When the engines are running, the FADEC is powered by:

The correct option indicates that the Full Authority Digital Engine Control (FADEC) system receives power from its own alternator when the engines are running. The FADEC is a crucial component for the management and control of engine functions, including fuel flow, engine performance, and throttle response.

When the engines operate, they drive an alternator that provides the necessary electrical power for the FADEC system. This setup ensures that the FADEC can function without relying on external sources of power, allowing it to maintain control of the engines efficiently and continuously. The internal design of the FADEC system is such that it is self-sufficient in generating the power required to operate under normal conditions.

Other options such as external sources of airplane electrical power or internal batteries are not utilized for powering the FADEC when the engines are running because the self-generating nature of the alternator is more efficient and reliable for this critical system. This design minimizes dependency on other power sources and enhances the overall reliability of the engine control system.