During what condition might one expect the need for immediate flight diversion due to icing?

Severe icing conditions in flight indicate significant and immediate concerns for aircraft performance and safety. When pilots encounter severe icing, the accumulation of ice on critical surfaces can disrupt the airflow, reduce lift, increase drag, and lead to a loss of control of the aircraft. This situation can escalate quickly, potentially jeopardizing the safety of the flight.

In response to encountering severe icing, pilots are trained to seek an immediate diversion to avoid further exposure. The risk factors associated with severe icing necessitate prompt action to change altitude or redirect to a safer route or airport where conditions may be more favorable. Situations classified as moderate or light icing typically allow for some degree of management and do not present the same level of immediate danger, so diversions may not be as urgent or necessary in those cases. Extreme icing, while it would also require immediate action, is categorized as a level of icing that is less frequently encountered in practical scenarios, making severe icing the point at which immediate diversion becomes critical.