If both sources of power to FADEC fail, what will happen to the engine?

• A. The engine will shut down
• B. FADEC will switch to backup manual mode
• C. The engine will maintain current thrust
• D. The Engine will go to idle

Answer: (A)

When the FADEC loses all power, it can no longer perform fuel metering, sensor monitoring, or the protective logic that keeps engine operation safe. The engine relies on the FADEC to continuously command the correct fuel flow and throttle schedule; without any electrical power, those commands can’t be issued. There’s also no power available to switch to a backup or manual mode, since manual operations depend on the FADEC’s control circuitry being powered. With no control authority, the safest and most consistent design outcome is to shut the engine down to prevent an uncontrolled state or compressor damage. Because of that, the engine will shut down. The other options aren’t viable because they require FADEC power to enact or maintain, which isn’t available when both power sources fail.