Under what conditions can de-ice equipment not be used?

The proper condition under which de-ice equipment should not be used is when the air temperature is less than -40 degrees. At this extremely low temperature, the performance and effectiveness of the de-ice systems may be compromised. Many de-ice systems rely on thermal properties or liquid de-icing agents that may not function properly when temperatures drop below this threshold. For example, some liquids may freeze or become less effective in providing the necessary protection against ice accumulation.

In contrast, the other scenarios do not pose the same inherent risks. For example, de-ice equipment can typically be utilized when the air temperature is greater than 30 degrees and even when flaps are extended beyond a certain degree, as long as the equipment is operational. Moreover, during these conditions, pilots and operators are trained to monitor for any icing phenomena and activate de-ice systems accordingly. Therefore, understanding the limitations of de-ice equipment in specific temperature ranges is essential for safe aircraft operations.