A mistake made by Boeing 787 on fasteners

Core tip: Let's turn the time back to 2008. After Boeing announced the delay of the delivery of the 787 Dreamliner, Boeing revealed that on the first ten 787 airliners that are being assembled, each has at least 8,000 fasteners due to installation problems. For replacement, most of these fasteners are bolt-nut connections.

Let's turn the time back to 2008. After Boeing announced the postponement of the delivery of the 787 Dreamliner, Boeing revealed that on the first ten 787 passenger planes that are being assembled, each has at least 8,000 fasteners due to installation problems. For replacement, most of these fasteners are bolt-nut connections.

The fastener in question is used inside the fuselage to fix the titanium alloy structure on the carbon fiber composite material. During the pressure test of a completed 787 passenger aircraft, it was found that there were tiny and unacceptable gaps in the head area of u200bu200bthousands of fasteners in the fuselage.

After Boeing's preliminary investigation and analysis, these problems only appeared in the internal structure of the fuselage shell, such as the floor grille. First of all, this will not be a security threat, but because of the existence of gaps, it will reduce the durability of the fuselage, so it is decided to replace all the fasteners that have problems. According to people familiar with the matter, nearly 2,500 to 5,000 fasteners need to be replaced for each aircraft or seat gasket in the entire plan. Boeing publicly stated that it is estimated that nearly 3% of installed fasteners need to be removed and reinstalled. (Guide: Solutions to various machine tool spindle failures)

Boeing emphasized that the problem lies in the installation of fasteners, not the fasteners themselves.

The senior engineering and mechanical personnel responsible for the project are working hard to solve the problems in the installation of Boeing aircraft fasteners and supporting structural equipment as soon as possible.

The difficulty of this project is how to remove the fasteners and reinstall them while avoiding possible damage to the composite material.

A senior engineer said: The risk involved is that some fasteners must be drilled more. This is a common practice in the production maintenance process.

The design of the fastening structure focuses on future reusability and is mainly used for maintenance in use.

When Boeing first demonstrated the 787 Dreamliner One in July 2007, they replaced the temporary fasteners with long-used fasteners and caused damage. Now Boeing is facing the time-consuming repair of the Dreamliner One.

Boeing is retraining all 787 mechanics on new fastener installation procedures. People familiar with the matter pointed out that the incident was another measure to delay workers' resumption of work following the end of the International Association of Machinists’ strike. According to the strike resolution, the mechanics will not resume work until after November 10. Only mechanics who have completed retraining can continue to work on the aircraft.

Some people familiar with the fastener market told Flightblogger that this problem originated from the installation of two different types of fasteners in four flight test and two ground test aircraft, and more than ten A currently supplied mount gasket.

The first problem stems from the drilling used to adsorb titanium and carbon fiber. When a hole is drilled into titanium, burrs will usually stay on the left edge of the hole. Due to the special strength of titanium, when a fastener is installed in the hole, the head will stay on the burr and will not be tightly combined with the surface.

As the head of the fastener stays on the burr, the load will be distributed at one point instead of being evenly distributed on the surface. In addition, in the worst case, if asymmetric high shear load occurs, high-strength titanium burrs will destroy the integrity of the fastener structure. Titanium is used in key structural parts of the aircraft, such as the connection between the fuselage and the horizontal stabilizer.

It is reported that the fastener problem was first discovered on the engine pylon during the static test of the airframe.

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