11-1 CHAPTER 11. AIRCRAFT BATTERY INSTALLATIONS Section 1. General
11.1 Purpose. This chapter contains structural and design considerations for the fabrication of aircraft battery installations.
11.2 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.
11.2.1 All tools must be insulated.
11.2.2 Care must be taken with all metal items, including 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.
11.2.3 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.
11.2.4 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.
11.2.5 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.
11.2.6 Always pour acid into water; never pour water into acid.
11.2.7 Do not use petroleum spirits, trichloroethylene, or other solvents.
11.2.8 Know the location and use of the emergency eyewash and shower nearest the battery charging area.
11.3 Additional References (current editions).
• AC 20-106, Aircraft Inspection for the General Aviation Aircraft Owner.
• AC 43-4, Corrosion Control for Aircraft.
• AC 120-27, Aircraft Weight and Balance Control.
• Civil Air Regulation (CAR) 6, Rotorcraft Airworthiness; Normal Category.
• FAA-H-8083-1, Aircraft Weight and Balance Handbook.
• FAA-H-8083-19, Plane Sense General Aviation Information.
11.4 Location Requirements. The battery installation and/or its installation should provide:
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11.4.1 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.
11.4.2 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 protection around the battery. Care should be taken not to interfere with the flow of engine-cooling air.
11.4.3 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.
11.4.4 Passenger Protection. Ensure 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 unintentional inverted flight.
11.4.5 Airframe Protection. To minimize damage to adjacent metal structures, fabric coverings 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.
11.5 Aircraft Storage Battery Design and Installation.
11.5.1 Lead Acid.
11.5.1.1 Each aircraft storage battery, whether approved to a Technical Standard Order (TSO) or not, must be designed as required by regulation and installed as prescribed by the manufacturer.
11.5.1.2 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.
11.5.1.3 Corrosive fluids or gases that may escape from the battery may damage surrounding structures or adjacent essential equipment.
11.5.2 Nickel Cadmium.
11.5.2.1 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.
11.5.2.2 Safe cell temperatures and pressures must be maintained during any probable charging and discharging condition. No uncontrolled increase in cell
11-3 temperature may result when the battery is recharged (after previous complete discharge):
• At maximum regulated voltage or power;
• During a flight of maximum duration; and
• Under the most adverse cooling condition likely to occur in service.
11.5.2.3 Compliance with paragraph 11.5.2.2 must be shown by tests unless experience with similar batteries and installations has shown that maintaining safe cell temperatures and pressures presents no problem.
11.5.2.4 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.
11.5.2.5 Corrosive fluids or gases that may escape from the battery may damage surrounding structures or adjacent essential equipment.
11.6 Duplication of the Manufacturer’s Installation. The availability of ready-made parts and attachment fittings may make it desirable to consider the location or type of installation, or both, 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.
11.7 Other Installations. If the battery installation has not been previously approved, or if the battery is to be installed or relocated in a manner or location other than provided in previously approved data, perform static tests on the completed installation as outlined in Chapter 2, Structural Data. 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.
11.8 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.
11.8.1 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.
11.8.2 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.
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11.8.3 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.
11.9 Battery Installation and Removal. The following instructions are generic. Refer to the airframe manufacturer’s maintenance manuals or Supplemental Type Certificate (STC) for instructions specific to a particular aircraft model.
11.9.1 Removal.
1. Set the master switch to the OFF position and tag the switch.
2. Disconnect any external power supply.
3. Open battery compartment access panels.
4. Disconnect the 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 the battery.
7. Carefully remove the battery.
WARNING: Batteries are heavy. Use appropriate lifting devices or equipment.
Use battery handles where provided.
11.9.2 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 the battery in the battery container or tray.
WARNING: Batteries are heavy. Use appropriate lifting devices or equipment.
Use battery handles where provided.
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7. Engage battery hold-down hardware, torque, and safety wire per airframe manufacturer’s maintenance manual.
8. Connect battery vent tubes.
9. Connect the battery quick disconnect plug and any auxiliary connector, or for ring terminals, install with a bolt and lock washer. Torque terminal bolts as recommended by the manufacturer.
10. Replace the electrical compartment access panel.
11. Perform an operational test.
12. Update aircraft Weight and Balance (W&B) data, if necessary.
13. Update the equipment list, if applicable.
14. Make a logbook entry with the battery serial number and date of installation.
Figure 11-1. Typical Battery Installation in the Aircraft
11-6 Section 2. Lead-Acid Battery Installations
11.10 General. In a lead-acid battery, the voltage will slowly drop as opposed to a nickel-cadmium 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.
11.11 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.
11.12 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 Par-Al-Ketone, 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 or rivets, or both, that 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 its vent tubes, receptacles, or terminals.
11.13 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-inch thick pad saturated with a five-percent solution of sodium bicarbonate (baking soda) in water or about a 3/8 inch of dry sodium bicarbonate. The inlet tube carrying fumes to the sump should extend into the jar about 1 inch from the lid (see Figure 11-2, Typical Battery Installation With Sump Jar).
