Which of the following is NOT a level of ice accumulation in flight?

In aviation meteorology, levels of ice accumulation refer to the intensity of ice that can form on an aircraft during flight in icing conditions. The classifications typically used are trace, light, moderate, and severe, which help pilots assess the potential dangers of icing and make decisions accordingly.

The term "extreme" is not a recognized standard level of ice accumulation in flight. The correct levels cover a range from minimal (trace) to substantial (severe), providing a clear framework for understanding the severity of icing risks. Trace indicates very light accumulation, while severe refers to substantial and potentially hazardous ice buildup. Since "extreme" does not fit within this established classification system, it is the correct answer for what is not a level of ice accumulation.

Understanding the definitions and implications of these levels is crucial for pilots to maintain safety and make informed decisions during flight operations in potentially icy conditions.