Boeing had pegged Dreamliner No. 4 as a turning point for its delayed 787 jet program. But now the crucial program has been set back by a production problem on this fourth flight-test airplane.

A major mishap inside a Charleston, S.C., assembly plant last week structurally damaged the upper half, or crown section, of Dreamliner No. 4’s center fuselage, Boeing confirmed Monday, the day the fuselage was to have been in Everett.

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