Despite the complexity and high-risk nature of the industry, the number of accidents and incidents involving commercial aircraft has steadily declined over the years. According to the International Air Transport Association (IATA), the global jet accident rate in 2021 was 0.24 per million flights, which is the equivalent of one accident for every 3.9 million flights. This is a significant improvement from the 1980s, when the accident rate was around 1 per million flights. The industry's commitment to safety is reflected in the rigorous testing and certification processes for aircraft and their components, including fasteners.

Fastening plays a critical role in the safety and reliability of aerospace structures, as they ensure that different components stay together and perform as intended during the harsh conditions they’re subjected to. While it may seem like a minor detail, the integrity of fasteners can make all the difference in the success or failure of a flight. This is why aerospace manufacturers have established rigorous standards and guidelines for the selection, installation, and maintenance of fasteners. 

In this article, we will outline the main fastening standards in the aerospace industry, explore the crucial role of smart torque tools in aerospace assembly, discuss the unique challenges and considerations for fastening quality control, and examine the latest innovations in fastening technology.

Fastening standards

Various associations, including ISO, SAE and AIA, as well as administrations such as the FAA and NASA, have developed strict quality and safety standards to assist aerospace manufacturers and suppliers in ensuring the highest quality in every part of the assembly and manufacturing process.
These standards include all aspects of fastener design, selection, installation, and inspection, as well as quality control procedures.
Most organizations operating in the aerospace industry are required to register to one of the following standards: AS 9100, AS 9110, or AS 9120. Kolver has been ISO 9001 compliant since 1998.

The Federal Aviation Administration has also provided a comprehensive guide of acceptable methods, techniques and practices for aircraft inspection and repair: AC 43.13-1B.
Particularly relevant to fastening is section 7-40, which focuses on torque, its introductory paragraph reading “The importance of correct torque application cannot be overemphasized. Undertorque can result in unnecessary wear of nuts and bolts, as well as the parts they secure. Overtorque can cause failure of a bolt or nut from overstressing the threaded areas. Uneven or additional loads that are applied to the assembly may result in wear or premature failure.“

Two key mandates are:

• calibrate the torque wrench at least once a year, or immediately after it has been abused or dropped, to ensure continued accuracy. For more information on this topic, check out our article “Tool calibration 101”.
• add the friction drag torque to the desired torque. This is referred to as “final torque”.

Kolver’s K-DUCER line of transducerized electric screwdrivers has an advanced-torque feature that dynamically monitors the prevailing torque encountered during fastening and can add it to the final torque, ensuring consistent clamping force applied across all joints.  For more information, read our series of articles on torque strategies starting with “Running Torque strategies in the assembly process”.

Compliance with these standards is essential for ensuring the proper selection, installation, and inspection of fasteners and torque tools used in aerospace applications, which is critical for the safety and reliability of aerospace systems.

Quality Control

Another reason why the aerospace industry has a good record when it comes to fastener reliability is because of the robust quality control practices implemented by both fastener manufacturers as well as the assembly lines installing those fasteners.
On the fastener manufacturing front, this includes testing each batch of fasteners to ensure that they meet the required specifications for strength, durability, corrosion resistance, and reliability. Various forms of testing are employed, including ultrasonic testing, magnetic particle inspection (MPI) and vibration testing, and any defective or non-conforming fasteners are rejected and not used in the final product. We will dive deeper into the specific topic of aerospace fasteners in a later article.

On the assembly front, production lines have fully embraced Industry 4.0 practices and utilize smart torque tools such as Kolver’s K-DUCER to ensure proper installation of each fastener according to its specifications; if any abnormalities are detected, or if a fastener is missed altogether, the assembly operation will not be able to progress any further. Full traceability of every tightening operation means all of this data is captured and stored to help identify potential issues in real-time, optimize processes, and ensure compliance with the aforementioned standards, resulting in higher production output and less rework.

Aerospace manufacturers are also increasingly using automation and robotics to assemble complex components with a high degree of precision and repeatability, reducing the frequency of human error and the resulting safety risks (as well as costly repairs and delays). Automating the assembly of an entire aircraft or spacecraft would be a colossal task, but automating sub-assemblies and narrow-domain tasks like hole drilling and low-torque fastening is much more feasible; with hundreds of thousands of fasteners being used for each aircraft, the efficiency gains are still massive. The quality and safety benefits are even greater when switching from manual tools with manual inspections and written verification on paper documents to cobots using smart, programmable tightening tools like Kolver’s K-DUCER that can dynamically detect and respond to complex fastening conditions, all while collecting and storing data on every single tightening operation for quality assurance. These smart tools also facilitate the essential task of scheduling of regular ISO-compliant calibration and the storage of calibration records for future reference, an often-overlooked but essential process.

As more parts of aerospace factories become automated and Industry 4.0 compatible, the benefits will continue to compound, further improving the final products and industry’s safety record.

The big picture

Aircraft and spacecraft are subjected to some of the harshest conditions of any transportation vehicle used by humans. Atmospheric forces, temperature extremes, ultraviolet rays, tremendous G-force and radiation put incredible strain on every component, big and small. 
A long tradition of robust quality control processes, combined with the stringent regulatory oversight it operates under, have given the aerospace industry a reputation for the highest standards of quality and performance. The recent trend towards integrating Industry 4.0 practices, automation and robotic technologies in its production lines has added additional momentum to the continuous improvement of the industry’s safety track record, and Kolver is at the forefront of this technological transformation. By providing Industry 4.0 electric screwdrivers like the K-DUCER to aerospace factories, often integrated into fully-automated solutions, Kolver helps manufacturers comply with all the standards they must abide to, improve productivity and quality control, and maximize the safety and reliability of the finished products.