From where does the FADEC obtain power during startup and shutdown?

The Full Authority Digital Engine Control (FADEC) system typically obtains its power during startup and shutdown from the aircraft's 28 VDC electrical system. This aligns with standard practices in aviation, where 28 VDC is commonly used across various aircraft systems for operational efficiency and safety. The 24 VDC and 32 VDC options do not match the typical voltage levels used in modern aircraft systems. Additionally, while a ground power unit can supply power to the aircraft during startup, the question specifically asks about the source of power for the FADEC system during those processes, which regularly relies on the aircraft’s onboard electrical system when it is operational. Therefore, the 28 VDC is the most accurate choice to indicate where FADEC derives its power during these critical phases of operation.