Which one is NOT one of the conditions that require solicitation of PIREPs?

The correct choice highlights that "Clear skies" is not a condition that necessitates the solicitation of PIREPs (Pilot Reports). PIREPs are crucial for gathering real-time information from pilots regarding current flying conditions, which helps enhance weather insights for other aviators.

The other conditions listed—light icing, ceilings below 5,000 feet, and visibility at or below 5 miles—are significant factors affecting flight safety and operations. These conditions can present challenges such as potential hazards from icing, restricted flight visibility, and low cloud cover, all of which necessitate obtaining updated and accurate pilot experiences through PIREPs. In contrast, clear skies suggest favorable flying weather where pilots are less likely to encounter adverse conditions, thus not requiring additional reports.