When should you disconnect external power from aircraft?

When should you disconnect external power from aircraft?

• A. Both engines running and external power unit is shut off
• B. After engines are shut down
• C. Before starting maintenance
• D. When the battery is low

Answer: (A)

External power is used to supply the aircraft’s systems on the ground, but once the engines are started, the aircraft’s own generators (engine-driven) can power the systems. Disconnecting the external power unit while both engines are running allows the aircraft to rely on its onboard power sources and prevents any electrical conflicts or backfeeding from the ground source. So, the best practice is to shut off and disconnect the external power after engines are running. This differs from waiting until engines are shut down (you’d lose power during any remaining operations or maintenance) and from disconnecting before maintenance (power is often needed for certain checks or operations). The battery being low isn’t the determining factor for disconnecting external power.

External power is used to supply the aircraft’s systems on the ground, but once the engines are started, the aircraft’s own generators (engine-driven) can power the systems. Disconnecting the external power unit while both engines are running allows the aircraft to rely on its onboard power sources and prevents any electrical conflicts or backfeeding from the ground source. So, the best practice is to shut off and disconnect the external power after engines are running.

This differs from waiting until engines are shut down (you’d lose power during any remaining operations or maintenance) and from disconnecting before maintenance (power is often needed for certain checks or operations). The battery being low isn’t the determining factor for disconnecting external power.