If one or both ice detectors fail, what must the crew do when icing conditions exist or are anticipated below 10°C TAT with visible moisture?

If one or both ice detectors fail, what must the crew do when icing conditions exist or are anticipated below 10°C TAT with visible moisture?

• A. Remain in AUTO
• B. Set the mode selector to ON
• C. Turn the anti-ice OFF
• D. Switch to MANUAL

Answer: (B)

When icing is possible, anti-ice protection should be active. In AUTO, the system relies on ice detectors to decide when to energize heat, so if one or both detectors are failed, the auto logic may not engage the anti-ice when needed. Setting the mode selector to ON provides continuous anti-ice heating regardless of detector input, giving protection in icing conditions or when icing is anticipated (below 10°C TAT with visible moisture). This ensures the leading edges and other protected surfaces stay heated to prevent ice buildup. Remain in AUTO would risk untreated icing, and turning the system OFF would remove protection. Switching to MANUAL isn’t the required action here; ON is the correct override to maintain protection when detectors are inoperative.

When icing is possible, anti-ice protection should be active. In AUTO, the system relies on ice detectors to decide when to energize heat, so if one or both detectors are failed, the auto logic may not engage the anti-ice when needed. Setting the mode selector to ON provides continuous anti-ice heating regardless of detector input, giving protection in icing conditions or when icing is anticipated (below 10°C TAT with visible moisture). This ensures the leading edges and other protected surfaces stay heated to prevent ice buildup. Remain in AUTO would risk untreated icing, and turning the system OFF would remove protection. Switching to MANUAL isn’t the required action here; ON is the correct override to maintain protection when detectors are inoperative.