11-7 Figure 11-2. Typical Battery Installation With Sump Jar
11.14 Venting. Provide suitable venting to the battery compartment to prevent the accumulation of hydrogen gas expelled during operation.
Note: Valve-regulated lead-acid batteries can use the same ventilation system as the original nickel-cadmium battery.
11.14.1 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 11-3, Battery Ventilation System. Fasten such hoses securely to prevent shifting and maintain adequate bend radii to prevent kinking.
11.14.1.1 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 on the downstream side to neutralize any corrosive vapors that may be discharged.
11.14.1.2 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 battery’s electrolyte.
11-8 Figure 11-3. Battery Ventilation System
11.14.2 Free Airflow Type. Battery cases or boxes that contain louvers may be installed without an individual vent system, provided that:
• The compartment in which the battery is installed has sufficient airflow to prevent the accumulation of explosive mixtures of hydrogen;
• Noxious fumes are directed away from occupants; and
• Suitable precautions are taken to prevent corrosive battery fluids or vapors from damaging the surrounding structure, covering, equipment, control cables, wiring, etc.
11.15 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 a 1/2 inch in diameter to prevent clogging.
11.16 Electrical Installation. 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.
11.16.1 Cables/Connectors. Use cables and/or connectors that are adequately rated for the current demand and are properly installed. Refer to AC 43.13-1, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, Chapter 11, Aircraft
11-9 Electrical Systems. Cable size can also be selected by using the same gage as used on a previously approved production aircraft with the same battery.
11.16.1.1 The cables should be of sufficient length to prevent undue strain on the battery connector or terminals.
11.16.1.2 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.
11.16.1.3 Route cables so that cable or terminals cannot short to the battery case or to the hold-down frame.
11.16.1.4 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.
11.16.1.5 Ensure 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.
11.16.2 Cable Installation. Cable installation must be designed and installed as follows:
11.16.2.1 Means of permanent identification must be provided for electrical cables, connectors, and terminals. Refer to AC 43.13-1, Chapter 11, Section 16, Wire Marking.
11.16.2.2 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.
11.16.3 Lead-Acid Batteries. 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 an Aircraft Flight Manual Supplement (AFMS) to override the emergency procedures regarding battery overheating.
Note: FAA field approval or STC is required for this kind of alteration.
11.16.4 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 11-4, Typical Battery Cutoff and Generator Alternator Control Circuit. 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.
11-10 Figure 11-4. Typical Battery Cutoff and Generator Alternator Control Circuit
11.17 Quick Disconnect. Look for and replace the terminal pins when:
• Excessive pitting or corrosion cannot be removed.
• Signs of burning or arcing.
• Cracked part or housing.
• Excessive wear on contact pins, socket lock pins, or a worm screw.
• Large deposits form on contacts, or plastic is discolored.
• Excessively loose handle and locking assembly.
Note: Most manufacturers sell or provide dimensions for tools to check the fit of the quick disconnect sockets.
11.18 Weight and Balance (W&B). After installation or alteration with the replacement battery, the W&B of the aircraft should be recomputed if:
• The weight of the replacement battery is different from that of the original battery.
• The location of the battery is different from that of the original battery.
Note: W&B procedures for aircraft are contained in AC 43.13-1, Chapter 10, Weight and Balance.
11-11 Section 3. Nickel-Cadmium Battery Installations
11.19 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.
11.20 Electrical Analysis. The ampere-hour capacity of a nickel-cadmium battery is selected to accommodate the aircraft load requirements. When making this selection, the following items should be considered:
11.20.1 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.
11.20.2 Compare the discharge characteristics curves of the batteries to make sure a reduced capacity nickel-cadmium battery is adequate regarding the following:
11.20.2.1 Ability to provide engine starting or cranking requirements. Some turbine engines require an initial surge of approximately 1,200 amperes, which tapers off within 10 seconds to approximately 800 amperes cranking current.
Reciprocating engines require approximately 100 to 200 amperes cranking current.
11.20.2.2 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.
11.20.2.3 Some nickel-cadmium batteries deliver greater power at temperature extremes than comparably rated lead-acid batteries; take care not to overload the cables and connectors.
11.21 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.
11.22 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.
11-12 Whenever the total installation weight and/or the overhang moment exceed those of the original installation, perform a static test as outlined in Chapter 2. If the battery compartment is to be relocated, follow the location requirement procedures outlined in paragraph 11.4.
11.23 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.
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 the ground.
11.24 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 nickel-cadmium battery cases: one with vent nozzles and one with viewports.
11.24.1 The vent nozzle type utilizes vent hoses to evacuate the gas overboard by use of forced air or by venturi effect.
11.24.2 Battery cases with viewports or louvers must have airflow sufficient to keep the mixture of air and hydrogen below four percent. The gases from this type of case are evacuated 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).
11.25 Preinstallation Requirements. 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, Lead-Acid Battery Installations, for battery venting and electrical connections.
11.25.1 Preinstallation 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.