BOEING has said that the discovery of a 787 Dreamliner manufacturing defect by wing-maker Mitsubishi Heavy Industries in Japan means 43 of the jets have to be inspected for small hairline cracks inside the wings.
None of the 787 Dreamliners involved has been delivered to airlines.
The affected wings are either on the production lines in Everett, Wash., and North Charleston, S.C., or still at the Mitsubishi plant in Nagoya, Japan.
Boeing spokesman Marc Birtel said inspections – and if necessary, fixes – for the problem will take one to two weeks for each aeroplane and will be accomplished before it is delivered. “While there may be some delays to deliveries, we are confident that we are doing what must be done,” Birtel said.
He said Mitsubishi informed Boeing in February that “a change in their manufacturing process may have led to hairline cracks in a limited number of shear ties on a wing rib in the 787.” The shear ties in question are small aluminium pieces used to fasten the composite wing skin panels to an aluminium rib that runs from the front to the back of the wing.
The cracks resulted from over-tightening of the fasteners.
“As soon as Mitsubishi became aware of the situation, it began inspections to ensure that all the hairline cracks were detected,” said Birtel. “They commenced inspections and made changes to the manufacturing process.” The affected planes are Dreamliner numbers 151 to 193.
According to data compiled by the All Things 787 blog, which tracks the progress of each Dreamliner through the manufacturing process, 17 of those jets have already rolled out of the factory and were undergoing final preparations for delivery.
Another 14 are under assembly – four of them in North Charleston, 10 in Everett.
The wings for most of the remaining 12 aeroplanes are still in Japan, though a few wing sets may have just arrived in the U.S. Birtel said initial inspections by Mitsubishi and Boeing have so far found hairline cracks that are “very small, less than an inch long.” The cracks have been found in more than one aeroplane at Boeing, he said, declining to be more specific.
According to people with knowledge of the problem, all the cracks were located at a specific rib – the second rib away from where the wing root joins the fuselage – where it connects to the lower wing skin.
Even small cracks in critical aeroplane structure, such as the wings, must be addressed promptly because the loads upon the structure during flight could potentially cause the cracks to spread and widen.
“We are confident that the condition does not exist in the in-service fleet,” Birtel said. “We understand the issue, what must be done to correct it, and are completing inspections of potentially affected aeroplanes.” The inspections are conducted both visually and by eddy current testing, which detects cracks invisible to the naked eye by monitoring changes in induced electromagnetic fields.
Birtel said that if a crack is found in a shear tie, the area will be repaired with a patch.
The manufacturing problem may cause a considerable slowdown in near-term jet deliveries.
But Birtel said deliveries will continue with some other Dreamliners that were built earlier than No. 151. And he said Boeing expects to get through the fixes and still deliver the 110 Dreamliners projected earlier this year.
The problem with the 787 wing cracks was first reported Friday afternoon by The Wall Street Journal.