Which type of washer has a special coating that prevents electrolysis between the ground stud and the aircraft?

The correct answer is the corrosion washer. This type of washer is specifically designed with a special coating to mitigate the effects of electrolysis, which can occur when dissimilar metals are used in an assembly. Electrolysis can lead to corrosion, compromising the structural integrity and functionality of components in aircraft systems.

In aviation, maintaining a reliable electrical connection is critical, especially for grounding applications. A corrosion washer typically has a coating that serves as a barrier, preventing moisture and electrolytic reactions from occurring between the ground stud and the surrounding materials. The proper selection and use of a corrosion washer help enhance the longevity and reliability of electrical connections in aircraft assemblies.

Other types of washers may not have the same protective features. For instance, a rubber washer is primarily used for sealing and vibration dampening but does not have the protective characteristics needed for preventing electrolysis. A spring washer is designed to provide tension and prevent loosening of bolted connections, while a flat washer serves to distribute loads. However, neither of these options includes a coating specifically engineered to protect against electrolysis.