What lighting configuration indicates that aircraft engines are running?

The correct response is that the beacon light being illuminated indicates that aircraft engines are running. The beacon light serves as a warning signal, typically flashing red or white, to indicate that the aircraft is in operation and alerts others in its vicinity that it's powered up and preparing for movement.

The other choices refer to different lighting configurations. Position lights are used to indicate the location and orientation of the aircraft but do not specifically signal engine operation. Taxi lights are typically used to illuminate the area in front of the aircraft while taxiing, but their activation indicates ground movement rather than specifically the state of the engines. Lastly, having all lights off would suggest that the aircraft is not powered on or is in a parked state, contrasting the indication of engine activity signaled by the beacon. Thus, the beacon light is the proper configuration indicating that aircraft engines are running.