What is a common symptom of a failing voltage regulator on an aircraft generator?

• A. Erratic or rising/falling bus voltage with stable engine speed
• B. Erratic or rising/falling bus voltage despite stable engine speed
• C. Voltage remains constant regardless of load
• D. Immediate generator trips on start

Answer: (B)

Voltage regulation is the process of keeping the bus voltage steady regardless of changes in engine speed and electrical load. The regulator does this by adjusting the generator’s field current so the output stays at the set value. When the regulator isn’t working properly, that control is lost, and the bus voltage can wander even if the engine speed is held constant. You’ll see the voltage rise or fall, or fluctuate erratically, because the regulator isn’t restoring balance between generation and demand.

That behavior matches the choice describing the bus voltage as erratic or rising/falling despite stable engine speed. If the voltage stayed constant no matter the load, that would indicate proper regulation or a regulator stuck in a fixed state, not a failing regulator. Immediate trips on start would point to a protection issue rather than a typical regulator fault.