How is the description of severe icing characterized?

Severe icing is characterized by conditions that significantly impact the safety and performance of an aircraft. In this context, the choice that indicates de-icing equipment failure necessitating immediate flight diversion aligns with the definition of severe icing conditions. When severe icing occurs, it can lead to a substantial accumulation of ice on the aircraft's wings and control surfaces, which can drastically affect aerodynamic performance, alter handling characteristics, and increase drag.

In these scenarios, the aircraft may no longer be able to maintain safe flight, making it critical for pilots to act quickly, often requiring them to divert from their planned route to avoid hazardous conditions. This urgency in addressing severe icing, especially if de-icing equipment is non-functional, underscores the seriousness of the situation and the necessity of immediate corrective action for safety.

The other options do not depict the seriousness associated with severe icing. Light icing and moderate icing imply manageable conditions that do not necessitate immediate flight changes, while no significant icing suggests that the icing is not severe at all. Thus, identifying de-icing equipment failure requiring immediate diversion accurately captures the critical nature of severe icing.