What happens when both channels of the left FADEC fail?

When both channels of the left FADEC (Full Authority Digital Engine Control) fail, the most likely outcome is that the left engine will cease to operate properly. The FADEC is responsible for managing the engine's performance by overseeing fuel flow, engine start/stop, and various other critical functions. If both channels fail, there's no longer any command or modulation from the FADEC for the left engine, which typically leads to a loss of control and resultant engine failure.

In contrast, the right FADEC can only control its own engine and does not take over control of the left engine when the left FADEC fails; this limitation in cross-channel operation is a critical aspect of FADEC system design. Therefore, without the operational input from the left FADEC, the left engine would not be able to function as intended, making it likely to fail.