Boeing said Friday that hairline cracks had been found on wings of about 40 Dreamliners under construction but that none of the 120 aircraft being flown worldwide were affected.
The cracks occurred in "shear ties" on the wings ribs, which run parallel to the fuselage. Boeing said it would take a week or two to inspect and fix the flaw, which The Wall Street Journal first reported.
The problem surfaced last month after the contractor making the carbon-fiber composite wings, Tokyo-based Mitsubishi Heavy Industries, changed its manufacturing process.
"We are confident that the condition does not exist in the in-service fleet," said Marc Birtel, Boeing's chief spokesman. "We understand the issue, what must be done to correct it, and are completing inspections of potentially affected airplanes. We are addressing affected airplanes as required."
Some deliveries may be delayed, but Boeing said it still expects to deliver 110 of the wide-body 787s by the end of 2014. One was delivered Friday, the ninth this year, Reuters noted.