FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 11. Aircraft Electrical Systems | 15. Grounding and Bonding | 11-191. Fuel Systems
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
composite materials.
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
(e.g. 7 by 37 AWG size 36 strands) jumper
Page 11-80
Par 11-191