In a dual DC generator failure, the tail rotor cannot power either main DC bus with which switches secured?

• A. FUSE
• B. BATTERY
• C. GENERATOR
• D. OFF

Answer: (B)

When both DC generators fail, the main DC buses have no generation source. The only way to power those buses in that situation is to connect the aircraft battery to them via the BATTERY switch. If the BATTERY switch is secured (isolated), the battery cannot feed the main DC buses, so the tail rotor’s power path to either bus is cut. That’s why securing the battery switch prevents powering either main DC bus. The other switches don’t establish the necessary battery-to-bus power path: a fuse is only protective, a generator switch would not provide power when the generators are failed, and OFF simply keeps a source disconnected, which is not the path the question is testing.