Four modes of control for HFRG

• A. Degraded, Reduced, Normal, Manual
• B. Normal, Degraded, Reduced, Manual
• C. Manual, Normal, Degraded, Reduced
• D. Normal, Manual, Degraded, Reduced

Answer: (B)

The four modes show how HFRG shifts from full automation to complete human control as issues arise, ensuring continued operation as long as possible. In Normal mode the system runs with full automatic control and standard procedures. If a fault occurs, it moves to Degraded mode, where some subsystems are unavailable but essential functions still operate. If problems worsen, it transitions to Reduced mode with more limitations on capabilities. If automation can no longer be relied on, it goes to Manual mode, where operators perform tasks without automated assistance. This progression—from Normal to Degraded, then Reduced, and finally Manual—is the correct sequence because it reflects the intended fault-tolerant path: keep as much automatic control as possible, stepping down only as needed. The other options mix or jump between levels in a way that doesn’t align with how the system is designed to degrade gracefully.