What defines the icing intensity classification of 'severe'?

The classification of 'severe' for icing intensity refers to conditions where immediate flight diversion is required. This classification indicates that the icing conditions present a significant risk to the safety of the aircraft. In severe icing, the ice accumulation can lead to critical performance degradation, affecting lift and control of the aircraft, which necessitates urgent action from the flight crew to divert to a safer environment.

To clarify further, severe icing conditions imply that the flight cannot safely continue under the existing circumstances, and immediate diversion to an alternate route or airport is essential to ensure the safety of the crew and passengers. Understanding this classification helps pilots and air traffic controllers make informed decisions regarding flight safety when encountering such conditions.