When must the anti-ice system not be used?

The use of the anti-ice system in the Dassault Falcon 7X is primarily dictated by temperature and conditions conducive to ice formation. The correct choice, indicating that the anti-ice system should not be used when the Total Air Temperature (TAT) is above 10°C, reflects a critical operational guideline to prevent unnecessary use of the system when icing conditions are unlikely.

At temperatures above 10°C, the likelihood of ice forming on the aircraft surfaces is significantly reduced. Ice typically forms in conditions where temperatures are at or near freezing, especially when combined with humidity. Thus, employing the anti-ice system in these warmer conditions would not only be unnecessary but could also affect the aircraft's performance and efficiency, leading to potential overheating or other operational issues.

In contrast, temperatures above 5°C or 0°C may still warrant caution but do not provide the same assurance that icing will not occur. Therefore, the specified threshold of 10°C serves as a clear demarcation for safe operations concerning icing conditions while ensuring the anti-ice system is utilized effectively and efficiently.