MIAMI – Late last month, eight Boeing 787 were removed from service due to two manufacturing issues in the fuselage. Earlier this week, the horizontal stabilizer was also reported to be under investigation, and there are now reports that the vertical tail fin might also be affected.
KOMO News Radio was the first to report on this new issue, stating that it has been known since the end of 2019. Boeing has stated that the manufacturing process has been changed to prevent it from occurring.
This new issue is found near the root of the tail fin, close to a joint where the Main Torque Box skin, Rear Spar, and Route Fitting #4 all come together. It can be on the left or right hand side.
An aircraft mechanic discovered dimpling on the skin, and reported it. Dimpling in aircraft skin can be a sign of damage or internal issues.
Investigators looking into the issue found that the shims were missing, and that there was a gap of 0.034 inches (0.0864 cm). Fastening parts together with a gap of this size will cause an increased preload.
During the drilling of the parts, the shims were properly applied. However, for some reason, the shims were removed during the final assembly.
When considering the design loads, this added preload could bring the total loading on this area above the limit load. The Section 47/48 issue from the end of August had a similar issue.
Keeping the loading on the aircraft under the limit load is very important. Engineers have designed each part to withstand the limit load for a given lifetime, and have designed maintenance tasks accordingly.
While the expected loading with the added preload is still under the ultimate load limit, operating above the limit load can cause further damage to the aircraft.
The structure in this area of the aircraft is considered to be a Principal Design Structure, meaning that the aircraft needs it to fly. Having a failure during flight could cause further damage, or even loss of control.
Boeing has stated that it has conducted an investigation and found it does not immediately affect the aircraft’s safety. Working with the FAA, the spokesperson stated that they expect a one-time inspection during standard maintenance.
Since the Boeing 787 uses a large amount of composite material, such as in the tail of the aircraft, it might be that the checks will need to be more in depth than a general visual inspection. When composites are loaded not according to design, it can cause unseen damage within the material, such as delamination.
In any case, the FAA and Boeing will need to perform further investigation, and develop and roll out final solution for the in-service fleet. The issue is estimated to affect 681 aircraft in total.
This brings the total manufacturing issues recently disclosed up to 4 for the 787. Beyond the type, Boeing has recently had issues with the 737Max, the KC-46, as well as the Starliner programs.
Featured image: Boeing 787 Dreamliner. Photo: Boeing