Explanation: GMDSS Radio Operators are trained to operate and perform routine, non-technical maintenance on GMDSS equipment. Their responsibilities include tasks that ensure the operational readiness of the system without requiring specialized technical skills or opening the equipment chassis. Aligning the power output stage for maximum power (D) is a technical adjustment requiring specialized test equipment and knowledge of electronic circuits. This is a task performed by a qualified radio technician, not a GMDSS Radio Operator, as it involves internal circuitry and fine-tuning beyond routine operational checks. In contrast, visual inspections (A), on-the-air verification checks (B), and scheduled battery condition testing (C) are all considered routine operational maintenance functions. These tasks ensure the equipment is physically intact, functioning correctly, and has adequate backup power, all of which fall squarely within the scope of a GMDSS Radio Operator's duties for maintaining system readiness.