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.
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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.
11.25.2 Compartment Cleansing. Compartments or battery boxes that 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 that cannot be thoroughly cleansed (hoses, etc.).
11.26 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.
11.26.1 Nickel-cadmium battery installations must have:
• A system to control the charging rate of the battery automatically to prevent battery overheating;
• 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
• A battery failure sensing and warning system with a means for disconnecting the battery from its charging source in the event of battery failure.
11.26.2 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.
11.27 Securing the Battery. Follow the procedures outlined in Section 1, General. 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.
11.28 Quick Disconnect. Look for and replace the terminal pins when:
• Excessive pitting or corrosion that cannot be removed.
• Signs of burning or arcing.
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• 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.
11.29 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.
11.30 Weight and Balance (W&B). After installation of the nickel-cadmium battery, the W&B of the aircraft should be recomputed if:
• The weight of the nickel-cadmium battery is different from that of the original battery.
• The location of the nickel-cadmium battery is different from that of the original battery.
Note: W&B procedures for aircraft are contained in AC 43.13-1, Chapter 10.
11-15 Section 4. Battery Installation Checklist
11.31 Structural Requirements.
11.31.1 Determine if the battery is installed in such a manner that it can withstand the required loads. The effect on other structures (primary or secondary) should be considered.
11.31.2 Determine whether suitable materials are used in the construction, including standard fasteners, and confirm that the method of fabrication will result in a consistently sound structure.
11.31.3 If a mounting bracket is used, determine if the method used in its fabrication will produce a consistently sound structure.
11.31.4 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:
11.31.4.1 By direct comparison with an existing approved installation having the same or similar (approximately the same weight and size) equipment installed.
11.31.4.2 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:
1. Determine the weight and CG position of the equipment item.
2. Mount the equipment in its position in the airplane or simulate the equipment with a dummy so that the required loads can be applied at the CG position of the actual equipment.
3. The required loads should then be applied by any suitable means. If the equipment is light in weight, the inspector could use their 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 14 CFR § 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 14 CFR §§ 23.341 and 23.473, whichever is greater.
4. 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 14 CFR § 23.561, the required loads (refer to 14 CFR § 23.301) are the
11-16 flight and landing load factors of 14 CFR §§ 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.
5. Supporting structure of other mass items should be designed to the critical flight or landing load factors of 14 CFR § 23.321, § 23.471, § 27.321, or § 27.471. The values shown in 14 CFR § 23.561 or § 27.561 may be used in lieu of determination of these values.
11.31.5 Determine if the equipment is installed so that it does not adversely affect another structure (either primary or secondary).
11.31.6 Confirm whether means are provided to permit proper inspections of the installation and related adjacent parts as components.
11.32 Hazards to the Aircraft and its Occupants.
1. Confirm whether the parts of the airplane adjacent to the battery are protected against corrosion from any products likely to be emitted by the battery during servicing or flight.
Note: Methods that may be used to obtain protection include acid-proof paint that will resist corrosive action by emitted electrolyte, drain to discharge corrosive liquids clear of the aircraft, positive pressure vents to carry corrosive fumes and flammable gases outside the aircraft, enclosed battery cases that would contain any amount of electrolyte that might be spilled, or a combination of these methods.
2. Determine whether the battery container or compartment is vented in such a manner that any explosive gases released by the battery during charging or discharging are carried outside the airplane.
3. Confirm that the battery container or compartment is vented in such a manner that any noxious gases emitted by the battery are directed away from the crew and passengers.
4. Verify whether the battery connector terminals or other exposed parts are protected against electrical contact with the battery container or compartment.
5. Determine if adequate provision is made for the drainage of spilled or excess battery fluid.
11.33 Operating Aspects. If a battery is the only source of electrical power, determine if the battery has sufficient capacity to supply the electrical power necessary for dependable operation of all electrical equipment essential to the safe operation of the airplane.
11.34 Detail Design Standards. Verify that the battery is accessible for inspection or servicing on the ground.
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11.35 Recordkeeping.
