In a cross-talking scenario, a FADEC will assume the other engine has failed when the N1 difference reaches what minimum percentage?

• A. 5%
• B. 10%
• C. 15%
• D. 20%

Answer: (C)

The main idea is that the FADEC constantly compares the N1 of both engines and uses that difference to decide if one engine has effectively failed. If the gap between the engines becomes large enough, the system treats the other engine as failed and switches to protections suitable for single-engine operation. This threshold has to strike a balance: it must be high enough to avoid nuisance trips from normal variations and sensor tolerances, but low enough to detect a real failure promptly. Among the given options, the choice that represents a moderate, balanced gap fits this requirement best, which is why it is considered correct. The other options would either react too easily to normal differences or too slowly to detect a genuine failure, compromising safety.