What are the FADECs powered by?

The FADECs, or Full Authority Digital Engine Controllers, are indeed powered by the DC electric system below 50% N2 and by the Permanent Magnet Alternator (PMA) above 50% N2. This dual power source is crucial for the operation of the FADECs since they need reliable electrical power to control engine functions throughout the various phases of operation, including startup, acceleration, and cruising conditions.

When the engine is below 50% N2, the FADEC relies on the aircraft's DC electrical system, which ensures that the FADEC has the necessary power to monitor and manage the engine effectively during start-up and early engine operation. Once the engine reaches a threshold of 50% N2, the PMA takes over as the primary power source for the FADEC. The PMA produces electricity from the rotating engine components, which provides a robust and reliable source of power suited for the engine's operational demands.

Other options do not accurately capture the power sources for the FADECs. For example, reliance solely on the battery at all times would not provide sufficient power during higher operational phases, and depending solely on the APU when in operation or strictly during engine start does not reflect the continuous nature of how the FADE