When should a fiber-type, self-locking nut not be used on an aircraft?

A fiber-type, self-locking nut should not be used on an aircraft when the bolt is subject to rotation. This is primarily because the self-locking mechanism relies on friction generated between the nut and the bolt threads to maintain tightness. When a bolt is subjected to rotation, such as in applications where it experiences continuous or cyclic motion, the nut can become loosened over time due to the rotational forces, which can exceed the frictional forces of the self-locking feature.

Using a self-locking nut in such situations can lead to significant safety hazards, as the connection may fail if the nut loosens. Therefore, for applications involving rotating components or bolts, other types of fasteners that can maintain a more secure hold under dynamic loads would be recommended. This ensures that the integrity of the assembly is maintained, which is critical in aircraft applications where safety and reliability are paramount.