In which scenario would the use of de-icing or anti-icing equipment become necessary?

The necessity for de-icing or anti-icing equipment is critical during moderate ice conditions. In these conditions, ice accumulation can significantly impact the aircraft's performance and handling qualities, increasing drag and potentially leading to loss of lift. Moderate ice can adhere more tenaciously to the aircraft surfaces, making it more difficult to remove without proper de-icing measures. Therefore, activating de-icing or anti-icing systems in such a scenario ensures the aircraft maintains safe operational characteristics.

In contrast, trace or light ice conditions may not warrant immediate use of such equipment since the ice accumulation is typically minimal and may not critically affect the aircraft's performance. However, even in these scenarios, pilots must remain vigilant, as conditions can evolve quickly. Flying above freezing levels generally eliminates the likelihood of ice formation, thus reducing the need for de-icing or anti-icing measures.