Boeing again faces a manufacturing quality issue, requiring inspections and repairs of its 787 fleet.
Structural stiffeners were found to be improperly joined to the composite skin in the aft sections of the aircraft, causing parts of the aircraft's carbon fibre structure to delaminate, confirms the airframer.
"Boeing has found that incorrect shimming was performed on support structure on the aft fuselage on certain airplanes in our facility in Everett, [Washington]," said the airframer.
Flightglobal has confirmed there are at least three affected airframes, Airplanes 56, for All Nippon Airways, where the problem was first discovered, and Airplanes 57 and 58, the first two aircraft for Qatar Airways.
Boeing declined to say how many 787s have this issue, though sources indicated that there are "significantly more" than the three initially identified in the factory.
Programme sources say the stiffeners, or longerons that run along the length of the aircraft, are delaminating around the rear opening of the Section 48 section above and below the cutout known as the "bird's mouth" that holds the Alenia Aeronautica-built horizontal stabiliser.
Boeing said the issue is a "straightforward repair" and poses no "short-term safety concern" and the airframer said its inspections have revealed "delamination in some instances."
Boeing is currently conducting inspections on the already built 787s and those waiting to be assembled, at least 50 airframes, in Everett and its North Charleston, South Carolina facilities.
"We have this condition well-defined and we are making progress on the repair plan," said Boeing and declined to say if the inspections were slowing preparations for delivering additional 787s.
The issue, identified around 24 January was traced to assembly of the aft fuselage by Boeing South Carolina, Formerly Vought Aircraft Industries, where Sections 47 and 48 are fabricated, assembled and stuffed with systems before being delivered to final assembly lines in North Charleston or Everett.
When the longerons are installed on the wound carbon fibre barrel, frames and longerons are secured to the skin of the structure to give it strength. When natural variations in the fit of parts exists, aerospace mechanics will install shims, or spacers, which compensate for variations and wedge into structure to create a tighter fit.
Without the shims, damage can be sustained to the composite when fasteners are installed by pulling the structure together, damaging the layers of carbon fibre.
Over the long-term composite delamination can decrease the fatigue life of the aircraft's structure.
Boeing said it has "already taken appropriate steps to address this issue" in South Carolina, declining to elaborate on what steps it has taken.
"We have already notified our early customers to ensure they are informed and aware of our plans to make repairs, should they be needed," the company said.
ANA, currently the sole operator of five 787s, said: "Currently we are not experiencing the issue; however, we are aware of this issue arising at the factory, and will take appropriate action when contacted by Boeing."
For the affected aircraft, Boeing said its "current plan", which one programme source described as "tedious", will not require the removal of the 787's tail cone and horizontal stabiliser to fix the longerons, its initial remedy for aircraft in the factory, and it can "address this condition without removal of any major structural parts."
"Repairs, should they be needed, will be implemented in the most efficient manner possible," said Boeing in order to maintain a design that conforms with its airworthiness certification standards.
Boeing has faced manufacturing quality issues before, most notably the June 2010 inspection, teardown and reinstallation of many Alenia Aeronautica-built horizontal stabilisers after many were assembled without proper shimming creating gaps in the structure that threatened the fatigue life of the empennage.