The eight in-service 787 Dreamliner jets that Boeing grounded last month for inspection and repair due to manufacturing quality flaws at its South Carolina plant were from a batch that came off the production line more than a year ago.
These eight planes — delivered to airlines including United, Air Canada and Singapore Airlines — were each found to have two separate quality defects at the same place in the aft fuselage.
Boeing engineers determined that while either one of the flaws alone was not a safety of flight issue, planes with both flaws could have compromised structural integrity and had to be grounded.
Jets with just one of the flaws may nevertheless need substantial repair work during future maintenance checks to fully comply with regulatory specifications.
The issue comes at a low point for Boeing, with its 737 MAX grounded due to safety concerns after two fatal crashes and demand for its other airliners severely curtailed by the worldwide COVID-19 pandemic.
In addition, the defects produced at the North Charleston, South Carolina, plant add to long-standing concerns about quality control at the site, even as Boeing studies the possibility of consolidating all 787 final assembly there, taking work away from Everett.
Last month, the Federal Aviation Administration (FAA) proposed fining Boeing $1.25 million for exerting pressure on safety reps at the South Carolina complex.
The aft fuselages for all 787s are fabricated there, whether they are final assembled in North Charleston or in Everett.
How much rework is needed?
Boeing doesn’t yet know how many jets there are that have only one of the two flaws or whether any rework will be needed.
“We are analyzing data on the in-service fleet,” spokesperson Jessica Kowal said Friday. “We’re still establishing the scope. No immediate action is required.”
The second flaw was discovered last month and prompted a reinspection of airplanes built before August 2019, when the first flaw was discovered.
A report Friday in trade magazine Aviation Week said there could potentially be “several hundred” 787s with just one of the two defects.
Since August 2019, about 110 of the aircraft have been built, suggesting that at least that number potentially have the second defect.
Both production flaws occur in the aft fuselage at the join between two barrel sections. One section is the back end of the pressurized passenger cabin, while the other is the unpressurized and tapered barrel section behind it where the jet’s tail is attached.
A heavy circular bulkhead at the join is strong enough to withstand the pressure difference between the two sections. Substructure around the join allows the sections to be bolted together inside and holds the bulkhead in place.
Each of the manufacturing flaws created gaps between the fuselage skin and this joining substructure.
Small gaps that routinely occur when sections are joined are typically filled with “shims,” pieces of material sized exactly to fill the gap. In August 2019, Boeing discovered that it had been producing shims of the wrong size.
The manufacturing process uses laser measurement to precisely align the barrel sections and to predict the size of any shims needed.
Kowal said the flaw arose when “software notification designed to alert when a shim exceeded the maximum thickness per engineering specifications was not being used.”
The second flaw was discovered last month: The inside surface of the fuselage skin at the join was not smooth enough.
“There are very tight tolerances for the flatness of the fuselage skin … where the join occurs; anything greater than 0.005 inches is outside of engineering tolerance,” Kowal explained. “Due to a manufacturing issue, some airplanes have been found to be beyond this limit.”
This discovery prompted a reinspection of airplanes built before August 2019 and the analysis showing that the combination of the two flaws — wrong-sized shims and a nonflat inner skin surface — could together create unacceptable gaps.
Boeing’s Kowal said engineers determined that with just one of the flaws the fuselage structure is still strong enough to meet “limit load” requirements, meaning the maximum load the plane’s structure is expected to encounter in service.
However, for full compliance with regulations, airliners must also meet a higher standard called “ultimate load.” For the jet’s wings, for example, ultimate load is 1.5 times limit load.
Kowal said that the eight 787s that have been grounded, “once reworked will meet limit load and ultimate load requirements as established by the FAA.”
Boeing is still analyzing what rework, if any, is needed, on the other planes.