Boeing engineers insist they are confident in the long-term structural integrity of the 787’s composite fuselage, saying extensive testing and examination has shown that the fuselages retain durability far longer than most airlines will ever fly the jets.
This, despite a report last week that a whistleblower warned the Federal Aviation Administration that a known issue involving gaps between fuselage sections could cause long-term problems.
“There is nothing in these composite joins – in anything we’ve seen, in any testing we’ve done, including the full-scale testing – that is demonstrating there is any concern with the fatigue or durability of this structure,” Boeing functional chief engineer of mechanical and structural engineering Steve Chisholm said on 15 April.
“I am not concerned about the durability or the fatigue performance of [the] composite structure,” he adds.
The New York Times reported on 9 April that the FAA is investigating a Boeing employee’s claim that the way the company is addressing the fuselage-gap issue could eventually lead to structural problems.
Boeing pushed back immediately, saying on 9 April, “Claims about the structural integrity of the 787 are inaccurate and do not represent the comprehensive work Boeing has done to ensure the quality and long-term safety of the aircraft.”
Now, Boeing has disclosed more information about the fuselage-gap problem, while stressing its confidence in the long-term durability of the 787’s carbonfibre fuselage.
The jets’ fuselages are composed of five massive barrel sections, each manufactured as single pieces that include stringers. The manufacturing process leaves a series of raised humps on the inside skin of the barrels. The humps are near the edges of the barrels, where they come together.
Boeing secures fuselage barrels to each other using splice straps, which overlap the edges of two fuselage sections to be mated. Fasteners secure the slice straps to the inside edges of fuselage sections.
To achieve a tight fit, however, workers hand sand the raised humps on the inside of the fuselage skins.
The problem arose because some of the bumps were sanded improperly. As a result, when fastened, the surfaces did not perfectly align, leaving gaps between the skins and the straps, Boeing says.
Small gaps are unavoidable in manufacturing, but the problem gaps exceeded Boeing’s FAA-approved 787 design and production specifications, which require they do not exceed five thousands of an inch or 0.12mm.
Boeing discovered the issue a few years ago.
It now says the gaps were actually present since the 787’s initial production, meaning most or all Dreamliners produced until recently may, or likely do, have out-of-specification gaps.
But Boeing insists that everything it knows about the gaps point to the problem being limited to a conformance issue – not a safety concern.
Chisholm, and Boeing vice-president of airplane programmes engineering Lisa Fahl, say the fuselage design has been thoroughly tested, They call Boeing’s gap-size requirement conservative and say larger gaps, according to analysis to date, do not threaten airframe durability or safety.
Chisholm notes that early during Boeing’s 787 development the company conducted full-scale 787 fatigue testing that simulated 165,000 flights – far exceeding normal operational expectations.
“There were no findings. Zero findings in fatigue in our composite structure,” he says, noting that in-service 787s operate an average of about 600 flights annually.
Chisholm also says Boeing examined older 787s and “didn’t find any issues in the composite structure”.
Still, the problem led Boeing to halt 787 deliveries in October 2020 as it worked to understand and address the gap problem. At the time, Boeing was sitting on about 120 undelivered 787s.
Prior to delivering those, Boeing has needed to remove more than 10,000 fasteners on each jet – more than 1 million fasteners across all its inventoried 787s – so workers can inspect for gaps.
Boeing must fill some of those gaps with shims. It can leave others as is – but only for specific gaps that Boeing has proven, and the FAA has agreed, are safe, Chisholm says.
The company has completed the rework on about 100 of the undelivered 787s and expects to finish inspecting all 120 jets by year-end.
Meantime, in the last few years, Boeing developed new methods to ensure gaps are within specification prior to assembling the jets. It does so by scanning the inside edge of the fuselage skins using a laser-measurement tool made by German company 8Tree.
Boeing resumed delivering 787s in August 2022.
