Boeing was forced to ground its 767-based KC-46 tankers for the past week after the Air Force expressed concern about loose tools and bits of debris found in various locations inside the completed airplanes, according to internal company memos.
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During the process of building aircraft, all airframes are supposed to be routinely swept for any kind of foreign object debris — especially anything metal. A loose object left, say, inside a wall cavity or under a floor, is potentially dangerous because over time it could damage equipment or cause an electrical short.