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• Wires (e.g., wire, cable, coax, databus,
feeders, ribbon cable).
• Bus bars.
• Connection to electrical devices (e.g.,
relays, push button, interrupters, switches,
contactors, terminal blocks, feed-through
connectors).
• Circuit breakers or other circuit protection
devices (not performance).
• Electrical contacts.
• Connector and accessories (e.g., backshell,
sealing boot grommet sealing plugs).
• Electrical grounding and bonding devices
(e.g., modules, straps, studs).
• Electrical splices.
• Shield or braids.
• Conduits that have electrical termination.
• Clamps and other devices used to route and
support the wire bundle.
• Cable tie devices.
• Labels or other means of identification
methods.
• Pressure seals associated with EWIS.
• Wiring inside shelves, panels, racks,
junction boxes, distribution panels, backplanes
of equipment racks (including circuit
board back-planes), wire integration units,
etc.
The following wires and devices (along with the mating connections at the termination points
of the wire on those devices) are not considered part of the “EWIS”:
• Wiring inside avionics equipment (e.g., flight management system computer, flight data
recorder, VHF radio, primary flight display).
• Equipment qualified to the standards of RTCA Document DO-160 or shown to be
equivalent (other than those specifically included in this definition).
• Equipment qualified to a technical standard order (TSO).
• Portable, carry on, or otherwise non-permanently mounted (not part of the certification
basis) electrical equipment.
• Fiber optics.
PROGRAM TO ENHANCE AIRCRAFT ELECTRICAL WIRING INTERCONNECTION SYSTEM MAINTENANCE
Appendix E Causes of Wiring Degradation 47
APPENDIX E. CAUSES OF WIRE DEGRADATION.
The following items are considered principal causes of wiring degradation and should
be used to help focus maintenance programs:
• Vibration - High vibration areas tend to accelerate degradation over time, resulting
in “chattering” contacts and intermittent symptoms. High vibration of tie-wraps or
string-ties can cause damage to insulation. In addition, high vibration will
exacerbate any existing problem with wire insulation cracking.
• Moisture - High moisture areas generally accelerate corrosion of terminals, pins,
sockets, and conductors. It should be noted that wiring installed in clean, dry areas
with moderate temperatures appears to hold up well.
• Maintenance - Scheduled and unscheduled maintenance activities, if done
improperly, may contribute to long term problems and wiring degradation. Certain
repairs may have limited durability and should be evaluated to ascertain if rework is
necessary. Repairs that conform to manufacturers recommended maintenance
practices are generally considered permanent and should not require rework.
Furthermore care should be taken to prevent undue collateral damage to EWIS
while performing maintenance on other systems.
Metal shavings and debris have been discovered on wire bundles after maintenance,
repairs, modifications, or STCs have been performed. Care should be taken to
protect wire bundles and connectors during modification work. The work areas
should be cleaned while the work progresses to ensure that all shavings and debris
are removed; the work area should be thoroughly cleaned after the work is
complete; and the work area should be inspected after the final cleaning.
Repairs should be performed using the most effective methods available. Since
wire splices are more susceptible to degradation, arcing, and overheating, the
recommended method of repairing a wire is with an environmental splice.
• Indirect Damage - Events such as pneumatic duct ruptures or duct clamp leakage
can cause damage that, while not initially evident, can later cause wiring problems.
When events such as these occur, surrounding EWIS should be carefully inspected
to ensure that there is no damage or potential for damage evident. The indirect
damage caused by these types of events may be broken clamps or ties, broken wire
insulation, or even broken conductor strands. In some cases the pressure of the
duct rupture may cause wire separation from the connector or terminal strip.
• Contamination - Wire contamination refers to either of the following situations:
a. The presence of a foreign material that is likely to cause degradation of
wiring.
PROGRAM TO ENHANCE AIRCRAFT ELECTRICAL WIRING INTERCONNECTION SYSTEM MAINTENANCE
Appendix E Causes of Wiring Degradation 48
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