to meet the manufacturer’s capacity requirements, are simply removed and replaced.
1014. BATTERY BOX. The battery box should have an open drain in case the electrolyte overflows.
The box should be vented to prevent an accumulation of flammable hydrogen gas.
1015. SECURING THE BATTERY. Install the battery in such a manner as to hold the battery securely in place without subjecting it to excessive localized pressure, which may distort or crack the battery case. Apply paralketone, heavy grease, or other comparable protective coating to battery cables terminal nuts/connectors. Ensure that proper torque is applied to the terminal nuts/connectors. Do not over tighten terminal nuts, which may result in fracturing of the terminal posts. Provide adequate clearance between the battery and any bolts and/or rivets which may protrude into the battery box or compartment.
WARNING: When installing or removing a battery, wear safety glasses and take special care to ensure that no sparks are created by tools, or loose jewelry that provide a short to ground. Always remove the ground cable first and install it last. If possible, attach the ground cable to the frame of the battery compartment. Do not lift the battery by their vent tubes, receptacles or terminals.
1016. SUMP JAR. Lead acid batteries are often installed with a sump jar in the exhaust vent that neutralizes vented acid fumes to protect the airframe from corrosive battery acid. If installed, the sump jar should have a capacity of approximately one pint.
The jar should contain a 1/2” think pad saturated with a 5-percent solution of sodium bicarbonate (baking soda) in water or about 3/8” of dry sodium bicarbonate. The inlet tube carrying fumes to the sump should extend into the jar about 1” from the lid. (See Figure 10-2.)
FIGURE 10-2. TYPICAL BATTERY INSTALLATION WITH SUMP JAR
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1017. VENTING. Provide suitable venting to the battery compartment to prevent the accumulation of the hydrogen gas expelled during operation.
NOTE: Valve regulated lead acid batteries can use the same ventilation system as the original nickelcadmium battery.
a. Manifold Type. In this type of venting, one or more batteries are connected, via the battery manifold(s) or battery box vents, to a hose or tube manifold system as shown in Figure 10-3. Fasten such hoses securely to prevent shifting and maintain adequate bend radii to prevent kinking.
(1) The upstream side of the system is connected to a positive pressure point on the aircraft, and the downstream side is usually discharged overboard to a negative pressure area. It is advisable to install a battery sump jar in the downstream side to neutralize any corrosive vapors that may be discharged.
(2) When selecting these pressure points, select points that will always provide the proper direction of airflow through the manifold system during all normal operating attitudes. Reversals of flow within the vent system should not be permitted when a battery sump jar is installed, as the neutralizing agent in the jar may contaminate the electrolyte within the battery.
FIGURE 10-3. BATTERY VENTILATION SYSTEM
b. Free Airflow Type. Battery cases or boxes that contain louvers may be installed without an individual vent system, provided that:
(1) The compartment in which the battery is installed has sufficient airflow to prevent the accumulation of explosive mixtures of hydrogen;
(2) Noxious fumes are directed away from occupants; and
(3) Suitable precautions are taken to prevent corrosive battery fluids or vapors from damaging surrounding structure, covering, equipment, control cables, wiring, etc.
1018. DRAINS. Position battery compartment drains so that they do not allow spillage to come in contact with the aircraft during either ground or flight attitudes. Route the drains so they have a positive slope without traps. Drains should be at least 1/2” in diameter to prevent clogging.
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1019. ELECTRICAL INSTALLATION.
a. Electrical equipment, controls, and wiring must be installed so that operations of any one unit or system of units will not adversely affect the simultaneous operation of any other electrical unit or system essential to safe operation. Any electrical interference likely to be present in the airplane must not result in hazardous effects upon the airplane or its systems.
b. Cables/Connectors. Use cables and/or connectors that are adequately rated for the current demand and are properly installed. (See AC 43.13-1, Acceptable Methods, Techniques, and Practices-Aircraft Inspection and Repair (as amended), chapter 11.) Cable size can also be selected by using the same gage as used on a previously approved production aircraft with the same battery.
(1) The cables should be of sufficient length to prevent undue strain on the battery connector or terminals.
