Under what condition is the Main Battery Knife Switch left Open?

Under what condition is the Main Battery Knife Switch left Open?

• A. When the engine is shutdown to prevent battery discharge
• B. During the start procedure if the engine is hard to rotate
• C. During normal operation
• D. After regular maintenance

Answer: (A)

The main idea is electrical isolation. The knife switch acts as a simple disconnect between the battery and the aircraft’s electrical system, so you can prevent any current from flowing when you don’t need power. When the engine is shut down, there’s no reason to keep the battery feeding idle loads or any parasitic drains from avionics, lights, or other equipment. Opening the switch stops that unwanted current path, preserving the battery for the next start or use. In contrast, during the start procedure you need the full battery supply, and in normal operation the system must be powered, so the switch is left closed. After maintenance, follow the specific procedure for isolating power, but the usual practice is to leave the switch as required by the checklist, not left open by default.

The main idea is electrical isolation. The knife switch acts as a simple disconnect between the battery and the aircraft’s electrical system, so you can prevent any current from flowing when you don’t need power.

When the engine is shut down, there’s no reason to keep the battery feeding idle loads or any parasitic drains from avionics, lights, or other equipment. Opening the switch stops that unwanted current path, preserving the battery for the next start or use. In contrast, during the start procedure you need the full battery supply, and in normal operation the system must be powered, so the switch is left closed. After maintenance, follow the specific procedure for isolating power, but the usual practice is to leave the switch as required by the checklist, not left open by default.