An avionics systems mechanic maintains and tests avionics and electrical systems on various aircraft like the C-17, C-130, and KC-135. Their responsibilities include conducting training, updating records, troubleshooting issues, and using various tools and equipment to perform maintenance, repairs, inspections, and modifications. They also ensure aircraft are available to meet mission requirements by coordinating maintenance activities. The mechanic has experience working directly with engineers to maintain and troubleshoot complex aircraft systems.