Which bus is the highest level of integrity (Powerline)?

• A. Essential Bus
• B. Main Bus
• C. Non-Essential Bus
• D. Cabin Bus

Answer: (A)

Power distribution is arranged so that flight-critical equipment stays powered first. The highest integrity path, the Essential Bus, feeds the instruments, flight controls, and other essential avionics. It’s designed to stay alive even if other power sources fail, backed by backup sources to keep critical systems operating for safe flight and landing. Other buses—Main, Cabin, and Non-Essential—support less critical loads and can be de-energized to conserve power when needed. So the Essential Bus is the highest integrity powerline.