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Reviewing and analyzing the findings from the fault current bond inspections revealed that there
were no fuel tank ignition hazards associated with these parts or their installations. All of the
electrical equipment that is bonded for fault current handling is installed external to the fuel tank.
Regardless, Boeing has taken action on the 747 by releasing Service Bulletin 747-28-2228,
Override / Jettison, APU, and Electrical Scavenge Pump Bonding Jumper Modification, dated
November 4, 1999. This service bulletin revises the electrical bond path for these pump
installations to provide additional margin between the design capability and the resistance
requirement.
In addition, for enhanced safety, Boeing is developing periodic maintenance recommendations for
the fault current bonds on specific components to ensure that they stay within acceptable limits for
the life of the airplane.
The proposal is to add a recommended periodic maintenance requirement for all pumps of all
Puget Sound–built airplanes. This maintenance activity would include measuring the bonding
resistance between the components and structure every heavy maintenance visit. If the measured
resistance is above the limit, the operator will rework the bond path to the requirements outlined in
the appropriate airplane maintenance manual.
5.0 Boeing Working Group Report (continued)
Page 50 Industry AFFSP Report August 4, 2000
Overall, there were no issues identified with respect to static, fault current, or lightning bonds that
would affect the continued airworthiness of the fleet.
5.6.2 Bonding Jumpers
The design of fuel system installations on Boeing-built aircraft incorporates a large number of
bonding jumpers for the bonding of tubing, mechanical components, and electrical components.
These bonding jumpers are made up of braided wire and incorporate a mating lug on each end. In
addition to the resistance measurement, the inspections included a visual inspection for signs of
wear / deterioration, breakage, corrosion, and integrity of the fastening hardware.
Data received from the Boeing fleet inspections indicates that the majority of the bonding jumper
installations looked as they did when they were originally manufactured. In those instances where
bonding jumper discrepancies were found, some of the noted conditions included bonding jumper
discoloration, bonding jumper corrosion, broken tube bonding clamps, and a few missing bonding
jumpers. None of the conditions found would impact the continued airworthiness or reliability of
the affected airplane because alternate bond paths typically exist, and design measures minimize
charging.
Of the conditions noted above, some types of bonding jumpers exhibited discoloration without any
effect on measurements. On a few airplanes, some bonding jumpers were found to be
deteriorating. Analysis of the deteriorated parts has identified issues with the tin plating not
properly sealing the copper wire from exposure to the sulfur in the fuel. In a few rare cases, the tin
had flaked off and the reaction between the copper in the wire and the sulfur in the fuel had caused
some of the strands in the bonding jumper braided wire to become brittle and break. No instances
have been identified in which the bonding jumper failed to perform its intended function. A few
bonding jumpers were found to be missing on a small number of Puget Sound–built airplane
models. Because of alternate bond paths, no safety issues were associated with the missing parts.
The AFSSP and its inspection program have brought about an increased awareness of bonding
jumper integrity and installation. The installation instructions for several pumps have already been
updated to incorporate lessons learned. Additionally, maintenance documentation and training
programs for manufacturing and maintenance personnel are both being revised to include
comprehensive instructions for inspection, installation, removal, and replacement of bonding
jumpers within fuel systems.
Boeing is evaluating issuing service bulletins to inspect the fuel tanks of all Boeing Puget Sound–
built airplanes. The purpose of the bulletins would be to inspect for missing bonding jumpers and
install bonding jumpers as required. Boeing is proposing that this service bulletin be accomplished
during the first heavy maintenance visit after the bulletin is released.
5.6.3 Tubing, Mechanical, and Electrical Component Condition
The service bulletins included condition checks for all the tubing and mechanical components
installed in the fuel tanks. Examples of mechanical components include fittings, pump housings,
valve housings, check valves, jet pumps, drain valves, pressure relief valves, vent scoops, and
　
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