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Kapton wires (not mentioned) were advised not to be used in high current carrying cables due
to arc-tracking and flashover concerns by the current Advisory Circular 25.16 . No mention of
the flammability of PVC wires (Table 7.1) in flammable materials removal discussions either.
FAA Remarks
• AC 25-16 recommends that aromatic polyimide insulated wire should be avoided in
installations where wires or wire bundles are expected to flex, such as landing gear harnesses.
• The AC also states that installation of this wire type in areas where it may be exposed to
condensation, rain, snow, hail, ice, or slush should be carefully evaluated.
• The statement in the AC that aromatic polyimide insulated wire should not be used in high
current carrying cables is used in the context that this type of wire should not be used in
where flammable fluids or vapors may be present, such as fuel tanks.
• The title of Table 7-1 is “Age Related Wire Conditions.” The table identifies conditions that
affect the aging of wires regardless of wire type.
b. Advisory Circular 25.16 also states that different wire types should not be routed in the same
bundles due to differences in hardness. Boeing has stated they have no in-house prohibition
against mixing different wire types. Clearly if ATSRAC hopes to have voluntary compliance
with only Advisory Circulars being issued, something has to change. How can we choose to
support some advisory material and ignore others?
FAA Remarks
• As addressed by AC 25-16, abrasion becomes a concern when wire installation allows relative
movement between wires in the same bundle. Additionally, this can also be a concern when
wires of different bundles cross each other and there is relative movement between the
bundles. However, the AC states that testing and service history may be used to demonstrate
that the mixing of wire types will not result in abrasion.
• Service history does not indicate abrasion problems for the type of wire used in aircraft
applications.
• As part of the EAPAS program, the FAA is conducting a research program to evaluate
concerns over mixing of wire types and how this applies to wire installed on the aircraft over
its expected lifetime.
c. The summation of nearly all of the green-lighted (closed) issues could be; already considered,
already being done, only needs improved housekeeping, reference to insufficiently mature
technology (arc-fault circuit breakers and non-destructive test equipment), need better
maintenance awareness through increased training, or will be covered by future Advisory
Circulars. It has already been shown that Advisory Circulars are being ignored. Boeing thinks
existing industry practices in design and maintenance are sufficient. The NTSB and the FAA
have declared that current best practices are inadequate.
FAA Remarks
• In terms of tracking the status of ATSRAC recommendation, the color green indicates that the
task is closed, closed with comment, or on plan (i.e., the item is expected to be completed on
schedule).
• Advisory circulars are effectively used by the global aviation community as a means to show
compliance to the applicable requirements.
GENERAL COMMENTS
8 April 19 2002 53
• The FAA along with other international regulatory authorities and the aviation industry has
taken a proactive approach to improve wire related requirements, advisory material, and
policy. Examples include current ATSRAC Task Nos. 6-9, recently released FAA wire
policy, and a best wiring practices training course that has been well received on a global
scale.
d. The intent of the Intrusive Inspection Group Report was to be as politically correct as
possible. This was done by softening the verbiage for example; hypothetical, plausible
scenarios, no mention of arcing of aromatic polyimides, etc. The result being that without any
concrete conclusions that visual inspections can't find the most common wire flaws, and that
the condition of the fleet is dangerous, these type of responses are to be expected. What
problem with wiring? If there is no problem then nothing needs to be done about the fleet of
wiring with; 1,100 cracks per aircraft, burned conductors, arced conductors, embrittled wires,
delaminated wires, etc. The whole context of the Intrusive Inspection recommendations could
be summed up by saying, we have a problem. We don't have test equipment (NDT) or
futuristic arc-fault circuit breakers but we sure need them. Boeing has said everything is as
designed and all is well, in this report. Boeing has agreed to the drafting of Advisory Circulars
that they will ignore as the ones they ignore now.
FAA Remarks
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