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 | 11-188. Bonding Inspection
9/8/98
AC 43.13-1B
f. Grounds for Sensitive Circuits. Spe
cial consideration should be given to grounds
for sensitive circuits. For example:
(1) Grounding of a signal circuit
through a power current lead introduces power
current return voltage drop into the signal cir
cuit.
(2) Running power wires too close will
cause signal interference.
(3) Separately grounding two compo
nents of a transducer system may introduce
ground plane voltage variations into the sys
tem.
(4) Single point grounds for signal cir
cuits, with such grounds being at the signal
source, are often a good way to minimize the
effects of EMI, lightning, and other sources of
interference.
11-187. BONDING. The following bonding
requirements must be considered:
a. Equipment Bonding. Low-impedance
paths to aircraft structure are normally required
for electronic equipment to provide radio fre
quency return circuits and for most electrical
equipment to facilitate reduction in EMI. The
cases of components which produce electro
magnetic energy should be grounded to struc
ture. To ensure proper operation of electronic
equipment, it is particularly important to con
form the system’s installation specification
when interconnections, bonding, and ground
ing are being accomplished.
b. Metallic Surface Bonding. All con
ducting objects on the exterior of the airframe
must be electrically connected to the airframe
through mechanical joints, conductive hinges,
or bond straps capable of conducting static
charges and lightning strikes. Exceptions may
be necessary for some objects such as antenna
elements, whose function requires them to be
electrically isolated from the airframe. Such
items should be provided with an alternative
means to conduct static charges and/or light
ning currents, as appropriate.
c. Static Bonds. All isolated conducting
parts inside and outside the aircraft, having an
area greater than 3 in2 and a linear dimension
over 3 inches, that are subjected to appreciable
electrostatic charging due to precipitation,
fluid, or air in motion, should have a mechani
cally secure electrical connection to the aircraft
structure of sufficient conductivity to dissipate
possible static charges. A resistance of less
than 1 ohm when clean and dry will generally
ensure such dissipation on larger objects.
Higher resistances are permissible in connect
ing smaller objects to airframe structure.
11-188. BONDING INSPECTION. In
spect for the following:
a. If there is evidence of electrical arc-
ing, check for intermittent electrical contact
between conducting surfaces, that may become
a part of a ground plane or a current path.
Arcing can be prevented either by bonding, or
by insulation if bonding is not necessary.
b. The metallic conduit should be
bonded to the aircraft structure at each termi
nating and break point. The conduit bonding
strap should be located ahead of the piece of
equipment that is connected to the cable wire
inside the conduit.
c. Bond connections should be secure and
free from corrosion.
d. Bonding jumpers should be installed
in such a manner as not to interfere in any way
with the operation of movable components of
the aircraft.
Par 11-186
Page 11-73