The two channels of each FADEC will never make a simultaneous input to the engine except when which condition is sensed?

• A. When an engine overspeed condition is sensed
• B. When the engine temperature rises
• C. When fuel pressure drops
• D. When N2 speed falls below IDLE speed

Answer: (A)

The concept being tested is redundancy with guaranteed protection in a dual-channel FADEC system. Normally one channel masters the control and the other shadows or validates, so the engine isn’t receiving two different, potentially conflicting commands at once. The only time both channels will drive the engine simultaneously is in a protective, safety-critical situation: an overspeed condition. When overspeed is sensed, both channels take action at the same time to enforce the speed limit, ensuring rapid and definitive protection of the engine.

Other conditions like rising engine temperature, fuel pressure loss, or N2 dropping toward idle are managed by the FADEC logic through normal control pathways and do not require both channels to issue the same command at once.