What should be reported in an urgent PIREP concerning icing?

In an urgent PIREP, severe icing must be reported because it poses a significant hazard to aircraft safety. Icing can adversely affect aircraft performance, control, and overall safety, especially when it reaches severe levels. Severe icing can lead to critical issues such as loss of lift, increased drag, and potential engine failure, which are essential for pilots and air traffic controllers to be aware of in real-time.

Reporting severe icing helps ensure that pilots in the vicinity are informed about the conditions they might encounter, allowing them to take necessary precautions, change flight plans, or avoid areas of known severe icing altogether. This information is crucial for maintaining safe operational practices in flight, particularly in winter or storm conditions where icing is prevalent.

Other options, like light frost, moderate weather, or clear sky conditions, do not contain critical information that would warrant an urgent attention level in a PIREP, as they do not represent a serious threat to flight safety in the same manner that severe icing does.