The problem, according to two people with knowledge of the modified manufacturing process, arose when a backup electrical power control unit was secured to a rack on the flight deck with fasteners — in place of the rivets previously used. This change was executed in such a way that it did not provide a complete electrical grounding path to the unit. The lack of secure electrical grounding could potentially cause malfunctions in a variety of electrical systems, such as the engine anti-ice system and the auxiliary power unit (APU) in the plane’s tail. Boeing said it discovered the issue “on a production airplane during normal build activity” and that inspections are needed to verify “that a sufficient ground path exists” for this control unit.
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