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 | 11-186. Grounding
AC 43.13-1B CHG 1
9/27/01
in order to minimize susceptibility to loosen
ing under vibration. If the structure is fabri
cated of a material such as carbon fiber com
posite (CFC), which has a higher resistivity
than aluminum or copper, it will be necessary
to provide an alternative ground path(s) for
power return current. Special attention should
be considered for composite aircraft.
d. Current Return Paths for Internally
Grounded Equipment. Power return or fault
current ground connections within flammable
vapor areas must be avoided. If they must be
made, make sure these connections will not
arc, spark, or overheat under all possible cur
rent flow or mechanical failure conditions, in
cluding induced lightning currents. Criteria
for inspection and maintenance to ensure con
tinued airworthiness throughout the expected
life of the aircraft should be established.
Power return fault currents are normally the
highest currents flowing in a structure. These
can be the full generator current capacity. If
full generator fault current flows through a lo
calized region of the carbon fiber structure,
major heating and failure can occur. CFC and
other similar low-resistive materials must not
be used in power return paths. Additional
voltage drops in the return path can cause volt
age regulation problems. Likewise, repeated
localized material heating by current surges
can cause material degradation. Both prob
lems may occur without warning and cause
nonrepeatable failures or anomalies.
e. Common Ground Connections. The
use of common ground connections for more
than one circuit or function should be avoided
except where it can be shown that related mal
functions that could affect more than one cir
cuit will not result in a hazardous condition.
Even when the loss of multiple systems does
not, in itself, create a hazard, the effect of such
failure can be quite distracting to the crew.
(1) Redundant systems are normally
provided with the objective of assuring contin
ued safe operation in the event of failure of a
single channel and must therefore be grounded
at well separated points. To avoid construction
or maintenance errors that result in connecting
such ground at a single point, wires that
ground one channel of a redundant system
should be incapable of reaching the ground
attachment of the other channel.
(2) The use of loop type grounding
systems (several ground leads connected in se
ries with a ground to structure at each end)
must be avoided on redundant systems, be
cause the loss of either ground path will re
main undetected, leaving both systems, with a
potential single-point failure.
(3) Electrical power sources must be
grounded at separate locations on the aircraft
structure. The loss of multiple sources of
electrical power, as the result of corrosion of a
ground connection or failure of the related
fasteners, may result in the loss of multiple
systems and should be avoided by making the
ground attachments at separate locations.
(4) Bonds to thermally or vibration-
isolated structure require special consideration
to avoid single ground return to primary
structure.
(5) The effect of the interconnection of
the circuits when ungrounded should be con
sidered whenever a common ground connec
tion is used. This is particularly important
when employing terminal junction grounding
modules or other types of gang grounds that
have a single attachment point.
Page 11-72
Par 11-186