Boeing Co said on Friday that “hairline cracks” had been discovered in the wings of 787 Dreamliner jets still in production, a condition that could delay deliveries of some jets but will not affect its 2014 guidance on overall deliveries for the year. Boeing said wing maker Mitsubishi Heavy Industries Ltd notified it of the problem, which arose after a change in the manufacturing process. The cracks in shear ties on wing ribs in the 787 affects about 40 planes and the fix will take one to two weeks per plane. “We are confident that the condition does not exist in the in-service fleet,” Boeing added.