Which of the following is a sign of corrosion that requires maintenance action?

Each of the listed signs indicates a potential issue related to corrosion that could impact the performance and safety of avionics equipment. Recognizing these signs is crucial for maintaining the integrity of both the aircraft and its systems.

Surface discoloration typically indicates a chemical reaction occurring at the material's surface, suggesting that corrosion is present. This visible change often serves as an early warning sign, prompting the need for further inspection and maintenance to prevent progression.

Unexplained loss of weight serves as a more direct indication that material is being degraded, often due to corrosion processes. When structural components lose mass, it can affect the strength and reliability of the equipment, signaling an urgent need for maintenance to address any compromised areas.

Increased electrical resistance is particularly significant in avionics systems, where electronics rely on optimal conductivity for operation. Corrosion can create insulating layers or other barriers that impede electrical flow, which could lead to failures in critical systems. Recognizing increased resistance is essential to ensure proper functionality of electrical components.

Since all these signs – surface discoloration, unexplained weight loss, and increased electrical resistance – can indicate corrosion and warrant maintenance action, selecting the option that encompasses all of them reflects a comprehensive understanding of corrosion indicators in avionics.