Boeing said Friday that 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 and North Charleston, S.C., or still at the Mitsubishi plant in Nagoya, Japan.
The discovery comes just when Boeing has managed to ramp up production of the much-troubled 787 to 10 jets per month. The problem will add further delays for customers, and will burden Boeing with more costly rework.
Boeing spokesman Marc Birtel said inspections — and if necessary, fixes — for the problem will take one to two weeks for each airplane and will be accomplished before each is delivered.
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“While there may be some delays to deliveries, we are confident that we are doing what must be done,” Birtel said. “We understand the issue, what must be done to correct it, and are completing inspections of potentially affected airplanes.”
Boeing is confident there are no such defects on the 123 planes already delivered to airlines, he said.
Birtel 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.”
Those shear ties are small aluminum pieces used to fasten the composite wing skin panels to an aluminum rib that runs from the front to the back of the wing.
The cracks resulted from over-tightening of the fasteners without the use of manufacturing fillers, according to The Wall Street Journal, which was first to report the problem Friday afternoon.
“As soon as Mitsubishi became aware of the situation, it began inspections to ensure that all the hairline cracks were detected,” Birtel said. “They commenced inspections and made changes to the manufacturing process.”
An industry source familiar with the Boeing supply chain said that in general “Mitsubishi is a pretty high-quality supplier.” The fact that in this case the Japanese supplier found and reported the problem before airplanes were delivered “proves that their quality process is catching issues,” said the person, who asked not to be identified because he works with Boeing.
However, there have been previous manufacturing defects with the wings.
In 2011, many of the early Dreamliners had to be reworked when sealant on fasteners inside the wings was found to have been applied incorrectly and was falling off into the fuel tank. Fixing that took weeks of painstaking work on each airplane.
The planes affected this time 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.
An additional 14 are under assembly — 10 of them in Everett, four in North Charleston.
The wings for most of the remaining 12 airplanes 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 airplane 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 spot: the second rib away from where the wing root joins the fuselage, where the rib connects to the lower wing skin.
Even small cracks in critical airplane 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.
“That has to be fixed or the cracks will continue to grow,” said Hans Weber, aviation-engineering consultant with Tecops International. “No airline would accept a plane with such a manufacturing defect.”
Two years ago, rival plane-maker Airbus discovered small cracks in structure inside the wings of its giant A380 superjumbo.
However, those cracks were found after years of service and required major retrofits on airplanes already flying.
Because the cracks inside the 787 wings did not occur in service, that means they are not fatigue cracks caused by the impact of repeated stresses over time.
Weber said because the cracks are instead the result of a one-time manufacturing flaw, this “makes it pretty straightforward to determine where the suspect areas are and what to do about it.”
Technicians are conducting the inspections 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 trimmed and then repaired with a patch.
Weber said such a repair will ensure any cracks cannot grow.
He said the inspections will take considerable time because Boeing will have to inspect all the wing ribs, not just rib no. 2.
That likely will entail taking off the wing skin. If cracks are found, mechanics may have to remove the shear tie fasteners and insert filler before a repair patch is applied.
The result may be 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 in 2014 the 110 Dreamliners it projected earlier this year.
Dominic Gates: 206-464-2963 or firstname.lastname@example.org