MIAMI – This week Boeing confirmed that eight 787 Dreamliners have been removed from service pending repairs. The company cited two separate manufacturing errors as the cause.
According to The Air Current, the manufacturing issues were found at the joint between two fuselage barrels. This section 47/48 is directly behind the pressure bulkhead at the rear of the fuselage.
Manufacturing Issue 1: the Shimming
There are two different issues in this joint area. The first is an issue with the shimming during joining. Shims are extra important as unlike aluminum, composite fuselage sections are very stiff. This means that any gaps between the barrels need to be filled with shims to allow for proper load transfer.
Boeing has had issues with shimming in the 787 in the past, particularly at the beginning of the 2010s. There have also been issues with the same rear fuselage area that were covered in an Airworthiness Directive for 5 aircraft. This shimming issue was discussed in the Boeing 787–8 Critical Systems Review Team Report that was published on March 19, 2014.
There was also an issue with shimming in the horizontal tail plane back in 2010. This issue had several facets, including improper shim installation and overtorque of bolts.
Manufacturing Issue 2: Joint Smoothness
In the case of these eight aircraft, there was a second manufacturing nonconformity. The inner skin of the joint area is supposed to be smooth without any ridges. On these aircraft, this was not the case. Smoothness is also important for load transfer, as even if the joint is properly shimmed if there are ridges there can be areas of high stress.
The combination of the two issues means that the joint strength limit load is not sufficient. This is an issue as the limit load, unlike the ultimate load, technically could occur during flight.
In essence, the two issues combined change the load path between the two fuselage sections. It could cause areas of high stress as well as lower stress, and could also cause fatigue damage to the structure. If there was a failure in this area of the aircraft during flight, it would most likely be catastrophic.
Repairs are expected to take about 2 weeks. More research is being conducted into the cause and detailed effects of these issues.
It is reported that there are three airlines affected by this repair. The airlines are Singapore Airlines (SQ), United Airlines (UA) and Air Canada (AC). In the case of SQ, the aircraft was not in service at the time of the pull from service.
Featured image: Boeing 787 roll out ceremony. Photo: Boeing.