(2) Clamp and protect cables, including the bus, in a secure manner. Since the batteries are not generally fused, any fault in the battery feeder cable could cause loss of the battery electrical system in addition to a possible fire hazard.
(3) Route cables so that cable or terminals cannot short to the battery case or to the hold-down frame.
(4) Route cables outside the battery box whenever practicable to prevent corrosion by acid fumes. When internal routing is unavoidable, protect the cable inside the box with acid-proof tubing.
(5) Assure that cables will not be inadvertently reversed on the battery terminals either by proper cable lengths and clamps or, if this is not practical, use conspicuous color coding.
c. Cable installation must be designed and installed as follows:
(1) Means of permanent identification must be provided for electrical cables, connectors, and terminals.
(2) Electrical cables must be installed and secured so that the risk of mechanical damage and/or damage caused by fluids, vapors, or sources of heat, is minimized.
d. When installing lead acid batteries in place of nickel-cadmium batteries some airframes require deactivation or removal of the temperature monitoring systems. Generally this alteration requires a flight manual supplement to override the emergency procedures regarding battery overheating.
NOTE: FAA field approval or STC is required for this kind of alteration.
e. Battery Cutoff. Install a battery cutoff relay to provide a means of isolating the battery from the aircraft's electrical system. An acceptable battery cutoff circuit is shown in Figure 10-4. Mount the relay so that the cable connecting the relay to the battery is as short as feasible to reduce the possibility of a fire occurring because of a short within this section of cable.
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FIGURE 10-4. TYPICAL BATTERY CUTOFF AND GENERATOR ALTERNATOR CONTROL
CIRCUIT
1020. QUICK DISCONNECT. Look for and replace the terminal pins when:
a. Excessive pitting or corrosion cannot be removed.
b. Signs of burning or arcing.
c. Cracked part or housing.
d. Excessive wear on contact pins, socket lock pins, or worm screw.
e. Large deposits form on contacts or plastic is discolored.
f. Excessively loose handle and locking assembly.
NOTE: Most manufacturers sell or provide dimensions for tools to check the fit of the quick disconnect sockets.
1021. WEIGHT AND BALANCE. After installation or alteration with the replacement battery the weight and balance of the aircraft should be recomputed if:
a. The weight of the replacement battery is different from that of the original battery.
b. The location of the battery is different from that of the original battery.
NOTE: Weight and balance procedures for aircraft are contained in AC 43.13-1 (as amended), chapter 10.
1022. THRU 1024. RESERVED Par 1020 Page 114
SECTION 3. NICKEL-CADMIUM BATTERY INSTALLATIONS 1025. GENERAL. Nickel-cadmium batteries fulfill a need for a power source that will provide large amounts of current, fast recharge capability, and a high degree of reliability. Nickel-cadmium batteries produce a constant voltage and can operate at lower temperatures. They are generally more expensive to purchase.
1026. ELECTRICAL ANALYSIS. The amperehour capacity of a nickel-cadmium battery is selected to accommodate the aircraft load requirements. When making this selection, the following items should be considered:
a. The low internal resistance permits it to recharge very quickly. This high recharge rate can exceed the generator rated capacity and deprive essential circuits of necessary operating current.
Total system load (battery recharging plus system loads) must not exceed the pre-established electrical capacity of the generator system.
b. Compare the discharge characteristics curves of the batteries to make sure a reduced capacity nickel-cadmium battery is adequate regarding the following:
(1) Ability to provide engine starting or cranking requirements. Some turbine engines require an initial surge of approximately 1200 amperes, which tapers off within 10 seconds to approximately 800 amperes cranking current. Reciprocating engines require approximately 100 to 200 amperes cranking current.
(2) Ability to provide sufficient capacity for low temperature starting. Nickel-cadmium batteries deliver their rated capacity when the ambient temperature range is 70°F to 90°F. For best engine cranking, replacement batteries with increased capacity will offset the lower power or reduced capacity available when the batteries are cold soaked.
(3) Some nickel-cadmium batteries deliver greater power at temperature extremes than comparable rated lead acid batteries; take care not to overload the cables and connectors.
