What must be tightly secured to avoid fasteners loosening during operation?

In the context of aerospace assembly, ensuring that components do not loosen during operation is critical for safety and performance. Lockwire is specifically designed to secure fasteners such as bolts in place. It prevents rotational loosening that can occur due to vibration and other dynamic loads. By threading lockwire through the heads of bolts or around fasteners and securing them to adjacent components, it provides an additional layer of security, keeping critical assemblies intact.

While bolts themselves need to be securely fastened and washers play a role in load distribution and preventing damage to surfaces, these items alone do not provide the same level of ongoing, dynamic security that lockwire does. Lockwire is a specialized method used specifically to combat the issue of fastener loosening in environments subjected to high levels of vibration and movement, making it the most directly relevant answer to the question regarding what must be tightly secured to prevent loosening during operation.