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AC 43.13-1B 9/8/98 11-191. FUEL SYSTEMS. Small metallic objects within an aircraft fuel tank, that are not part of the tank structure, should be electrically bonded to the structure so as to dissipate static charges that may otherwise accumulate on these objects. A practical bonding design would use a flexible braided jumper wire or riveted bracket. In such situations, a DC re sistance of 1 ohm or less should indicate an adequate connection. Care should be taken, in designing such connections, to avoid creating continuous current paths that could allow lightning or power fault currents to pass through connections not designed to tolerate these higher amplitude currents without arcing. Simulated static charge, lightning, or fault cur rent tests may be necessary to establish or ver ify specific designs. All other fuel system components, such as fuel line (line to line) ac cess doors, fuel line supports, structural parts, fuel outlets, or brackets should have an elec tromechanical (bonding strap) secure connec tor that ensures 1 ohm or less resistance to the structure. Advisory Circular 20-53A Protec tion of Aircraft Fuel Systems Against Fuel Va por Ignition Due to Lightning, and associate manual DOT/FAA/ CT-83/3, provide detailed information on necessary precautions. 11-192. ELECTRIC SHOCK PREVEN- TION BONDING. Electric shock to person nel should be prevented by providing a low re sistance path of 1/100 ohm or less between structure and metallic conduits or equipment. The allowable ground resistance should be such that the electric potential of the conduit or equipment housing does not reach a dangerous value under probable fault conditions. The current carrying capacity of all elements of the ground circuit should be such that, under the fault condition, no sparking, fusion, or danger ous heating will occur. Metallic supports usu ally provide adequate bonding if metal-to metal contact is maintained. 11-193. LIGHTNING PROTECTION BONDING. Electrical bonding is frequently required for lightning protection of aircraft and systems, especially to facilitate safe conduc tion of lightning currents through the airframe. Most of this bonding is achieved through nor mal airframe riveted or bolted joints but some externally mounted parts, such as control sur faces, engine nacelles, and antennas, may re quire additional bonding provisions. Gener ally, the adequacy of lightning current bonds depends on materials, cross-sections, physical configurations, tightness, and surface finishes. Care should be taken to minimize structural re sistance, so as to control structural voltage rises to levels compatible with system protec tion design. This may require that metal sur faces be added to composite structures, or that tinned copper overbraid, conduits, or cable trays be provided for interconnecting wire har nesses within composite airframes. Also care must be taken to prevent hazardous lightning currents from entering the airframe via flight control cables, push rods, or other conducting objects that extend to airframe extremities. This may require that these conductors be electrically bonded to the airframe, or that electrical insulators be used to interrupt light ning currents. For additional information on lightning protection measures, refer to DOT/FAA/CT-89-22. Report DOT/FAA/ CT 86/8, April 1987, Determination of Electri cal Properties of Bonding and Fastening Tech niques may provide additional information for compositematerials. a. Control Surface Lightning Protection Bonding. Control surface bonding is intended to prevent the burning of hinges on a surface that receives a lightning strike; thus causing possible loss of control. To accomplish this bonding, control surfaces and flaps should have at least one 6500 circular mil area copper Page 11-80 Par 11-191 (e.g. 7 by 37 AWG size 36 strands) jumperPDF Image | AFS-640
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