1027. MAINTENANCE CONSIDERATIONS.
To provide for ease of inspection and because nickel-cadmium batteries are generally not serviced in the aircraft, it is important that the battery be located where it can easily be inspected, removed, and installed. Some battery cases are designed with view ports on each side of the case for visual monitoring of the cell electrolyte level. If this type of case is to be used, carefully consider the location of the battery compartment to accommodate this feature.
1028. STRUCTURAL REQUIREMENTS.
Most lead-acid battery compartments provide adequate structure attachment for the installation of nickel-cadmium batteries. However, cantilever supported battery boxes/compartments may not be suitable for nickel-cadmium battery installations unless modified to compensate for an increased over-hang moment. This may be caused by a change in battery shape and center of gravity (CG) location even though the replacement battery may weigh less than the original lead-acid battery. Whenever the total installation weight and/or the overhang moment exceed those of the original installation, perform a static test as outlined in chapter 1. If the battery compartment is to be relocated, follow the location requirement procedures outlined in paragraph 3.
1029. ISOLATION OF BATTERY CASE.
Because of the material from which nickel-cadmium battery cases are generally made (stainless or epoxy coated steel), it is desirable to electrically isolate the case from the aircraft structure. This will eliminate the potential discharge current produced when spillage or seepage of the electrolyte provides a current path between the cell terminal or connector and the exposed metal of the battery case.
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NOTE: Epoxy coated nickel cadmium battery cases serve to isolate the battery from the airframe thus eliminating electrical leakage to ground. Some batteries use a series of liners that are inside the battery. This isolates the battery from the airframe and helps eliminate electrical leakage to ground.
1030. VENTILATION. During the charging process, nickel-cadmium batteries produce hydrogen and oxygen gases. This occurs near the end of the charging cycle when the battery reaches what is called the gassing potential. To avoid a buildup of these gases, and possible accidental ignition, ventilation should be provided to evacuate this gas from the aircraft. There are two types of nickelcadmium battery cases, one with vent nozzles and one with viewports.
a. The vent nozzle type utilizes vent hoses to evacuate the gas overboard by use of forced air or by venturi effect.
b. Battery cases with viewports or louvers must have airflow sufficient to keep the mixture of air and hydrogen below 4 precent. The gases from this type of case are ev acuated into the battery compartment. Regardless of the ventilation system used, the airflow should be provided at a minimum rate of 0.040 cubic feet per minute (CFM), this equates to 1.13 liters per minute (lpm).
1031. PRE-INSTALLATION REQUIRE- MENTS. Inspect the replacement battery for possible damage incurred during shipment or storage. Give particular attention to signs of spilled liquid within the shipping container, as it may indicate a damaged cell. Follow procedures outlined in section 2 for battery venting and electrical connections.
a. Pre-installation Battery Servicing. Check the following in accordance with the battery manufacturer's instructions:
(1) Remove the shipping plugs (if used) and clean and install the filler cap vent plugs.
(2) Check the tightness of terminal hardware including each cell connector strap to the proper torque values.
(3) Check the polarity of each cell to be sure they are connected in the proper series or sequence.
(4) Prepare the battery for installation in accordance with the manufacturer’s requirements.
b. Compartments or battery boxes which have previously housed lead-acid batteries must be washed out, neutralized with ammonia or a baking soda solution, allowed to dry thoroughly, and painted with alkaline-resistant paint. Remove all traces of sulfuric acid and its corrosive products from the battery vent system to prevent contamination of the potassium hydroxide electrolyte and/or possible damage to the battery case material. Replace those parts of the vent system, which cannot be thoroughly cleansed (hoses, etc.).
1032. NICKEL CADMIUM BATTERY INSTALLATION. Each installation must have provisions to prevent any hazardous effects on structure or essential systems that may be caused by the maximum amount of heat the battery can generate during a short-circuit of the battery or individual cells.
a. Nickel-cadmium battery installations must have:
(1) A system to control the charging rate of the battery automatically to prevent battery overheating;
(2) A battery temperature sensing and over-temperature warning system with a means for disconnecting the battery from its charging source in the event of an over-temperature condition; or
(3) A battery failure sensing and warning system with a means for disconnecting the battery Par 1029 Page 116
Par 1032 Page 117 (and 118) from its charging source in the event of battery failure.
b. In the event of a complete loss of the primary electrical power generating system, the battery must be capable of providing at least 30 minutes of electrical power to those loads that are essential to continue safe flights and landing. The 30-minute time period includes the time needed for the pilots to recognize the loss of generated power and take appropriate load shedding action.
