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on this aircraft was the unexplained occurrence of a high number of bonding leads found broken or
frayed in a localized area within the wing tanks. At that time, Airbus did not have sufficient
inspection data to determine whether this was an isolated case.
Subsequently, a 133-aircraft data set—the majority of which representing A300/A310 widebody
family inspections—showed clearly there is no issue with bonding-lead degradation. As expected,
this inspection data proved that the A300B4 MSN 161 findings were an isolated case. Because the
issue of broken leads may be linked to mechanical damage resulting from tank entry, Airbus will
add warning notices to its aircraft maintenance manuals (AMM) advising that special care be
taken when work is performed inside fuel tanks.
Overall, the Airbus AWG inspection data showed the vast majority of bonding leads to be in good
condition and performing their intended function. The number of leads requiring removal for
corrosion and fraying damage was very low, and the number of missing or broken leads requiring
replacement was rarer still. These minor instances of incorrect bonding-lead findings on pipes and
couplings did not present any loss of bonding function because redundancy is designed and built
into the system.
This inspection program also proved that even on heavily corroded, frayed, or otherwise damaged
bonding leads, as long as the attachment points are secured and sealed for corrosion protection, the
bonding functions remain intact. Actual bonding checks showed that they were still within the
initial-build-standard value.
This inspection program indicates that the current schedule for visual inspections is sufficient to
identify and remove degraded or broken leads.
Finally, this inspection data from aircraft operating in different regions and environments around
the world does not shown any aging effect attributable to geographic differences.
3.7.2 Component Bonding
All the key components in the fuel system were checked using the SIL. The results have shown
that a vast majority of the components having a specified bond requirement remain within their
initial build standard. There were a very small number of bonding value exceedances, most of
which have no impact on the ability of the bond to perform its intended function. The very few
number of exceedances do not require immediate action.
The inspection data indicates no evidence that bond values degrade to an unacceptable level with
age. There is also no evidence to indicate any geographic variations among the widespread
operator base within the Airbus inspection program.
Airbus also wanted to assess if there were any indication that the different tanks (i.e., center wing,
wing, and tail-plane tanks) exhibit any differences in condition. Clearly there was no evidence to
3.0 Airbus Working Group Report (continued)
August 4, 2000 Industry AFFSP Report Page 27
suggest that they do. Airbus-designed fuel tanks have no other variables except in the sequence
that some tanks are depleted in use relative to other tanks.
3.7.3 FQIS Wiring and Probes
There were no discrepancies with FQIS wiring and probes apart from the one finding of a level
sensor wire insulation protection conduit found chafed on an A300B aircraft. Investigations had
shown that the wire conduit was in close proximity to a magnetic level indicator (MLI) housing
and subsequently chafed against it. This finding only relates to the A300B and A300-600 type, in
which the installation of the sensor conduit are similar. No other Airbus model type is affected.
The chafing did not reach the wire insulation. However, the finding was immediately relayed to
the continuous airworthiness process for action. An alert SB was issued to inspect the wiring
protection conduit in this sensor location, with a restoration work to tie back the conduit so that it
cannot chafe against the MLI housing.
3.7.4 General Tank Condition and FOD
No discrepancies found with the number of aircraft inspected.
3.7.5 Tank Structure
There were findings of corrosion and fretting damage on some manhole covers. However, because
the Airbus inspection program calls for a bonding check before access panel removal, there was no
impact on the bonding function.
There are launched actions within the Airbus Support division to address the corrosion findings.
3.7.6 Flame Arrestors
No discrepancies found with the number of aircraft inspected.
3.8 Conclusions
3.8.1 Bonding Leads
The inspection data received to date has shown that the degradation of bonding leads has minimal
impact on Airbus aircraft. The data shows that the number of leads requiring removal is very low
and that these leads are not in a concentrated area. The minor instances of incorrect bonding lead
　
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