Final answer:
The four levels of reportable icing are Trace, Light, Moderate, and Severe, respectively ranging from minor to potentially hazardous conditions that require the use of aircraft de-icing or anti-icing systems.
Step-by-step explanation:
The four levels of reportable aircraft icing that pilots may encounter are Trace, Light, Moderate, and Severe. Trace icing is a level where de-icing or anti-icing equipment is not necessary unless encountering it for an extended period of time. Light icing may create a problem if encountered for over one hour during flight and requires occasional cycling of de-icing or anti-icing equipment. Moderate icing is a condition that requires the immediate use of de-icing and anti-icing equipment and may create a hazard if not managed properly. Lastly, Severe icing is a dangerous condition that exceeds the capabilities of protective systems on aircraft and often requires immediate diversion to a lower altitude or landing.