1033. SECURING THE BATTERY. Follow the procedures outlined in section 1. Make certain that the hold down bolts are not drawn up too tightly.
Ensure that the case to cover seal is installed so that the battery case/cover does not become distorted.
CAUTION: In installations where care has been taken to isolate the battery cases, inadvertent grounding may occur through improper or careless use of safety wire.
1034. QUICK DISCONNECT. Look for and replace the terminal pins when:
a. Excessive pitting or corrosion that cannot be removed.
b. Signs of burning or arcing.
c. Cracked part or housing.
d. Excessive wear on contact pins, socket lock pins, or worm screw.
e. Large deposits form on contacts or plastic is discolored.
f. Excessively loose handle and locking assembly.
NOTE: Most manufacturers sell or provide dimensions for tools to check the fit of the quick disconnect sockets.
1035. VOLTAGE AND CURRENT REGULATION. It is essential that the charging voltage and current be checked and, if necessary, the voltage regulator reset to meet the requirements of the nickel-cadmium battery being installed.
IMPORTANT: Improper charging current or voltage can destroy a battery in a short period of time.
1036. WEIGHT AND BALANCE. After installation of the nickel-cadmium battery the weight and balance of the aircraft should be recomputed if:
a. The weight of the nickel-cadmium battery is different from that of the original battery.
b. The location of the nickel-cadmium battery is different from that of the original battery.
NOTE: Weight and balance procedures for aircraft are contained in AC 43.13-1 (as amended), chapter 10.
1037. THRU 1040. RESERVED.
Par 1041 Page 119 SECTION 4. BATTERY INSTALLATION CHECKLIST 1041. STRUCTURAL REQUIREMENTS.
a. Determine if the battery is installed in such a manner that it can withstand the required loads.
The effect on other structure (primary or secondary) should be considered.
b. Determine whether suitable materials are used in the construction, including standard fasteners, confirm that the method of fabrication will result in a consistently sound structure.
c. If a mounting bracket is used, determine if the method used in its fabrication will produce a consistently sound structure.
d. If the equipment is mounted either on the existing structure or on a bracket attached to the existing structure, confirm whether all of the structure (including the bracket, if used) is adequate to support the required loads. This answer can be determined by either of two methods:
(1) By direct comparison with an existing approved installation having the same or similar (approximately the same weight and size) equipment installed.
(2) By structural analysis or static test.
Such installations do not lend themselves readily to analysis, but are normally adaptable to a static test.
In conducting a static test, the following procedure may be used:
(a) Determine the weight and CG position of the equipment item.
(b) Mount the equipment in its position in the airplane or simulate the equipment with a dummy so that th e required loads can be applied at the CG position of the actual equipment.
(c) The required loads should then be applied by any suitable means. If the equipment is light in weight, the inspector could use his own strength and/or weight to determine if the installation will withstand the required loads.
NOTE: All items of mass likely to injure the passengers or crew in a minor crash landing should have their supporting structure designed to the crash load requirements of Title 14 of the Code of Federal Regulations (14 CFR) part 23, § 23.561, insofar as the forward, upward, and sideward directions are concerned. The applicable downward load factor shall be the critical flight or landing load factor specified in §§ 23.341 and
23.473, whichever is greater.
(3) In lieu of a calculated determination of the down load factor, the ultimate factors of 6.6,
6.6, and 9.0 may be used for the normal, utility, and acrobatic categories, respectively. For equipment location not covered by § 23.561, the required loads (ref. § 23.301) are the flight and landing load factors of §§ 23.337, 23.341, and 23.473. In lieu of a calculated determination of these loads, the down load factors referenced above may be used.
(4) Supporting structure of other mass items should be designed to the critical flight or landing load factors of § 23.321, 23.471, 27.321, or
27.471. The values shown in § 23.561 or 27.561 may be used in lieu of determination of these values.
e. Determine if the equipment is installed so that it does not adversely affect another structure (either primary or secondary).
f. Confirm whether means are provided to permit proper inspections of the installation and related adjacent parts as components.