The system as originally designed utilized plastic bearing inserts on the actuator rod ends which isolated the jacks on both systems. The slat and flap drive lines utilized plastic bushings at all flange points. These bushes were impregnated with a conductive material that was supposed to drain any static charge to either end of the respective drive lines which were grounded to the wing structure and the airframe via a grounded PCU and the wing tip brakes. This was never proved in practice. In fact the conductive bushes would act like an insulator instead of a conductor when pasing high currents resulting from a lightning strike. This could result in the bushes exploding and you would have a complete disconnect of the drive line. The step back gear boxes and the "T" gear box were anodized and therefore did not conduct electricity. Even though both ends of the two systems were bonded to the airframe every thing in between was floating. The above referenced TDD required that Airbus run a conductivity test on the entire airframe. If this test were run they would have found the problem and corrected it. The thinking of the builders of the wing actuation systems was that if they identified the problem they would be financially responsible to correct the problem. Even though the contract required them to noitify Airbus of any problem relating to Reliability, Maintainability and Systems Safety they chose not to do it for the above reasons. They did the same thing when they found the failure that caused a PCU to drive when the computer didn't command it. Another point I brought out in a previous posting was that the Slat / Flap computer was never fully tested and the Flap drive system was never fully tested because the manufacturer of the computer did not furnish the flap drive system manufacturer with a full up computer. They only had 1/4th of a full computer and therefore could not develop complete control functions and resultant trouble shooting on the drive system. The computer manufacturer also refused to comply with the contract which required an FMEA that went down to the smallest piece part. By not developing a FMEA they were never able to tell what effect a failure of a piece part would have on the computer and the ultimate effect on the aircraft. To prove the point,
the first revenue flight for Lufthansa was to Cairo. When they landed they could not retract the flaps. They ended up flying in a non revenue status back to Frankfurt with the flaps partially extended. When they got back to Frankfurt the top mechanics could not diagnose the problem and the computer didn't even know there was a problem. They finally disconnected the system and hand cranked the flaps to the retracted position and they reset the PPUs and the IPPU on the PCU.
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The Cat