by Dominic Gates, Seattle Times Aerospace Reporter 19 Nov 2021, update 20 Nov
The litany of manufacturing defects on the 787 Dreamliner is expanding as Boeing engineers take apart planes and discover new or more widespread issues, a Federal Aviation Administration internal memo indicates.
The FAA memo, which was circulated internally Monday and reviewed by The Seattle Times, points to new concerns about a previously unreported defect caused by contamination of the carbon fiber composite material during fabrication of the large structures that make up the 787’s wing, fuselage and tail.
The memo also adds detail about the small out-of-tolerance gaps that have been discovered throughout the airplane structure: at the joins of the large fuselage sections, at a forward pressure bulkhead and in the structure surrounding the passenger and cargo doors.
The FAA memo, which lists safety conditions affecting airplanes currently in service worldwide, states that these tiny gap defects are thought to be present in more than 1,000 Dreamliners. These are not considered an immediate safety concern but could cause premature aging of the airframe.
“We’re looking at the undelivered airplanes nose to tail, and we have found areas where the manufacturing does not conform to the engineering specifications,” a Boeing spokesperson said Friday. “None of these issues is an immediate safety-of-flight issue.”
Those planes currently in service can be inspected and reworked later during routine maintenance, the spokesperson said.
However, complicating the process, the FAA memo states that Boeing doesn’t have the detailed configuration data on each plane to know which may have the defects.
It’s unclear if coming up with fixes that will satisfy the FAA will further delay resumption of 787 deliveries into next year.
Such a delay could increase the total cost to get the 787 program back on track above Boeing’s previous $1 billion estimate and would risk an accounting write-off in the fourth quarter.
Contamination of composite material
The internal FAA memo relates how, early this year, Boeing reported to the FAA that Mitsubishi Heavy Industries in Japan — which builds the jet’s carbon composite wings — had discovered contamination of the composite material during fabrication that could potentially weaken the bonding when two composite parts are bonded together with adhesives.
For example, when a stiffening rod is bonded to the inside of the wing skin.
In the fabrication process for composites, carbon fibre tape impregnated with epoxy resin is laid on a mould, then hardened in a high-pressure oven called an autoclave.
Bags are placed around the composite material to create a vacuum, and a thin sheet may be placed between the composites and the mould to facilitate release when it comes out of the autoclave. The contamination occurred because some of the bagging and release materials contained polytetrafluoroethylene — commonly known by the brand name Teflon.
The use of PTFE, which left a residue after removal, did not comply with Boeing’s manufacturing specifications.
Initial tests conducted by Boeing and reported to the FAA in April showed a positive outcome: although the bond strength was reduced, it was still within the design limits.
However, the memo includes a new update from late last month, in which Boeing told the FAA that the same contamination has now been found at other major suppliers and affects not only the wing but also the fuselage and tail.
In addition, further tests of small pieces of the composites now indicated that the strength of the bond between contaminated parts in some cases was below the allowed design limits.
Boeing last month suggested to the FAA an approach to evaluating the integrity of the bonds in the affected structures. But the FAA isn’t convinced. It responded that the proposed evaluation method is not approved and not validated by testing.
“The FAA will investigate,” the memo states.
Boeing’s communications team said Friday it did not immediately have details on the contamination issue and could not comment on that specific issue before press time.
An FAA spokesperson said, “We don’t comment on ongoing discussions with manufacturers.”
Fixing tiny gaps at the airplane doors
The FAA memo also highlights the discovery of small gaps in the structure surrounding the passenger and cargo doors in the aft fuselage section, built by Leonardo in Italy.
This is another instance of the tiny gaps that have been discovered in the airplane structure during final assembly, previously found at the major fuselage section joins and at the forward pressure bulkhead, a dome-shaped structural barrier behind the plane’s nose that is crucial to maintaining air pressure within the cockpit and passenger cabin.
Like those previous instances, the gaps in the structure around the aft fuselage doors result from waviness in the composite material at the joins.
The FAA notes that these discrepancies between the manufactured structure and the engineering specification are the result not of bad workmanship by mechanics, but of imprecision in the robotic equipment used to fabricate the airplane’s structures.
Such gaps, which may occur in metal airplanes, too, are typically filled with small pieces of material called shims during assembly. But somehow the gaps were missed during the building of the airplane sections by Boeing suppliers.
The lack of shims can cause the skin fasteners to pull away, the FAA said.
The FAA memo notes that Leonardo relies on mechanics to inspect their own work when they assemble the structures, with limited or no oversight by quality inspectors. And it states that the Italian supplier had two formal notices of missed inspections for surface waviness in 2018 and two more in 2020.
In an update this month, the FAA said that although Boeing provided a presentation contending that the gaps in the structure around the aft fuselage doors were within engineering requirements, it did not provide detailed manufacturing data on the condition of assembly of each plane.
The memo declares the FAA “skeptical.”
As it awaits FAA approval of an inspection method, Boeing is going ahead with fixes on some planes.
The Boeing spokesperson said that its engineers had been trying to come up with a standard procedure to remove the doors and inspect the surrounding structure that would satisfy the FAA, but that because this was taking too long it had begun reworking some initial planes.
“We have been trying to determine a door removal and inspection approach to see [if we can] plan a nondestructive inspection method to determine what we need to do going forward. That’s taken more time,” the spokesperson said. “So we have started rework on the door structure just in the near term, to try to be able to move forward with certain airplanes.”
Meanwhile, Boeing has paused assembly of the aft fuselages in South Carolina while it sorts out the problem.
The Wall Street Journal was first to report Friday the latest issue with the structure around the door. The Journal cited unidentified people familiar with the plans saying that it is increasingly likely that Boeing won’t resume delivering 787s until “February or March at the earliest.”
The FAA memo reviewed by The Seattle Times also provides updates on another 787 defect problem: the use of an incorrect alloy of titanium in certain fittings installed in fuselage sections made by Leonardo in Italy.
Parts with this incorrect metal included fuselage frame and floor beam fittings and were installed on more than 450 Dreamliners. Boeing identified the most critical installation as the floor-beam-to-fuselage-frame fittings at the side of body area where the wings attach.
The FAA said this could produce an unsafe condition if two or more adjacent fittings had used the wrong titanium alloy. Two aircraft with this immediate safety concern were identified, both All Nippon Airways jets that were parked in Victorville, California.
ANA agreed to keep the aircraft grounded while Boeing fixed them. That work was completed as of last month.
Finally, the memo notes that the FAA is still evaluating Boeing’s proposal to use statistical sampling to determine which airplanes are affected by the lack of shims and tiny gaps at the joins.
The memo states that more than 1,000 airplanes currently flying are affected and that the FAA is concerned about the lack of detailed assembly data on every airplane. Boeing submitted its proposal for inspections and indicated that the process would not require FAA approval.
“We firmly disagree,” the memo states. This standoff over what level of inspections is appropriate remains the major stumbling block to Boeing resuming 787 deliveries.
Correction: This story was updated early Saturday to correct the description of the composites contamination problem. The Teflon residue doesn’t reduce the strength of the part. Rather it reduces the strength of the join when two such composite parts are bonded together with adhesives.