1. Confirm that a maintenance record entry has been made.
2. Determine if the equipment list and W&B has been revised.
11-18 Section 5. Instructions for Continued Airworthiness
11.36 Lead-Acid Batteries.
11.36.1 Airworthiness Limitations.
11.36.1.1 Battery Inspection. To ensure continued airworthiness, the battery should be removed and the capacity tested. Follow the battery manufacturer’s recommended instructions for continued airworthiness (ICA) to determine service periods.
11.36.1.2 Connector/Wiring Inspection. Check for mechanical integrity, resiliency, pitted or corroded mating surfaces, burn marks, condition, and type of wiring.
11.36.1.3 Electrolyte Levels. Electrolyte levels must be maintained just over the plates at all times. Replenish consumed water with distilled or demineralized water.
11.36.1.4 Sump Jar Maintenance. Inspect the electrolyte levels and the sump jar every 100 flight-hours.
11.36.2 Capacity Test. The capacity test should be performed as follows:
1. Check for proper battery installation per the STC or the manufacturer’s ICA when performing annual and 100-hour inspections and when replacing the battery after a capacity test.
2. Stabilize the battery at 15 °C (59 °F) or higher for at least 24 hours.
3. Remove the battery from the aircraft and charge it according to the recommended charging instructions. Allow the battery to stand on an open circuit for 1 hour.
4. Connect the fully charged battery to a capacity tester that incorporates a load resistance, ammeter, voltmeter, and a timer.
5. Discharge the battery at the C1 rate to 1.75 volts per cell (10 volts for a 12-volt battery and 20 volts for a 24-volt battery). Note the discharge time.
6. The battery is considered airworthy if it meets 80 percent of its C1 (1 hour) capacity rating. However, it is recommended to return batteries to service when their capacity is above the minimum (i.e., 85 percent minimum or 51 minutes to end point voltage).
7. If the battery fails to meet the minimum runtime, continue using the constant current C1 method in the manufacturer’s ICA. Allow the battery to stand on an open circuit for 1 hour.
8. Repeat the discharge test as indicated. If the failure persists, replace the battery.
9. If the battery is found to be airworthy, it must be recharged with constant potential (CP) prior to reinstalling it in the aircraft.
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11.37 Nickel-Cadmium Batteries.
11.37.1 Airworthiness Limitations. To ensure continued airworthiness, the battery should be removed and inspected per the manufacturer’s recommendations.
11.37.1.1 Connector/Wiring Inspection. Check for mechanical integrity, resiliency, pitted or corroded mating surfaces, burn marks, condition, and type of wiring.
11.37.1.2 Voltage Regulator. Periodic checks to correct out-of-tolerance regulators and replacement of defective units will reduce the possibility of inadvertent increases in charging voltage with the resultant rise in charge current and battery temperature and water consumption.
11.37.1.3 Battery. Inspect the can and cover for dents, damage, epoxy coating separation, vent tube obstruction, latch function, and cover seal condition.
Remove the battery cover and clean the top of the cells and connectors with a nylon brush. Verify torque on every intercell connection. If disassembly is required, discharge the battery first.
11.37.1.4 Electrolyte Levels. Electrolyte levels should be adjusted during the last 15 minutes of the topping charge and while the current is still flowing because the cells are at their most uniform electrolyte level at this time. Replenish electrolyte levels with distilled, deionized, or demineralized water only. Refer to the component maintenance manual for the syringe/nozzle specifications to ensure that the proper nozzle and syringe assembly are used to level the cells.
Using the incorrect nozzle may impact battery serviceability and longevity.
11.37.1.5 Electrical Leakage. Determine if external leakage is of such a magnitude that a complete battery cleaning is required. Follow the manufacturer’s recommended procedures.
11.37.1.6 Sensor Assembly. Inspect the battery for proper placement of thermostats, heaters, thermistors, or other sensor elements. Inspect wiring and receptacle for insulation damage, corrosion, and crimping or other defects. If the sensor/harness assembly fails testing or is damaged, it must be replaced.
Perform a functional test on the temperature sensor assembly at least once each calendar year.
11.37.2 Capacity Test. The capacity test must be performed in accordance with the manufacturer’s recommendations.